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Volume 79, 1951
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Seasonal Changes in Micro-plankton in the Otago Harbour during the Years 1944 and 1945

[Read before Otago Branch an May 1, 1951; received by Editor, May 7, 1951]

Historical Survey

Plankton stations in New Zealand waters were made by the Terra Nova expedition in 1910 and by the Dana expedition in 1928 and 1929. However in neither case was the stay in New Zealand waters sufficiently long to enable an account to be given of the seasonal changes in the plankton. Data concerning the macroplankton appears in the Terra Nova reports, but no account of the phytoplankton collected by this expedition has as yet been published. Most of the Dana material still remains in Copenhagen awaiting investigation. Two reports have been published—one on Ceralium and one on Quantitative Investigations on the Distribution of Macroplankton in Different Oceanic Regions. In Australian waters regular plankton collections and hydrological investigations were made by members of the Great Barrier Reef expedition off the north-east coast from July, 1928, till July, 1929, and by Dakin and Colefax off the south-east coast from 1929 till 1934 and full accounts of the seasonal changes in both regions are available. Little is known of the plankton of the Polar Regions south of New Zealand, as the various antarctic expeditions have concentrated on the South Georgia Region and the Northern Region east of it.

The present survey was made with the idea of comparing seasonal changes in the New Zealand region with those recorded elsewhere.

Description of the Locality

Investigations were carried out at the Portobello Marine Biological Station (Lat. 45·52°S, Long. 170·40°E) situated on the north-west extremity of the Portobello Peninsula (Text-fig. 1), which extends halfway across the Otago Harbour and which with Quarantine and Goat Islands forms a broken chain of land incompletely separating the harbour into an upper three-fifths and a lower two-fifths. The harbour is fifteen miles in length, less than four miles in breadth at its widest part, and full of sandbanks partly exposed at low tides. Two channels connect the upper and lower parts of the harbour, the main one between Goat and Quarantine Islands, and the Portobello one, into which the wharf at the Marine Station extends (Text-fig. 1). The only stream of any importance draining into the harbour is the Leith, which empties into the upper end, and it has been calculated that the amount of fresh water from the watershed area is approximately 3,750,000,000 cubic feet per year—an amount that would have no appreciable effect upon the salinity, the average inflow of a single tide being but slightly less in volume. The amount of extraneous nitrogenous material present is negligible, as no sewage system enters the harbour.

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Text Fig. 1—Sketch-plan of Otago Harbour between Port Chalmers and Portobhello showing the site of the Portobello Marine Biological Station. Scale 2,000 feet to the inch.

The Marine Station is in an exposed position, the wind being usually either fresh to strong from the south-west or moderate to fresh from the north-east. Sea temperatures recorded at the end of the jetty during 1945 showed a maximum of 18°C. in the middle of February, and a minimum of 3·3°C. towards the end of July. This wide range can be accounted for partly by the fact that the incoming water flows over extensive sand banks exposed to air temperatures for a considerable period of the day. As would be expected from the fact that the Marine Station is situated six miles from the harbour mouth, the plankton is almost entirely coastal in nature and but few oceanic forms appear.

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Methods

Surface nettings of one hour duration and water samples for centrifuging were taken fortnightly, sometimes weekly, from the end of the wharf at the Marine Station and always on the incoming tide. Collection of plankton under standard conditions began on October 9, 1944, and was continued until November 3, 1945, all samples being taken about noon or in the early afternoon. Time, temperature of the water, light, and force and direction of the wind were recorded during each netting period. In addition, daily records of temperature and wind kept by the curator of the station and daily records of the number of hours of bright sunshine in Dunedin kept by the Meteorological Office were available for the entire period under survey. Unfortunately, it was impossible to get analyses of the phosphate and nitrate contents of the water.

