The upper limit of the barnacles in quantity, the” Chamaesipho–line,” is best seen on steep, exposed faces, where it is sharply defined, the thick barnacle cover ending abruptly. The level of the” Chamaesipho-line” varies in height in relation to the intensity of surf experienced, as noted by Evans (1947b) for the” Chthamalus-line” on the English shore. In sheltered localities the upper limit lies in the region of M.H.W.S., while on steep, semi–exposed faces it reaches up to E.H.W.S. Where the rocks are exposed to strong wave action the effect of the surf is to raise the upper limit considerably. This is particularly evident on sloping rock faces where the waves run up the shore as they break. Here the upper limit of the barnacles may extend up to several feet above E.H.W.S. On one shaded, exposed, sloping face, on the west side of the bay, with an angle of about 45° the upper limit reached by the barnacles is 20 feet above M.L.W.N. The lower limit of the barnacle zone is also frequently marked by a barnacle line on exposed vertical faces. This line is, however, not as clearly marked as the upper one, and varies with the amount of exposure to direct wave action. On very exposed faces the barnacle zone extends down to the upper limit of Durvillea at about M.L.W.N. In some localities, however, there is a band of pink” Lithothamnion” extending up to 18 inches above the upper limit of the bull kelp; in others there is a similar band of Corallina. The presence of these calcareous algae appears to limit the downward extension of the barnacles. With increase in shelter the upper limit of the algal zone of the infralittoral fringe is raised and the lower limit of barnacles in quantity ends at E.L.W.N., with scattered individuals extending down to M.L.W.S. Evans (1947a) and Moore (1935) both note the effect of surf in lowering the lower limit of Balanus, the English equivalent of the local species. The same effect is noted for C. columna and E. plicatus. This may be partly due to competition with algae and mussels with increasing shelter or, as Moore (1935) suggests, to the increased aeration of the water that occurs where surf action is strong.

The nature of the rock surface bears a direct relationship to the density of the barnacle cover; smooth, polished rocks may be completely bare, while adjacent rough rock may have a dense population. Movable material has an adverse effect on the development of both Chamaesipho and Elminius, barnacles being absent or sparsely represented on the boulder beaches, where the abrasive action of the shifting rocks destroys the newly settled larvae.

The negative correlation between barnacle and brown algal distribution noted by British workers (Moore, 1935; Evans, 1947b) does not occur in the areas studied. The main species of algae in the barnacle zone, Scytothamnus, Adenocystis, Colpomenia, Ulva and Porphyra are of seasonal occurrence, and the year round breeding season enables the barnacle larvae to become established in the absence of the algae. However, as mentioned above, there is a negative correlation between barnacle development and the growths of Codium adhaerens. This latter species occurs only locally in the lower half of the barnacle zone.

Elminius modestus. Range: M.T.L −1. 0 ft. to below E.L.W.S.; 55% to 0.0% exposure.

This species, although common throughout the area studied, does not form a dense cover except under special circumstances. It is not tolerant of strong wave action, being absent in semi-exposed and exposed situations, but characteristic of the more sheltered regions. As mentioned by Moore (1944) and Dellow

(1950) its most striking ecological attribute is its ability to withstand brackish and very muddy water. Thus it is found high on the shore, often above the upper limit of the other species, where fresh or brackish water seeps over the rock surface. The upper limit of E. modestus normally lies about a foot above M.T.L., while its lower limit, unlike that of the other species of barnacle, extends down below E.L.W.S. It also differs from the other species in that it can tolerate shade to a much greater extent, being found on the under sides of fixed boulders. When the lower parts of stones are buried in the sand or mud there is usually a thick fringe of E. modestus around the embedded edge. This ability to tolerate coverage by sand and mud is another characteristic of this species, enabling it to colonize substrata, such as level platforms, that may be covered by fine sand or silt. E. modestus is also a characteristic species of the mussel beds of the lower portion of the midlittoral zone and the infralittoral fringe, often forming a dense cover on the shells of M. planulatus and M. canaliculus. In some localities few specimens of the mussels are without a few attached Elminius.

Melaraphe oliveri. Range: E.H.W.S. + to about M.T.L.; 100% to 50% exposure.

