Ocean scientists have long known that juvenile coral reef fishes use coastal seagrass and mangrove habitats as nurseries, later moving as adults onto coral reefs. But the fishes' movements, and the connections between different tropical habitats, are much more complex than previously realized, according to a study published September 3 in Proceedings of the National Academy of Sciences. The findings have important implications for management and protection of coral reefs and other marine environments.
A number of studies have demonstrated a strong relationship between the presence of coastal wetlands and offshore fish abundance and fisheries yield, but it has proved difficult to develop quantitative assessment of habitat use by fish or their movement among different habitats. "The rationale for this study,"says Simon Thorrold, a biologist at Woods Hole Oceanographic Institution (WHOI), "was to determine the relative importance of different nursery habitats to reef fishes that spend their adult lives on coral reefs but may spend at least part of their juvenile residency elsewhere."
The study also advances understanding of the functional connectivity of coral reef fish in a tropical seascape, says WHOI biologist and study lead author Kelton McMahon. "Traditional methods of assessing nursery habitats visual surveys of abundance and size of fish in different locations provide important but indirect evidence of connectivity among essential habitats. We developed a quantitative method that identifies essential nursery habitat, and allows reconstruction of migration within the seascape."
The method analyzes isotopic signatures recorded in fish tissue. These signatures, unique to each environment in which a fish lives and feeds, are laid down in its otoliths, or ear bones, creating a record similar to that of tree rings.
"Otoliths are constantly and permanently recording the conditions a fish is experiencing at any time," ex
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Woods Hole Oceanographic Institution