A plan of the bolting silk nets used and of the associated gear is given in Text-fig. 2. This collecting method was planned by the author and Miss E. J. Batham, the latter being responsible for the survey of the macroplankton collected in the coarser net (65 threads to the linear inch). Experiments were carried out to estimate the speed of the current in feet per second and as it was found to be directly correlated with the pull registered by a spring balance inserted in the rope carrying the nets. During each netting period five balance readings were taken and the average reading for the period calculated. From this a correction factor for current was worked out for each plankton haul and applied to the counts so that in each case the resulting figures would be given as for a balance pull of one and a half pounds. The catch from the finer net (100 threads to the linear inch) was used for the estimation of microplankton only, three samples each of 0·1 cc. being counted in a squared Rafter cell. Owing to the fact that in collections made as above statistical accuracy is impossible, the results of this investigation can be used only to indicate the general trend of seasonal changes and no true quantitative significance can be given to the counts obtained. Hence in the charts symbols are used to indicate numerical ranges as stipulated below:

Symbol Phytoplankton
vs. less than 300,000 haul
s. 300,000–600,000 haul
c. 600,000–1,000,000 haul
a. more than 1,000,000 haul

From water samples taken at the surface at the same time as the nettings 12·5 cc. were placed in each of four tubes and centrifuged for 15 min. at 1,000 revs. per min. The surface water was then pipetted off until 2·5 cc. remained in each tube and the contents of two tubes were transferred to the other two and recentrifuged for 15 minutes. Again the surface water was pipetted off till 2·5 cc. remained. From these three samples each of 0·1 cc. were counted in a Rafter cell and the number of organisms in 50 cc. estimated. It was found that small naked Dinoflagellates, ciliates and flagellates were not damaged by the long period of centrifuging and were well represented.

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Text-fig. 2—Sketch-plan of the bolting silk nets and associated gear.

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Micro-Plankton Calendar Based on Net Samples

November, 1944—Sea temperature, 10·0°C.–14·5°C.; weather, mainly fine; winds, fresh; rainfall, 0·07 in.; monthly sunshine total, 168·0 hrs. Mainly pennate forms, Grammatophora, Nitschzia, and Striatella. Coscinodiscus, though not present in large quantities, more abundant than in any other month.

December, 1944—Sea temperature, 11·6°C.–16·6°C.; weather, mainly fine; winds, fresh; rainfall, 0·19 in.; monthly sunshine total, 130·3 hrs. Mainly pennate forms. Grammatophora, Striatella and various Navicula sp.

January, 1945—Sea temperature, 13·3°C.–17·8°C.; rainfall, 0·1 in.; monthly sunshine total, 165·4 hrs. Mainly pennate forms, Grammatophora, Lycmophora and various Navicula sp.

February, 1945—Sea temperature, 13·9°C.–18·0°C.; winds, mainly light; rainfall, 0·18 in.; monthly sunshine total, 143·8 hrs. Scarce, mainly pennate forms. Small outbursts of Leptocylindricus and Bacillaria.

March, 1945—Sea temperature, 11·6°C.–16·1°C.; weather, mainly fine; rainfall, 0·06 in.; wind, light; monthly sunshine total, 165·3 hrs. Autumn peak with outbursts of Skeletonema and Eucampia towards the end of the month; otherwise diatoms scarce, represented mainly by Navicula sp.

April, 1945—Sea temperature, 8·3°C.–13·9°C.; weather variable; rainfall, 0·10 in.; monthly sunshine total, 114·5 hrs. Marked increased in numbers of Chaetoceros, Coscindosicus, Thallassiosira; Eucampia still abundant; Streptotheca, Ditylium and Asterionella appear; pennate forms not so numerous.

May, 1945—Sea temperature, 7·2°C.–10·0°C.; weather variable; winds, fresh to strong; rainfall, 0·30 in.; monthly sunshine total, 75·8 hrs. Chaetoceros, Coscinodiscus, Eucampia, and Streptotheca present; Stephanopyxis appears; marked increase in Asterionella, Nitschzia, and Biddulphia.

June, 1945—Sea temperature, 5·5°C.–7·2°C.; weather, overcast at the beginning of the month, later fine with clear frosty nights; rainfall, 0·07 in.; monthly sunshine total, 92·5 hrs. Chaetoceros, Coscinodiscus, Stephanopyxis, and Chaetoceros socialis abundant; most of the centric forms present. but not in large numbers.

