Reproductive biology of the Asiatic clams Corbicula fluminalis and Corbicula fluminea in the river Rhine
Rajagopal, S.; van der Gelde, G.; bij de Vaate, A.
published: Nov 14, 2000
ArtNo. ESP141014903012, Price: 29.00 €
Morton (1986) revised the genus Corbicula and distinguished two species, viz., Corbicula fluminalis and Corbicula fluminea, each with a contrasting reproductive strategy. In the river Rhine, where C. fluminalis and C. fluminea have coexisted in large numbers since their invasion in 1988, their reproductive aspects were studied from April 1991 to January 1993. C. fluminalis is dioecious, with a small percentage (about 3 %) of hermaphrodites, while C. fluminea/i> is a simultaneous hermaphrodite, which incubates fertilised eggs within its inner demibranchs and releases pediveligers (200 µm shell length). C. fluminalis and C. fluminea exhibited different spawning periods: C. fluminea released its pediveliger larvae from May to September, when mean water temperature exceeded 15 °C, while C. fluminalis released its gametes during October-December and March-April, when mean water temperature was between 6 °C and 15 °C. Both species showed two spawning peaks per year, viz. October/November and March for C. fluminalis and May/June and September for C. fluminea. In both species, the second spawning peak was shorter than the first, and the percentage of spawning individuals was much lower during the second period. Spawning frequency of C. fluminea correlated positively with the chlorophyll-a content of the water. Body mass development also showed a close correspondence with spawning, with two peaks per annum. In contrast to C. fluminea, C. fluminalis body mass increased from December to March, when chlorophyll-a concentrations were very low, indicating alternative food sources for this species other than algae (bacterioplankton, detritus). C. fluminea, which shows brood care, allocated more energy resources (51 % in May and 21 % in September) to reproduction before spawning than C. fluminalis (33 % in October and 20 % in March). The co-existence of C. fluminalis and C. fluminea in the Rhine branches is probably explained by their different reproductive strategies, reproductive periods and possibly different food preferences.