NO. 9 MARINE INVERTEBRATES, ALASKA — MacGINITIE 3 1 



Predators, or those feeding on other animals, are either pelagic or 

 bottom-dwelling, but seldom, if ever, both. The first are indirectly 

 dependent on diatoms, and include jellyfishes, ctenophores, and 

 chaetognaths. The latter are indirectly dependent on detritus, and 

 include starfishes, flatworms, sea anemones, certain isopods, amphi- 

 pods, and crabs, and certain snails such as Natica and Polinices. 



Debris feeders, or scavengers, are bottom dwellers feeding at the 

 surface on larger particles of plant or animal debris. These are ex- 

 emplified by sea urchins, crabs, hermit crabs, and some snails. 



Seaweed feeders are very rare. 



No commensal algal feeders are known to live in the Arctic. 



ABUNDANCE OF ANIMALS 



The abundance of marine animal life at Point Barrow, especially 

 in the rubble zone, was little short of astonishing. There are far fewer 

 species of marine invertebrates in the Arctic than in the equatorial, 

 tropical, or temperate regions, but in general individuals of species 

 occur in far greater numbers. For example, as has been mentioned 

 elsewhere, there are swarms of mysids, euphausiids, pteropods, and 

 copepods. In addition to these, there are great numbers of jellyfishes 

 (Aurelia and Cyanea), ctenophores {Beroc and Mertensia), and 

 chaetognaths, although the last are probably often as abundant in the 

 north-temperate waters as they are in the Arctic. Individuals of a 

 number of species of bottom dwellers are numerous ; and in certain 

 areas of the rubble zone there are large numbers of sea anemones, 

 sea urchins, sea cucumbers, bryozoans, barnacles, and sponges. Where 

 the stones of the rubble are small, the clam Hiatella arctica, barnacles, 

 and bryozoans are extremely abundant. 



Because of the difficulty of dredging in the blue-mud zone it is im- 

 possible to give any estimate of the abundance of animals living within 

 the mud, but on the surface were found two species of crabs, 

 Chionocetes opilio and Hyas coarctatus alutaceus, and one hermit 

 crab, Pagurus trigonocheirns, that were particularly abundant. Dur- 

 ing the summers of 1949 and 1950 when the ice was far offshore, the 

 heavy surf disturbed the bottom sufficiently to furnish some idea of 

 the marine population in this mud zone, for certain burrowing forms 

 were washed ashore in large numbers. Among these were the 

 echiuroid worm Echiurus echiurus alaskanus, the polychaete Areni- 

 cola glacialis, two species of burrowing anemones, and two species 

 of mud-dwelling tunicates. 



Two species of amphipods, Melita formosa and Anonyx nugax, 