The habits and habitat of this species are very similar to those of the British species Littorina neritoides. The supralittoral zone above E.H.W.S. is populated almost exclusively by M. oliveri, in addition to M. cincta in some localities. It is absent where the upper parts of the beach are covered with movable boulders; but abundant on rock masses, headlands and cliffs, especially on steep, rough, exposed faces. The species occurs in decreasing numbers from semi–exposed to sheltered situations, being scarce or absent under conditions of extreme shelter. It is also absent where the water is normally laden with muddy sediment as in the upper reaches of Lyttelton Harbour. Shade favours the development of a M. oliveri zone, the upper limit extending up considerably higher on rock faces that are normally shaded. On faces exposed to direct sunlight the snails are restricted to cracks and crevices.

The upper limit of distribution is extremely variable, depending on the amount of shade and the degree of exposure to wave action. On one very exposed, shaded, steep stretch of coast, where there is considerable splash, keeping the cliff face constantly moist, specimens have been found up to 48 feet above C.D. (i.e., E.H.W.S. + 40 ft.). On sunny faces, however, the upper limit extends about 10 feet above E.H.W.S. The optimum lower limit lies at about M.T.L. + 1.0 ft. Below this point scattered individuals are found, especially where there is a good cover of barnacles.

Melaraphe cincta. Range: E.H.W.S. + to E.H.W.N.; 100% to 75% exposure.

The vertical range of this species is more restricted than that of M. oliveri. The lower limit is relatively constant at E.H.W.N., while under sheltered shaded conditions its upper limit is a little lower than that of M. oliveri. This snail prefers rather more sheltered conditions than M. oliveri, and is best developed on irregular broken rock with plenty of cracks and crevices. It is also more tolerant of water laden with fine sediment, being found further up Lyttelton Harbour than M. oliveri.

Melagraphia aethiops. Range: E.H.W.N. −0.5 ft. to M.L.W.S.; 60% to 0.0% exposure.

Melagraphia is intolerant of exposure to surf, and is found on the open rock surface only in sheltered situations. On broken surfaces it may be found in

crevices and on the landward side of projecting rocks and ledges, where there is a degree of local protection from surf action. The favourite habitats of the species are boulder banks, where it is often the most abundant species in the spaces between the stones, areas of flat rock near M.T.L. and among the brown algae between E.L.W.N. and M.L.W.S. In the range of habitats M. aethiops resembled the European species Gibbula umbilicus, which prefers stony gullies, boulder areas and flat rocks (Evans, 1947). The vertical ranges of the two species are also similar, that given by Evans for Gibbula being from E.H.W.N. to M.L.W.S.

The upper limit of M. aethiops generally lies below E.H.W.N., although in rock pools it may be found as high as M.H.W.S. It is generally most abundant between M.T.L. and E. L.W.N. The lower limit is rather variable, depending on the type of cover. It is absent from areas covered by Corallina and among the mussel beds, but plentiful among the brown weeds, Carpophyllum and Cystophora, down to E.L.W.S.

Lepsiella scobina albomarginata. Range: M.H.W N. + 0.5 ft. to midway between M.T.L. and E.L.W.N.; 85% to 40% exposure.

Throughout the midlittoral zone this is the most abundant gastropod, occurring in large numbers throughout the upper barnacle zone. Barnacles appear to form its main article of diet and there is a definite correlation between the distribution of Lepsiella and that of the barnacles, especially C. columna, the snail being more abundant on growths of the small Chamaesipho than on the larger Elminius plicatus. The small black bivalve Modiolus neozelanicus also forms part of the diet of Lepsiella, which occurs throughout the zone occupied by Modiolus, although not as abundantly as on barnacle covered rocks.

Lepsiella resembles the species Nucella lapillus, which occupies a similar ecological niche on the British coast, in that while it is more tolerant of waves and surf than the Trochidae, it still requires a certain amount of local shelter in barnacle areas (Evans, 1947a). Where the wave action is strong Lepsiella is absent from vertical exposed faces; but is present in large numbers in crevices and on the landward sides of rocks and boulders.

The upper limit of the species generally lies midway between M.H.W.S. and M.H.W.N., although in situations where the height of the barnacle zone is extended upwards by wave action the upper limit may be raised considerably. The lower limit is rather more variable. In the area studied the lower limit of Lepsiella in quantity lies about halfway between M.T.L and E.L.W.N., although occasional specimens are found down to the lower limit of the barnacles at M.L.W.N. On other parts of the coast of Banks Peninsula the lower limit may extend down to M.L.W.N.

Sporadically throughout the region studied there occurs a colour variety of the species with a reddish orange interior to the shell opening. This is regarded as a sub-species Lepsiella scobina rutila; but appears to be simply a colour variety of the sub-species albomarginata, as the two occur on the same rock surface, with the variety rutila much less numerous.

Sypharochiton pelliserpentis. M.H.W.S. to E.L.W.S. -0.5ft.; 95% to 0.0% exposure.

This is one of the most ubiquitous animals on the shore, ranging from conditions of extreme exposure to those of extreme shelter. It extends practically

throughout the inter-tidal zone, and is tolerant of a wide range of substrates and conditions of shade. In habits and habitat this species resembles the limpets Cellana radians and C. ornata, occupying a similar ecological niche.

The upper limit of the species generally lies at M.H.W.S., although occasional individuals may be found above this point, especially on well shaded faces. Exposure to wave action, with consequent increase in the amount and height of splash, raises the upper limit several feet, coinciding with that of the barnacles From M.H.W.S. down to the upper edge of the kelp zone of the infralittoral fringe, Sypharochiton is evenly distributed, except where Pomatoceros encrustations and dense mats of Modiolus occur. It is common among the mussel beds of both the lower midlittoral and the infralittoral fringe; but is rare where there is a thick covering of algae, except in the holdfasts of Durvillea. The lower limit lies a few inches below E.L.W.S.

Throughout the barnacle zone this species competes with the barnacles for space, and where dense growths of the latter occur it is often confined to cracks and crevices. Its articulating shell enables it to cling to very irregular surfaces that are not suitable for the attachment of limpets. With regard to slope and type of substrate S. pelliserpentis is extremely tolerant; it occurs on all types of surface, from very rough pitted rock to smooth polished surfaces; is common on all angles of slope, even under overhangs, and is plentiful on the undersides of boulders.

The shells of specimens on the lower region of the shore are often encrusted with “Lithothamnia,” while those of the upper regions are usually deeply eroded. Sypharochiton is also a common inhabitant of rock pools, especially those high on the shore, being found in lithothamnia-encrusted pools above E.H.W.S.

Limpets. Three species of Cellana, C. radians, C. ornata and C. redimiculum, occur within the region, the latter having a restricted local distribution. Other common species of limpets are Patelloida corticata, Notoacmea pileopsis, Notoacmea parviconoidea, Notoacmea daedala and Atalacmea fragilis. In addition there occur four species of the limpet-like Siphonariidae, Siphonaria australis, Siphonaria zelandica, Siphonaria cookiana and Benhamina obliquata. As it is planned to deal with the distribution and ecology of these species in a subsequent work, the zonation of a few selected species will be briefly summarized.

Cellana ornata. Between E.H.W.S. and M.H.W.S. to E.H.W.N. -; 95% to 60% exposure.

This species is characteristic of the upper region of the midlittoral zone. Its upper limit generally lies below E.H.W.S.; but where conditions of shade and moisture are suitable it may be, with the exception of the Littorinids, one of the highest animals on the shore. It is found from sheltered to exposed situations, being highly characteristic of the latter, and typically prefers rough rock surfaces. The lower limit in quantity lies between E.H.W.N. and M.T.L., although individuals may be found below these levels.

Cellana radians. Range: M.H.W.N. to E.L.W.S.; 80% to 0.0% exposure.

This limpet is less tolerant of exposure than C. ornata, being more characteristic of situations where there is local shelter from direct wave action. It also differs in that it is common on the undersides of boulders and on smooth polished surfaces. Its zone of abundance begins where C. ornata decreases in numbers and

is common right down to E.L.W.S., except where there is a thick covering of algae. C. radians is also common in rock pools up to above E.H.W.S.

Notoacmea parviconoidea. Range: M.H.W.S. to E.L.W.S.; 95% to 0.0% exposure.

Notoacmea occurs throughout the inter-tidal zone in situations ranging from extreme shelter to extreme exposure. The upper limit is variable, depending on the amount of shade and splash. Where conditions are suitable the species may be found up to several feet above E.H.W.S.

