Population structure and life history of Hemimysis margalefi (Crustacea: Mysidacea), a ‘thermophilic’ cave-dwelling species benefiting from the warming of the NW Mediterranean

Abstract

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 the dominant 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. margalefi and here, we provide the first information about its demographic structure and reproductive biology in a cave recently affected by the species shift. We conducted monthly sampling for 4 yr in the Jarre Island cave, near Marseilles (France), where a population of H. margalefi established itself in the late 1990s. Population dynamics were followed by monitoring length-frequency histograms and the influence of temperature on several life-history traits was investigated. H. margalefi reproduces all year round and the brood size depends on female size. Recruitment is discontinuous and occurs 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 successive cohorts 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 an affinity 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.

Feeding strategies and resource partitioning ­mitigate the effects of oligotrophy for marine cave mysids

“…Mysids were sampled using a hand-operated suction bottle (Chevaldonné et al 2008), then identified and sorted in vivo under a dissecting microscope. When possible, juveniles and adults (immature and mature) were separated following Tattersall & Tattersall (1951) and Lejeusne & Chevaldonné (2005), since their diet may differ (Takahashi 2004). When not possible, only adults were used.…”

Preliminary DNA-based diet assessment of a gutless carnivore, the sponge Asbestopluma hypogea

“…In the two Mediterranean caves from which we collected A. hypogea (Jarre and 3PP), the most abundant species of cave-dwelling mysids are Hemimysis margalefi and H. speluncola Ledoyer, 1963. The first is very abundant in both caves (Lejeusne & Chevaldonné 2005;Rastorgueff et al 2014) whereas the latter is now only found in 3PP cave due to regional warming of the Mediterranean Sea (Chevaldonné & Lejeusne 2003). In situ observations (Fig.…”

Local scale connectivity in the cave-dwelling brooding fish Apogon imberbis

“…The use of steppingstone relay habitats between large caves has also been proposed to explain why the rare, inner-cave mysid H. mariannae displays a lower genetic structure than H. margalefi Lejeusne and Chevaldonné, 2006;Rastorgueff et al, 2014). H. margalefi needs to live in large swarms (Allee effect; Lejeusne and Chevaldonné, 2005) and therefore presents a narrower ecological niche than the solitary H. mariannae able to use any suitable crevicular habitat as a stepping stone Rastorgueff et al, 2014).…”