Intertidal Communities of the Poor Knights Islands, New Zealand.
[Read before the Auckland Institute, June 9, 1937; Received by Editor, October 1, 1937; issued separately, March, 1938.]
Description of Poor Knights.
General Environmental Conditions.
The Biotic Communities.
Novastoa-encrusting coralline Association.
Carpophyllum elongatum Association.
Alternatives to C. elongatum.
Notes on Special Habitats.
Discussion and Comparison with Other Areas.
One of the most striking features of certain of the off-shore islands of the North Auckland coast is the many-ranked and beautifully symmetrical zonation of intertidal communities. Bands of sessile shellfish and seaweeds run like white, red, and brown ribbons around the shores, a striking local expression of the incidence of certain major factors operating throughout the whole littoral region.
An evaluation of these factors has nowhere been completed satisfactorily, and little attention has been paid them in New Zealand. After a period of observing and collecting on the mainland and various islands from East Cape northwards almost to Cape Brett we chose the Poor Knights Group, which illustrates an extreme of exposure for this coast, for an analysis of the biotic communities, in the hope that there, under exceptionally uniform conditions, controlling factors might be more easily recognisable.
Published work on the ecology of the group has been restricted to descriptions of the remarkable land vegetation by Cockayne (1906), Oliver (1925), and Cranwell (1937), and of the breeding habits of certain seabirds by Falla (1934). Notes on birds have also been given by H. Hamilton (1925) and there are odd references to the vegetation in our paper on the Hen and Chickens Islands (1935). It is hoped that the present account may suffice for comparison with other parts of the New Zealand coasts, although with the time available,
even favoured by fairly good weather and spring tides, it was, of course, impossible to make anything approaching a complete survey of the littoral flora and fauna.
Through the courtesy of the Minister of Internal Affairs, in whose Department the group is vested, we were able to make two visits, one as a Museum party in November, 1933, with Messrs. R. A. Falla, A. T. Pycroft, and A. B. Deeming, and another in February, 1937, with Mrs. A. R. Pickmere and Miss Katie Pickmere, of Whangarei. On the first trip several hours were spent on each of three of the main islands: on the second a camp was established on Aorangi, and five days were spent in collecting from the shore or from Miss Pickmere's dinghy. Transport in his yacht “Arethusa” was provided by Mr. H. Pickmere, who made possible a rough check of the belts right round the coastline even in places where it would have been difficult or impossible to land. We are glad to acknowledge our indebtedness to the friends without whose assistance this survey would have been beyond us. We have to thank the following for identifications: Dr. V. J. Chapman (Enteromorpha); Dr. A. B. Hastings (Polyzoa); Mr. A. W. B. Powell (Mollusca); Professor W. A. Setchell (various algae); Mr. H. Skuja (Entophysalis); and Mr. R. M. Laing and Dr. H. H. Allan for much assistance and advice relating to marine ecology in general. The collections of lichens and encrusting algae are still held for study by Dr. Allan and Professor Setchell respectively.
Description of Poor Knights.
The small group of islands, called the Poor Knights by Captain Cook, lies in longitude 174°45′ East and latitude 35°30′ South, some 40 km. N.N.E. of the Whangarei Heads and 25 km. off the nearest point on the East Coast of Northern New Zealand. It has been uninhabited since the massacre of the Maori inhabitants, the Ngati-Wai hapu or sub-tribe on Tawhiti Rahi and the Ngati-Toki hapu on Aorangi (see map) by the Hikutu tribe from Hokianga about the year 1808. Distant from the mainland, with no good anchorages and only a few rather treacherous landing places, the islands have long been almost exempt from human interference. The pigs, that since the days of Maori occupation rooted and scavenged even to the water's edge on the one island Aorangi, were exterminated in October, 1936, by Captain G. F. Yerex, of the Department of Internal Affairs, who thus removed the only serious extraneous modifying influence.
The main islands, Tawhiti Rahi (318 acres) and Aorangi (163 acres), are separated by a narrow gap across which stretches a chain of smaller and for the most part unscaleable islets. Two others (Aorangaia being the larger) lie only a short distance offshore. A couple of rocks which barely break water at high tide complete this compact group. Some four miles to the south lie the majestic Poor Knights Rocks. All are of volcanic origin, of “well-compacted, bedded, rhyolitic breccia” (Bartrum, 1936), weathering to a yellowish tone which shows only where the prevailing cover of grey or greenish-grey lichens is broken, or where a bare band occurs here and there in the upper littoral.
The islands are tall (180–200 m.) and plateau-like on top. They almost invariably meet the sea in vertical cliffs which frequently run not only the whole height of an island, but to some 100 m. down into the water. Indentations are few and mostly in the form of straight-sided clefts or inlets. Caves and tunnels, some with dry walls and roofs, and many of great size, run deep into or through all except the pinnacles, which probably arose through isolation as stacks in this way.
No sign was seen of “wavecut platforms” such as are a feature of conglomerate rock at Whangaroa or on the west coast near Auckland. In two places on Aorangi the terrain drops away in a series of low terraces from about 30 m. above the sea. Fraser (1925) refers to these few sloping shores as Maori landing-places. On Tawhiti Rahi are prepared platforms on to which canoes could be hauled up the cliff face. There are no sand, mud or pebble deposits; the only free rocks are a few boulders of great bulk fallen from unstable cliffs, as at the head of Rock-lily Inlet.
General Environmental Conditions.
The tides are of the semi-diurnal type with the heights of the two daily tides approximately equal. No tide records have, so far as we know, ever been taken on the island; but from the data in the New Zealand Nautical Almanac for Whangaruru and Tutukaka on the mainland opposite, the minimum tidal range is about 1.1 m., the maximum about 2.41 m., and the mean range about 1.65 m. The time of the tide is probably about fifteen minutes later than at Auckland, giving the highest high tides at about nine o'clock, the lowest low tides at between two and three o'clock. Low spring tide falling at nearly the hottest time of the day and the coldest time of the night means that when the lowest intertidal organisms are exposed it is to the most severe atmospheric conditions. Tidal movements will sometimes be intensified or almost cancelled by wind action while waves almost always increase the effective range.
There is apparently no strong definite current known to shipping near the islands. In 1933 we found the bull kelp D'Urvillea antarctica growing on the Poor Knights, the first record for the east coast of the Auckland Province (Cranwell and Moore, 1935). Later it was collected by a Museum party at the Three Kings. Drift fronds of the same alga found near Whangarei Heads (forwarded to us by Mr. A. R. Pickmere, 1931), near Waipu Cove (L. M. C., 1931) and on the Hen Island (L. M. C. and L. B. M., 1933) seemed then to indicate a set down the coast: however, from information recently given us by Miss H. M. Shakespear, of Whangaparoa, it appears that D'Urvillea might have come from an unrecorded east coast station, e.g., the Needles near Great Barrier Island.
Other evidence of current was provided by water-worn tussocks of Xeronema Callistemon found on the largest island of the Chickens Group (L. M. C. and L. B. M., 1933). Certainly this rare species
is present on Hen Island, 6 km. south of the Chickens, but we have not yet seen it there in any place from which it could pitch into the sea. On the Poor Knights, however, great clumps are perched on the outermost cliffs, and frequently fall as bulk and weight increase.
Winds and Waves.
Winds are probably stronger and steadier than on the mainland, though this is not reflected in any marked pruning of the land vegetation. The brunt of their force is taken by the cliffs that shoot them straight up past the clinging tufts of Xeronema and Danthonia bromoides, but this does not lessen their importance in relation to wave action.
All the islands and the chain they form are elongated in a north and south direction so that they catch both prevailing westerlies and occasional, but fierce, north-easterlies broadside on with little mutual protection. From every quarter the winds come over long stretches of unbroken and relatively deep sea. (Ferrar, 1925, in his map shows 850 fathoms to the east.) As a result, a strong and fairly constant surge runs practically all round the coast, probably rarely less than 3 dcm. in range even in calm weather and rising to much greater heights in storm. Large plants of Lessonia tossed into phanerogamic vegetation 20–25 metres above the sea give an indication of the maximum. On the windward side one finds always a good deal of spray and splash, but to leeward there is rarely much break against steep walls so that here aeration of water is effective very little below the lowest level of surge at any given time. Surf with continual deep aeration develops whenever strong waves meet projecting ledges.
Transparency of Water.
The water is very blue and very clear owing to its great depth and the absence of suspended mud and sand. Any material weathering off the coastal rocks is immediately carried away. There is no inlet where anything approaching estuarine conditions could develop. The air is dust-free and sunny days are many, giving penetration of strong light far below the limits usually accepted for the littoral, especially where breakers do not form. The effect of air-bubbles in turbulent water is to decrease light penetration and so cause upward displacement of rhodophycean growths.
For Cuvier and Mokohinau Islands, south-east from the Poor Knights and distant 145 km. and 60 km. respectively and for Cape Brett on the mainland 50 km. to the north-west, temperature records over a number of years are available. The figures given by Hounsell (1935) in a table of monthly average sea temperatures for 1929–32 agree so nearly for the three stations that it is very unlikely that those at the Poor Knights in an intermediate position would differ materially. Mokohinau in general features most resembles the Poor Knights, and we give a graph showing the average monthly temperature there for 1929–37. The figures for the last five years were
supplied by Mr. A. E. Hefford, Chief Inspector of Fisheries, from the log of the m.v. “Nora,” the supply boat that visits the lighthouse each month. The number of readings taken on each visit varies from 0 to 7, but they would presumably never cover more than 2 to 3 days of the month. The temperature given is that “at the surface in 6 fathoms.”
