SUBLETHAL PREDATION ON POLYDORA-CORNUTA (POLYCHAETA, SPIONIDAE) - PATTERNS OF TISSUE LOSS IN A FIELD POPULATION, PREDATOR FUNCTIONAL-RESPONSE AND POTENTIAL DEMOGRAPHIC IMPACTS

Patterns of tissue loss due to sublethal predation and potential effec ts on population dynamics were investigated in the polychaete Polydora cornuta Bose, 1802. Field observations in southeastern Connecticut sh owed that the percentage of adult worms regenerating segments and/or f eeding palps varied temporally from May to November 1982, but the gene ral pattern suggests a constant level of sublethal encounters. Over al l sampling dates, a mean of 14.9 and 7.0% of the population was found regenerating posterior segments and palps, respectively. Worms lost a mean of 19.1% of their segments. There was a weak, but statistically n on-significant, size-specific difference in the number of regenerating segments per individual. Worms with 20 to 39 segments and 60 to 80 segments lost an average of 13.8 and 17.2% of their segments, respecti vely, but worms with 40 to 59 segments lost an average of 23.4% of the ir segments. The incidence of regeneration (palps and segments) increa sed linearly with increasing adult density in the population. There wa s also a strong positive linear relationship between the number of seg ments available and the number of segments lost at the population leve l. This suggests that the constant level of sublethal predation can be explained by predators taking prey in proportion to their density and /or the number of segments available. This pattern is supported by res ults from a laboratory functional response experiment which indicated that at high prey density, partial consumption of P. cornuta by the pr edatory polychaete Eteone heteropoda was greater than lethal consumpti on. Lethal predation of P. cornuta by E. heteropoda did not vary acros s experimental density treatments. Demographic modelling suggested tha t sublethal predation can reduce the population growth rate of P. corn uta, but the reduction is less than if the added predation pressure wa s solely:lethal. It was estimated that up to 25% of the population cou ld be preyed upon in a sublethal manner before the potential for popul ation growth fell below population maintenance levels.