July, 1945—Sea temperature, 3·3°C.–6·1°C.; weather, fine and frosty; rainfall, 0·03 in.; monthly sunshine total, 130·4 hrs. The spring peak occurred at the beginning of the month. Huge increases in Chaetoceros socialis, and other Chaetoceros sp., in Thalassiosira, Eucampia, Lauderia, Stephanopyxis and Asterionella; slight increase in Skeletonema; Ditylium and Rhizosolenia appear; Streptotheca disappears.

August, 1945–Sea temperature, 5·0°C.–7·7°C.; weather mostly fine and frosty; rainfall, 0·01 in.; monthly sunshine total, 106·4 hrs. Diatom numbers not so great as in July; Chaetoceros, Thalassiosira, Eucampia, Lauderia still abundant; Chaetoceros socialis, Ditylium, Asterionella, and Rhizosolenia still present; marked increase in Nitschzia.

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September, 1945—Sea temperature, 6·6°C.–10·0°C.; weather, cloudy; rainfall, 0·06 in.; monthly sunshine total, 131·5 hrs. Diatoms few, Nitschzia the most important genus; Rhizosolenia more abundant than in any other month; Chaetoceros socialis absent.

October, 1945—Sea temperature, 8·3°C.–11·6°C.; weather, mainly fair but changeable; rainfall, 0·08 in.; monthly sunshine total, 153·3 hrs. Diatoms few; Grammatophora alone abundant.

Composition of the Micro-Plankton as Shown by the Fine Net Samples

Dinoflagellates. Dinoflagellates were very poorly represented and made up only one per cent. of the unicellular organisms caught in the fine net. The only ones seen were a few Gyrodinium species, two specimens of Ceratium furca (Ehrenberg) Dujardin and thirty-one specimens of Peridinium divergens Ehrenberg. It is of interest to note that in Hardy and Gunther's report of the Discovery expedition (1935) it is stated that the genera Ceratium and Peridinium are unimportant in the Antarctic phytoplankton, whilst in Dakin and Colefax's report on the plankton of the Australian coastal waters (1940) it is stated that they are an important group, Peridinium being well represented as well as related genera and species of Ceratium. The almost complete absence of Ceratium in the Otago Harbour is to be expected in an almost entirely coastal plankton, but the paucity of other dinoflagellates, especially of Peridinium species rather indicates that in thecate dinoflagellate production the waters of the Otago Harbour more closely resemble those of the Antarctic region. Another point of interest is the fact that, whilst Peridinium is regarded as a summer form in most regions of the world and was definitely found to be so in Australian waters (Dakin and Colefax, 1940), in the Otago Harbour in 1945 it was a spring form (July to October) and was not found at all in the summer tow nettings.

Other Unicellular Organisms. Apart from diatoms and dinoflagellates the unicellular organisms seen in the fine net samples were present in numbers so small as to be negligible. Those present were a few specimens of Tintinnopsis, a few naked ciliates, several foraminifera of the genera Globigerina, Spiroloculina and Textularia, and a few radiolaria of the genus Acanthometron. Halosphaera viridis, though common in hauls taken from the middle of April until the end of September, never got into the fine net samples and hence was recorded with the macro-plankton. Coccosphaerales, Silicoflagellates and Phaeocystis were not represented at all.

Diatoms. Diatoms made up almost ninety-nine per cent. of the fine net samples. A real seasonal cycle of growth was shown, such as has been recorded by numerous workers for the colder waters of the northern hemisphere and by Dakin and Colefax (1940) for Australian coastal waters in the southern hemisphere. In the Otago Harbour the spring maximum was well marked with well over a million cells per haul and occurred early in August in 1944, early in July in 1945,

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Text-fig. 3—Graph showing abundance of phytoplankton in surface collections from October, 1944, to November, 1945. The asterisk at the top of the spring phytoplankton peak indicates that the total number of diatom cells is higher than indicated, as the number of cells present in each Chaetoceros socialis colony was not estimated.

Following the 1945 spring maximum there was a small subsidiary maximum late in August, 457,000 cells per haul (Text-fig. 3). Centric diatom numbers were low in summer and early autumn. In 1945 a small autumn maximum of short duration occurred late in March, 635,800 cells per haul.

