NATURE ADR ITT 



the larger diatoms, as well as swallow the more convenient ones whole. 

 Copepods are the most important of the herbivorous zooplankton, although 

 some copepods are carnivores and others are detritus feeders. Other notable 

 herbivores are the salps and doliolids (pp. 78, 80 and Fig. 23), which pump 

 water through a perforated gill for breathing and at the same time fdter off 

 the phytoplankton as food. 



The next link in the food chain is the feeding of carnivorous species on 

 the herbivores or on other carnivores. When thinking of land animals the 

 name carnivore conjures up the fierce lions, tigers, jaguars and the other big 

 cats, hi the plankton so often it is the apparently harmless creatures that are 

 the most voracious carnivores, the worst offenders being the small jellyfish 

 and sea gooseberries. These have no powerful claws or teeth; the jellies and 

 the siphonophores (Figs. 13-17) quietly paralyse their prey with stinging 

 cells and the gooseberries catch theirs by entanglement in sticky tentacles 

 (p 57). However there are also the carnivores that actively chase their 

 prey and are well equipped with powerful seizing jaws — e.g. the arrow- 

 worms, p. 59. Others grab their food in their mouths, e.g. young fish and 

 adult pelagic fish such as herring, or they catch their food with modified 

 legs or other appendages — e.g. copepods and other carnivorous Crustacea, 

 and indeed these legs may be provided with pincers as in the larval lobsters, 

 crabs, some shrimps and amphipods. 



Not all the plants are eaten by herbivores, and not all the animals by 

 carnivores, many simply die a natural death due to lack of food or intolerable 

 conditic^ns of temperature, salinity, depth or other factors. These are 

 disintegrated by bacteria, and the products oi disintegration including the 

 bacteria themselves, then form the food of innumerable filter and detritus 

 feeders in the plankton. Many invertebrate larvae in the plankton feed this 

 way and also copepods, some euphausids and amphipods, feeding more or less 

 indiscriminately on whatever particles they filter, digesting what they can 

 and ejecting the remainder. Even the faecal pellets contain something of 

 value to some other creatures and are included in the detritus they feed on. 

 When the plant food is particularly abundant the herbivores feed to excess 

 and this has the two-fold effect of grazing down the plants, thus slowing 

 down their use of nutrients and extending the growing season; also, as the 

 animals cannot digest all they feed on, there is a great increase of food value 

 in the faecal pellets. These, being heavier than the water, sink and help to 

 provide food more quickly and abundantly in the sub-surface and deeper 

 layers. 



There are hosts of bottom-dwellers and attached animals that feed on 

 detritus, including most of the bivalve molluscs — the cc-)ckles and mussels 

 and their kin — the barnacles, and the worms. These, too, take their place 



124 



