It starts at home: The influence of nursery habitats on the reproductive life history of coastal fishes
Habitat can affect an organism’s fitness by providing varying amounts of food and refuge. However, certain habitats may have extended impacts on the life-history dynamics of individuals even after they have left that habitat, especially for species that make broad ontogenetic migrations. For example, nursery habitats may influence later-in-life performance through carry-over effects that confer fitness advantages during subsequent life stages. If organisms are exposed to multiple nursery habitats, individuals that utilize nurseries offering specific carry-over effects, such as increased growth rates, may transition to reproductive maturity earlier. Our study identifies whether alternative estuarine and offshore nursery habitats can influence life-history and sexual transition of the black sea bass (Centropristis striata). Natal origins of captured adult black sea bass have been determined by matching geochemical signatures in the juvenile portion of adult otoliths to a multi-annual atlas of signatures from juvenile fish captured in estuarine and offshore habitats. These signatures were used to quantify the function of natal habitats as a source contributing to the spawning, adult population. Additionally, we have begun to measure the following potential carry-over effects resulting from the use of estuarine versus offshore nurseries: (1) juvenile-through-sub adult growth rates and (2) timing of male sexual transition.
Elemental analysis of juvenile otoliths from both inshore (estuarine) and offshore (open-coast) habitats from the years 2009-2014 indicated clear environmental differences between putative nursery alternatives and that geochemical signatures could be used to successfully determine past nursery utilization of collected adults. Indeed, using linear discriminant function analysis, we were able to correctly identify 95% of all juveniles to the inshore or offshore nursery habitats where they were captured. Signatures from hundreds of adult fish otoliths are being analyzed to determine the proportional contributions of estuarine versus offshore habitats in maintaining the black sea bass stock. Additionally, comparisons of juvenile and sub-adult growth rates and percent mature males at age for fish utilizing either nursery will demonstrate the presence of carry-over effects. If carry-over effects for specific nurseries are found, we will have novel evidence of the links between nursery habitat use and post-juvenile life histories (i.e., reproductive ecology). Furthermore, these data can be used to create demographic population models to more broadly identify the impact of nursery habitat use on population-level fitness and life history dynamics. Although applied to coastal fish here, these results would be applicable for a wide range of taxa with ontogenetic habitat migrations across life histories.