Littoral Browsers

In the littoral zone where large quantities of attached benthic plants are produced, many herbivorous or omnivorous animals also are found that feed directly upon the growing plants and are therefore to be considered a complement to the small but numerous planktonic grazers and the plant detrital feeders so vital in converting plants into animal substance. The large benthic algae have their greatest significance as a source of animal food in the temperate and boreal regions (p. 293).

Numbered among these littoral algal grazers are many gastropods, crabs, shrimps, and amphipod and isopod crustaceans. The devices used in mincing the plants consist of horny rasplike radulae in the gastropods, and claws, pinchers, and mandibles of heavy chitin in the crustaceans. A number of fishes, for example the rudder fish (Kyphosus) and the butterfly fish (Chaetodon) as well as other reef and littoral fishes, also browse on the attached algae.

It is not feasible to separate sharply the browsers from the detritus feeders and scavengers, since they perhaps all feed more or less indiscriminately upon growing plants or upon living or dead fragments, some of which may be washed far to sea. Indeed, most plants are eaten after they have become detached from their moorings and while in the process of breaking up mechanically or through decay. This was also the conclusion of Hewatt (1937) in special observations on food relations of intertidal animals at Monterey Bay. Petersen (1918) reports that eel grass is utilized mainly as detritus and that it may either be spread over the bottom or carried as fine particles in the water.

The relation of marine wood-boring organisms to their food supply constitutes an unusual one in the sea and may be arbitrarily mentioned under this presnent heading.

Much organic material is washed or blown into the sea from land which incidentally becomes available as food for marine life. Few instances can be cited wherein typical organisms of the sea are directly dependent upon organic products from the land. Such dependence is

---

the rule, however, with the molluscan wood-borers, such as Teredo, Bankia, and with the wood-boring crustacean Limnoria, which bore into wood that has been carried into the sea by streams or through activities of man. The wood diet of the molluscs may be supplemented by various plankton organisms, but it has been shown (Boynton and Miller, 1927, Yonge, 1931) that these borers are able to produce a special enzyme, cellulase, which converts the cellulose of the wood into glucose, making it available as food. A cellulase has not been demonstrated in Limnoria but the persistent boring and swallowing of wood by these animals strongly suggests that they must obtain a good portion of nourishment from the wood. Isolated specimens have been kept alive and actively boring and moulting in unsterile cultures for over three years at La Jolla. Their only source of food during this time was the wood or such bacteria and other minute organisms as might be present on the wood.