The first use of the term 'plankton' is attributed in several texts (Ruttner, 1953; Hutchinson, 1967) to Viktor Hensen, who, in the latter half of the nineteenth century, began to apply quantitative methods to gauge the distribution, abundance and productivity of the microscopic organisms of the open sea. The monograph that is usually cited (Hensen, 1887) is, in fact, rather obscure and probably not well read in recent times but Smetacek et al. (2002) have provided a probing and engaging review of the original, within the context of early development of plankton science. Most of the present section is based on their article.
The existence of a planktic community of organisms in open water had been demonstrated many years previously by Johannes Muller. Knowledge of some of the organisms themselves stretches further back, to the earliest days of microscopy. From the 1840s, Muller would demonstrate net collections to his students, using the word Auftrieb to characterise the community (Smetacek et al., 2002). The literal transla tion to English is 'up drive', approximately 'buoyancy' or 'flotation', a clear reference to Muller's assumption that the material floated up to the surface waters - like so much oceanic dirt! It took one of Muller's students, Ernst Haeckel, to champion the beauty of planktic protistans and metazoans. His monograph on the Radiolaria was also one of the first to embrace Darwin's (1859) evolutionary theory in order to show structural affinities and divergences. Haeckel, of course, became best known for his work on morphology, ontogeny and phylogeny. According to Smetacek et al. (2002), his interest and skills as a draughtsman advanced scientific awareness of the range of planktic form (most significantly, Haeckel, 1904) but to the detriment of any real progress in understanding of functional differentiation. Until the late 1880s, it was not appreciated that the organisms of the Auftrieb, even the algae among them, could contribute much to the nutrition of the larger animals of the sea. Instead, it seems to have been supposed that organic matter in the fluvial discharge from the land was the major nutritive input. It is thus rather interesting to note that, a century or so later, this possibility has enjoyed something of a revival (see Chapters 3 and 8).
If Haeckel had conveyed the beauty of the pelagic protistans, it was certainly Viktor Hensen who had been more concerned about their role in a functional ecosystem. Hensen was a physiologist who brought a degree of empiricism to his study of the perplexing fluctuations in North Sea fish stocks. He had reasoned that fish stocks and yields were related to the production and distribution of the juvenile stages. Through devising techniques for sampling, quantification and assessing distribution patterns, always carefully verified by microscopic examination, Hensen recognised both the ubiquity of phytoplankton and its superior abundance and quality over coastal inputs of terrestrial detritus. He saw the connection between phytoplankton and the light in the near-surface layer, the nutritive resource it provided to copepods and other small animals, and the value of these as a food source to fish.
Thus, in addition to bequeathing a new name for the basal biotic component in pelagic ecosystems, Hensen may be regarded justifiably as the first quantitative plankton ecologist and as the person who established a formal methodology for its study. Deducing the relative contributions of Hensen and Haeckel to the foundation of modern plankton science, Smetacek et al. (2002) concluded that it is the work of the latter that has been the more influential. This is an opinion with which not everyone will agree but this is of little consequence. However, Smetacek et al. (2002) offered a most profound and resonant observation in suggesting that Hensen's general understanding of the role of plankton ('the big picture') was essentially correct but erroneous in its details, whereas in Haeckel's case, it was the other way round. Nevertheless, both have good claim to fatherhood of plankton science!
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