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Functioning of Disturbed and Undisturbed Coral Reef and Adjacent Ecosystems in Tortugas Ecological Reserve
ISSUE: This comparative study began in 2000, one year before Tortugas Ecological Reserve (TER) was designated, and will continue through 2005. The ultimate goal of this program is to provide a measurement of the effectiveness of TER.
Over the five year period of this stage work, we have proposed:
- a preliminary characterization and inventory of the benthic habitat and fish communities in the extreme depths of the Tortugas South reserve component;
- characterization of spawning aggregations and initiating the development of a probabilistic model of the fate of snapper larvae, focusing on Riley's Hump;
- comparative characterization of shallow and deepwater seagrass and associated communities and their contribution to fishery resources in disturbed (outside the reserve) and undisturbed sites (inside the Reserve);
- evaluation of gear impact elimination in the historic Tortugas pink shrimp grounds (northern boundary of TER) on ecosystem recovery;
- determination of the accuracy of existing habitat delineations within the proposed ecological reserve as a function of depth and disturbed and undisturbed sites;
- examination of how high resolution ecological data of a given habitat type can be scaled to the larger spatial context of the proposed ecological reserve;
- determine the effect of location on coral settlement within Dry Tortugas National Park.
EXPERIMENTAL APPROACH: This study employs 1a BACI (Before - After Control Impact) experimental design. Thirty permanent stations are sampled annually. The stations are evenly distributed among six strata determined by level of protection (Reserve, Park, Outside) and location (north or south of prevailing currents). Each year, video transects are recorded by divers and fish counts are made along 60m transects spanning the reef ñ algal plain interface at each station. Benthic cores and faunal collections for stable isotope analysis are also made. To compare differing methods of habitat characterization, the areas surrounding the permanent stations have been mapped extensively at increasing scales including in situ video transects, towed video and sonar transects, multi-beam sonar transects, aerial photography, and satellite images.
RESULTS AND MANAGEMENT IMPLICATIONS: Although no definitive conclusions can be made at this stage regarding the effectiveness of TER, some interesting patterns have begun to emerge. Preliminary stable isotope data suggest that the shallow water benthic habitats surrounding the coral reefs of TER will prove to be a significant source of the primary production ultimately fueling fish production throughout TER and downstream throughout the range of larval fish dispersal. The majority of the fish analyzed so far have exhibited a C isotope signature consistent with a food web which incorporates a significant amount of benthic primary production. In addition, there is significant microalgal biomass at depths between 10 and 30m in the soft sediments at the coral reef interface, and this community may play an important role in the food web supporting reef organisms. Our fish counts indicate a significant increase in the abundance of large fish (>20cm) in the reserve relative to the unprotected and park strata. These increasing trends within the TER are surprisingly evident among a variety of prominent species directly exploited by fisheries, including white grunt, yellowtail snapper, hog fish, and red grouper. Our faunal collections from open and protected soft bottom habitat near the northern boundary of Tortugas North strongly suggest that relaxation of trawling pressure has increased benthic biomass and diversity in this area of TER.
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