Background

The grouper gag life cycle in the northeastern Gulf of Mexico (Fig. 5, below) is complex. Adults live on offshore reefs. In late winter, they gather on the shelf edge (50 - 120 m deep) to spawn in isolated aggregations. Males remain on these sites year round. Outside of the spawning season, females move between aggregation sites and shallower reefs. The larvae spend about 6 weeks in the plankton and during this phase are passively transported from the shelf edge to inshore seagrass beds, where they metamorphose into benthic juveniles. Their survival is high and growth is rapid because the seagrass habitat provides shelter and abundant food in the form of small crustaceans and fish (Koenig and Coleman, 1998). After 6 months, the juveniles migrate to shallow reefs, where they live for several years before joining the offshore adult population.

Among the keys to a species' population biology, and thus its management, is a knowledge of the causes of variability in the growth rates of its members during ontogeny. Although studies of gag biology (Collins et al., 1987; Keener et al. 1988; Ross and Moser, 1995; Koenig and Coleman, 1998; Stelcheck et al., 2003; Fitzhugh et al., 2003; Renan et al., 2006) have revealed much, little is known about the effects of weather on growth rates. Because early juvenile gag live in water that is < 2 m deep, they will be exposed to local weather, particularly to variation in atmospheric temperature and to variation in salinity caused by local and regional precipitation. Temperature and salinity are biologically important variables and can be expected to influence growth rates. For example, because growth rates generally increase with temperature, we expect that individuals exposed to warmer temperatures during a particular phase of development will grow faster if the effects of weather are important relative to other sources of variability. Weather could also influence the diet of early juveniles because of its effects on the success of prey populations. One of our goals is to assess the importance of variation in local weather conditions on variation in growth rate and in diet of early juvenile gag as they develop in seagrass meadows of the northeastern Gulf of Mexico.

The project will also for the first time generate a database of Dissolved Organic Carbon (DOC) and Nitrogen (DON) concentrations and their dynamics in the northern Gulf of Mexico. So far, such a database is missing. DON, DOC, and inorganic nutrient data are essential for the interpretation and prediction of production processes in the water column and at the sea floor and for the assessment of the cycles of organic matter and nutrients on the shelf. The data produced by this project provide fundamental data that are central for modeling efforts, interpretation of satellite data, prediction of red tides and reference data for future projects monitoring, e.g., eutrophication of the Gulf coast.

This project will also produce the first characterization of faunal communities in seagrass beds across the spatial extent of the BBR. The patterns from the project will likely produce additional questions about the processes that are driving them, which will be amendable to experimentation. We will also incorporate these region-wide data from seagrass beds with data from our proposed work (Year 3) to investigate the secondary nursery role of shallow reefs. Ontogenetic movements of animals and habitat coupling are common in both other marine and terrestrial systems and our work will therefore be of keen interest to ecologists working elsewhere.