As can be seen from Text-Fig. 4 and from the seasonal calendar, the two diatom species mainly responsible for the autumn maximum were Skeletonema costatum and Eucampia zodiacus, Leptocylindricus danicus having reached a maximum in the preceding month and its numbers being somewhat on the decline at this time. Dakin and Colefax (1940) report that in Australian waters, 33°S., the diatom genera responsible for the autumn maximum in 1931 were Leptocylindricus, Rhizosolenia, Chaetoceros and Asterionella. Of these only Leptocylindricus was at all prominent in the waters of the Otago Harbour, 46°S. Lebour (1917) reports that at Plymouth, 50°N., the genera responsible for the autumn maximum in 1915 were Mastigloia, Chaetoceros, Lithodesmium, and Skeletonema. Of these, only Skeletonema was a major factor in the autumn maximum with us. It is worthy of note that Chaetoceros which is a very important genus in the autumn maximum in most places was present only in very small numbers at this season.

Diatoms were, on the whole, low after the autumn maximum and remained low during the winter months. In this period Streptotheca, Biddulphia, Asterionella, Ditylium and Chaetoceros socialis appeared

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for the first time in 1945, Streptotheca, Biddulphia and Asterionella reaching their maxima and a definite increase in numbers being shown by Nitzschia seriata.

The spring maximum was heralded by increases in Coscinodiscus and in Chaetoceros species, especially in C. socialis. Thalassiosira and Asterionella, which are reported as heralding the spring peak in Australian waters (Dakin and Colefax, 1940) were not conspicuous, both having explosive maxima at the time of the spring peak. The genera mainly responsible for the spring maximum were Chaetoceros, Thalassiosira, Lauderia, Eucampia, Stephanopyxis and Asterionella (Text-fig. 4). At this time Skeletonema reappeared and Rhizosolenia was seen for the first time in 1945. The diatom genera forming the spring maximum in the Otago Harbour are practically the same as those listed for the spring maximum at Plymouth (Lebour, 1917) and in Australian waters (Dakin and Colefax, 1940), though the order of their appearance differs slightly in the different localities.

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Text-fig. 4—Occurrence of the main diatom genera during the period from November, 1945, to October, 1946. The main maxima are indicated by a thick black line, the subsidiary maxima by cross hatching.

Following the spring peak there was a marked falling off of diatom production, though the numbers of Thalassiosira, Lauderia, and Eucampia remained fairly high until the end of August (Text-fig. 4). With the development of maxima in Nitzschia seriata and Lepto-cylindricus danicus, diatom numbers increased greatly towards the

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end of August and a subsidiary spring peak occurred, after which diatom production again fell and numbers remained low throughout the rest of the spring. During the late spring and the summer months when centric diatom production was at its lowest, most of the pennate forms reached their maxima and marked increases were recorded in Navicula, Grammatophora, Lycmophora, Striatella, Gyrosigma, Bacillaria and Nitzschia.

Among the centric forms Chaetoceros, Coscinodiscus, Leptocylindricus, Thalassiosira, Lauderia and Eucampia and among the pennate forms Navicula, Grammatophora, Striatella and Gyrosigma were present throughout or practically throughout the year. Skeletonema appeared about the times of the autumn and spring peaks, but was not seen at other seasons. Nitzschia seriata disappeared for a short period in late summer and early autumn and was characterised by three maxima (November, May and August). The autumn and winter diatoms were Streptotheca, Biddulphia, Asterionella, Chaetoceros socialis, Ditylium and Stephanopyxis. All these with the exception of Streptotheca formed part of the spring maximum. Rhizosolenia appeared in July, remained throughout the spring months and then disappeared. Among the pennate diatoms Lycmophora and Bacillaria were the only two with short seasonal appearances, Lycmophora being present as a spring and summer form and Bacillaria being present as a late summer and autumn form. Diatoms with two maxima in the year were Coscinodiscus (November and May), Leptocylindricus (February and August), Eucampia (March and July), Asterionella (May and July), and Navicula (November and March) (Text Fig. 4).

