Reference: li'wl. Hull.. 148: (>0-(>7. ( February, 1975) A RADIOACTIVE TRACER STUDY OF FOOD UPTAKE BY PINNOTHERES MACULATUS IX MOLLUSCAN HOSTS W. L. KRUCZYNSKI Saline Marsh Eeolot/y Project, Florida A & M University, Tallahassee, Florida 32307 The Pinnotheridae, pea crabs, is a group of decapod crustaceans adapted for living with other marine animals. Pearce (1962) discussed adaptations of these crabs for symbiotic existence, and Gotto (1969) listed bivalves, gastropods, sea slugs, chitons, polychaetes, echinoderms, burrowing crustaceans and sea squirts as known hosts. Associations of most pinnotherids with their hosts have not been defined. Many have long been recognized as commensals, and some have been labeled parasitic (Cheng, 1967; Gotto, 1969). Pinnotheres ostrcinn (Say), for example, is known to cause gill and palp damage to Crassostrea virginica (Gmelin) and reduce growth and reproduction of the oyster (Overcash, 1946; Sandoz and Hopkins, 1947; Flower and McDermott, 1952; Haven, 1958; Christensen and McDermott. 1958). McDermott (1962) found that both P. ostrcitm and Pinno-theres macnlatits Say caused similar damage in Myti/us ednlis Linne. Fabia sitbqnadrata Dana was observed to damage gills and cause cyst-like anomalies in mantle tissues of Hlodiolus niodiohts Linne (Pearce, 1966a) and Pinnotheres sp. damaged gill, mantle and gonad of Meretri.v easta (Chemnitz) (Silas and Ala-garswami, 1967 ). The mode of feeding of some pinnotherids has been investigated. Pearce (1966b) noticed that Pinni.va jahra (Dana) caused damage to its host clam. Tresus capa.v (Gould), and found that the crab ingested food which would other-wise be available to the clam. Stealing of food which a host has concentrated into food strings has also been reported for Pinnotheres pisit/n ( Pennant ) (Coupin. 1894; Orton, 1921), Pinnotheres eoneharin/i ( MacGinitie and MacGinitie, 1968) and P. ostreitiu (Stauber, 1945). Campbell (1969) found plant pigments in the gut of P. pisitin which indicated ingestion of algae. Orton (1921) and Gotto (1969) suggested that some crabs may also filter food from water currents created by hosts. All of these studies are descriptive and no experimental quantification of crab-host associations are known except that adult female P. macnlatits stunted growth of bay scallops, Argopecten irradians concentricus (Say), grown in cages ( Kruczynski, 1972). Radioisotope techniques arc common tools to studv physiological processes, but few studies are known employing these methods to quantify trophic relation-ships in natural ecosystems. Poole (1974) discussed some methods of measuring ingestion using radioactive tracers and reviewed research which quantified com-ponents of some terrestrial and stream ecosystems by these methods. Smith, Muscatine and Lewis (1969) reviewed quantification of carbohydrate movement using 14 C from autotrophs to heterotrophs in parasitic and mutualistic symbiosis. Pardy and Muscatine (1973) used labeled green algae to quantify uptake of symbionts by II\dra riridis. 60
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