Effect of nutrient enrichment on Tridacna derasa seed: dissolved inorganic nitrogen increases growth rate

Abstract

A significant growth enhancement in juvenile giant clams, Tridacna derasa, was achieved under experimental mariculture conditions with regular additions of nitrate or ammonium to seawater. During a 60-day trial, a 2.5 order-of-magnitude increase in background dissolved inorganic nitrogen (DIN) concentration (0.2 to 50 μ M) for 16 h per day yielded a mean 17–21% improvement in length increment and a mean 288–375% improvement in weight increment over untreated controls. Ammonium and nitrate were equally effective as growth enhancers. Treated clams maintained their size advantage for at least 90 days after transferal to ambient conditions in a subtidal ocean nursery. No detrimental physiological effects of DIN enrichment were detected, nor was there any evidence of long-term DIN storage by enriched clams. In tropical giant clam hatcheries characterized by nitrogen-poor seawater, the seed production cycle can be shortened significantly with regular DIN enrichment. The low cost of applying suitable agricultural fertilizers and the impressive improvements attainable in yield and production efficiency suggest that DIN enrichment should be “standard operating procedure”.