Notes on the Diatoms Present. In the list of species that follows, only the more abundant and more readily recognised species are included. As the coastal plankton only was under survey, many of the genera that have been recorded both from Australian and Antarctic waters are either missing or sparsely represented. Examples of such genera are Planktoniella, Dactyliosolen, Corethron, Bacteriastrum and Rhizosolenia, the latter being represented with us by one species only.

  • Coscinodiscus concinnus W.Sm.

  • " radiatus Ehr.

  • Thalassiosira rotula Meunier

  • Lauderia borealis Gran.

  • Skeletonema costatum (Greville)

  • Stephanopyxis turris (Greville)

  • Leptocylindricus danicus Cleve

  • Corethron sp., one specimen only

  • Rhizosolenia imbricata var Shrubsolei (Cleve)

  • Chaetoceros convolutus Castracane—rare

  • " decipiens Cleve

  • " didymus Ehr.

  • " pseudocurvisetus Mangin

  • " socialis Laud.

  • Biddulphia mobiliensis (Bail.)

  • Ditylium Brightwelli (West)

  • Eucampia zodiacus Ehr.

  • Streptotheca thamensis Shrub.

  • Fragillaria sp.

  • Asterionella japonica Cleve and Möller

  • Thalassiothrix sp.

  • Striatella unipunctata Agardh.

  • Grammatophora marina Kutz

  • Grammatophora serpentina Kutz

  • Lycmophora Lyngbyei (Kutz)

  • " sp.

  • Navicula sp.

  • Navicula membranacea Cleve—

  • Gyrosigma sp. [rare

  • Bacillaria paradoxa Gmel.

  • Nitzschia closterium (Ehr.)

  • " seriata Cleve

  • Surirella sp.

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Composition of the Plankton as Shown by Centrifuged Water Samples

In the period under survey the total number of organisms per litre in individual water samples ranged from 11,500 to 69,000. The major part of the total number was made up of small naked dinoflagellates and diatoms, ciliates and flagellates being present in comparatively small numbers, and radiolaria and foraminifera being so rare as to be almost negligible. No Silicoflagellates, Coccosphaerales, Cyanophyeeae or thecate dinoflagellates were seen. No correlation could be found between the number of organisms present and the seasonal changes, the number of organisms present and the temperature, or the number of organisms present and the wind force. (Two valuations were taken of wind force, that of the day of sampling and the average of that of the day of sampling and of the previous day.) Samples were taken at approximately the same time on seven consecutive days (30/3/45 to 5/4/45 inclusive) and as considerable variation was found in the total number of organisms present, in the numbers of each group present, and in the relative abundance of the two major groups and as the variations noted could not be correlated with any single factor, it is obvious that data such as are given below (Table I) based on samples taken at weekly or fortnightly intervals has but little quantitative significance. Its value lies in the fact that small organisms which pass through the meshes of the fine net can be collected and their seasonal distribution noted and in the recording of the number of organisms per litre for comparison with such data published from other marine stations.

It is of interest to note that in 1945 the number of organisms per litre in this region is measured in tens of thousands, not in hundreds of thousands as recokoned for temperate coastal waters by Lohmann (1920).

Table 1—Average Number of Organisms in 1 cc. for Each Month
Month Dinoflagellates Centric Diatoms Pennate Diatoms Total Diatoms Flagellates Ciliates Total Organisms
1944
Oct. 7.5 10.2 6.1 16.3 2.2 1.4 27.4
Nov. 19.8 6.5 4.9 11.4 1.4 0.7 33.3
Dec. 13.4 13.0 13.6 26.6 5.7 2.3 48.0
1945
Jan. 14.0 3.7 7.5 11.2 4.1 0.7 30.0
Feb. 9.7 5.9 6.3 12.2 0.5 1.1 23.5
Mar. 15.7 10.0 8.3 18.3 4.5 1.7 40.2
Apr. 16.3 17.8 13.3 31.1 0.7 1.8 49.9
May 21.6 4.8 8.0 12.8 0.2 0.5 35.1
June 16.5 2.6 2.2 4.8 0.6 0.2 22.1
July 10.9 17.6 1.0 18.6 2.4 0.4 32.3
Aug. 17.8 8.8 0.8 9.6 1.2 0.3 28.9
Sept. 15.7 4.6 1.1 5.7 1.7 0.3 23.4
Oct. 25.5 5.7 1.0 6.7 1.0 33.2