Patelloida corticata. Range: E.L.W.N. + 1.0 ft. to E.L.W.S.; 40% to 0.0% exposure.

Patelloida is characteristic of exposed situations, especially on vertical rock faces above the upper limit of the infralittoral fringe. Here there is often a band of “Lithothamnion” about 18 inches wide between the upper limit of the algae and the lower limit of the barnacles. Large numbers of Patelloida with lithothamnion-encrusted shells are found in this zone.

Mytilus canaliculus. Range: E.H.W.N. -1.0ft. to below E.L.W.S.; 60% to 0.0% exposure.

M. canaliculus, the green mussel, can be regarded as an indicator species of localities subject to strong wave action, being characteristic of the infralittoral fringe of the outer exposed headlands. With increase in shelter the species is less frequent and is replaced by M. planulatus and species of red and brown algae.

Although isolated specimens and small clumps may be found up to a foot above M.T.L. the optimum upper limit of the species in quantity lies at about E.L.W.N., just above the upper limit of the brown kelps. Where M. canaliculus and M. planulatus overlap the former species is dominant in the lower part of the “mussel zone” from M.L.W.N. down, while the latter is dominant in the upper part between E.H.W.N. and M.L.W.N. Although scattered individuals of one species may be found in the band occupied by the other, the transition between the M. canaliculus and M. planulatus zones is usually sharply defined. The development of both species is favoured by surf as noted by Fischer (1929) and Newcombe (1935) for Mytilus edulus and by Guiler (1950) for M. planulatus. Dense beds of M. canaliculus are also only found where the water is comparatively clean, being replaced by beds of M. planulatus where the water is muddy.

Beveridge and Chapman (1950) recognize a Durvillea-Mytilus association at Piha, occurring in the form of two separate consociations dominated either by Durvillea or Mytilus, the two species appearing to be antagonistic to each other. This antagonism has not been observed at Taylor's Mistake, Durvillea and Mytilus usually occurring together. Where one of these species occurs alone the angle of rock slope and the type of substrate is generally responsible for the absence of the other. On broken, exposed headlands, where a good growth of Durvillea is usually found, the spaces between the holdfasts are covered with densely packed mussels often several layers deep. The older mussels often have deeply eroded shells and bear encrusting coralline algae. The densest beds are found where there are platforms and projecting broken rock below M.L.W.N.

M. canaliculus is absent on smooth, vertical, exposed faces, being replaced by “Lithothamnia” and other species of red algae. The species is also found well into the infra-littoral, growing abundantly in several fathoms of water.

Mytilus planulatus. Range: E.H.W.N. + to M.L.W.S. + 0.5ft.; 75% to 10% exposure.

This species is more characteristic of the midlittoral zone and of regions of moderate exposure to wave action. It is also much more tolerant of shelter than M. canaliculus. Optimum development in the form of extensive beds, from E.H.W.N. down to just above M.L.W.N. is seen on semi-exposed faces and platforms where there is a considerable amount of wave movement. Under such conditions M. planulatus competes with barnacles for space and mussel beds are absent on steep, smooth faces, which are colonized almost exclusively by barnacles, but are well developed on broken or fissured rock where the dense growth of mussels prevents the barnacles from colonizing the rock surface. Barnacles, however, are abundant on the shells of the mussels, E. modestus being characteristic of the lower part of the M. planulatus zone and E. plicaius of the upper part.

M. planulatus is more tolerant of shade than M. canaliculus, growing well under overhangs. It can also tolerate muddy water and sediment to a much greater extent, penetrating considerably further up Lyttelton Harbour. In sheltered situations, where the Pomatoceros encrustations are developed, M. planulatus is restricted to a narrow band, a foot to eighteen inches in vertical height, above the upper limit of the Pomatoceros zone.

The lower limit of the M. planulatus zone is usually well defined, lying about half way between M.L.W.N. and M.L.W.S.; below it is replaced by thick growths of algae, or by M. canaliculus.

Aulacomya maoriana. Range: E.H.W.N. - 1.0ft. to below E.L.W.S.; 60% to 0.0% exposure.

