Symbiodiniacean cell supply method for improvement in survival of Tridacna squamosa seeds

Abstract

　Tridacnid giant clams are large bivalves found in coral reefs. Giant clams harbor symbiotic dinoflagellate, which is essential for their survival. Artificial seedling production is necessary because the natural stock of giant clams is declining, but this process usually results in low larval survival, likely caused by a failure to establish the symbiosis between clam larvae and symbiotic algae under artificial conditions. In the present study, experiments were conducted to determine how the origin of symbiont algae fed to larvae and the frequency of algal supply affect the survival rate of Tridacna squamosa larvae. Although the frequency of algal supply did not affect larval survival, enhanced larval growth was achieved in the bottle-scale experiment when algal cells were supplied once every 2 days. At the actual seedling production scale, a survival rate of 21.4 (20.9-21.7)% [average (minimum-maximum)%] was achieved in tanks supplied with algae extracted from several small T. squamosa individuals, which represented a two-fold increase as compared to the conventional method 9.4 (8.0-10.9)% of extracting algae from a single medium T. squamosa individual.