Natural tags to Estimate the Value of Juvenile Nurseries

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The use of tags has longstanding value in ecology for estimating vital rates in populations. Although largely developed by wildlife biologists, the use of tags is invaluable in estimating population dynamics in marine organisms. This proposal will use a natural tag to determine habitat-specific survival of an organism from birth to adulthood. We use otolith chemistry as our natural tag and we measure the relative survival of fish as a function of their seagrass nursery. However, the technique to measure relative survival can be done with any organism that carries a natural tag during its lifetime. The natural tag could be a genetic marker and the organism could be a euphausid. The problem could be estimating the value of a seagrass nursery to fish, or the impact of the breakup of an Antarctic ice shelf on euphausid populations. To study either scenario, it is first necessary to have a reliable natural tag that is habitat specific and a method of estimating survival with it. Otoliths provide an ideal natural tag because they form before hatching, are metabolically inert, form daily and yearly layers that are not resorbed and reflect the environment in which the fish has lived. They provide a chronology of habitat provenance; every habitat change is recorded and can be matched to a calendar of life-history events. Otolith chemistry has seen burgeoning use to measure population structure and connectivity. It has provided better spatial resolution than genetic markers, allowing scientists to mark habitat use at sub-population levels. For example, in seagrasses, habitat use can be measured at the order of 10 km resolution. Scientists worldwide now use otolith chemistry to measure movement and mixing of populations. However, to our knowledge, otolith chemistry has not yet been used to measure habitat-specific survival from early life-history to adulthood as we propose here. A habitat-specific measure of survival to adulthood will open many lines of research: evaluating anthropogenic watershed effects on estuarine ecosystems, providing reliable measures of essential fish habitat, and helping to choose sites for marine protected areas, among others.Intellectual Merit - The relative contribution of nursery habitats has been recognized but rarely tested in the field directly. It is not sufficient to measure a single factor such as density of juveniles; the importance of a nursery habitat relies on its relative production of adults compared to other juvenile habitats. This project will provide a direct test of seagrass habitats as nurseries for a valued fish, spotted seatrout, in Chesapeake Bay. Although otolith chemistry is widely used as a natural tag to demonstrate philopatry and movement, it has not been used to establish provenance and subsequent survival that is habitat-specific. This project will be the first use of otolith chemistry to establish habitat-specific survival of recruits. Development and demonstration of this technique will expand the value of this natural tag and will help inspire others to advance the use of natural tags in resource management.Broader Impacts - This project will provide training for graduate and undergraduate students in otolith chemistry (isotope and trace element geochemistry) and statistical modeling. Two minority students with interest in the project will work on it, a Hispanic PhD candidate and an African-American undergraduate. Further, parts of this project will be used to support minority undergraduates in the REU MUST program at ODU. The novel approaches will be used as examples of teaching modules in marine science, in collaboration with scientists in the departments of Biology, Chemistry and Oceanography at ODU.