Diatoms. The total number of diatoms per litre ranged from 1,330 to 48,000, being as a rule higher than those recorded for the tropical station of Low Isles (Marshall, 1933), the only other Southern Hemisphere station from which continuous centrifuge records are available, and a comparison of the monthly average number of diatoms per litre from Otago Harbour and the monthly average number of diatoms per

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litre from other stations (shown in tabulated form by Marshall, 1933, p. 133) shows that the production of diatoms in the Otago Harbour is most nearly comparable with that recorded for Plymouth (Lebour, 1917) and falls well below that recorded for Kiel Bay (Lohmann, 1908) and that recorded for Loch Striven (Marshall and Orr, 1927).

Centric diatoms were present in the water sample throughout the year, maximum numbers being recorded in July, 1945, in late March and in early April, 1945, and in December, 1944 (Table I). The larger species of diatoms, which are known from the study of the samples taken in the fine net to form a fair proportion of the spring maximum (see Plankton Calendar), were not present in the water samples in anything like a representative number and hence the spring increase was not well marked, being slightly less than the autumn maximum (late March, early April) caused by increases in the number of smaller diatoms (see Plankton calendar). The maximum December, 1944, was less than the maxima spring and autumn, 1945, and was due to a marked increase in Chaetoceros spp. alone, an increase shown to a less marked extent in samples collected at the same time in the fine net, and one for which it is very difficult to account.

Pennate diatoms were present in the water samples throughout the year, but as can be seen from Table I, they were not well represented in the samples collected in June, July, August or September, 1945. Marshall (1933) found that at Low Isles the number of pennate diatoms present was correlated with wind force. Such was not the case in Otago Harbour. In Otago, maximum numbers were recorded in December, 1944, and April, 1945, both of which were months of fairly strong winds, though not markedly more so than several other months.

Dinoflagellates. The number of dinoflagellates per litre ranged from 2,800 to 25,000, and in periods of low diatom production, winter, late spring and early summer, exceeded the number of diatoms present per litre. As can be seen from Table I, there is little seasonal variation in the number of dinoflagellates present, small maxima occurring in November, 1944, and in May, 1945, and in October, 1945. The 1945 October maximum is interesting in view of the fact that in October, 1944, dinoflagellates were few in number. The great majority belong to minute naked Gymnodinium spp., but an occasional Gyrodinium species was seen. Comparison of the monthly average numbers of dinoflagellates per litre from Otago and from other stations (shown in tabulated form by Marshall, 1933, p. 135) shows that production of dinoflagellates in the Otago Harbour is greater than that recorded for Low Isles, Plymouth, and La Jolla, more nearly approximates that recorded for Loch Striven, and is less than that recorded for Kiel Bay, where at certain seasons the dinoflagellates per litre were numbered in hundreds of thousands.

Flagellates. Colourless flagellates were present in small numbers, never more than 540 per litre, from the end of April until the middle of September. Euglenoid flagellates occurred in small numbers throughout the year, the maximum being 1,040 per litre recorded on December 16, 1944. The number of flagellates did not vary with the seasonal changes, the temperature of the water, or the wind force.

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Ciliates. Ciliates of the genus Tintinnopsis were present in small numbers, 20–140 per litre, except in the months of May, June and July. Naked ciliates were seen occasionally throughout the year, but only one species was present in large numbers, up to 3,000 per litre being recorded from the beginning of November, 1944, until the end of May, 1945.

The number of ciliates did not vary with the seasonal changes in the temperature of the water or the wind force.

Radiolaria and Foraminifera. These groups were extremely rare, three specimens of Acanthometron and one of Globigerina being noted during the year's survey.