As has often been stated in relation to marine and other ecological work it is not always the average temperature that is the limiting factor for species or communities. Maxima and minima are more important in this respect, e.g., 10.7° C. in August, 1929, and 22.4° C. in February, 1935, might well have been detrimental to certain organisms on Mokohinau, and similar extremes probably occur from time to time on the Poor Knights. The few isolated records we could have obtained on our visits would have given little clue to the general temperature conditions, though, had it not been for the early breaking of our thermometer, we might have made useful observations about pool temperatures.
Obviously, from the data available no conclusions can be drawn as to the influence of temperature in the differentiation of association-complexes of the islands and the mainland but interesting correlations can be traced between temperature change and seasonal development, especially of certain algal species, e.g., Porphyra columbina.
Chemical Qualities of Water.
The salinity is high, probably exceeding 35.25—the figure given for the Noises waters in the Hauraki Gulf by Hounsell (1935)—since (1) the islands are far from the discharge of any large river, (2) the sea is deep, (3) the rainfall is not high, probably less than that of the mainland opposite, which is about 150 cm. per annum (Kidson, 1932). There is a quick run-off over cliffs and platforms from a few small but fairly well-defined streams that acquire either a magnesian flavour from rocks or else a good deal of organic matter from humus-rich soil and guano-saturated bird “sitz-platze” and burrows (so strong that they have a special restricted florula). The relations in tide pools are discussed elsewhere.
High acidity shows in the corroded shells of barnacles and certain mollusca, e.g., Nerita melanotragus, Guildingia obtecta, Cellana spp. and Lepsiella scobina.
The chief habitats available for fixed organisms and the life they harbour are narrowed down through the absence of sand and mud. The intertidal rock is invariably hard, frequently with small jagged protuberances that increase surface area and make for ease of attachment of organisms. The rock holds little moisture except in cracks. Stalactites of magnesian limestone in caves, even some of the driest of which have splashes of microscopic green algae on walls never reached by rain, testify to seepage of water through rock fissures from above.
Slope, since it affects the degree of insolation, exposure, and amount of surf as distinct from surge, is the most important variable cutting across the vertical zonation of intertidal communities.
Among the long, straight, almost unbroken vertical walls forming the greater part of the coastline variety is afforded according to aspect and the angle at which they meet the main surge and one another. Rock channels are a special case of this.
Under-sides of huge boulders, undermined ledges, tunnels, and caves provide a series with diminishing exposure to insolation and desiccation.
A pool-salt-pan complex is developed only in the two places where selective weathering of sloping rocks has resulted in series of steps and roughly horizontal terraces. Master joints are bordered by harder rock that persists as regular walls from a few centimetres to several decimetres high, thus dividing off rectangular pools and shallow pans, which at the upper limits of the stretch especially investigated are partly shaded by tufts of halobiotic phanerogams, such as Deyeuxia Forsteri (frequently with viviparous branchlets floating in the brackish water), Leptocarpus simplex, and Samolus repens var. stricta. These pools, fed by telluric water, rain, spray and the tides always fiercely insolated and open to evaporating winds, naturally show the greatest range in salinity, the intermittent accumulation of solid salt being a lethal character of the habitat.
The Biotic Communities.
The conditions peculiar to the littoral demand a wide range of adaptability in the organisms found there and especially in the dominants which have the power, within certain limits, either to exclude all invaders of similar life-form and requirements or else to ameliorate conditions so that they may, together with less adaptable species, form an interdependent unit in equilibrium with the existing environment. Such units (which we term associations) here form a vertical series, each sensitively adjusted to the special conditions of a narrow horizontal belt that it either occupies exclusively or shares with some alternative association. Lack of competition may slightly increase the bathymetric extent, but even then the upper and lower limits are usually of knife-edge definition on the Poor Knights. Parallel and almost unwavering bounding lines emphasise the importance of the tide-pattern even where perpetual and always varying surge might be expected to blur its outlines. A study of the belts, firstly where they are most striking and secondly where they are interrupted, should give the key to other effective factors. Richards (1932) has pointed out that “an obvious approach to the ecological problem is to study exceptional habitats … where the influence of certain factors is shown in an extreme degree.”
This is not the place nor do we feel competent to enter upon any general discussion of the terminology of marine communities. In the literature to which we have had access the most comprehensive account of the history and current views on these vexed questions is that of Gislen (1930). We must, however, try to define as precisely as possible the terms we intend to use.
That portion of the earth's surface that is covered permanently or intermittently by the sea or even strongly influenced by close proximity to it has been divided into vertical regions of which we are concerned only with the littoral and its boundaries with the supra-littoral and the sub-littoral.
As examples of definitions of the littoral we choose those of (1) Sernander (1917)—“it lies beneath the normal high water line and is laid bare regularly at the ebb”; (2) Gislen (1930) (for exposed coasts)—“between that boundary where the daily ground swell is able to soak through the strand and the lower edge of the coast laid bare by the retirement of the normal ground swell”; (3) Johnson and Skutch (1928) (as submersible)—“subjected to alternate submergence and exposure”; (4) Oliver (1923)—“all that part of the shore between highest wash and the lowest level of spring tides.” The last, the broadest of all, is perhaps the most suitable for us to use in an area where we had no opportunity of determining any regular, average, or normal tide levels and where the swell varies so enormously. We could deduce the position of Kylin's “physiological high water line” (1918) only from our knowledge of the requirements of plants and animals growing near this boundary, that is, by biotic limits: for example, barnacles must presumably live below the level of the “highest wash” even if this height is attained only once in a month or more: similarly any organism fixed vertically below the highest barnacle must at least tolerate occasional submersion. Spray is effective considerably above the barnacles as is shown in salinity of rock pools. These then would be in the supralittoral, the sturmgürtel of Sernander (1917) and Du Rietz (1925).
The lowest level of spring tides we placed approximately by our acquaintance with the algae especially of more frequently visited areas. Thus Lessonia we know to belong to the sublittoral, although here and there groups of plants may be exposed as the swell drops at low tide. This fixes our lower boundary fairly definitely at the upper limits of the Lesonia association, and perhaps cutting across the belt of Rhodophyceae, which has a striking development on the Poor Knights.
As the substratum is everywhere of hard rock, we have to deal only with what Gislèn (loc. cit.) has termed “epibioses of the hard bottom facies.”* Endobioses (i.e. “biocenoses buried or bored in the substratum”) and hypobioses (i.e. “biocenoses occurring in
[Footnote] * This use of the term facies does not agree with that sanctioned by the Zesde International Botanisch Congres, 1935 (Proceedings, vol. I, app. I, resolution II. “Subassociation and Facies can where necessary be used for their subordinate units,“ i.e., subordinate to associations!)
preformed holes, in free water, on the underside of stones”) are alike absent.
With regard to the actual plant-animal communities—bioses, biocenoses, or halobioses—we have restricted ourselves to the use of a minimum number of terms. Thus we refrain from grouping our associations into formations. In the sense most used at present a formation includes all the associations with the same dominant life-form and main ecology (Gams, 1932), i.e., associations of which the dominants are physiognomically and to some extent physiologically alike—but it has been used in marine ecology in a very different sense, e.g. Cotton's (1912) rocky shore formation. In any case formations are more appropriately treated in a regional survey than in the description of one small area.
Our unit (as stated above) we take to be the association. In a “Table of Principal Marine Littoral Formations in New Zealand” Oliver (1923) groups in separate Series of Formations, associations dominated on the one hand by plants and on the other hand by animals. It seems to us that it is possible for plant and animal species to be co-dominant and co-extensive in one community that is either permanent, e.g. the Novastoa-encrusting coralline association, or seasonal, e.g. the Chthamalus-Porphyra aspect of the Chthamalus association.
In our usage the belt is a continuous horizontal strip of the coast occupied throughout most of its length by one association which may, however, be interrupted over a shorter or longer stretch where its place in the belt is taken by another community whose presence depends on slightly different local conditions. This alternative community has equally strict though not necessarily coinciding horizontal boundaries. Thus we may speak of an association-fragment of D'Urvillea occurring in the Xiphophora belt.
Along the coast the associations in successive belts follow one another in a regular constantly recurring sequence. Such a sequence is an association-complex, e.g. Gislèn (p. 91) compares an inner association-complex in the fjord proper with an outer association-complex outside or in the mouth of the fjord. Similarly we compare and contrast the association-complexes of the cliffs of the Poor Knights and the Whangarei Heads, etc.
Sequence of Belts.
