FOOD VALUE OF SEA MUSSELS. 
95 
The organisms included in this list are of the most primitive type, and, as Peck 
(1896) has demonstrated, are the ultimate source of food for all marine animals. The 
food of diatoms is the dissolved mineral matter removed from the soil and carried by 
rivers and the smaller streams down to the sea. It is absorbed through the surface 
of their bodies and transformed into living tissue. When their bodies have increased 
to a certain size, each individual divides into 2 ; as these grow they divide into 4, the 4 
into 8, 8 into 16, etc., in geometric ratio. Under favorable conditions multiplication 
by this means is so rapid that millions may be produced in a day from a single individual. 
The Protozoa on which the mussel feeds multiply in much the same way, but in feeding 
habits differ from the diatoms in that they consume solid food, chiefly diatoms, in 
addition to absorbing soluble nourishment through the surface of the body. It is 
interesting to note, as Professor Brooks has pointed out, that these unicellular organ- 
isms are the means of bringing back to us in the form of food our mineral wealth which 
is continually being lost through the agency of erosion and solution. 
ENEMIES AND PARASITES. 
The enemies of the mussel are numerous. Killifish, cunners, and scup are very fond 
of the young mussels, greedily stripping them from the wharf piles, seaweeds, and other 
objects of attachment. The squeteague and tautog eat them from the beds. Among 
the mollusks the drill, Urosalpinx cinereus, destroys large numbers by boring a hole 
through the shell to the soft parts on which it feeds. On nearly every mussel bed 
numbers of shells may be found pierced with a hole about the size of a pin head which 
testify to the ravages of this voracious snail. Another snail, Neverita duplicata, is 
supposed to feed upon them in the same manner but the hole drilled is much larger. 
The so-called whelks, Busycon canaliculata and B. carica, also prey upon them to 
considerable extent. Perhaps the worst enemy is the starfish, which destroys them to 
as great a degree as it does the oyster. In England, Lebour (1907) reports that one 
whole bed of mussels at the mouth of the River Tyne was completely destroyed by 
this echinoderm. Crows and rats are said sometimes to eat mussels from the beds when 
they are exposed. Seaweeds like Ulva and eel grass ( Zostera marina ) are very injurious 
to the health and growth of mussels when they spread over the beds. Two of the largest 
beds near Woods Hole, Mass., have been practically ruined this year (1908) by a dense 
mass of eel grass which has sprung up over them. The weed by its growth not only 
gradually smothers the mussels, but causes the sand and mud to silt over them at such 
a rate that in a few months all signs of the bed are obliterated. The decaying bodies 
of the shellfish fertilize the soil and finally what was once a bed of mussels is a thrifty 
bed of eel grass. 
The parasites of the mussel are few. The most common one is a little crab, Pinno- 
theres maculatum, which is very similar to the oyster crab but larger and with a tougher 
shell. It apparently works no injury to either the health or growth of the shellfish. 
Indeed, some observers believe the relation is symbiotic rather than parasitic. The 
