Ecological Studies of Symbiosis in Convoluta roscoff ensis

The size of the Convoluta roscoffensis population on a beach in Herm, Channel Islands is subject to wide seasonal variation, being very low in early summer and high in autumn and winter. Of the ecological factors measured, only light -expressed a s photosynthetically active radiation showed a correlation with population size. Low worm numbers, and also low numbers of algae and chlorophyll a content per worm, were associated with high light intensities, and vlce versa. Worm spacing within colonies, however, remained relatively constant, with a mean value of 9 X 105 worms m-*. Estimates of photosynthetic cover (chlorophyll biomass) of 320 mg chlorophyll a m-', and annual primary productivity for 1977, of 872.9g carbon fixed m-' of colony, approach estimates for coral reefs; they were remarkably high for the potentially disturbed environment of the intertidal sandy beach.