The dominant organisms of successive belts happen to be of contrasting colours with light and dark alternating as is shown in the following table in which, as is usual, each association receives the name of the physiognomic dominants. The sequence is from above downwards, as it appears on every fairly steep cliff that receives a certain minimum of sunlight.
|Sessile and carpeting:|
|(1) Tufted and encrusting lichen communities||Greenish grey|
|(2) Verrucaria and Cyanophyceae (Melaraphe towards lower limit) communities||Blackish|
|(3) Chthamalus association||White|
|(4) Apophloea-Elminius association||Dark red|
|(5) Novastoa-encrusting coralline association||Pinkish white|
|Short to medium fronds:|
|(6) Xiphophora association||Brown|
|Long flexible fronds:|
|(7) Carpophyllum elongatum association||Brown|
|Finer strap-like fronds:|
|(8) Rhodophyceae association||Dark red|
|Stout stalked fronds:|
|(9) Lessonia association||Brown|
Of these (3) Chthamalus to (7) Carpophyllum elongatum fall within the limits of the littoral as defined above. Associations (8) Rhodophyceae and (9) Lessonia, though frequently exposed, reach their best development in rather deeper water and will be discussed only because of their tendency to be displaced upwards, as a whole, or in part, to the exclusion of associations (6) and (7) where cliffs are very shaded and the water sometimes very tumultuous as well.
Scope of Survey.
Our aim is to define and describe, with some indication of limiting factors, the five major associations of the littoral, together with a few minor alternative communities, to refer briefly to the immediate extra-littoral communities, and to give a more general description of the places in which the sequence is seriously disturbed by the presence of pools, channels, tunnels, and caves where, with more variety of habitat, many more communities are represented, but each developed only within a very restricted area (e.g. Hormosira Banksii in one pool). A detailed analysis was out of the question and would perhaps have elucidated few general points, except in the case of the caves. Wherever possible these were entered and enough was seen to show that, given ample time with favourable weather and using special photometric apparatus, one could very profitably investigate there the light relations of large numbers of species and the communities they form.
Our descriptions deal almost exclusively with the sessile and especially the fixed organisms. These latter, because of their inability to move in the adult form, must reflect differences in habitat more accurately than those that can betake themselves elsewhere during recurring unfavourable periods that may limit permanent residence in any one spot. This does not mean that we are oblivious to the importance of the reactions of moving and fixed, but only that, with the short time available, the study of the fixed (and macroscopic) gave more promise of useful results. Active animals are listed in those belts where we noted them, but as Gislen says (1930, p. 76), “The assemblages, which … the freely moving animals and among them the predatory animals especially … can bring about are too ephemeral and too dependent on accidental circumstances for any sociological importance to be attached to them.” Our description, like that of Hewatt (1937), “holds for the low tidal periods when the ecologist is at work, but not for the high tide intervals” when limpets, chitons, and “snails” creeping forth from under cover of the algae, various kelp fish swimming close inshore in search of food, and even the long fronds of the brown seaweeds, lashing upwards with the waves, must all have their influence at higher levels.
“Leptograpsus variegatus is abundant and militant at the landing places and here, as described by Hedley (1915) in Sydney, ranges along the edge of the water, following the sea up and down. The only other large crab seen was Plagusia chabrus in narrow clefts on vertical faces, but even here the Leptograpsus was much more abundant. Otherwise active animals were rather scarce. No starfish at all were seen.
There were a few small blennies in rock-pools and by line-fishing in a deep cleft at dusk with a rising tide we caught a few larger fishes. These included the red pig fish Verreo oxycephalus, the red rock cod Scorpaena cruenta and large dark brown wrasses (parrot fish) apparently belonging to at least two species. A conger eel and more rock cod were caught from the yacht in the bay. Shoal fishes of various kinds are abundant and follow the plankton right to the cliff edges. One kind is medium sized, swift moving and a beautiful blue (Girella cyanea?). Trevalli (Caranx georgianus) and even large snapper (Pagrosomus auratus) were caught in such a place. No further reference will be made to fish in the descriptions that follow.
A. Dominant species: Life-forms and autecology.
(a) Chthamalus sp.: This is a medium-sized barnacle, of average basal diameter of about 1 cm., attached always directly to the rock. A solitary individual has the form of a rather flat cone sharply truncate above and more or less crenate below. Crowding leads to more columnar shape, but the opercular diameter remains much less than the base. It is characteristic of the species that the six parietal valves become completely fused at a very early stage (at Anawhata the largest specimen with distinct valves is just over 1 mm. in diameter). At all later stages the animal is enclosed in a complete ring of thick marble-like shell which, in spite of its apparent hardness, is extensively corroded so that all older individuals show a series of smooth, dense, white, concentric laminae. Oliver (1923) suggests that these are growth-rings and gives an excellent sketch of a typical specimen, under the name of Chamaesipho columna.*
Sporadic observations in various localities suggest that (1) very little spat becomes established in any one year, (2) once established, individuals grow quickly since the proportion of immature specimens in a population is small. (3) After attaining a certain size it grows very slowly and is comparatively long-lived. Moreover, the thick shell protects it from borer or other attack with the result that empty shells and gaps are very few, in strong contrast to Chamaesipho, and most other intertidal barnacles.
[Footnote] * The present species often, in fact usually, occurs in close proximity to Chamaesipho columna, with which it has hitherto been confused. Early fusion of the parietal valves is a feature common to both and brings about a superficial resemblance in individuals of like size. The Chthamalus grows larger and is amply distinct in detail, while the early juvenile shows six valves with the arrangement characteristic of the genus. It differs from all the species of which descriptions are available and would appear to be undescribed. Specimens have been forwarded to Dr. Bassindale, of Manchester, and it is hoped when his opinion is received to publish a note on the form and distribution of this barnacle.
This species is confined to rough coasts with fairly clean water well aerated by strong wave action. It will stand maximum insolation, but can still endure shading, though it shows little tendency to congregate in crevices.
In tolerating, or perhaps even requiring, long periods of exposure to air, it agrees with other species of its genus. It grows with few exceptions above high-water neap tides, where it must often pass one or two days without being touched by the sea, and stops short abruptly at margins of quieter pools. The highest individuals on the Poor Knights, quite 5 metres above mean high tide, have at most only trickles of water flowing over them when these, as well as fine spray, are thrown up by storm waves.
H. B. Moore (1936) writes of Chthamalus stellatus at Amory Bight where it reaches up above high water of highest spring tides: “It is very hard to understand how an apparently plankton feeding animal manages to survive in a situation where the only food-bearing seawater which reaches it is the splash during high tide on rough days.” Yet Vaillant (1870, p. 175, quoted by Gislèn, 1930, p. 48) found that barnacles could live on dry land for at least 24 days, but that they are finally dependent on immersion. The local example would rarely need to fast so long.
(b) Porphyra columbina. This laver occurs freely in the higher littoral in many northern localities and forms conspicuous societies of seasonal development on sloping shores or boulder-beaches on some very rough coasts, e.g. at Anawhata and Te Henga, where shallow bay-heads are full of moving sand. Despite an appearance of delicacy the silky, frilly thalli are extremely drought resistant, consisting of small close-packed cells covered with a gelatinous sheath that allows them to take up water rapidly after prolonged drying. The thallus is always dampest in the deep folds. It frays at the edges when subject to sand abrasion.
The barnacle is by far the most abundant and characteristic organism, at its best development forming a closed community covering many square metres at a time. The eroded shell surface is often quite clean, but may be covered by Arthropyrenia balanophila, or entirely hidden under a thicker tarry lichen (unidentified).
Porphyra appears to be best developed in the spring when it is fairly abundant in the form of large, fully mature fronds (13 cms. diameter) drying taut across the barnacles, but it is practically absent over wide stretches in late summer when insolation would normally have been most severe. The largest seen in February was 9 cm. across, but more were 2–4 cm., persisting in greatest amounts on surf-exposed knobs. It is a characteristic species of the Chthamalus association, but occurs as well in upper parts of the Apophlaea belt.
The limpet Notacmaea pileopsis is occasional: Melaraphe oliveri moves through the band in varying numbers: in damper crevices towards the lower limit may be anemones—the dark red Actinia tenebrosa and a smaller sand-coloured Sagartia-like one were noted on Tawhiti Rahi.
At higher levels where barnacles are more scattered the rock surface is covered with the thin dark thallus of Verrucaria maura; below, Apophlaea Sinclairii may enter as a minor constitutent, its conspicuous fertile branches projecting well beyond the Chthamalus. Damp trickles throughout are often lined with Hildenbrandia Crouanii.
The Chthamalus association girdles all the islands, and is represented in an attenuated form by individuals on shelving shores. It takes charge completely between wide limits where wave action is strongest. Where the lower limit is well defined, e.g. on a vertical insolated face exposed to moderate surf, it lies at about high-tide mark, above Apophlaea. In such a situation the vertical distance covered is about a metre, though individuals may go much higher. Extension of the association upwards depends on configuration of coastline to give high splash of big waves, e.g. where a cliff face plunges into deep water. It is under these conditions that the highest Chthamalus is about 5 metres above the lowest. Extension downwards accompanies (1) strong surge, particularly where shading is sufficient to exclude competition from Apophlaea; (2) surf, as opposed to surge. A boiling swirl of thoroughly aerated water provides conditions so favourable to Chthamalus that it forms a solid cover almost down to the Xiphophora level, quite eliminating Apophlaea even in strong sunlight.
