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pelagic

bacterioplankton

planktic prokaryotes

mycoplankton

planktic fungi

Zooplankton

planktic metazoa and heterotrophic protistans

Some more, now redundant, terms

The terms nannoplankton, ultraplankton, ß-algae are older names for various smaller

size categories of phytoplankton, eclipsed by the classification of Sieburth et al.

(1978) (see Box 1.2).

In this way, plankton comprises organisms that range in size from that of viruses (a few tens of nanometres) to those of large jellyfish (a metre or more). Representative organisms include bacteria, protistans, fungi and metazoans. In the past, it has seemed relatively straightforward to separate the organisms of the plankton, both into broad phyletic categories (e.g. bacterioplank-ton, mycoplankton) or into similarly broad functional categories (photosynthetic algae of the phytoplankton, phagotrophic animals of the zooplankton). Again, as knowledge of the organ isms, their phyletic affinities and physiological capabilities has expanded, it has become clear that the divisions used hitherto do not precisely coincide: there are photosynthetic bacteria, phagotrophic algae and flagellates that take up organic carbon from solution. Here, as in general, precision will be considered relevant and important in the context of organismic properties (their names, phylogenies, their morphological and physiological characteristics). On the other hand, the generic contributions to systems (at the habitat or ecosystem scales) of the photosynthetic primary producers, phagotrophic consumers and heterotrophic decomposers may be attributed reasonably but imprecisely to phyto-plankton, zooplankton and bacterioplankton.

The defintion of phytoplankton adopted for this book is the collective of photosynthetic microorganisms, adapted to live partly or continuously in open water. As such, it is the photoau-totrophic part of the plankton and a major primary producer of organic carbon in the pelagic of the seas and of inland waters. The distinction of phytoplankton from other categories of plankton and suspended matter are listed in Box 1.1.

It may be added that it is correct to refer to phytoplankton as a singular term ('phytoplank-ton is' rather than 'phytoplankton are'). A single organism is a phytoplanktont or (more ususally) phytoplankter. Incidentally, the adjective 'plank-tic' is etymologically preferable to the more commonly used 'planktonic'.

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