Résumé: The study of organism dispersal is fundamental for elucidating patterns of connectivity between populations, thus crucial for the design of effective protection and management strategies. This is especially challenging in the case of coastal fish, for which information on egg release zones (i.e. spawning grounds) is often lacking. Here we assessed the putative location of egg release zones of the saddled sea bream (Oblada melanura) along the southeastern coast of Spain in 2013. To this aim, we hindcasted propagule (egg and larva) dispersal using Lagrangian simulations, fed with species-specific information on early life history traits (ELTs), with two approaches: 1) back-tracking and 2) comparing settler distribution obtained from simulations to the analogous distribution resulting from otolith chemical analysis. Simulations were also used to assess which factors contributed the most to dispersal distances. Back-tracking simulations indicated that both the northern sector of the Murcia region and some traits of the North-African coast were hydrodynamically suitable to generate and drive the supply of larvae recorded along the coast of Murcia in 2013. With the second approach, based on the correlation between simulation outputs and field results (otolith chemical analysis), we found that the oceanographic characteristics of the study area could have determined the pattern of settler distribution recorded with otolith analysis in 2013 and inferred the geographical position of main O. melanura spawning grounds along the coast. Dispersal distance was found to be significantly affected by the geographical position of propagule release zones. The combination of methods used was the first attempt to assess the geographical position of propagule release zones in the Mediterranean Sea for O. melanura, and can represent a valuable approach for elucidating dispersal and connectivity patterns in other coastal species.

Résumé: The Mozambique Channel (western Indian Ocean) is a dynamic environment characterised by strong mesoscale features, which influence all biological components of the pelagic ecosystem. We investigated the distribution, abundance and feeding behaviour of seabirds in the Mozambique Channel in relation to physical and biological environmental variables, with a specific interest in mesoscale features. Seabird censuses were conducted in summer and winter during 7 cruises in the southern and northern Mozambique Channel. Tropical species accounted for 49% of the 37 species identified and 97% of the individuals, and species from the sub-Antarctic region constituted 30% of the identifications. The typically tropical sooty tern (Onychoprion fuscata) was the dominant species during all cruises, and overall accounted for 74% of the species observations and 85% of counted birds. Outputs of Generalised Linear Models at the scale of the Mozambique Channel suggested that higher densities of flying and feeding birds occurred in areas with lower sea surface temperatures and lower surface chlorophyll a concentrations. Most of the flocks of feeding birds did not associate with surface schools of fish or marine mammals, but when they did, these flocks were larger, especially when associated with tuna. While tropical species seemed to favour cyclonic eddies, frontal and divergence zones, non-tropical species were more frequently recorded over shelf waters. Sooty terns foraged preferentially in cyclonic eddies where zooplankton, micronelcton and tuna schools were abundant. Among other major tropical species, frigatebirds (Fregata spp.) predominated in frontal zones between eddies, where tuna schools also frequently occurred and where geostrophic currents were the strongest. Red-footed boobies (Sula sub) concentrated in divergence zones characterised by low sea level anomalies, low geostrophic currents, and high zooplanlcton biomass close to the surface. Our results highlight the importance of mescoscale features in structuring the tropical seabird community in the Mozambique Channel, in addition to segregating tropical and non-tropical species. The mechanisms underlying the segregation of tropical seabirds seem to partially differ from that of other tropical regions, and this may be a consequence of the strong local mesoscale activity, affecting prey size and availability schemes. Beyond characterising the foraging habitats of the seabird community of the Mozambique Channel, this study highlights the importance of this region as a hot spot for seabirds; especially the southern part, where several endangered sub-Antarctic species over-winter.