Effects of the parasitic nematode Echinomermella matsi on growth and survival of its host, the sea urchin Strongylocentrotus droebachiensis

It has been suggested that the parasitic nematode Echinomermella matsi sign ificantly affects the population dynamics of its host, the sea urchin Stron gylocentrotus droebachiensis. The effects of infection on both host fecundi ty and host survival may be of importance. The fecundity of sea urchins is related to their size. Negative effects of infection on host growth will th erefore reduce reproductive rates. I estimated the effect of infection on h ost growth and survival in two naturally infected wild sea urchin populatio ns using a capture-mark-recapture approach. Infected and uninfected sea urc hins were captured and marked with unique tags or recaptured seven times fr om June 1994 to September 1996. The increment in the diameter of marked sea urchins between captures was used to measure sea urchin growth. The effect of E. matsi infection on host growth was small. Mortality rates were estim ated using survival probability models based on the methodology developed b y Cormack, Jolly, and Seber. The effect of infection on host survival was p ronounced, with estimated sea urchin Life expectancies reduced by 33-86% by E. matsi infection. This suggests that E. matsi may affect the population dynamics of S. droebachiensis significantly through the effect on host surv ival.