Connectivity of reef fish between juvenile nursery habitats and coral reefs: tracking migration with compound-specific stable isotope analyses and trace element geochemistry
|(A) Study site in the northern Farasan Banks along the Saudi Arabian coast of the Red Sea. (B) Ehrenberg’s snapper (Lutjanus ehrenbergii, Peters 1869) is a commercially important reef-associated snapper species in the Indo-West Pacific. (C) Conceptual diagram of habitat configuration and potential seascape connectivity of L. ehrenbergii in the study area. ()|
Dr. Simon Thorrold (WHOI) Dr. Michael Berumen (WHOI and KAUST) Dr. Marilyn Fogel (Carnegie Institition of Washington)
The ecological integrity of tropical habitats, including mangroves, seagrass beds and coral reefs, is coming under increasing pressure from human activities. Many coral reef fish species are thought to use mangroves and seagrass beds as juvenile nurseries before migrating to coral reefs as adults. Identifying essential habitats and preserving functional linkages among these habitats is likely necessary to promote ecosystem health and sustainable fisheries on coral reefs. This necessitates quantitative assessment of functional connectivity among essential habitats at the seascape level. This project presents the development and first application of a method for tracking fish migration using amino acid (AA) δ13C analysis in otoliths. In a controlled feeding experiment with fish reared on isotopically distinct diets, we showed that essential AAs exhibited minimal trophic fractionation between consumer and diet, providing a δ13C record of the baseline isoscape. We explored the potential for geochemical signatures in otoliths of snapper to act as natural tags of residency in seagrass beds, mangroves and coral reefs in the Red Sea, Caribbean Sea and Eastern Pacific Ocean. The δ13C values of otolith essential AAs varied as a function of habitat type and provided a better tracer of residence in juvenile nursery habitats than conventional bulk stable isotope analyses (SIA). Using our otolith AA SIA approach, we quantified the relative contribution of coastal wetlands and reef habitats to Lutjanus ehrenbergii populations on coastal, shelf and oceanic coral reefs in the Red Sea. L. ehrenbergii made significant ontogenetic migrations, traveling more than 30 km from juvenile nurseries to coral reefs and across deep open water. Coastal wetlands were important nurseries for L. ehrenbergii; however, there was significant plasticity in L. ehrenbergii juvenile habitat requirements. Seascape configuration played an important role in determining the functional connectivity of L. ehrenbergii populations in the Red Sea. The compound-specific SIA approach developed in this project will be particularly valuable for tracking the movement of species and life-stages not amenable to conventional tagging techniques. This work provides quantitative scientific support for establishing realistic population connectivity models that can be used to design effective marine reserve networks. This work was established in the Red Sea during my doctoral research in the MIT-WHOI Joint Program in Oceanography, and has since been expanded to other regions and species to gain a more global understanding of the role of nursery habitats to coral reef fishes.
McMahon KW, Fogel ML, Johnson BJ, Houghton LA, Thorrold SR (2011) A new method to reconstruct fish diet and movement patterns from δ13C values in otolith amino acids. Canadian Journal of Fisheries and Aquatic Sciences 68:1330-1340
McMahon KW, Berumen ML, Mateo I, Elsdon TS, Thorrold SR (2011) Carbon isotopes in otolith amino acids identify residency of juvenile snapper (Family: Lutjanidae) in coastal nurseries. Coral Reefs30:1135-1145 (Best Paper Award finalist)
McMahon KW, Berumen ML, Thorrold SR (2012) Linking habitat mosaics and connectivity in a coral reef seascape. Proceedings of the National Academy of Science, DOI: