328 ON A SPONGE DESTRUCTIVE TO OYSTER CULTURE, 



That tlie sponge does not draw its nourishment, as a parasite 

 would, from the oyster animal, can also be demonstrated by the 

 fact, that the sponge grows on other submerged bodies besides the 

 oyster shell. 



The sponge can therefoi-e on no account have a direct etfect on 

 the old oysters. 



The sponge might, however, perhaps have a detrimentary effect 

 in an indirect manner. 



Both the sponge and the oyster live on microscopic particles of 

 a digestable nature. 



The sponge overgrowing the oyster will therefore intercept and 

 retain a great portion of that food, the whole of which would, were 

 the sponge not present, be available for the oyster. The sponge 

 takes the food away from the oyster and thrives at the expense of 

 the latter. 



In this way the sponge will have a bad effect on adult oysters, 

 but in no other. It appears clear, however, that the sponge will, 

 where it is dominant, prevent the setting of the spat, as the spat 

 cannot set on the sponge itself and the sponge takes up the whole 

 of the area. I think that these conclusions will satisfactorily 

 explain the facts observed. 



The sponge settled on the oyster bed and spread there rapidly 

 taking up all the space. The spat could not set. The old oysters 

 died for want of nourishment and finally no live oysters remained 

 in the locality. 



The fact that the sponges are now again disappearing shows that 

 they depend to a certain extent, probably, on the oysters. 



Around the oysters always a superabundance of microscopic 

 animals congregate, which feed on the excrements of the oysters, 

 and it is probable that the sponges lived to a great extent on them. 



Some species of sponges are found only in water with strong 

 currents, and it seems not improbable that that is also the 

 case with our Chalinula Coxii. In the locality where the sponges 

 have taken possession of the oyster bed the channel is narrower 

 and shallower than it is in other parts, and consequently the 

 currents in that part must be stronger than elsewhere. 



