Evidence of ontogenetic migration from mangroves to coral reefs by schoolmaster and french grunt: Otolith chemistry and stable isotope approach

Juvenile and Adult French grunt (Haemulon flavolineatum) and schoolmaster (Lutjanus apodus) were captured in mangrove and forereef stations in St. Croix and Puerto Rico in 2006, 2007 and 2008 to determine ontogenetic movement by otolith chemistry and stable isotopes.  Concentrations of 13 elements were determined in 0-group fish and adult otoliths using (LA-ICPMS).  (δ¹⁸O) and (δ¹³C) stable isotopes in otoliths and muscle tissue were also analyzed. Multi-elemental signatures for both species differed significantly (MANOVA p < 0.001) among mangrove and coral reef offshore stations within both Islands.  Furthermore, concentrations of six elements (Sr, Ba, Cu, Mg, Co, Na) and (δ¹⁸O and δ¹³C) in otoliths as well as in muscle tissues (δ¹⁵N and δ¹³C)  differed significantly among mangrove and coral reef offshore stations for both species within each year within Islands (ANOVA p < 0.001).  The percentage of the French grunt subadults collected from fore-reef stations in St Croix, identified as having resided as juveniles in mangrove habitats in 2006 and 2007, was 40% and 68 % while for Puerto Rico, it was 70% and 74%.  By contrast for schoolmaster almost 100% of all fish in both islands resided as juveniles in mangrove habitats across years.