INFESTATION OF THE TEHUELCHE SCALLOP (CHLAMYS TEHUELCHA (D’ORBIGNY) BY POLYDORA WEBSTERI HARTMAN (POLYCHAETA: SPIONIDAE) IN SAN JOSE GULF (CHUBUT, ARGENTINA): A QUANTITATIVE APPROACH.

Abstract

Studies were done to quantify the infesiation of the bivalve Chlamys tehuelcha by the spionid polychaete Polydora websteri, and lo compare ihe infestation rale with individual growth rale, density and age composition of Ch. tehuelcha from 5 natural grounds. Data were pooled by valve, age of the bivalve, and ground. P. websteri affects indistincily both valves of Ch. tehuelcha. The intensily of infestation increases significantly with the age of the bivalves. The intensity of infestation varied significantly among grounds. The highest levels of infestation coincidied with the lowest rates of bivalve growth. Scallop densities, total and by age groups, varied significantly among grounds. Bivalves 1 + and younger were slightly affected in localities with high densities,as well as in grounds with littledensitiesof scallops0 + and 1 + . Amongscallops morelikely tobe infested (age 2 + and older), high intensity of attack generally occurred in grounds with high densities of bivalves of age 2 + and older. Intensity of the infestation of Ch. tehuelcha by Polydora websteri and scallop growth are inversely related. Growth. In his turn. is affected by interpopulational differences in the food availability due to environmental gradient and depressions of the food availabilily due to intraspecific competition (density-dependence). Relationships among infestation rate, condition and bivalve growth are discussed. A feed-back relation is suggested as the most probable relationship among the above mentioned variables.