Notes on the Timing of Diatom Maxima

The Spring Maximum in the Otago Harbour. In 1944 the spring maximum occurred in August. In 1945 it came early in July when the sea temperature was practically at its lowest and snow was lying on the hills. In 1945 a marked increase in the number of hours of bright sunshine was noted for the majority of the fourteen days immediately preceding the spring outburst of diatom growth. Such was not the case in 1944, when longer hours of bright sunshine per day were recorded for the month of June and early in July than in the period preceding the spring peak. Thus, as has been found elsewhere, increase in the number of hours of bright sunshine alone is not responsible for the occurrence of the spring diatom increase nor is temperature alone the causal factor.

The Spring and Autumn Maxima in Various Latitudes in the Northern and Southern Hemispheres. The timing of the diatom maxima in comparable latitudes in the Northern and Southern Hemispheres is shown in Text-fig. 5. In the far north there is only one maximum which extends over the summer months and the first month of autumn (Greenland, Vanhoffen, 1897). South of this region typical spring and autumn maxima occur which retreat farther and farther from the summer months until finally the two meet in the winter months (with a smaller maximum appearing in the summer months) [Gulf of Trieste, 45·30°N.; Steuer, 1903, Stiasny, 1908, Gran, 1909, Leder, 1917]. In the far south conditions somewhat parallel those in Greenland waters, a large maximum occurring in the last month of summer and the first month of autumn (Hart, 1940). [Climatic conditions in this region make sampling in autumn and winter impossible: hence the presence or absence of a smaller maximum is still in doubt.] North of this region in the Southern Hemisphere as in the Northern Hemisphere typical spring and autumn maxima occur, but as one approaches the tropics in the Southern Hemisphere, only the spring maximum retreats from the warmest season, the autumn maximum showing a tendency to move towards it. Conditions found in the Otago Harbour, 45·52°S., do not parallel those recorded for the Gulf of Trieste, 45·30°N., the latter being more nearly approximated at Sydney, 38°S., where observations of the seasonal changes in plankton have been made over a number of years (Dakin and Colefax, 1940) and where the large diatom maximum may occur in mid-winter, but more usually in the last month of winter and the first month of spring, whilst the small

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Text-Fig. 5—Diaton maxima in comparable latitudes in the North and South Hemisphers, monnths arranged so that northern summer is shown direcly above southern summer, etc.

maximum comes in the last month of summer or the first months of autumn. It is interesting to note that at Low Isles, 16°S., Marshall (1933) reports the number of diatoms as remaining fairly constant throughout the year, no great increases occurring as in temperate waters.

Acknowledgments

I wish to thank the Royal Society of New Zealand for a grant for equipment, the Portobello Marine Fish Hatchery Board for accommodation and the use of the Laboratory at the Station, and Professor B. J. Marples for general assistance.

Summary

Samples collected in a bolting silk net (100 threads to the linear inch) and centrifuged water samples have been examined and counted throughout a year.

In the net samples diatoms predominated, thecate dinoflagellates being extremely rare in this locality. In the water samples large numbers of small naked dinoflagellates were present as well as the smaller species of diatoms. Owing to the fact that the larger species of diatoms, which contributed largely to the spring outburst, did not get into the water samples, the spring peak recorded from centrifuged material is a relatively small one.

Ciliates, flagellates, radiolaria and foraminifera were not abundant at any time and Silicoflagellates, Coccosphaerales, and Phaeocystis were not seen at all.

A list of the commoner diatom species is given. Practically all of these are neretic.

There are well-marked spring and autumn outbursts of diatom growth, and in 1945 a small subsidiary spring peak was noted.

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The results from centrifuged water samples are compared with those from similar work elsewhere.

An account is given of the timing of the diatom maxima for various places in the Southern Hemisphere and comparisons are made between those of places of similar latitude in the Northern and Southern Hemispheres.

Literature Cited

Dakin and Colefax, 1940. The Plankton of the Australian Coastal Waters off New South Walcs, Pt. 1. Sydney: Australian Medical Publishing Company, Ltd.

Hardy and Gunther, 1935. The Plankton of the South Georgia Whaling Grounds and Adjacent Waters, 1926–1927. Disc. Rpts., vol. xi, pp. 1–456.