A. Dominant species: Life-forms and autecology.
(a) Apophlaea Sinclairii. This is a small endemic encrusting red alga of cartilaginous texture, able to colonise smooth rock or completely cover the thinner crusts of Melobesia and Hildenbrandia. The isolated warty patches may eventually coalesce to form a dense immovable coating 2–3 mm. thick, these being the sterile thalli. The fertile condition is marked by the production of stout, crowded, finger-like outgrowths about 1.5 cm. high, usually showing a rough dichotomy. These are also deep red in colour. They are quite rigid and yet extremely resistant to wave attack and desiccation. Even when with prolonged drying the basal discs develop radial cracks these branches are uninjured.
Reproductive activity is apparently of long duration. Fertile plants were the rule in both November and February (i.e., covering the warm season) and the same stage was collected on the Noises Islands in May, 1933, but absent in May, 1937. Complete sterility of the large communities on Waiheke Island in March and June, 1937, can probably be related to less favourable habitat conditions for the species.
As a species it is strongly light-demanding and able to thrive on flat, sloping, or vertical shores within its belt. Our experience beyond the Poor Knights shows that it does not thrive under estuarine conditions. It is best suited by the pounding of a heavy surf on a shallowing shore, but is eliminated by competition in positions of maximum exposure.
(b) Elminius plicatus. This whitish balanoid barnacle reaches a basal diameter of 1.5 cm. and a height of 2 cm. It usually colonises bare rock, but the spat shows the common tendency to settle on older shells of the same species and, thriving there, to form bulky knobs. On the Poor Knights it apparently nowhere reaches this order of abundance though occasionally a dozen or so individuals will be sufficiently close together on the rock to make lateral contact. The form varies somewhat with age and three groups could be distinguished: (1) juveniles of 7 mm. diameter and 3 mm. height, represented in our collections by a few examples attached near the base of large shells; (2) rather flat, spreading, delicately fluted, little-eroded specimens, dimensions 13 × 3.5 mm.; (3) large steeply conical individuals, the fluting sometimes much intensified by erosion and the whole surface of the valves minutely pitted, offering a suitable substratum for attachment of certain seaweeds and lichens. Many specimens collected in February were filled with eggs or embryos.
The species is widespread, going as far south as Auckland Islands (Broch, 1922). About Auckland it forms a fairly definite band within the Chamaesipho association, reaching to a foot or so below its upper limit and not so far down as its lower limit. It can maintain itself on fairly soft rock and on the horizontally bedded Waitemata sandstones as at Mahurangi Heads, Waiwera, and Narrow Neck, closely packed individuals form a complete cover for many square yards at a time. Oliver (1923, p. 534) describes a similar occurrence at Maori Papanui Bay, Otago Peninsula. His statement that the species avoids the underside of overhanging rocks seems not quite generally applicable though it certainly tolerates strong light and long exposure. It is absent from both the roughest parts of the west coast and the more sheltered parts of the east. On the Poor Knights its distribution is limited by the aggressiveness of competing species even better adapted to local conditions.
Apophlaea forms the chief algal constituent of this association, sometimes so abundant that from 100 metres distance the whole unit may be recognised by its colour—deep red when wet, dulling to resemble congealed blood when dry. Its basal parts may cover as much as half the total rock surface, but it rarely forms an unbroken crust. Interspaces are occupied by shelled animals of low conical form clinging by broad bases to the rock. Of these, by far the most characteristic and abundant is Elminius plicatus, mostly in small but frequent groups of twos and threes. Cellana ornata is much more abundant than C. radians, and Siphonaria zelandica is occasional. Patelloida corticata occurs near the lower limit of the association. Algal members are few, as might be expected under such conditions. Porphyra occurs sparingly, Nemastoma oligarthra and another Nemastoma (related to N. Feredayae) come in toward the lower limits, while on pitted rocks, especially where kept damp by brackish water from the land, societies of Enteromorpha bulbosa var. hollandiae, with bright green fronds, were conspicuous in a few places in November. Odd plants were seen in February. Ulva as well occurs in the wet pockets shunned by Apophlaea.
A small wormy alga, identified by Professor W. A. Setchell as Nemalion lubricum ?, was found fairly freely on valves of Elminius, which was a host also for the encrusting Hildenbrandia Crouanii, Ralfsia sp., and the blackish Arthropyrenia. The thick dark lichen mentioned for the association above occurs here also, coating the barnacles like tar. In its irregularities nestle numbers of a minute Kellya. More active animals found in this zone, but not restricted to it, and probably free to wander out of it, include gasteropods: Nerita melanotragus abundant, Melaraphe oliveri occasionally coming down from above, Lepsiella scobina abundant and Lepsia haustrum occasional, coming up from below, all showing in various degrees a tendency to seek protection, like the “limpets,” in gaps in the Apophlaea. Far more conspicuous because of its size, its bright colour, and its noisy active movements is the crab Leptograpsus variegatus.
The association is developed in a belt following almost all the coastline of the islands and continuous along the margins of larger channels and pools. It drops out only where overshadowed, as on sheer southerly-facing cliffs, and in caverns, or where with heavy surf it is excluded by the Chthamalus association. On a vertical face the depth is perhaps 0.75–1 m.; on a sloping shore where the area and physiognomic importance are naturally increased, it may be 12–14 metres wide. The upper level seems to coincide with that of neap high tide, Apophlaea's need for daily soaking being the limiting factor. The lower limit at about half-tide is fixed presumably by the light demands of the dominants, as Apophlaea individuals do not wander much lower, even where competition is not intense.
Novastoa-Encrusting Coralline Association.
A. Dominant species: Life-forms and autecology.
(a) Novastoa zelandica. In Novastoa zelandica, a Serpulid-like mollusc, the tight spiral protoconch is attached firmly, usually to rock, but occasionally to the shell of a large barnacle, while shells up to 2 mm. diameter may even be found on more active animals such as whelks.
On the Poor Knights at least the shell as it grows does not diverge very far from the spiral form, the later whorls being laxer and more open, attached more or less continuously on one side and remaining fairly flat so that the wide terminal aperture faces only obliquely upwards. The coils of an individual are sometimes as much as 2 cms. from side to side, the tube itself being circular in transverse section with an internal diameter of about 0.5 cm. The inner surface of the shell is smooth and darkly mottled, but the outer layers form coarse irregular overlapping lamellae, purplish if neither strongly eroded nor overgrown with algae.
The strong low-growing shell, with extensive surface for attachment, and the heavy operculum (often itself covered with calcareous algal growth) that when withdrawn completely plugs the lumen of the tube, suit this animal to alternate buffeting by strong waves and
exposure to desiccating sun. It has not been noted by the writers in other localities, but on the largest island of the Noises Group, in one corner where conditions are suitable for Xiphophora, its place in the corresponding belt is taken by the nearly related Stephopoma roseum, very similar in life-form and apparently in ecological demands. A granular yellow sponge is there an important accompanying organism.
Factors limiting the upward extension of Novastoa seem to be connected with competition, and the balance between ability to withstand prolonged exposure and time required for food collecting which is interrupted during dry periods.
(b) Corallines. The corallines were of four main life-forms, thin films, curling crusts, nodular branches and jointed branches, the last being modified to form a low dense almost inseparable mass. Full notes on them were not made as field identification was impossible.* Their abundance at this level must be related to anchorage provided by Novastoa, mutual protection, need of frequent wetting and strong aeration provided by surf and surge. Some are light-demanding or light-tolerating at least, but there are more species in shaded habitats.
Within the limits of this community most of the rock is covered to a depth of 1–3 cm. by a sheet of almost stony calcareous structures. The greater part of the bulk and thickness consists of the twisting and intertwined tubes of Novastoa, the strong surface sculpture of which gives a suitable substratum for the attachment of corallines and of small gelatinous algae, especially Nemalion, the nemastomas, Laurencia virgata, Trematocarpus (Dicranema) aciculare, upright and creeping gigartinas—among them G. alveata, so dwarfed and olive-green as to be almost unrecognisable. Tufts of Polysiphonia, Ceramium, Ulva, and Colophyllis decumbens occur also in shaded places. The result is a rather undulating pinkish surface broken by the outwardly turned orifices of the Novastoa, and less regularly by ragged gaps exposing Melobesia spp., Hildenbrandia Crouanii, or the dark rock below. Interstices are often filled with fine polychaete tubes, and in the lower layers of the sheet, amongst gritty coralline debris, is lodged a rich and varied crypto-fauna of small isopods, amphipods, loricates (e.g. Maorichiton caelatus), Polychaeta errantia (mostly Nereis sp.), etc. Especially characteristic of the gaps are the inconspicuous Patelloida corticata and its variety corallina (23 × 14 × 5 mm.) clinging firmly to the bare rock, and themselves almost entirely coated with encrusting coralline algae, as are also the valves of the big loricate Guildingia obtecta found here and there. Lepsiella scobina, young Neothais scalaris, and Lepto-grapsus variegatus roam here also, and in this community two living specimens of Proximitra obscura were found. Risellopsis varia is occasional in cracks.
[Footnote] * The collections are in the hands of Professor W. A. Setchell, who is revising the group. The [ unclear: ] involved are chiefly Melobesia, Lithothamnion, Lithophyllum, Corallina, and Amphiroa.
