PLANKTON OF THE GULF OF MAINE 471 



and the many smaller forms, but even for Zostera time brings progressive decomposi- 

 tion. After it has disintegrated to a line dustlikc slate, further oxidization probably 

 takes place more rapidly, particularly when it is suspended in the upper, more illu- 

 minated water layers. Is it not reasonable, then, to think of such organic particles 

 or aggregates of particles as foci around which diatoms can multiply, being nourished 

 by the nitrogenous substances as these ((instantly go into solution, just as the weeds 

 in our gardens thrive around the particles of manure or of nitrogenous fertilizers 

 that are similarly disintegrating or dissolving in the soil? At any rate, whether or 

 not this particular picture be correct, a vast supply of organic matter is derived from 

 the Zostera, the constituents of which must eventually join the general nutritive 

 store of the sea water in which it decays and from which it was taken in the first 

 instance. Even such of it as passes through the digestive tracts of bottom-dwelling 

 mollusks must also travel the same path in the end, either as excreta or by the final 

 death and decay of the endless chain of animals that feed one on another. What is 

 true of Zostera is equally true of the more rapidly decaying marine algse. 



Qualitatively, at least, all this applies as well to the Gulf of Maine as it does to the 

 other side of the North Atlantic, Zostera, with the "rock weeds," "kelps," etc., 

 being abundant, with the general conditions of temperature, etc., under which they 

 live, die, and decay, much the same. And since Zostera forms dense fields in the sandy 

 and muddy bottoms of sheltered bays, estuaries, etc., all around the coast from Cape 

 Cod to Nova Scotia, with beds of "rock weeds" (Fucaceas), Laminarise, etc., along 

 the rocky or stony shores where it fails, the organic debris produced by the annual 

 decay of submerged marine vegetation along the coast, spermophyle and algal, 

 must reach very large proportions. 



The decay of the dead bodies of the members of the animal communities that 

 thrive so abundantly in the gulf, both on the bottom and planktonic, are also con- 

 stantly making nitrogenous compounds available in the first instance as detritus, 

 finally to find their way into solution. The importance of the rain of dead bodies 

 of planktonic organisms, which is constantly descending through the water, as 

 providing pastures for animals living on the bottom below, has long been realized. 

 Some are devoured by other animals en route; others, like the medusa? and cteno- 

 phores, may entirely decompose and go into solution as they sink; but it is probable 

 that in moderate depths, such as those of the Gulf of Maine, fragments at least of 

 most of them reach the bottom before they entirely disintegrate. Naturally a 

 larger amount of plant detritus accumulates on bottom in shoal water near land 

 than out at sea because nearer the source of supply, and animal debris may also be 

 expected to be most abundant in moderate depths. Think, for instance, of the product 

 of the death rate in an extensive mussel (Mytilus) bed. But the following analyses 

 prove that there is some nitrogenous debris (derived from plants and animals com- 

 bined) everywhere in the uppermost layer of mud, silt, or sand on the bottom of 

 the gulf, in deep water as well as in shoal. 