This species, the ribbed mussel, has a much more scattered distribution than the previous mussel species. It is found singly or in scattered clumps throughout the lower midlittoral zone and the infralittoral fringe, never forming a closed community as to M. canaliculus and M. planulatus. Aulacomya grows well on a wide range of substrates, from smooth rock faces to stable boulder banks, and is tolerant of varied conditions of exposure, being found on very exposed head-lands and in sheltered muddy situations. It also differs from M. canaliculus and M. planulatus in that it is common on the undersides of boulders.

Modiolus neozelanicus. Range: M.H.W.N. + to E.L.W.N. - 1.0ft.; 85% to 40% exposure.

This species is extremely tolerant of a wide range of environmental conditions, occurring on all types of substrate in situations of extreme exposure to those of extreme shelter. It resembles E. modestus in that one of its most striking ecological attributes is its ability to withstand brackish and muddy water. It penetrates right to the upper end of Lyttelton Harbour, where it is found on level platforms that are covered by a layer of silt and mud. M. neozelanicus can also tolerate coverage by sand to a much greater extent than any of the other dominant sessile animals of the littoral zone. Thus Modiolus is able to colonize rock surfaces, between M.H.W.N. and M.L.W.N. that subject to periodic coverage by shifting sand, and is often the only species in such situations. On isolated rocks projecting from the sand in the centre of the bay Modiolus is well developed on the sides and forms a compact mat on the flattened tops where sand accumulates.

The development of a Modiolus zone depends largely on the degree of exposure to wave action. In exposed situations the species competes with C. columna, E. plicatus and M. planulatus both for space and for food, while in sheltered regions it competes with Pomatoceros coeruleus. On sheltered faces where Pomatoceros encrustations are developed the vertical range of Modiolus is very much restricted, forming a vertical band, about 2 feet wide, from between M.H.W.S. and M.H.W.N. down to E.H.W.N. On the open exposed coast, on the other hand, the lower limit lies well below E.L.W.N. and the upper limit varies considerably with the degree of wave action.

On steep, vertical, exposed faces Modiolus forms a band, about 6 feet wide, commencing about 3.5 feet above the upper limit of the infralittoral algae. Throughout this band Modiolus is mixed with C. columna, the greatest density of the former occurring in a band about 2 feet wide, between 4.5 and 6.5 feet above the upper limit of the algae. Surf has the same effect on the upper limit of this bivalve as on that of the barnacles. On the sloping exposed face on the west side of the bay, mentioned above in connection with the distribution of C. columna, the upper limit of Modiolus lies about 18 feet above the upper limit of the infra-littoral fringe, to within 3 feet of the upper limit of the barnacles.

On smooth vertical faces in situations of extreme exposure Modiolus is usually absent; but is well developed in crevices and on platforms and ledges between M.H.W.S. and M.L.W.N.

Pomatoceros coeruleus. Range: M.H.W.N. to M.L.W.N.; 75% to 10% exposure.

The calcareous tubes of this species may be found singly or in small groups at almost any level of the midlittoral zone, except on exposed vertical faces. Where the surface is broken it occurs in cracks and crevices and on ledges where there is a degree of local shelter from direct wave action. However, in sheltered areas Pomatoceros occurs as an encrusting mass of tubes, closely packed and intertwined, completely covering the rock surface. These encrustations may reach a thickness of eighteen inches, the bulk of the mass consisting of empty tubes packed with sand, pieces of shell and other debris. The worms occupy the outer ends of the tubes, which grow out more or less at right angles to the rock surface and are so closely packed that when they are covered by water the protruding gill filaments form a dense blue carpet.

These encrustations are particularly well developed on vertical faces at right angles to the wave front, and on exposed shores similar growths are found on the sheltered landward sides of fixed boulders, projecting rocks and ledges. In its inability to tolerate strong wave action Pomatoceros shows a marked resemblance to the common Australian, intertidal Serpulid, Galeolaria caespitosa (Dakin, et. al., 1948; Guiler, 1950), which forms similar encrustations under sheltered conditions.

The lower limit of the Pomatoceros zone is sharply marked at about M.L.W.N., the region below being occupied by M. planulatus, M. canaliculus and the algae of the infralittoral fringe. On vertical sheltered faces the zone extends up about 4 feet from this level to E.H.W.N. with scattered individuals up to M.H.W.N. In semi-exposed areas, although Pomatoceros occurs only as isolated tubes and in the form of small patches of tubes attached lengthwise to the substratum, the limits are approximately the same.