PHYTOPLANKTON 



bloomed it could kill every living diing in die sea around it.' Such a story, 

 based on fact, but made sensational and distorted by the omission of other 

 facts, can cause mischiet. Indeed, this story eventually led to a question in the 

 House, with the best intention of attempting to forestall trouble for the 

 fisherman. With the constant mixing of the waters round the British Isles 

 by both tides and currents, there is little chance of any sudden concentrations 

 of nutrients forming and even if they did the chance that a rare poisonous 

 dinoflagellate would bloom instead of one of the thousand other non- 

 poisonous species is indeed remote and no cause for the worry so sensationally 

 expressed by the reporter. Some further details of this type of effect on the 

 fish and fisheries are given in Chapter lo. 



Some dinoflagellates are parasitic, living inside other organisms in the 

 plankton, particularly radiolarians (p. 48). Some live in fish eggs where they 

 do not seem to affect early development seriously — perhaps there is plenty 

 of food for both — although the young fish seem to suffer and die soon after 

 hatching. 



Fig. II. Coccolithophores. (a) Coaolithus {Pontosp]idera) liiixlcyiy (h) MicluiclsLirsici araiica, {c) a 



single coccolith from 'a' as reconstructed from photographs by an electron microscope. As 



reproduced here it represents a magnification of 17,000 diameters. 



Minute plants, usually considered part of the nanoplankton, are the 

 coccohthophores. These form a rather specialized group as each cell pro- 

 duces a layer of minute calcareous plates round it, often of fantastic shapes 

 (Fig. 11). The cells themselves are so very small, mostly only 15 /it, that it is 

 difficult or even impossible to see the structure of the plates — called cocco- 

 liths — even with a first-class high-power microscope. Only with the inven- 

 tion of the electron microscope have the details been resolved. Coccolitho- 

 phores being plants need the sun's energy, but seem to require only the very 

 minimum of light and live most abundantly at about 300 metres depth in 

 the clear blue oceanic waters. Here they serve as a much needed food supply 



41 