Hart, T. J., 1942. Phytoplankton Periodicity in Antarctic Surface Waters. Disc. Rpts., vol. xxi, pp. 261–356.

Lebour, M. V., 1917. The Microplankton of Plymouth Sound from the Region beyond the Breakwater. J. Mar. Biol. Ass. U.K., vol. xi, pp. 133–182.

Lohmann, H., 1920. Die Bevolkeung dez Ozeans mit Plankton nach den Ergebnissen der Zentrifugenfange wahrend der Ausreise der “Deutschland,” 1911. Arch. Biontol., iv, Heft 3, pp. 1–617.

Marshall, S. M., 1933. The Production of Microplankton in the Great Barrier Reef Region. Gt. Bar. Reef Exp. 1928–29, So. Rpts., vol. III, no. 5, pp. 111–157.

Steuer, A., 1903. Beobachtungen uber das Plankton des Trienter Golfes im Jahre 1902. Zool. Ans., vol. XXVII, no. 5, pp. 145–148.

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William Donovan (1879–1950)

William Donovan died at his home, 51 Washington Avenue, Brooklyn, Wellington, on December 4, 1950.

He was born at Thames in 1879 and received his foundation education at a State school and at Thames High School; at both schools he was among the brightest pupils. He then attended Thames School of Mines for three years; his record was outstanding and he there wen a University Mining Scholarship on which he proceeded to the University of Otago for three years. His University career was adversely affected by a severe attack of rheumatic fever, but notwithstanding this, when he completed his course at the Auckland College, he had won the college prize and a senior university scholarship in Chemistry and obtained second class honours in both Chemistry and Geology. His Chemistry thesis was on the sulphides, selenides and tellurides of gold, and was highly commended by the examiner, Sir William Ramsay. He was then employed for a period in the Waikino Mill of the Waihi Gold Mining Company as assayer and in the cyanide works, where he gained valuable practical experience. In January, 1905, he accepted the position of assistant analyst in the Mines Laboratory, Wellington, where Dr. J. S. Maclaurin was analyst to that Department and Colonial Analyst. Under various designations he occupied the position of first assistant until 1930, when he succeeded Dr. Maclaurin as Director of the Dominion Laboratory and Dominion Analyst. He retired in 1940 owing to failing health.

When he joined the laboratory, the newly organised Geological Survey was actively at work and for several years gave special attention to the known metalliferous areas, which resulted in many samples of wide variety being submitted to the laboratory for analysis.

Donovan's training and outlook made him most efficient in dealing with this class of work and at the same time enabled him effectively to plan for the expansion of activities which had then commenced. This resulted, after a few years, in the laboratory becoming, except for agriculture, a general service laboratory for Government Departments.

It is usual to assess a worker's contribution to the advancement of his science by a consideration of his published work. Donovan's published papers are not numerous, although of a high standard in their several fields. They deal mainly with our mineral resources, and particularly with coals, clays, and titaniferous iron sands. In these three he was a foremost authority and in regard to coals he dealt with many aspects including utilization and safety in mines.

Important as these papers may be, they are not his outstanding contribution to the progress of applied chemistry in New Zealand. This is to be found rather in his work for Government over his thirty-six years of service, which covered a period of great development in the application of chemistry in New Zealand. One evidence of this was the very large increase in scientific staffs over the period, in the case of the laboratory it was at least twentyfold. Donovan took a lead-

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William Donovan

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ing part in this development, particularly in seeing that the Government Departments concerned were given laboratory services of the highest possible standard. He also did much to further the application of chemistry in industry. He took no narrow view of his professional obligations and held that they included a responsibility to the profession as a whole. He therefore actively associated himself with the early chemical organisations sponsored by Victoria University College and by the Wellington Branch of our Society.

In 1926 he was made Fellow of the Royal Institute of Chemistry. He was a foundation member and a Fellow of the New Zealand Institute of Chemistry, and in 1946, in recognition of his eminent services to applied chemistry in New Zealand he was made an Honorary Fellow of that Institute.

He was, for the same reason, elected a Fellow of the Royal Society of New Zealand.

R. L. Andrew.