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PREFACE During the Meeting of the International Council for the Exploration of the Sea at the end of May 1935 a number of lectures on various subjects were given at two Special Meetings held during the week of the session. On Monday, May 27th, a Special Plankton Meeting was held at “Eltham” on which occasion Mr. F. S. Russell of Plymouth, Professor A. C. Hardy of Hull and Mr. S. Landberg of Bornø lectured on the questions recorded in the list of contents below. On May 31st a Meeting was held at the premises of the “Kongelige Danske Videnskabernes Selskab” ; on this occasion Professor B. Schulz of Hamburg reported on some results obtained from the Kattegat investigations of internal waves undertaken in 1931 (a summary of this lecture also appears in the following pages). Further Professor Johan Hjort of Oslo lectured on “Fishing Experiments and Administrative Problems”. Professor Hans Pettersson of Gothenburg demonstrated a film showing internal waves originating from the action of an oscillating magnetic force in a paramagnetic fluid. Professor N. Z e i 1 o n of Lund demonstrated internal waves produced in a whipping trough with water layers of different densities. TABLE OF CONTENTS Page I. A Review of some Aspects of Zooplankton Research, by F. S. Russell, Plymouth ........................................................................................................................ 3 II. Further Investigations upon the Photosynthesis of Phyto-plankton by constant Illumination, by H. Hög lund and S. Landberg, Bomø .. 31 III. The continuous Plankton Recorder: a new Method of Survey, by A. C. Hardy, H u ll............................................................................................................... 35 IV. Die Ergebnisse der internationalen hydrographischen Beobachtungen im Kattegat im August 1931, by B. Schulz, H am burg.............................. 49 A REVIEW OF SOME ASPECTS OF ZOOPLANKTON RESEARCH. BY F. S. RUSSELL, Naturalist at the Plymouth Laboratory of the Marine Biological Association of the United Kingdom. T is now nearly one hundred years since the In reviewing the present position I shall try to tow-net was first introduced by Johannes embrace all the aspects of the situation. It is Müller (1846). Zoology was still in its necessary to take the wide view without unduly I early descriptive stage and a rich ground for the stressing any particular problem, because we have investigation of new species was thus opened up. suffered in the nast from a tendency to pursue About that time also the theory of evolution was certain directions of enquiry to a disproportionate assuming concrete form, to be firmly established extent. As a result plankton research has become by the publication of Darwi n’s “Origin of somewhat uncoordinated, and advance has been Species” in 1859. The evolutionary theory was the held up by a lack of consideration as to which are main directing force for the study of embryology, the problems that require special attention in order and in the development of this branch of zoology, to bring our various fields of knowledge into line. research on plankton animals has played a greater With such a wealth of data scattered amongst part than that on any other population of the the biological literature of the world the task of animal kingdom. We owe to the labours of the review becomes impossible unless we first fix upon zoologists of the latter half of last century most certain outstanding events around which the main of our present knowledge on the affinities and sequence of the review can be evolved. natural classification of the major groups of in­ I have adopted the following landmarks as vertebrate animals. With the exception of insects, representative of the sequence of events after the the invertebrates are essentially inhabitants of the introduction of the quantitative method by Hensen, sea, and almost all spend the earlier stages of their leading to the publication of his Methodik (1895) lives drifting in the water layers in the plankton community. 1. The Plankton Expedition in the “National” Among the first workers in this line of research under the leadership of Hensen in 1889. was T. H. Huxley who sailed in 1846 in the 2. The comprehensive scheme for the collection “Rattlesnake” to Australian waters. In these days of plankton throughout the North Sea and of elaborate and costly apparatus it is well to bear adjacent waters of the Atlantic, Channel and in mind what far reaching results can be obtained Baltic, during the years 1902 to 1908 by the by the simplest means. Huxley used as his International Council. townet a bag of the bunting of which flags are 3. The completion byLohmannin 1906 of made. With this simple net he sieved the sea at a year’s detailed survey of the total plankton every available opportunity. As a result be production at Laboe in Kiel Bay. demonstrated the true position of the medusae and During these two latter periods