NATURE ADRIFT 



harhata is 8 niillinictres long, and Me^acalaiiiis priiiceps is 12 millimetres and 

 Batliycahvnis rii^idiis shown in Plate XVIII is 11 millimetres. 



The most important and the most studied of the truly planktonic marine 

 copepods is called Cahviiis (Fig. 20; 6: Plate XVII) and a whole book has 

 been written about it alone.* This species is one of the dominant food 

 organisms of plankton-feeding fish like herring. Although most prolific 

 in northern waters it is common, even abundant, in the North Sea, English 

 Channel, Mediterranean, Black Sea, Red Sea, Indian and Pacific Oceans, 

 Malaya, Australia etc., and is thus quite cosmopolitan. It feeds directly on 

 the phytoplankton as do many other species living in the upper water layers, 

 but some other copepods, for example, Amviiciloarci (Plate XVIII: Fig. 20; 

 lo-ii) and Ca)idacia (Fig. 20; 8), are carnivorous. The deep-water forms, 

 living below the level of plant growth, are either carnivorous or feed on 

 particles of detritus which they filter from the water. 



Most copepods have 'eyes' which are sensitive to light, but they cannot 

 see in the accepted detailed sense, although some of the more developed eyes 

 like those of the male Aiuvnaloara might be able to detect movement but not 

 shape. The planktonic species are usually very transparent, some like 

 Anomalocera are very blue; some \ikcCalanus are reddish due to a reddish oil 

 in the body, and several of the deep sea species are truly red (e.g. Bathycalaiuis 

 ri^idus, Plate XVIII). Aiuvnaloara deserves special mention because it is a real 

 surface form, dancing about at the actual surface, jumping out and in, and 

 causing a shimmer like rain on very calm water. It is more abundant in 

 oceanic water than inshore but is often brought into the North Sea and 

 Norwegian coastal waters where it is called 'blue bait'. One that the keen 

 naturalist may find most convenient to obtain is Eurytcmora liiriiiidoides (Fig. 

 20; 5) because it inhabits estuaries; here it feeds on the protozoa which in turn 

 have fed on the bacteria (p. 48). There are many hundreds of species of 

 copepods and only a small selection are illustrated here. They also probably 

 form the largest proportion, by volume, of most plankton collections and 

 their total numbers in the sea must indeed reach astronomical figures. They 

 are excellent food value being rich in proteins and oils and are the natural food 

 of almost all the small fish (including the young stages of the big fish). No 

 wonder they are so important in the economy of the sea. Rock-pool copepods 

 like those in Fig. 18; 2 and 3, are very easy to catch alive (p. 14) and most 

 delightful to watch. One of them Ti{iriopiis (Plate XVII) is about i /20 inch, 

 bright orange and lives in those pools near the high-water mark where the 

 green filamentous weed EiiterotHorpha lives and decays. It can reach fantastic 



* The Biology of a Marine Copepod, by S. M. Marshall and A. P. Orr, Oliver & Boyd, 

 1955, 21S. 



66 



