Motivation

We hypothesize that regionally and economically significant fisheries are maintained in the Big Bend Region (BBR) through a combination of terrestrial and marine processes that arise from the unique character of the area. For example, the shoreline is made up of marshes, estuaries and seagrass beds from which originates a carbon flux to the BBR of unknown magnitude. Resident in the shallow shelf zone are enormous seagrass beds where the early juveniles of regional fisheries mature; the processes linking the juveniles to the open ocean stock are unclear but quite likely reflect a competition between physical and biological mechanisms. The transport connections between the deeper (40m) shelf and the shallow seagrass beds no doubt involve local and remote meteorological forcing and connections to the open Gulf, including fish migration (flux on the fin). Finally, the exceptional clarity of the waters potentially enable the benthic zone to contribute significantly to the regional primary production, a possibility we propose to test. The cycles of organic matterand nutrients control productivity and levels of oxygen are affected by marine pollution (e.g., eutrophication problems associated with sewage release or nutrient-contaminated ground waters). The data that will be accumulated in this project are essential for the understanding of the dynamics of primary productivity and associated secondary production of zooplankton and fish.

The aim of our integrated program is to uncover the basic regional processes at work with a view to the successful ecosystems-based management of the area.

Physical Oceanography

There is need of purely descriptive cataloging of the region. It is not known if the environment is estuarine in its flow characteristics or if significant vertical shear exists. Such knowledge is essential to quantifying transport characteristics. Key to many marine life cycles, including Gag grouper, is the transport of eggs and larvae across the continental shelf. A so- far unexplored mechanism to do this is the Stokes' drift transport of particles due to surface waves. Preliminary calculations based on historical wave data indicate that this mechanism plays a primary role in transporting particles across many continental shelves, including the Big Bend shelf. It is hypothesized that the surface wave field drives an on-shore Stokes drift that provides the primary means by which the pelagic larvae of gag grouper, which are spawned off shore, reach the seagrass beds, where they metamorphose into benthic juveniles and continue their development. In year 3 we propose to calculate Stokes' drift in the Big Bend Region using directional wave spectra obtained using NGI instruments. This will be compared to cross-shelf wind driven Ekman transport. The development of responsive ecosystem-based management policy cannot occur without the development of this data base.

Meteorological Fluxes

Heat and freshwater fluxes of atmospheric origin will emerge as of primary significance in defining the environment characteristics of the BBR. Outstanding questions in air/sea interaction, relevant to the Northern Gulf of Mexico, are (1) the influences of swell on surface fluxes, (2) the influences of shoaling waves, and (3) the fluxes that occur at high wind speeds (U10 > 20 m/s). The BBR is exceptionally well located for studies of questions (1) and (2) and reasonably located to expect high wind speeds from the rare, very strong cold front and from Gulf of Mexico tropical cyclones. The analysis of these data can be used to improve oceanic and atmospheric model parameterizations of fluxes and thereby improve the accuracy of forcing fields for oceanographic studies. These observations can also be used to validate atmospheric models, particularly the diurnal variability associated with the land/sea breezes. A meteorology graduate student and COAPS staff will be working on quality control of all of the standard meteorological, oceanographic, and flux data and also directional sea state influences on surface turbulent fluxes. In particular, we plan to test how stress (direction and magnitude) and turbulent energy fluxes change due to swell. By using high resolution three dimensional models for the Gulf, and higher resolution simulations over Apalachee Bay, we hope to test new air-sea flux formulations developed from observations on N7 tower. One dimensional column models will be useful for this purpose, as well.

Analysis of fluxes will be carried out using direct measurment and gradient methods. N7 Tower is instrumented at three levels (4, 19, and 25 m). We can provide direct turbulence flux measurements at a single level beginning in August 2008 (estimated) and are already providing in situ meteorological data at two levels following our deployment cruise on 24 June. All collected data are available in public files on our ftp server at ftp://146.201.0.163/. In a timeseries directory, the file ts.dat shows 1 min. comma-delimited data files from our data logger telemetered to the FSU Coastal & Marine Lab in real time (in ten minute blocks). The diagnostics folder contains output from the FSU-designed power management and distribution system, which switches between solar and rechargeable marine battery cells. A full array of photos is online at http://yankee.met.fsu.edu/~paul/N7, and will be organized into a separate web space after the last deployment cruise is completed in August.

