FOOD-MATTERS IN THE SEA 323 



on more accessible ground with more sedentary animals, 

 and Dr. C. G. Joh. Petersen, of the Danish Biological Station, 

 has for some years been pm^suing the subject in a series of 

 interesting reports on the " Evaluation of the Sea." ^ 

 He uses a bottom-sampler, or grab, which can be lowered 

 down open and then closed on the bottom so as to bring 

 up a sample square foot or square metre (or in deep water 

 one-tenth of a square metre) of the sand or mud and its 

 inhabitants. With this apparatus, modified in size and 

 weight for different depths and bottoms, Petersen and his 

 fellow-workers have made a very thorough examination 

 of the Danish waters, and especially of the Kattegat and 

 the Limfjord, have described a series of " animal communi- 

 ties " characteristic of different zones and regions of shallow 

 water, and have arrived at certain numerical results as to 

 the quantity of animals in the Kattegat expressed in tons 

 — such as 5,000 tons of plaice requiring as food 50,000 tons 

 of " useful animals " (moUusca and polychset worms), and 

 25,000 tons of starfish using up 200,000 tons of useful animals 

 which might otherwise serve as food for fishes, and the 

 dependence of all these animals directly or indirectly upon 

 the great Beds of Zostera, which make up 24,000,000 tons in 

 the Kattegat. Such estimates are obviously of great biologi- 

 cal interest, and, even if only rough approximations, are a 

 valuable contribution to oik understanding of the meta- 

 bolism of the sea and of the possibiHty of increasing the yield 

 of local fisheries. 



But on studying these Danish results in the light of 

 what we know of our own marine fauna, although none of 

 our seas have been examined in the same detail by the 

 bottom-sampler method, it seems probable that the animal 

 communities as defined by Petersen are not exactly appli- 

 cable on our coasts, and that the estimates of relative and 

 absolute abundance may be very different in different seas 



1 See Reports of the Danish Biological Station, and especially the 

 Report for 1918, " The Sea Bottom and its Production of Fish Food." 



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