Reproductive cycle and biochemical composition of the ark shell Scapharca broughtonii (Schrenck) in a southern coastal bay of Korea

Abstract

The reproductive cycle and biochemical composition of the ark shell Scapharca broughtonii (Schrenck) in Chinju Bay, a southern coastal bay of Korea, were studied from July 1999 to August 2000 in relation to environmental conditions (temperature, salinity and available food). Animals were cultured in the bottom. S. broughtonii from Chinju Bay was characterized by a spawning period during July to September due to a monocyclic gametogenesis throughout the year. Clear seasonal cycles in biochemical composition of the animal tissues were recorded. Summer spawning of S. broughtonii was followed by a clear accumulation period of reserve materials in autumn (from October to December). A great increase in animal tissue weight was attributed to the rapid accumulation of protein and carbohydrate during that period. A new cycle of gametogenesis began at the lowest water temperature in February. The gonadal growth during winter to spring when the available food was poor took place at the expense of reserves (mainly glycogen) accumulated previously in autumn. Lipid biosynthesis during gametogenesis was associated with glycogen breakdown. Blooms of phytoplankton in the ambient waters took place in the low saline summer period when water temperature was highest, depending on the addition of excessive nutrients via streams. Spawning of S. broughtonii occurred at the time when the available food was very abundant. This seemed to enable larvae to be produced at the most opportune moment with regard to food availability, as previously proposed. Our results indicate that this bivalve may be considered a typical conservative species in gametogenic pattern.