Still water is antagonistic to this association, which seems to march parallel with the other major communities all round the islands on steep or moderately inclined slopes, but is lacking or poorly developed in tide pools or on shelving rocks where water is likely to lie. On the whole, it needs to be reached by the surf as regularly as the big brown algae, but can stand a greater range of both heat and shade. The last point is particularly well demonstrated in that it continues uninterrupted above the red algae that occupy the Xiphophora belt where browns are eliminated by inadequate light. Over longer stretches, where the same factor is responsible for absence of the whole Apophlaea association, the top boundary of the Novastoa-coralline community is displaced upwards to meet the depressed lower boundary of Chthamalus. Where the belts are broken up by the irregularities of shelving shores the association may be absent though its species are scattered as subordinates in some minor local community, e.g. in the Nemastoma association. A number of its constituents likewise penetrate to the undersides of ledges and into caves.
A. Dominant Species: Life-form and autecology.
Nemastoma (Catenella) oligarthra: This is our smallest Nemastoma, with Adenocystis-like bladders 1 ½−2 cm. long, attached by their narrow bases to one small firm disc. They are brownish-red, and filled with mucilage: when overdried the walls become taut. They probably suffer little between the tides as they are often pressed against damp rock.
On flatter areas where Apophlaea picks out all the drier knobs, any pockets between being held by Ulva, the damp slopes below have an inconspicuous coating of this Nemastoma, in open association with a few other algae of small size, with disc bases and stores of mucilage, as protection against excessive wave-action and desiccation. The second Nemastoma occurs freely, and a Nemalion is frequent where Elminius plicatus occurs. Novastoa is scattered throughout, and limpets Cellana radians and C. ornata may be abundant, but Siphonaria zelandica seems most characteristic.
Where the water regularly runs highest as on barriers across the surge, Nemastoma may reach 2–3 metres above Novastoa and Xiphophora, and it is there associated with Porphyra columbina, small sterile Gigartina alveata, Laurencia virgata (abundant in 1933 and rare in 1937) and the other red algae already mentioned.
Physical conditions do not favour this association in many places: its members may be merged in other communities through competition telescoping their habitats. The richest occurrence was on the northern shores of Aorangi.
This community forms a belt where Novastoa is lacking in sunny places. This is its tide-position at Harriet Kings (E. Coromandel Coast), on Taranga Island, and at Whangarei Heads, according to field-notes (L. M. C.). The only other records are from outside the Bay of Islands where the plant was first found by Berggren and described as a Catenella by Agardh (Kylin, 1934).
A. Dominant Species: Life-form and autecology.
Xiphophora chondrophylla is recognised to be a polymorphic species. All the northern forms were accepted as var. minus by Heine (1932). Throughout its range on the mainland this variety is long, stout, heavily-branched with deeply channelled, buttressed discs. Closely repeated dichotomous branching with round axes gives an attractive appearance to the yellow-olive branches with their linear terminal receptacles.
The Poor Knights plant, first collected by Mrs. A. R. Pickmere and forwarded from the Auckland Museum to Miss Heine, differs consistently in its smaller basal parts and rather shorter branches, which are conspicuously flattened only near the base and almost terete above. Branching is sparser, only the main dichotomies persisting in summer. In February most of the plants consisted of these lanky branches topped by tufts of small shoots—apparently as regeneration after the loss of old fertile receptacles, as no sign of these remained on the truncated apices. This condition has been noted in mainland specimens, but is more marked in the Poor Knights material because of the fewness and bareness of the branches. Great vigour of recovery is shown as well by the holdfasts, which may be in one piece, or much divided, the auxiliary attachments growing down secondarily, or perhaps separating under strain. The main branches emerge more or less in one plane from a zone immediately above the holdfasts, and usually on the upper and typically least shaded portion of the plant. It is interesting to note that the arrangement of the conceptacles, despite the narrowness of the receptacles, is very reminiscent of var. maximus.
We agree with Miss Heine that the plant must be an epharmonic variant conditioned by spray and turbulent water through the greater part of the year, but as already stated the water is very deep, clean, and saline, and not estuarine, with strong currents, as suggested by this author.
“Normal” var. minus is found freely on rougher coasts at Hokianga Heads, and on the eastern side of the North Island, as far south as Poverty Bay. Our experience shows that where its association develops there is invariably a strong ocean swell. Even individuals such as are found at their harbourward limit on Waiheke and Motutapu Islands in the Hauraki Gulf are sure indicators of this. The plant demands strong insolation and aeration and will not tolerate a combination of warm, muddy water without tidal scour.
Ecologically, its requirements seem most closely allied to those of Pachemenia himantophora which replaces D'Urvillea in comparative shelter on the west coast near Auckland, and is found also
on the ocean headlands near Waipu and to a lesser extent at Whangarei Heads. In the same way Xiphophora is displaced by D'Urvillea in a few places on the Poor Knights where very heavy surf runs.
The Xiphophora sets its stamp on this association, in which the animals, though abundant, are mainly hidden. Most frequently Xiphophora is a pure dominant, forming a heavy screen of pliable khaki-coloured stems shading a few shorter algae and the rich mixed cover of rock surface and crowded holdfasts. The junction with the pale Novastoa-coralline belt above appears clean cut because of the striking colour contrast, but there is nevertheless a kind of tension zone, the upper few centimetres of which are occupied mainly by the carpeting species of the “ground layer' of the Xiphophora association proper. This merges into a band of “stubble” Xiphophora composed of small crowded sterile plants no more than 2–4 cm. high, usually with a lateral spread of 8–9 cm., warty tips on the upper surface replacing, in most cases, the rich dichotomy of the normal plants. The fronds are now deep yellowish-brown or blackish from over-exposure.
A constant member of this association, but of varying frequency, is a large leathery-looking deep-red Gigartina, an undescribed species that runs to yellowish-olive in strongly insolated places. The shape is oblong, the attachment to the rock by massive discs even stronger than those of Curdiaea crateriformis. Being almost sessile and wide of base these ear-like growths are difficult to remove undamaged. Very occasionally they grow above Xiphophora, but they are more abundant in its shelter and on the shaded walls where Xiphophora may be lacking altogether. Along the organisms that grow upon it the commonest is a delicate encrusting polyzoan (Mucronella sp. ?) that is almost constantly present in patches covering slightly tumid areas on either side of the thallus.
Distinct stratification characterises the association. Of the carpeting species in the basal layer the most bulky is a pale, yellow, rather soft sponge, with small ostioles on low mounds, that fills most of the gaps between the many other organisms attached directly to the rock. Among these were noted as especially abundant on shaded vertical faces a white anemone with flaccid body 2 cm. long × 1 cm. diameter and Balanus tintinnabulum var. concinnus 2 cm. × 2 cm. often clean, but sometimes overgrown with sertularians and polyzoa. The blue and white Cnemidocarpa coerulea is occasional. A much more abundant tunicate is the small tough Pyura trita of nondescript colour, very firmly fixed and often almost hidden, except for the blue-green apertures of the siphons, by surrounding growths, amongst which an alcyonarian (? Sympodium sp.) with leathery fused stolons and projecting cuplets predominates. This last appears not to attach itself to bare rock, but to creep over any firm organic sub-stratum that is available. On and amongst the smooth holdfasts of Xiphophora this assemblage is enriched by the addition of Emma crystallina, a delicate, feathery, white, circinnately branched, limy polyzoan.
The main axes of the big brown alga are often covered in their lower parts by the wine-red, pinnate fronds of Aglaeophenia laxa (?), and nearer their tips by a stiff, dark pile, 2 cm. deep, of an un-branched Sertularia. Pleurostichidium Falkenbergii, a characteristic epiphyte of Xiphophora, forms heavy, dark red, scattered tufts, 2 cm. long, among the branches.
The red algae Melanthalia abscissa, Pterocladia lucida, Rhodymenia leptophylla, Hildenbrandia Crouanii, Callophyllis sp., Champia sp., are to be found scattered throughout the community.
The Xiphophora association is missing in its belt only where shading or wave action is too great. The dominant species is perhaps near its limit on the Poor Knights, maintaining itself there by the development of the peculiar local epharmonic form. Thus round the shallower bays at the north end of Aorangi it is better developed than are other major communities that demand excessively rough conditions: D'Urvillea, as already pointed out, displaces it at certain points: where it is eliminated by shade the Rhodophyceae that first become abundant in the lower canopy of the Carpophyllum-elongatum association move upwards. Just how the distribution of the associated species, except for such striking forms as the Gigartina, is affected by this very local change of dominant was not closely investigated.
The area of attachment of Xiphophora on a vertical wall is narrow, but the length of the heavy fronds makes them very conspicuous. The upper limit of the Xiphophora itself forms an almost straight horizontal line which, if it agrees with what we have seen elsewhere, is at about low water neap tide. The tension zone with its mixture of species has a much more ragged junction with the Novastoa-coralline community. It may be practically absent or as much as 15 cm. deep.
A. Dominant Species: Life-form and autecology.
D'Urvillea antarctica is one of the best-known of our algae. Its strong, air-filled, pliant fronds, here much narrower than in Cook Strait, are from 2 to 6 m. long. Their magnificent yellowish-brown discs are unharmed by the assault of the waves until, after-several years, age and burrowing animals cause them to lift from the rocks, usually in late winter when the fronds are fertile.
