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Are Mangroves Important Juvenile Fish Nurseries?

Travis S. Elsdon, Simon R. Thorrold, and Leah A. Houghton.

The importance of mangrove systems as juvenile nursery areas for coral reef fish populations remains controversial. Resolving the issue is critical, however, due to the rapid loss of mangrove habitats throughout the tropics.

At least 35% of the world’s mangrove forests have been eliminated during the last two decades – rates of habitat loss that exceed both tropical rainforests and coral reefs. Direct quantification of the importance of mangroves to tropical fisheries requires a method of retrospectively identifying juvenile habitat utilization in adult fish. Conventional tagging approaches are logistically difficult in marine environments because of high mortality rates that make the recovery of marked individuals difficult.

Naturally-occurring geochemical markers in calcified tissues, including fish otoliths (“ear bones”), have proved particularly useful in marine systems because they eliminate the need to physically tag an individual.

We propose to develop new analytical methods, based on compound-specific stable isotope analyses of the organic component of otoliths, which will allow retrospective determination of mangrove use during the juvenile stages of coral reef fish. This will, in turn, provide for the first direct and rigorous assessment of the importance of mangrove systems to reef fish populations.