Natal signatures of juvenile Coris julis in the Azores: investigating connectivity scenarios in an oceanic archipelago

To estimate connectivity between populations, we used trace-element composition in otoliths of the temperate wrasse Coris julis as a proxy for the environmental conditions experienced from hatch to settlement. Recruits collected at different sites in the Azores archipelago (northeastern Atlantic) differed significantly in their natal chemical signatures, and were sufficiently diverse to be separated into in 4 distinct natal types. Types 1 and 4 were both low in Mg and Ba, although Mg was dominant in Type 1, and Type 4 was more Ba enriched. Type 2 had high Ba and intermediate Mg concentrations, while Type 3 showed the highest Mg and intermediate Ba concentrations. We identified at least 2 natal types present in recruits at each site, which suggests multiple larval sources per site. Recruits from 3 sites did not differ greatly in their natal type composition, suggesting a common set of sources, but also limiting our ability to describe meaningful connectivity and dispersal scenarios. In contrast, we found that the prevalent Natal Type 4 was absent at 1 site, suggesting that the source characterized by Natal Type 4 does not contribute to the replenishment of C. julis populations at the site. The most striking difference was observed at the smallest scale (10s of kilometers), where we found distinct natal type compositions between north and south shores on the same island, suggesting that these 2 sites have consistent differences in the contribution of specific natal sources. Further, the south shore site had recruits with elevated Mg:Ca concentrations from the otolith core to edge, which suggests that these larvae developed in inshore areas and experienced local retention.