ISSUE: An ecological reserve is intended to protect habitats and species which utilize those habitats. The marine reserve concept is increasingly accepted as an effective tool for conservation due, in part, to the results from careful scientific studies investigating reserve effectiveness. One of the few fully protected marine reserves in the United States is the Tortugas North Ecological Reserve, which was implemented in 2001. The TNER, located within the Florida Keys National Marine Sanctuary and west of Dry Tortugas National Park (DTNP), has an area of 90 square nautical miles. It includes the pristine coral reefs of the Tortugas Banks and the contiguous soft-bottom habitats of the West Florida Shelf (Fig 1). Our study contributes to the TNER assessment by showing the change in marine resources over time and describing the distribution of marine resources relative to the Reserve’s boundaries.
Figure 1. Location of the Tortugas Bank, and the permanent stations sampled as part of the assessment of the impact of the TNER.
In order to determine the effects of marine protected areas on the coral reef community, we compare changes in the reef communities inside the Reserve to those outside the Reserve, where fishing regulations are more relaxed. In addition to sampling within the TNER, we also sample permanent stations within the Dry Tortugas National Park (DTNP), where recreational fishing is allowed, and the Exclusive Economic Zone (EEZ), which is open to both recreational and commercial fishing. Our sampling methodology specifically addresses reef edges and adjacent soft-bottom communities. To determine fine scale changes, divers conduct detailed sampling of fishes and benthic plants and animals along transects. At a larger scale, sonar equipment on the research vessel is used to determine the shape of the sea floor and the distribution of fish. Additional aspects of our study specifically address the spatial distribution of both reef and soft-bottom shelf marine resources relative to the Reserve boundary. Comparing trends in the abundance of natural resources within the different management zones provides evidence of how effectively the TNER is accomplishing its management goals.
Figure 2. Mean counts of juvenile and adult yellowtail snapper from three management zones around the Tortugas Banks, 2001-2007.
RESULTS AND MANAGEMENT IMPLICATIONS: Comparative analysis of fish abundance within the different management zones indicates that closure of the TNER to fishing has reversed the well documented decline of commercially exploited fishes in the region. Evidence of this impact is strongest for the commercially exploited species, especially the yellowtail snapper – the principal target species around the Tortugas Banks (Fig. 2).
Fish production on the reefs of the Tortugas Banks is believed to be based largely on the plants and animals of the soft-bottom habitats of the shelf that surrounds the Banks. Isotopic analysis of reef fishes from the Tortugas Banks shows they exhibit a carbon isotope signature consistent with a food web based on benthic rather than planktonic primary production. The shelf around the Tortugas Banks is highly productive with high densities of many bottom dwellers, notably the pink shrimp for which there is an important trawl fishery north and east of the Banks. Implementation of the TNER closed a portion of this fishing ground to trawling and provides a refuge for pink shrimp that breed in this area. Comparative studies of the soft bottom shelf around the northern boundary of the TNER indicate that in years when pink shrimp are abundant in the area, densities are higher inside the Reserve than outside. Video observations of the bottom outside the Reserve reveal the impact of trawl gear on the benthic habitats. However, sampling suggests that most benthic populations are resistant to trawling disturbance, as biomass and diversity of the soft-bottom community is similar inside and outside the TNER’s boundary.
Figure 3. Survey diver uses high resolution photography to quantify the distribution of sessile animals that make up the living portion of the reef.
Our goal is to learn as much as we can about the ecological system of the Tortugas Banks and how it is changing. During our 2009 research cruise, we plan to revisit all our permanent stations from reef and soft-bottom habitats of the Tortugas Banks This will increase the fish and habitat data set that describes changes through time. We also plan to sample a portion of the Tortugas Banks that is still undescribed. Using multibeam sonar we intend to develop a detailed contour map of the sea floor. Our split-beam sonar system will show how fishes are distributed relative to this landscape. Where the boundary bisects this area of the Banks, divers will provide a detailed description of the distribution of benthic resources (Fig. 3). Such data on the distribution and trends of natural resources is critical to understanding how establishment of the TNER has affected the ecological balance of the region.
Visit these links to read the daily cruise logs for previous expeditions to the Tortugas Banks in 2005, 2007, and 2008.
Visit these links to find out more about NCCOS research in the Tortugas Banks region.