Effect of Light on Rate of Growth of Bivalves

Abstract

GROWTH bands on the epithecae of fossil corals, apparently representing yearly and daily growth increments, have recently been used to determine the number of days in the year in the geological past and reveal a possible slowing of the rotation of the Earth^1–3. The yearly bands probably result from seasonal temperature variation and the daily bands may well reflect differential growth rate between periods of light and dark as a consequence of the presence of the symbiotic algae Zooxanthellae in the coral tissue^4,5. Similar bands have more recently been described in bivalves^6–10, but the lack of symbiotic algae in the bivalves makes explanation of the daily bands more difficult than in the corals. To determine whether growth rate in bivalves varies between periods of light and dark, we have conducted a series of radioisotopic tracer experiments.