The annual reproductive pattern of the Antarctic clam, Laternula elliptica from Marian Cove, King George Island

Abstract

The annual reproductive cycle of the Antarctic soft-shelled clam, Laternula elliptica, in Marian Cove, King George Island was studied over a 2-year period from February 1998 to January 2000. Annual changes in the gametogenesis were investigated by measuring the percentage of area occupied by oocytes in a follicle (follicle index, FI) and the oocyte size. In 1998, the monthly mean FI increased significantly from October to November, peaked in December, and decreased rapidly from December to January. In February and March 1999, degenerated eggs were observed in the spent follicles. Degeneration and resorption of residual eggs by phagocytosis occurred mostly in February and March in both 1998 and 1999, although the resorption process was observed year-round. The histology indicated that complete vitellogenic growth of L. ellpitica at Marian Cove takes at least a year and the clams spawn annually during the austral summer. The ripening and subsequent spawning of clams at Marian Cove in 1998 and 1999 was coincided with the algal blooming (September-October 1998 and December and January 1999-2000) suggesting that in coastal Antarctica food supply is a crucial factor that governs gonad maturation and subsequent spawning along with the water temperature.