Distribution and dynamics of shell-­‐boring Polydora on Crassostrea gigas

Abstract

The proportion of live Crassostrea gigas infected with Polydorid spionid worms was surveyed at several locations around San Juan Island. Thirty infected C. gigas were collected from the Argyle Lagoon locations and worm galleries and holes on the inside and outside of shells were counted and assigned to a shell region. The proportion of borings that penetrate the inner layer of nacre was calculated. The area of each shell region was determined to find the density of worm populations and shells were cut to measure the thickness of different regions. Oyster populations with the highest proportion of infected individuals also had higher per--‐ shell population densities. The proportion of nacre invasions remained constant as the population density of worms varied. Although the average thickness of the whole shell did not affect the proportion of inner nacre borings, the adductor scar and hinge regions showed a negative correlation between nacre bore holes and thickness.