The biology, exploitation, and mariculture of giant clams (Tridacnidae)

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Abstract
Eight giant clam species have been overfished for meat and shells throughout their tropical Indo‐Pacific distributions. The 1960s through the 1980s were particularly severe for the two largest species, due in part to international poaching for their adductor muscle meat. Low densities, erratic recruitment, and a relatively long period to reach harvestable size make these populations prone to overfishing. Declining giant clam stocks and local extinctions were a major stimulus for research into mariculture methods. The life cycles of most species are well understood and a variety of mariculture methods have been developed. However, heavy mortality of the early juvenile stages remains a problem. Recent research has revealed new aspects of giant clam biology, such as the housing of their symbiotic zooxanthellae in a unique complex diverticulum of the stomach. Research has quantified dual modes of nutrition (photosynthates from zooxanthellae and effective filter feeding) that give giant clams a nutritional and growth advantage over normal heterotrophic bivalves. Whereas the economics of giant clam farming have been demonstrated, commercial farming is still in its infancy. Conservation measures, such as the development of marine reserves, establishing breeding aggregations, and restocking wild populations with cultured clams, have only been attempted to a limited extent.