B. Composition and (C) Occurrence.
The only station we were able to collect from was unfortunately atypical, as shade during the greater part of the day permitted the growth of a wider range of associated species than usual, mainly because the D'Urvillea was not large, and not dominant.
Further search from the yacht in 1937 revealed more communities on the roughest points on the northern island. All were much larger than the first. The abundant growth seemed to exclude
most of the species mentioned as associates, but the pink pavement of encrusting corallines was conspicuous as it is on similar rocks on the west coast near Auckland.
Corpophyllum elongatum Association.
A Dominant Species: Life-form and autecology.
The dominant of this association is C. elongatum, one of the large endemic members of the Fucaceae. The plants grow in clumps as pure dominants with numbers of whip-like stems about 75 cm. long emerging from a crowded base of rigidly fixed haptera with spreading and coalescing “sucker-pad” disc-tips. The strength of attachment is amazing, a handful of these fronds providing a safe hold when scrambling from a dinghy. In the sterile condition the plant may consist of a single branch with a few tough, rather sickle-shaped “leaves” given off alternately in one plane over the greater part of its length. The main axis is nowhere broad. In its narrowness, diminishing rapidly from 4 mm. at the rather flattened apices to 2 mm. below, where it becomes decidedly terete and twisted, and in its dense tissues this form is ideal to withstand the onrush and plucking backwash of the surge. In severest exposure it is always well aerated, and perhaps because of this floats may be altogether lacking. They were collected, however, in a number of specimens, and during calm spells or on the leeward side of the island could be depended on to help float a frond well up in the water. The type material at Kew possesses large vesicles unlike those developed on the Poor Knights, which are narrow and pyriform.
The species is fertile during the cooler months. This was the general condition of a good series of specimens forwarded by Captain Yerex in September (1936). In November (1933) the plants were still patchily fertile, while in February (1937) no receptacles were seen. In the axils of the primary “leaves” arise small shoots with the normal branching produced in miniature. The smaller and thinner “leaves” subtend the clusters of receptacles. Later, older leaves and fertile shoots are represented only by scars on the elongated axes. At some stage the plant must be freed from its substratum and this allows of the establishment of sporelings, but we have no evidence as to the average length of life of the individual.
Outside the Poor Knights we have seen this species near Bream Head (distant 40 km.), but it is absent at Matapouri Bay (25 km. away). Along the rougher portions of the Coromandel coastline on the eastern side only it is again abundant, and one of us has seen it at Mayor Island. It was collected originally near the Bay of Islands by Berggren, and further north, floating near Raoul Island, by Moseley, of the Challenger Expedition. From its distribution it is a species of clean, well aerated, and rather warm waters. We have never seen it near a muddy shore.
The physiognomic dominance of Carpophyllum with its rich brown fronds, turning dark blackish-brown in periods of long exposure, is the first characteristic to strike the observer. The long
supple tresses swing below the shorter stiffer plaits of Xiphophora, and in turn hide the rich assemblages of areas less regularly bared by tide and surge. There is, however, a very characteristic structure and specific composition to this community, the long fronds having their own epiphytic growths and providing shade for the organisms which form a carpeting undergrowth wedged amongst the fluted haptera. In some cases a middle stratum of Rhodophyceae will be found. In the cooler months the fronds are heavily infested with the small red thalli of Abroteia suborbicularis, completely gone by February.
The special habitat conditions support a rich growth of soft-bodied animals, a tendency initiated in the moderate shelter of Xiphophora above. The sertularians are common to both communities, but the sponges are more varied, more bulky and of brighter colours. The following associates were specially noted: (algal) Calophyllis decumbens (?), Champia sp., Rhodymenia leptophylla, Plocamium brachiocarpum, Pterocladia lucida, P. capillacea, Rhodymenia sp., Pandorea Traversii, Vidalia Colensoi; (faunal) Emma crystallina, Aglaophenia laxa (?), Sympodium (?), encrusting Polyzoa (especially towards the base), pycnogonids, Hochstetteria munita.
The association follows all round the shores of the Poor Knights islands and most of the Poor Knights Rocks. It occupies all steep faces within its bathymetric limits except where both Xiphophora and Carpophyllum are eliminated by overshading and in a very few places where exceptional eddies and broken water seemed the only explanation for the absence of both associations and their replacement by tufted coralline or longer red algae characteristic of lower levels. Normal plants lined one deep clean pool regularly filled by the surge. Apart from this it was not seen except where its fronds would hang free in the air fairly frequently.
The depth of the belt naturally varies with aspect and wave incidence, but on the whole it is remarkably uniform, being about 25–40 cm. judged on an anchorage basis.
Alternatives to C. elongatum.
C. elongatum is peculiarly sensitive to swell. In most habitats where it does not grow Carpophyllum maschalocarpum is dominant, with a richer admixture of other brown species, e.g. Sargassum Sinclairii, Landsburgia quercifolia, Glossophora Harveyi, perhaps stunted Lessonia, and a very little Ecklonia radiata var. Richardiana. Some of these are rare and poorly adjusted to their environment, and are species really forming a transition stage between regular exposure of the lower littoral and complete submergence of the sub-littoral. They grow in open channels that should perhaps be grouped with the tide pools because of the different sets of conditions they introduce.
As far as carpophyllums are concerned, however, they are not typical of tide-pools and deserve special mention as a federation of association-forming species often with a wide geographical range almost confined to the lowest littoral, and with sensitive ecological requirements among themselves.
A. Rhodophycean Communities.
Sometimes the Lessonia association continues in direct sequence with the Carpophyllum, as it does in the shallower shores of Bream Head opposite, but more usually, as in many localities, a rhodophycean community intervenes between the Fucaceae above and the Laminariaceae below. This red community is formed very largely of the species of the undergrowth of the Lessonia association and might be treated as a society of that: but similar communities occur elsewhere with the same tide relations and in places where Lessonia (or the equivalent Ecklonia) is quite absent. It is very striking physiognomically, as when exceptional swell reveals cascade-like growths on the steep rocks or at higher levels in those shaded places-where some or all of the brown algae are eliminated.
B. Lessonia association.
An extensive association dominated by Lessonia variegata and clearly visible below the surface of the water, would not be included here did it not crop up in small societies here and there to interrupt the perfect symmetry of the other belts. From its members also are recruited shade-loving species of the lower littoral which add greatly to the interest, beauty and range of species of many of the tide pools. Some grow normally if they establish in shaded or deep pools or are protected by a fringe of browns, e.g. Pterocladia lucida, P. Capillacea, Rhodymenia leptophylla, Rhodymenia n.sp. (?), Melanthalia obscissa, Vidalia Colensoi, or they may be damaged by blackening of tips or loss of normal red tones; frequently they remain sterile. In addition the dominant species may here and there invade the littoral, e.g. near the canoe landing, where specimens grow in association with odd plants of D'Urvillea, and a wealth of shade-loving red algae.
Notes on Special Habitats.
Because of their varying nature, with all the catastrophic influences of exposure accentuated with vertical distance from low tide mark, pools naturally present great contrasts in species content, some being only seasonally inhabited by macroscopic forms, others having a rich population, augmented by introductions from lower levels. The wide range is due to the depth of the inter-tidal belt and its spray-zone, not to change in the substratum, whose hard compact surface eliminates burrowing animals and many algae, especially those with rhizoidal holdfasts, found at comparable levels on the mainland
nearby. Most of the algae have small discs pressed to the rock, or only separated from it by thin films or crusts of pioneering corallines. In brackish and salt trickles grow patches of Hildenbrandia, Ralfsia and Verrucaria, of very similar life-form, the algae appearing as dark brownish-red, and the lichen as greenish-black splashes on the rock. The same association is recorded for Clare Island by Cotton (1912), who traces it through its vertical range in the manner of Lippmaa's unistrate associations (1934). Hildenbrandia and Verrucaria occur freely between tide-marks, Ralfsia being abundant only in a few high pools. We cannot yet say whether the same species are involved throughout, as these genera are notoriously difficult to identify in the field, and they are by no means easy to collect from smooth, hard rock.
A few important pools were noted elsewhere, but they are abundant only in the northern bay of Aorangi. In this part can be traced all transitions from those rarely reached by tide to those rarely uncovered by it. We group them as (1) pools of spray zone and (2) pools of littoral proper.
Pools of spray zone.
At the uppermost limits the influence of fresh water is most strongly felt. A little Bangia sp. may be found here, while erect tufts of white-flowered Samolus repens var. stricta fill wet cracks. Seepage maintains chains of shallow but fair-sized pools (up to 15 m. diameter), the concentration of salt depending on stormy weather and evaporation. In dry weather the shallowest act as pans from which coarse solid salt can be scooped.
Above high-tide mark pools heat much above the temperature of the ocean water. These are the breeding places of the shore mosquito (Opifex fuscus) characterised by quiet flight and malicious nocturnal biting. The dark larvae are often so numerous as to alter the colour of a whole pool, and newly-emerged resting imagines may almost hide the surface in February. An example typical in most respects but with some special features is that of Rock-lily Inlet. This remarkable pool, located from a ridge top on Tawhiti Rahi, was not accessible until the 1937 visit. It is recessed into the cliff about 12 m. above the sea and is about 20 m. long, broadest in the middle and shallowest along the outer lip, which is covered with Pertusaria sp. on the dry knobs. High salinity must be maintained through evaporation and storm waves.
