Laboratory studies on eelgrass seed and seedling predation

Ten species, including crustaceans, molluscs and fish, were examined for predacious activity onZostera marina L. seeds and seedlings. Predation was examined initially by offering seeds or seedlings as a sole food source for a maximum period of one week. Species exhibiting predation of 10% or more of the seeds or seedlings were tested further with bits of clam or scallop as an alternative food source. In these experiments, animals were tested in each of three conditions: 1) alternative food plus seeds or seedlings; 2) alternative food alone; 3) seeds or seedlings alone. In the initial experimentsOvalipes ocellatus, Pagurus longicarpus, andPanopeus herbstii preyed on seeds, andIlyanassa obsoleta, Littorina littorea, andP. longicarpus preyed on seedlings. Limited predation occurred, however, when these animals were presented with seeds or seedlings plus an alternative food. These data suggest that several common crab and snail inhabitants of eelgrass meadows are capable of preying on eelgrass seeds and seedlings, but that this activity may be influenced by the availability of an alternative food source.