SEA-MEADOWS 91 



animals shows that the food consumed consists very 

 largely of this valuable debris. Thus the main 

 food of oysters and other bivalves is vegetable dust 

 " which is found, either in suspension in the water, 

 or deposited as the thin upper layer of the bottom 

 itself, lifting and spreading at times in stormy 

 weather, but only to be precipitated anew later on." 

 Some of Professor Petersen's statistics are very 

 interesting. His valuation of the sea-meadows of 

 Danish waters inside the Skaw shows a total of 

 24 million tons for the plants, 5 million tons for 

 those animals that are " useless " both directly and 

 indirectly, I million tons for the " useful' ' forms 

 that furnish or may furnish food for fishes, and only 

 some few thousands of tons (5 to 7000) for each of 

 the short list of valuable food fishes, such as plaice 

 and cod. Starfishes make up 25,000 tons, more 

 than all the important food fishes lumped together, 

 while crabs and Gastropods amount to no less than 

 50,000 tons. We see that food-fishes form only 

 an insignificant part of the total stock of animal 

 life in waters like the Kattegat. The reason is to 

 be found in the relations that govern the circulation 

 of matter or the metabolism of the sea. To make a 

 pound of cod requires 10 Ib. of whelk or buckie; 

 to make a pound of buckie requires 10 Ib. of 

 worms; to make a pound of worm requires 10 Ib. 

 of vegetable matter, which may be given in the 

 form of dust! So a pound of a carnivorous fish 

 like a cod requires 1000 Ib. of sea-grass. If there 

 be fewer links in the House-that-jack-built nutri- 