Odd boulders lying in the water have probably produced the smooth floor, which bears a wonderful cover of encrusting red and brown seaweeds (Hidenbrandia Crouanii and Ralfsia) together with an unidentified (?) Verrucaria. Rusty-looking shells of the very abundant Zeacumantus subcarinatus are coated with the same species which, with rotting pieces of storm-tossed Lessonia, etc., give a dark tone to the water and a suggestion of stagnancy. A little living Enteromorpha sp. and Centroceros clavulatum were noted as well. Important animals were prawns (unidentified), mosquito larvae (more abundant still in smaller water-filled cracks nearby), many large crabs (Leptograpsus variegatus) and an cyster determined
by Mr. A. W. B. Powell as belonging to an undescribed species fairly common in the Hauraki Gulf, and most nearly allied to Ostraea hefferdi. The oysters were small (35 × 27 × 20 mm.) and very firmly attached to rock by a broad base (a character distinguishing them from the mud oyster O. sinuata). They have a deep body cavity and thick blunt-edged valves usually well plastered with the algae already mentioned, or with a greenish species of Arthropyrenia. Small scattered groups of four to six form white patches especially conspicuous in the shallower parts. At least half the shells in the pool were empty as were many more above the level of the water as we saw it. Oysters were found nowhere else on the island, and the problem of their arrival, establishment, and maintenance there as a small colony is not readily solved.
Pools of littoral.
Where tides wash regularly there are both shallow pools (a few centimeters to 2 dm. deep) and deep basins, smooth-walled because of loose boulders that have helped to grind them out in the manner of potholes.
Along the lower course of trickles small water-holding pockets of this kind are occupied by sea-urchins (Evechinus chloroticus). Nerita melanotragus wanders between pools but seemed most abundant here where the rock surface was always damp.
Broad shallow pools are characterised by transient societies. In them the large fronds of Enteromorpha bulbosa var. novae-hollandiae were lushly developed in November, 1933, while in February, 1937, Entophysalis granulosa had developed conspicuously, on wet knobs as well as in the pools, and Enteromorpha and Ulva were of minor importance.
In one sunny pool, about 40 cm. deep in the centre, Hormosira Banksii was found a little above Apophlaea level; it grew nowhere in the open. Around the shallow edges of the pool the fronds were reduced to hard, cavity-less structures, sterile, and about 4 cm. high. The middle of the pool was filled with regular ranks of beadlike fronds (not as narrow as the Sieberi form of some rocky shores) with the tips lying on the surface, and blackened by exposure to sun and wind.
In the deep bath-like pools that are characteristic of the lower part of the bay in question the species-content depends on shading and tides. In one pool which escaped daily filling the water was very warm, salty and turbid: crabs were abundant: Nerita crept up and down round the margin. There was a light fringe of Ulva rigida and Enteromorpha and a white band of Spirorbis sp. just covered by water.
Below was a much larger pool which drained away over the lowest step in its jagged seaward wall into other pools and channels in which the ordinary banding was little broken. On the inside walls of this pool and on boulders in it the following sequence was noted: (1) bare—no barnacles, (2) dense Apophlaea in a deep band: no competitors, (3) bare: or Novastoa occasional, (4) Ulva present: no Xiphophora, (5) Carpophyllum maschalocarpum, mainly covered
by water, also more Ulva, Sargassum Sinclairii, Melanthalia abscissa, and Rhodymenia angustifolia. This sequence is described here because the enclosing barrier favours the pool-dwellers and eliminates the surge-loving barnacles and Xiphophora.
Many combinations of factors are represented even in such a small area. In another pool, for instance, Apophlaea will be abundant on the walls, Novastoa be absent and yet Xiphophora be present, while on steep dark walls little grows. At the bottom of such pools, which reflect a great deal of light, attached to boulders at a depth of 4–6 metres grows Rhodophyllis angustifrons, appearing a Cystophora-yellow from the surface.
Where surge becomes more important one can scarcely distinguish between large pools and channels, some of which however end in funnels where the water shoots up with great force. To their dripping walls cling mainly encrusting and large branched corallines, and many tufted and gelatinous algae with bright patches of Ulva rigida as well. Animals are mostly of limpet form, Cellana, Patelloida, Siphonaria, and a few chitons. Barnacles are few.
Undermined ledges provide gently or sharply concave faces which at about the Novastoa belt remain sufficiently damp to support a rich and varied collection of organisms.
Large brown seaweeds are absent. Pink pavement corallines (Melobesia, Lithothamnion, etc.) are abundant here, and Ulva rigida occurs in small rosettes of brightest green, with tufts of dark red Rhodymenia leptophylla and small roseate thalli of Callophyllis decumbens (?). Sponges dominate in quantity, in number of species, and in variety of form. The pale soft yellow one of the Xiphophora association, a thinner crust of scarlet, and the orange punctate globes of Tethya sp. are everywhere. Level with the lowest Xiphophora are great pads up to 15 cm. square and 7 cm. deep of that evil-smelling, bulky, black-surfaced sponge that is so abundant just at low spring tide on any rocky part of Waitemata shores.
Ascidians too are of major importance here, especially the compound ones (?) Fragaria spp. like delicate semi-transparent coral pink mushrooms 3–4 cm. high. There are some encrusting species, at least one dark fleshy one, and one white and limy.
Novastoa is scattered throughout and (?) Sympodium is everywhere abundant. We made no attempt to collect the various Actiniaria. Under higher ledges, well away from light but often out of water for two hours or more, a fragile pale pink polyzoan Catenicella (Pterocella) alata forms lacy tangles up to a decimetre in diameter, dotted all over with the white coils of Spirorbis sp.
Amongst this riot of colour is the light almost shining green of a new Codium* in fat oval cushions attached by a narrow base.
[Footnote] * Shortly to be described by Professor W. A. Setchell.
A single specimen of a smaller species (of the C. adhaerens group) suggested by Professor Setehell to have tropical affinities, was also found here.
Where water sweeps through a miniature tunnel at this level Balanus tintinnabulum var. concinnus reaches a size of 70 cm. × 40 cm. Amongst its epifauna are Tetraclita porosa (?), a Pilumnus and Vermicularia sipho, all species not seen elsewhere. More time spent in examining such places would add materially to the species list.
Small pools 1–2 dm. diameter overhung by Xiphophora have almost the same population, which in colour resembles that of vertical submerged walls of the larger tunnels where also shade and absence of drying are outstanding factors.
Caves and Tunnels.
It was not possible to investigate caves and tunnels thoroughly. As might be expected, sunny and shaded channels, tunnels and cave interiors are all strongly affected by swirl and eddies as well as by changes in light intensity.
In each case Xiphophora and Carpophyllum elongatum dropped out near the entrance and Lessonia soon followed, although subdued lighting would affect it less. Novastoa likewise was eliminated in the caves we entered, and Rhodophyceae in general increased until corallines with a widening band of Bostrychia arbuscula above took the place of the associations of exposed walls. The depth of the coralline belt increased towards the middle, where the pent-up force of the waves would be felt. Above it a band of delicate shade-loving Ceramiaceae increased even more noticeably. As the surge retreated a rich band of brilliantly coloured sponges, ascidians and sertularians was seen to project from the walls. In the water swam many maomao (Scorpus violaceus) of a glorious blue.
Comparison with Other Areas.
The biotic communities described are not merely of local incidence. Workers in other areas, especially Oliver, have paid attention to either faunal or algal constituents of some, but the following associations are recognised as such and described for the first time:—Chthamalus association: Apophloea-Elminius association: Novastoa-encrusting coralline association: Nemastoma association: large Rhodophyceae association.
Table 1 locates the Poor Knights communities in a schematic arrangement of association-complexes of the coasts of the Auckland. Province with which we are best acquainted. Definite localities are selected and only the communities of insolated rock surfaces are treated. East coast profiles are given first, Narrow Neck providing a calm water contrast. Anawhata on the west coast introduces a typical D'Urvillea association.
In each of these localities the complex that we have chosen for illustration is only one of several that might be counted typical.
Each of the islands has a more exposed and a more sheltered side, the latter usually involving a certain amount of sand. At Anawhata, rocks of the ends of headlands have a different population from those of the sides of bays and even the seaward and landward sides of one boulder may differ widely. There are many alternative communities then that we have made no attempt to place. Our efforts have been directed rather towards choosing one regular constantly recurring sequence that is well represented in the selected locality whatever other complexes may also be present. This demonstrates afresh the exceptional uniformity of conditions on the Poor Knights where the one association-complex is continuous round almost all the islands.
It is seen that important adjustments occur at the expense of one association or another if biotic competition changes. Thus in the absence of the dominant of a widely-spread association another may take its place, e.g. on the Poor Knights the almost ubiquitous Chamaesipho columna is missing and its potential area is held by converging Chthamalus and Apophloea-Elminius. The table shows also the position the Gigartina alveata association would take had its development been favoured on the Poor Knights as it is at Anawhata, and at Sandy Bay or Lang's Beach on the eastern mainland.