Ecosystems Functioning

Gag (Mycteroperca microlepis), a flagship species among economically important US groupers, spawns on the shelf edge (50 - 120 m deep) many miles from the inshore seagrass beds that they inhabit during their early development. Survival and growth of early juveniles is high in seagrass habitat, where food resources occur in the form of small crustaceans and other fish (Koenig and Coleman 1998). Early juveniles remain in this habitat for months before egress to shallow reefs, and ultimately to offshore spawning populations. Pre-spawning female gag store energy during the fall in preparation for late winter spawning. They feed on small fishes (e.g., pinfish Lagodon rhomboides, pigfish Orthopristis chrysoptera) that have migrated from coastal estuaries in huge numbers to shelf and shelf-edge locations, where they overwinter.

We are focusing on three aspects of Gag ecology: (1) Because early juveniles live in water < 2 m deep while in the seagrass beds, they are exposed to the local weather and thus to variations in biologically important variables, such as temperature and salinity. We are testing to see if this variation has an important impact on the growth rate of early juveniles. (2) The prey that are hypothesized to be of most importance to the accumulation of energy by prespawning females mature in seagrass meadows and egress to deeper waters. We are testing the hypothesis that these species are the important food for prespawning gag females. Nelson is currently focusing on collection of offshore species and has conducted 4 collection trips in late 2007/2008. The hypothesis we are testing is that seagrass nearshore benthic production supports the spawning of offshore species by the egress of pinfish and pigfish to deeper waters in the fall. We have previously shown that these benthic foraging species have unique stable isotopic composition relative to fishes supported by water column primary production (Chanton and Lewis, 2002; Chasar et al., 2005). The laboratory studies described below by Nelson et al (in prep) document that the turnover times of gag grouper muscle and gonad material are sufficiently rapid so that a pulse of benthic derived seagrass carbon carried offshore by the egress of pinfish would be readily observable. Our research plan is to conduct a two year study of offshore grouper isotopic composition, and we hypothesize that we will observe a signal for benthic derived seagrass fauna in the late fall, early winter which coincides with spawning. This would indicate that the fall egress of nearshore species to offshore is an important carbon flux supporting the offshore fishery. We are also working with Dr. DeVries (NOAA-NMFS Panama City Lab) who has collected a number of offshore species on which we have conducted stable isotopic analysis. (3) We propose to investigate how prey availability to late-stage juvenile gag is affected by the proximity of seagrass meadows to salt marshes. Salt marshes are highly productive habitats that support abundant and diverse communities (Pennings and Bertness, 2001). Movement of these animals to adjacent seagrass habitats may provide important prey subsidies (Polis et al., 1997) that benefit late-stage juvenile gag growth and survival. Export of energy via nutrients and detritus from salt marshes may also affect gag by both direct and indirect benefits to resident prey in seagrass beds (this component will be addressed separately in coordination with members of FSU's Department of Oceanography). This work is important from an ecosystem-level approach to determine the level of connectivity among habitats in nearshore areas. Although salt marshes and seagrass beds are both extensive habitats in the Big Bend Region, studies typically separate the two, and addressing linkages between them is sorely needed.

Primary Production

Microphytobenthos consist of photosynthetic microorganisms on the sea floor including cyanobacteria, benthic diatoms, and flagellates, and can contribute a significant portion to the overall continental shelf primary production. Highest production of microphytobenthos occurs on shelves where the overlying water is low in nutrients and therefore relatively clear as on the BBR. Light limitation results in a declining gradient of microphytobenthos production with increasing depth, buton the West Florida Shelf primary production may reach as deep as 200 m (Vargo, unpublished data). Jahnke et al. (2000) found that on the South Atlantic Bight shelf, benthic primary production extends at least down to 40 m water depth and contributes approximately 60% to the total primary production, emphasizing the role of the microphytobenthos as base for the food chain on the shelf. The latter is the most important source for the global fisheries including that of the Gulf of Mexico.

Organisms living over continental shelves utilize the primary production of microphytobenthos directly (e.g., shrimp) or indirectly (e.g., fish preying on shrimp and benthic dwellers). Anthropogenic nutrient input into the coastal zone enhances phytoplankton growth thereby increasing water turbidity. Ensuing shading may decrease microphytobenthos productivity and shift communities from assemblages that rely on benthic primary production towards those that rely on planktonic primary production. This shift could have far reaching implications for benthic-pelagic coupling, cycling of carbon, nutrients and pollutants, and fisheries yield. Our light measurements near the sea floor at the three stations permit incubation of sediment cores in the lab at in-situ light intensities. Here we investigate the oxygen production and consumption of the sediments at the three stations and link these data to the benthic chlorophyll dynamics. The nitrate data that are collected simultaneously with the light and oxygen data at K-Tower provide information on the links between the nutrient and production dynamics. The combination of the results from our in-situ recordings and laboratory experiments produces new insights in the role of the benthic phototrophs for the carbon cycles. In year three, we propose to extend the laboratory production/consumption measurements to stations K and B.