Hemimysis speluncola Ledoyer, 1963 (Fig. 8): an unexpected model for Mediterranean climate change and evolutionary ecology

Being among the first SME researchers to use SCUBA, in 1958 Laborel &Vacelet (1958) reported of surprisingly dense swarms of a small red mysid (Crustacea: Mysida) in the darkest reaches of a small underwater marine cave of the Bay of Marseille at Niolon. Closely resembling the well-known Atlantic species Hemimysis lamornae (Couch 1856), it was later recognized that such swarms were common in dark caves of the Marseille area, and that some of them were made of a new species, Hemimysis speluncola Ledoyer, 1963 . For twenty years (1966–1986), the new species then became a model for behavioural ecology and ecophysiology, as it was found relatively easy to maintain in aquarium (e.g. Macquart-Moulin & Patriti 1966; Gaudy et al. 1980; Bourdillon & Castelbon 1983; Passelaigue & Bourdillon 1986). Among other things, H. speluncola displayed original horizontal circadian migrations in and out of caves to feed, in a way similar to the vertical migrations of deep-sea zooplankton. Suddenly, in the late 1990s, concomitant with the first marine heat wave and invertebrate mass mortalities recorded in the NW Mediterranean, Chevaldonné & Lejeusne (2003) provided evidence that, in most of its known geographic range, H. speluncola had vanished, gradually being replaced by the more thermophilic Hemimysis margalefi Alcaraz, Riera & Gili, 1986 . This was the first documented Mediterranean warming-induced species shift and it triggered a series of studies on the Hemimysis species (many of which cryptic) present in the Atlantic-Mediterranean area, to investigate their molecular phylogeography and evolutionary history. Today, cave-dwelling Hemimysis, including the nowendangered H. speluncola, have become a model to study the effect of natural habitat fragmentation on population connectivity (Lejeusne & Chevaldonné 2006; Rastorgueff et al. 2014).