Tuatara: Volume 17, Issue 1, May 1969
Marine Diatoms — Past and Present Distributions
Marine Diatoms — Past and Present Distributions
In Many Parts of the world diatoms can be found in sediment at the bottom of the sea. If we merely separate and identify their silica frustules or shells (described in ‘Tuatara’ by Cassie, 1959), we may be able to extend their classification and possibly indicate their mode of evolution. But if we also count them and find the proportions of species at different levels of sediment cores, the way is opened to fascinating interpretations of past distributions of water and land masses. These are based on whether the same species occurs at the present day in warm or cool currents, and more or less saline water. For instance Jousé. or Zhuze, (1966) has deduced the fluctuations of the Quarternary climate from cores in the Indian and Pacific oceans, as has Donahue (1966) for the Southern ocean.
The species composition of buried layers is more validly compared with the present surface of the sediment than with the plankton floating above, as those species most abundant in the plankton may be hardly found in the sediment; Round (1967, 1968) proved this for the Gulf of California. The presence of a particular silica frustule depends on its thickness and the time for which it drifted in ocean currents after losing its organic skin, (Lewin 1959). Much of the finer sculpturing is lost by all frustules before reaching the sediment. Freshwater diatoms are sometimes found in mid-ocean cores. This may indicate the possible extent of drifting according to Kolbe (1956) who found them in the Indian Ocean, or Zhuze et al. (1959) in the Southern Ocean, but Kolbe (1957) suspected that in his Atlantic cores freshwater species were wind-blown over 1000 km from the Niger swamplands. Unfortunately, some of the principal planktonic genera — Rhizosolenia, Chaetoceros and Bacteriastrum — have very thin walls to aid flotation, so they only occur in sediments as occasional spores of Chaetoceros and ‘ends’ of Rhizosolenia (see Round 1968). Ethmodiscus rex, on the other hand, is an elusive diatom in the plankton but strangely is dominant in subtropical sediments. As some diatoms can live by absorbing sugar solutions rather than by photosynthesising (Lewin 1953), Wood (1956) thought that live E. rex might inhabit bottom sediments. This now seems unlikely, so Zhuze et al. (1959) consider that its abundance is due to resisting dissolution and to being sorted by bottom currents. As diatoms are widely grazed by ciliates, copepods and other animals, many sinking frustules are broken (Raymont 1963).page 31
Before we can decide on the geological ages of different levels of cores, or on past climatic and oceanic fluctuations, reasonable correlations should be sought in evidence from different groups of fossils. Riedel and Funnell (1964) found Tertiary radiolarians frequently reworked among Quaternary coccoliths and foraminifera in Pacific cores, showing this stratigraphy based on radiolarians alone would have been incorrect. Pollen spectra and diatoms from the Argentine basin show that a warmer land climate coincided with the presence of subtropical water masses (Groot et al. 1965). In New Zealand, a previous issue of ‘Tuatara’ (April, 1968) reported a symposium on the Tertiary climate here, at which evidence from such varied organisms as higher plants, corals, foraminifera, molluscs, coccolithophores and diatoms indicated that the mid-Tertiary climate became nearly subtropical before cooling down. It was suggested that although the earth as a whole was cooling, New Zealand's drift towards the equator compensated for this at the beginning of the Tertiary. It is essential for any study of this type to have accurate information on the present day distribution of the organisms involved.
