188 American Fisheries Society 



The plankton, heretofore considered as of greatest 

 significance, he does not list as an important source of 

 food. Whereas previous observers have emphasized the 

 great importance of plankton, Blevgad emphasizes the 

 importance of detritus. He furthermore questions 

 Putter's (1908) theory to the effect that the carbon com- 

 pounds present in solution in the sea water are of very 

 extensive importance as food for certain animals of the 

 bottom fauna. At least it must for the present be re- 

 garded as unproved. It is possible, however, that some 

 organisms may live on dissolved organic matter and so 

 for the sake of convenience Blevgad classifies dissolved 

 organic matter under detritus. 



The commonest animal forms in Danish waters are 

 classified into three groups according to their mode of 

 feeding. (1) Herbivores which include certain Gastro- 

 pods, two Echinoderms and some Crustacea. (2) Pure 

 detritus eaters which comprise all the Lamellibranchs, 

 Holothurians, Sipunculidae, Cumacea, Diptera larvae and 

 Ascidiae, two Gastropods, Balanoglossus, Amphioxus, 

 Ostracods, Bryozoa, Porifera and Foraminifera. The 

 great mass of material in the alimentary tracts of these 

 animals is detritus and when analyzed chemically it cor- 

 responds to that on the ocean floor. Plankton organisms 

 are only incidentally present. These observations led 

 Blevgad to make the extreme statement, "The living 

 phytoplankton is thus of no importance at all as a food 

 for the bottom fauna." (3) Purely carnivorous animals 

 including a few Polychaeta, some Gastropods, some 

 Crustacea, some Echinoderms, Coelenterates, Nemer- 

 teans, Planarians and Pantopods constitute the last 

 group. Quite a large number of animals are both carni- 

 vores and detritus feeders. 



The investigations tend to show the extreme import- 

 ance of detritus as a food for the fauna on the sea bot- 

 tom. To use Blevgad's words, "Detritus forms the prin- 

 cipal food of nearly all the invertebrate animals of the 

 sea bottom, next in order of importance being plant 

 food from fresh benthos plants. The value of the live 



