Population structure and life history of Hemimysis margalefi (Crustacea: Mysidacea), a ‘thermophilic’ cave-dwelling species benefiting from the warming of the NW Mediterranean
Lejeusne, C.; Chevaldonné, P. (2005). Population structure and life history of Hemimysis margalefi (Crustacea: Mysidacea), a ‘thermophilic’ cave-dwelling species benefiting from the warming of the NW Mediterranean. Mar. Ecol. Prog. Ser. 287: 189-199
Dark submarine caves are an extreme and fragmented habitat in which mysids (Crustacea:Mysidacea) of the genus Hemimysis can be found. Hemimysis speluncola has long been thedominant mysid species of the NW Mediterranean caves, but with the recent warming of this region,its congener H. margalefi has replaced it. Nothing is known about the biology and ecology of H. margalefiand here, we provide the first information about its demographic structure and reproductivebiology in a cave recently affected by the species shift. We conducted monthly sampling for 4 yr inthe Jarre Island cave, near Marseilles (France), where a population of H. margalefi established itselfin the late 1990s. Population dynamics were followed by monitoring length-frequency histogramsand the influence of temperature on several life-history traits was investigated. H. margalefi reproducesall year round and the brood size depends on female size. Recruitment is discontinuous andoccurs when post-nauplioid larvae are 1.3 to 2.0 mm long. Four annual and overlapping cohorts(about 6 mo long) underline more intensive periods of breeding. Females can produce up to 2 successivecohorts during their life. Whatever the maturity stage, females present larger sizes than males.Seasonal variations of water temperature have a strong influence on different life-history traits of H.margalefi, such as mean sizes of the different cohorts, length of intermoult stages and growth rate.Some population dynamics features of H. margalefi are a further indication that it is a species with anaffinity for warm water, which has recently benefited from the warmer conditions in the NW Mediterranean,colonising new areas and replacing its congener H. speluncola in most of its former range.