Diatoms have been identified in water samples taken at various seasons from several places round the coast of New Zealand (Cassie, 1961, Taylor 1968) and New South Wales (Wood 1964) and the pattern of their distribution tentatively correlated with the currents and water masses described by Brodie (1960) and Rochford (1957). More complete pictures have been built up of the seasonal cycles in the Hauraki Gulf (Cassie 1966) and Wellington Harbour (Cassie 1960), and some progress has been made on cycles in Cook Strait (Crawford 1947) and Otago Harbour (Brewin 1952). South of New Zealand the oceanic diatom flora changes abruptly at the Antarctic Convergence (Cassie 1963), and becomes circumpolar round Antarctica, (Hart 1942). Wood (1964) has divided the plankton populations of the Coral and Tasman Seas into subequatorial, tropical, subantarctic and antarctic communities. A similar general zonation has been recognised in the more rarely sampled oceanic plankton of the South Pacific Ocean (Jesperson 1935), where sampling has been concentrated just off the South American coast, because of the importance there to the tuna fishery (Forsbergh and Joseph 1964) of large phytoplankton populations in regions of upwelling. A similar upwelling off the New Zealand coast at Waitarere has been thoroughly investigated by Cassie and Cassie (1960); toheroas eat phytoplankton washed up on the beach. Our understanding of the place of diatoms in the biology of even the North Sea is very limited in spite of regular sampling from weather, and other, ships (Wimpenny 1966). Littoral diatom populations are more readily sampled, as their adhesion to mud, sand, rocks or seaweeds eliminates the vagaries of ocean currents moving them about in the same way as plankton populations. Nonetheless their presence in New Zealand has been scarcely noticed (see Morton and Miller page 32 1968, pp. 417, 542) although littoral diatoms are usually more abundant than planktonic diatoms and probably essential in forming food for the inshore larvae of many fishes (Hendey 1964).
Several methods which do not involve counting individual cells are used to obtain an indication of the quantity of phytoplankton present in a water sample. Only the simplest measurements work in clear water which is free of silt or mud; these are the depth at which a white ‘Secchi disc’ can no longer been seen, dry weight, or colour shade estimation of acetone-extracted pigment from fine net samples (Hardy 1956). More refined techniques have been developed which separate active chlorophyll from its degradation products, or which attempt to measure actual photosynthetic rates by C14 carbonate uptake or oxygen evolution. These methods are used in assessing ‘primary production’ and they have been critically reviewed by Strickland (1965). Chlorophyll a values have been followed for two years at Kaikoura (Bradford 1968), but as Kaikoura is situated at the Subtropical Convergence variations of water masses tend to obscure the seasonal cycle. Cassie and Cassie (1960) estimated the primary production of their August bloom of Chaetoceros armatum and found it to be far greater than any previous measurements in the Pacific Ocean. Many ‘hit and run’ determinations of chlorophyll concentrations and primary production have been made in the oceans without much consideration of diurnal, seasonal or technical variations; the results are compared by Anderson and Banse (1961).
As the population of New Zealand increases attention will turn more towards exploitation of its surrounding waters, to fish-farming and to measurement and control of water pollution. Just as success in stock-rearing demands care and understanding of pastures, so developing fish-farming will need a deeper knowledge of the growth of algae. In this broad field biologists and others from very different disciplines will come across problems worth investigating not only for their local value but also for their worldwide interest.
I wish to thank Dr. J. F. Harper and Mr. J. W. Brodie for critical reading of the manuscript.
Anderson, G. C., and Banse, K., 1961. Hydrography and phytoplankton production. In Primary productivity measurement, U.S. Atomic Energy Comm. TID-7633: 61-71.
Bradford, J. M., 1969. Studies on New Zealand plankton and pelagic copepoda from central New Zealand, with key to pelagic genera. N.Z.D.S.I.R. Bull. (In press).
Brewin, B. I., 1952. Seasonal changes in the microplankton in Otago Harbour during the years 1944 and 1945. Trans. Roy. Soc. N.Z. 79: 614-627.
Brodie, J. W., 1960. Coastal surface currents around New Zealand. N.Z. Jl Geol. Geophys. 3: 235-252.
Cassie, R. M. and Cassie, V., 1960. Primary production in a New Zealand West Coast phytoplankton bloom. N.Z. Jl Sci. 3: 173-199.
Cassie, V., 1959. Marine plankton diatoms. Tuatara 7: 107-118.
——, 1960. Seasonal changes in diatoms and dinoflagellates off the East Coast of New Zealand during 1957 and 1958. N.Z. Jl. Sci. 3: 137-172.
——, 1961. Marine phytoplankton in New Zealand waters. Bot. Mar. vol. 2, suppl. 1-54. 8 pls.
——, 1963. Distribution of surface phytoplankton between New Zealand and Antarctica in December 1957. T.A.E. Scientif. Rept. 7: 1-13. 1 pl.
