A comparison of reproductive cycles and reproductive output in four southern African mussel species

Abstract

The sex ratios in Aulacomya ater. Choromytilus meridionalis and Perna perna were biased in favour of males, but this was not the case for Mytilus galloprovincialis. The calorific value of females was higher than that of males in all species. A. ater spawned three times a year; spawning events differed considerably in timing and intensity between years. C. meridionalis and M. galloprovincialis generally showed two protracted spawning seasons, one each during summer and winter. P. perna from Natal spawned over an extended period from May/June to December, while those from the Cape and Transkei had a well-marked winter spawning, accompanied by either one extended, or two discrete, spring or summer events. Gamete build-up and release resulted in marked variations in flesh yield. This was greatest in M. galloprovincialis, where dry flesh weight can vary three-fold between ripe and spawned conditions at a length of 65 mm. Equivalent values for A. ater, C. meridionalis and P. perna were 2.3-, 2.8- and 2.2-fold respectively. Total individual reproductive output was greatest in A. ater, because of its three annual spawnings, followed by M. galloprovincialis, C. meridionalis and P. perna. When extrapolated to a population level, beds of mussels released 3.4-10.4 wet mass gametes m-2 yr-1, a large energy subsidy to adjacent benthic and pelagic communities. -from Authors