plankton study siphonophores in the coelenterate kingdom, and received a constant leavening element in the in­ also traced the affinities of the pelagic tunicates tensely biological outlook of Professor Gran. to the sessile ascidians of our sea shores. Of even 4. The post-war period. more far reaching importance was the result of his examination of the medusae whereby he indicated Three publications previous to the last period the existence and importance of the germ-layers in should also be mentioned as having left their mark the development of metazoa. in the history of plankton research and stimulated But to-day I do not wish to take as my theme many workers, these were Adolf Steuer’s the examination of plankton animals with the “Planktonkunde” published in 1910; “Conditions ulterior aim of elucidating problems purely of Life in the Sea” by James Johnstone, in morphological or embryological in nature. I wish 1908 and the “Depths of the Ocean” by Murray rather to review those aspects of zooplankton and Hjort in 1912. research whose concern has been the study of I have taken these four periods because they plankton animals as members of a community, and illustrate the main problems that confront those for the part they play by their habits and concerned with zooplankton research. The first is abundance in the balance of life in the sea. The the necessity of knowing the distribution and review will be concerned only with metazoa. abundance of the plankton in the open ocean. - 6 — IA. 1 £ • H - :- +■ V\ v*- li fv’v ^.-1 I Fig. 1 Distribution regions of oceanic plankton organisms (after Steuer, 1933, p. 292, Fig. 8, for Copepods). For explanation see Text. Secondly comes the desire for a similar knowledge biology and as regards the zooplankton much of of the conditions in the coastal waters whose origin our present knowledge has been built up from the and movements are so largely governed by the results of the collections of the great oceano­ oceanic circulation. In intimate connexion with graphical expeditions. Many years must elapse this is the use of our knowledge of the plankton before the description of all the species of plankton distribution as an aid to the interpretation of hydro- animals is brought to completion. We can however graphical data. Thirdly, knowing something of the say with gratitude to the workers in the past that animals’ distribution we need to know about their in many groups today the necessary knowledge is relations with their animate and inanimate environ­ reaching its final stages. Coincident with the ment, and the causes of their fluctuations in descriptive work our knowledge of geographical abundance. This is a work that has so far only distribution has grown and as the groups have been attempted in coastal waters where the been better known the distribution of the species necessary observations can be made at frequent among their faunistic regions has become more intervals throughout the year with the facilities of detailed. a laboratory close at hand. And finally the re­ It is probable that in ocean waters one of the search has shown the need for even more detailed main barriers to distribution is that of the tem­ observations, for a close study of life-histories and perature conditions. Animals adapted for success­ habits, and for the examination of the more ful reproduction in any given temperature range specialised problems that have arisen such as tbe will be carried in the water masses and ocean relations between the plankton and the fish that current systems so far as the necessary temperature are used as food by man. conditions are maintained. Before any work on the biology of animals can When the temperature conditions have been be attempted the animals that we wish to study taken into consideration the chief clues to the must be described and classified. This is a task geographical distribution of the species are to be that has gone on from the earliest days of marine found in the systems of oceanic circulation. The — 7 — geographical distribution more complete. The data oceans can now be divided into definite masses of thus obtained will act as bench-marks for the study water with different characteristics. These different masses are constantly moving and are separated in years to come of the secular changes in the ^vate'’ movements of the ocean. With this idea in mina I from one another by regions of mixed water which have produced a preliminary table (Table I) giving may be wide or narrow according to the locality. the number of known species in the more important Such regions are the antarctic, the subtropical and plankton groups and their subdivision into broad the tropical convergences in the south, and the geographical areas. It has only been possible to transition regions in the north which vary from produce such a table with the cooperation of many narrow zones with well defined boundaries between specialists in plankton animal groups.

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