——, 1966. Diatoms, dinoflagellates and hydrology in the Hauraki Gulf 1964-1965. N.Z. Jl Sci. 9: 569-585.
Crawford, D. A., 1947. A phytoplankton season in Cook Strait. Trans. Roy. Soc. N.Z. (Rept. 6th Science Congress) 77(5): 173-175.
Donahue, J., 1966. Diatoms as indicators of Pleistocene climatic fluctuations in the Pacific sector of the Southern Ocean. In M. Sears (ed.); Progress in Oceanography 4. Oxford: Pergamon. 133-148.
Forsbergth, E. D., and Joseph, J., 1964. Biological production in the Eastern Pacific Ocean. Inter American Tropical Tuna Commission 8(9): 479-526.
Groot, J. J., Groot, C. R., Ewing, M., Burckle, L., and Conolly, J. R., 1965. Spores, pollen, diatoms and provenance of the Argentine basin sediments. In M. Sears (ed.); Progress in Oceanography 4. Oxford: Pergamon 179-217.
*Hardy, A., 1956. The open sea: its natural history: the world of plankton. London: Collins. 335 pp.
Hart, T. J., 1942. Phytoplankton periodicity in Antarctic surface waters. Discovery Rept. 21: 261-347.
Hendey, N. M., 1964. An introductory account of the smaller algae of British coastal waters. V: Bacillariophyceae (Diatoms). Min. Ag. Fish and Food. Fish. Inv. Series IV. 317 pp. 45 pls.
Jesperson, P., 1935. Quantitative investigation on the distribution of macroplankton in different oceanic regions. Dana Rept. 7: Carlsburg Fndn. 1-44.
Jousé, A. P., 1966. Stratigraphic and paleogeographic significance of planktonic algae. 2nd Int. Oceanographic Cong. Moscow. Abstracts p. 183.
Kolbe, R. W., 1956. Diatoms from equatorial Indian Ocean cores. In: sediment cores from the Indian Ocean. Rept. Swedish Deep-Sea Exped. 1947-8 9(1): 1-62.
——, 1957. Freshwater diatoms from Atlantic deep sea sediments. Science 126 (3282): 1053-1056.
Lewin, J. C., 1953. Heterotrophy in diatoms. J. gen Microbiol. 9: 305-315.
——, 1959. Dissolution of silica from diatom walls. Int. Ocean. Cong. N.Y. Preprint, p. 950.
*Raymont, J. E. G., 1963. Plankton and productivity of the oceans. Oxford: Pergamon. 660 pp.
Riedel, W. R. and Funnell. B. M., 1964. Tertiary sediments and microfossils from the Pacific Ocean floor. Quart J. Geol. Soc. 120: 305-368.
Rochford, D. J., 1957. The identification and nomenclature of the surface water masses in the Tasman Sea. Aust. J. Mar. Freshw. Res. 8: 369-413.
Round, F. E., 1967. The phytoplankton of the Gulf of California. I. Its composition, distribution and contribution to the sediments. J. exp. mar. Biol. Ecol. 1: 76-97.page 34
——, 1968. The phytoplankton of the Gulf of California. II. The distribution of phytoplanktonic diatoms in cores. J. exp. mar. Biol. Ecol. 2: 64-68.
Taylor, F. J., 1969. A preliminary annotated check list of diatoms from New Zealand coastal waters. Trans. Roy. Soc. N.Z. (In press).
Tuatara, April, 1968. The Tertiary climate of New Zealand. V.U.W. Geol. Soc. Symp. Tuatara 16: 3-80.
*Wimpenny, R. S., 1966. The plankton of the sea. New York: Elsevier. 426 pp.
Wood, E. J. F., 1956. Diatoms in the ocean deeps. Pacif. Sci. 10: 377-381.
——, 1964. Studies in microbial ecology of the Australasian region. Nova Hedwigia 8: 5-54, 453-568. 39 pls.
Zhuze, A. P., Petelin, V. P., and Udintsev, G. B., 1959. Concerning the origin of diatomaceous muds containing Ethmodiscus rex Wall. (Hendey). Transln. Dok. Akad. Nauk. S.S.S.R. 124: 1301-1364.
* Indicate books of general interest.