Title

THE POPULATION ECOLOGY OF THE HARD CLAM, MERCENARIA MERCENARIA, IN EASTERN LONG ISLAND SOUND (DENSITY-DEPENDENT, PREDATION, RESOURCE MANAGEMENT)

Date of Completion

January 1985

Keywords

Biology, Ecology

Degree

Ph.D.

Abstract

A combination of in situ manipulative field experiments, sampling of an unexploited natural population, and computer simulations were used to study the population ecology of Mercenaria mercenaria in Eastern Long Island Sound.^ More than 99% of the mortality of juvenile clams at both sites was the result of crustacean predators. The green crab (Carcinus maenus) was the dominant predator of clams up to 10mm, while lobsters (Homarus americanus) readily consumed larger size classes at one site only. Clam survival was significantly influenced by clam size, and planting site, time, and density. Average full season survivorship of clams during the first two years of life was about 10% per year at both sites and 20% and 80% for third year class clams at the outer harbor and estuarine sites, respectively. The dramatic difference in survivorship of larger clams between sites is attributable to the absence of lobsters at the estuarine site. Of all variables tested, density had the most significant effect on juvenile clam survivorship.^ Adult survivorship averaged 91-95% and was not influenced by clam density or size. Clam density significantly affected clam meat displacement volume at only the highest density tested (which was unrealistically high). Natural population samples revealed an average density of 12 clams/m('2) and a dominance of large, relatively old clams (>15 years old). More than 50% of all clams (LESSTHEQ)15 years old belonged to two age classes. During the last fifteen years, there was an average rate of recruitment into the adult age classes of .45 clams/m('2)/year (enough to sustain the observed population density). Historical patterns of population recruitment and growth were not influenced by population density. Even though this population has a high density, it could not support a sustained fishery.^ In light of the extremely high rates of mortality during the early life history and infrequent pulses of recruitment, low adult mortality and long life span are important components of the organism's life history. Theoretical analyses of a variety of bivalve resource management strategies suggest that only persistent predator control can potentially increase hard clam yields. ^