Measurements are omitted as of no immediate value as tide range differs so from place to place over the whole area while constant swell tends to carry all belts higher. The proportions held by the same communities on comparable slopes agree within any one complex showing the outstanding importance of periods of emergence, governed by tides.
The absence or scarcity of certain species and the consequent non-development on the Poor Knights of some of the communities important on nearby mainland shores are probably related to incompatibility with ecological factors rather than to lack of germules in the water: to take an obvious example, spores, eggs or larvae of sand and mud-dwellers must frequently arrive but have no chance of establishing where rock is the only substratum. The nice balance between organism, community and environment is particularly well shown where an important species has demonstrated its ability to reach the islands by the presence of scattered individuals, but has been unable to develop its characteristic association in the appropriate belt. Examples are Hormosira Banksii, Gigartina alveata, Ostrea sp., Pyura trita. Missing communities that might well have been expected under existing conditions include those dominated by Lichina pygmaea, Chamaesipho columna, Vermilia carinifera, Ostrea spp., Volsella spp., Mytilus canaliculus (there are few bivalves of any kind), Codium adhaerens, Pachymenia himantophora, Gigartina alveata and G. atropurpurea, Splachnidium rugosum, Scytothamnus australis, Carpophyllum maschalocarpum + C. phyllanthus + Cystophora spp. Others could scarcely develop with so little mud, e.g. Hormosira + Corallina + Onchidella; Colponemia + sponges + sea squirts; Elminius modestus.
It is too early to indicate the general occurrence of any of the communities outlined, as even the distribution of some of the most
striking dominants, notably D'Urvillea and the barnacles, is imperfectly known. It is however possible to state that many of the associations of both supralittoral and littoral on the Poor Knights are found equally well developed (though as yet unrecorded) on some of the rougher shores of the east coast from the Bay of Plenty to the North Cape and even to some degree on the west coast. Running south, equivalent associations may have as dominants the same (e.g. D'Urvillea antarctica) or closely allied forms (e.g. Xiphophora chondrophylla var. maxima). Between the latitudinal extremes a sorting out of associated species according to local conditions is to be expected. Only further observation and collecting will eventually show what change there is from north to south and what contrast between east and west.
Bartrum, J. A., 1936. Notes on the Geology of Three Kings and Other Outlying Islands of Northern New Zealand, N.Z. Jour. Sci. and Tech., vol. 18, pp. 520–530.
Broch, H., 1922. Studies on Pacific Cirripedes, Papers. Dr. Th. Mort. Pac. Exped. 1914–16, X, pp. 215–358.
Cockayne, L., 1906. Notes on a Brief Botanical Visit to the Poor Knights Islands, Trans. N.Z. Inst., vol. 38, pp. 351–360.
Cotton, A. D., 1912. Clare Island Survey, 15. Marine Algae, Roy. Irish Acad. Proc., vol. 31: 1, 158 pp.
Cranwell, L. M., and Moore, L. B., 1935. Botanical Notes on the Hen and Chickens Islands, Rec. Auck. Inst. Mus., vol. 1, no. 6, pp. 301–318.
Cranwell, L. M., 1937. New Plant Records from the Poor Knights Islands. Rec. Auck. Inst. Mus., vol. 2, no. 2, pp. 101-110.
Du Rietz, G. E., 1925. Die Hauptzüge der Vegetation der Insel Jungfrun, Svensk Bot. Tidskr., Bd. 19, H 3.
Falla, R. A., 1934. The Distribution and Breeding Habits of Petrels in Northern New Zealand, Rec. Auck. Inst. Mus., vol. 1, no. 5, pp. 245–260.
Ferrar, H. T., 1925. Soundings in the Seas around New Zealand, N.Z. Jour. Sci. and Tech., vol. 7, pp. 295–297.
Fraser, W. M., 1925. The Poor Knights Islands. A Brief Account of the Maori Occupation, N.Z. Jour. Sci. and Tech., vol. 8, pp. 8–14.
Gams, H., 1932. Bryo-Cenology (Moss-Societies), ch. 12 in Manual of Bryology, Ed. by F. Verdoorn, The Hague.
Gislen, T., 1929. Epibioses of the Gullmar Fjord I, Kristinebergs Zoologiska Station 1877–1927, N:r 3, pp. 1–123, Stockholm.
— 1930. Epibioses of the Gullmar Fjord II, Ibid., N:r 4, pp. 1–380.
Hamilton, H., 1925. Birds of Poor Knights and Hen Islands, N.Z. Journ. Sci. and Tech., vol. 8, pp. 15–18.
Hedley, C., 1915. An Ecological Sketch of the Sydney Beaches, Jour. Roy. Soc. N.S.W., vol. 49, pp. 15–77.
Heine, E. M., 1932. The New Zealand Species of Xiphophora with some account of the development of the Oogonium, Ann. of Bot., vol. 46, pp. 557–569.
Hewatt, W. H., 1937. Ecological Studies on Selected Marine Intertidal Communities of Monterey Bay, California, Amer. Midl. Nat., vol. 18, pp. 161–207.
Hounsell, W. K., 1935. Hydrographical Observations in Auckland Harbour, Trans. Roy. Soc. N.Z., vol. 64, pp. 257-271.
Johnson, D. S., and Skutch, A. F., 1928. Littoral Vegetation on a Headland of Mt. Desert Island, Maine, Ecology, vol. 9, no. 3, pp. 307-338.
1. Banding a little interrupted by shading which
much higher. The arrow indicates the position of a patch of D'Urvillea: Landing-place, Tawhiti Rahi. The bay is full of plankton.
2. View showing Carpophyllum elongatum, submerged Lessonia, and surface-swimming trevalli at the same landing.
Kidson, E., 1932. Average Rainfall in New Zealand for period 1891–1925, Report N.Z. Dept. of Sci. and Tech.
*Kylin, H., 1918. Svenska Västkustens Algregioner, Svensk Bot. Tidskr., Bd. 12, pp. 65–90.
— 1934. Bemerkungen über einige Florideen aus. Neu-Seeland, Kungl. Fysiogr. Sallsk. i Lund., Förhandl 1–8.
Laing, R. M., 1926. A Reference List of New Zealand Marine Algae, Trans. N.Z. Inst., vol. 57, pp. 126–185.
Lippmaa, T., 1934. La Méthode des Associations unistrates et le Système écologique des Associations, Acta Inst. et Horti. Botanici Universit Tartuensis, vol. 4, fasc. 1–2, 6 pp.
Moore, H. B., 1936. The Biology of Balanus balanoides V. Distribution in the Plymouth Area, Journ. Mar. Biol. Assoc., NS., vol. 20, pp. 701–716.
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Oliver, W. R. B., 1923. Marine Littoral Plant and Animal Communities in New Zealand, Trans. N.Z. Inst., vol. 54, pp. 496–545.
— 1925. Vegetation of Poor Knights Islands, N.Z. Jour. Sci. and Tech., vol. 7, pp. 376–384.
Powell, A. W. B., 1933. The High-Tidal Mollusca of Rangitoto Island, with Descriptions of a New Genus and Two New Species, Trans. N.Z. Inst., vol. 63, pp. 144–153.
Richards, P. W., 1932. Ecology, ch. 13, in Manual of Bryology, Ed. by F. Verdoorn, The Hague.
*Sernander, R., 1917. De nordeuropeiska havens växtregioner, Svensk Bot. Tidskr., Bd. 11, pp. 72–124.
Southern, R., 1915. Clare Island Survey 67. Marine Ecology, Proc. Roy. Irish Acad., vol. 31, 110 pp.
*Vaillant, L., 1870. Observations faites à Saint Malo sur les zones littorales supérieures, Bull, de la Soc. Philomatique de Paris, pp. 144–146.
[Footnote] * Not seen by writers.
Intertidal Communities Of Auckland Coasts.
Typical Association-Complexes of Exposed Rock Faces.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Poor Knights.||McGregor's Is (Whangarei Heads)||Hen Island.||Noises Island.||Rangitoto.||Narrow Neck.||Anawata.|
|Splash zone||Verrucaria +Cyanophyceae+ Melaraphe||Lichina +Melaraphe||Melaraphe +Lichina (rare) or Bostrychia||Lichina +Melaraphe||Lichina +Melaraphe||Lichina +Melaraphe||Lichina +Melaraphe|
|H.W.N.T.||Chamaesipho||Chamaesipho||Chamaesipho +E. plicatus||Chamaesipho||(+E. plicatus)||Chamaesipho|
|Apophlaea +Elminius plicatus||Apophlaea||Apophlaea +E. plicatus||Apophlaea||Apophlaea Oysters||Oysters||Apophlaea +igartina alveata|
|Novastoa+ encrusting coralline||Hormosira +Corallina||Hormosira||Oysters||Hormosira||Hormosira|
|L.W.N.T.||Xiphophora||Xiphophora||(Nemastoma) Xiphophora||Xiphophora or Mytilus||Corallina||Corallina||Pachymenia D'Urvillea|
|L.W.S.T.||Carpohyllum elongatum||C. maschalocarpum||C. maschalocarpum||C. maschalocarpum||C. maschalocarpum||C. maschalocarpum||C. maschalocarpum encrusting corallines|