Natural resource condition assessment: Dry Tortugas National Park

Bryan, David; Ault, Jerald

Dry Tortugas National Park (DRTO), located 100 km west of Key West, Florida, is perhaps the most remote marine National Park in the United States, offering visitors a rare opportunity to see and experience an intact and relatively pristine coral reef ecosystem. As a result of its remote location, DRTO typically hosts less than 80,000 visitors a year. Commercial fishing has been banned since 1935, when the Natural Monument was established. Recreational fishing is now restricted to the eastern half of the park, and the western half is a fully protected “no-take” research natural area. The combination of its remote location, low visitation and substantial fishing restrictions have largely preserved the integrity of the natural ecosystem that now provides an important refuge for more than 700 species of fishes, birds, mammals, plants, and hard and soft corals. DRTO, and the surrounding Dry Tortugas region are located upstream at the southwestern most point of the highly connected Florida coral reef ecosystem. The Dry Tortugas region provides breeding habitat for a number of species and is important in delivering coral and fish recruits to the rest of the ecosystem. “Healthy” resource conditions in DRTO are not simply a concern for the park, but are also vital for the sustainability of the entire regional ecosystem. This natural resource condition assessment (NRCA) has identified seven key natural resources vital to the park: seagrasses, terrestrial vegetation, corals, marine macroinvertebrates, reef fishes and sharks, sea turtles, and birds. Assessment of the condition and trend for each of these natural resources was guided by the best available science and the National Park Service (NPS) framework for structured resource assessment and reporting. The availability and quality of data for condition scores varied substantially amongst resources; overall, this NRCA analysis found this suite of natural resources to be in “moderate condition”, with various trends observed. Seagrasses form “beds” that are highly productive biologically, and comprise an essential component of a healthy marine ecosystem. Seagrasses provide essential habitats for a wide range of marine species and life stages, both as foraging and nursery grounds. In DRTO, seagrasses comprise about 14% of the mapped benthic substrate. Data suggest that their species compositions and densities have been relatively stable over the past 20 years, and that they are in good condition. More than half of the other key natural resources assessed here (e.g., marine macroinvertebrates, reef fishes, and turtles) depend directly upon the health of the seagrass community. Their continued “healthy” status provides a valuable foundation for a sustainable environment within the park. Although DRTO is principally a marine park (99% water), the seven islands within the park boundaries provide unique habitats for nesting and migratory birds, as well as, pristine beaches for nesting sea turtles. About 50% of land area in DRTO is comprised of either sparsely vegetated or non-vegetated sand; and, the remaining area contains a highly-adapted plant community capable of surviving the harsh maritime conditions. Exotic plants, in particular the Australian pine, were previously a major threat to this community, but focused restoration and removal of non-native species during the 1990s eliminated almost all exotics. Currently, the terrestrial vegetative community appears to be in good condition. There is some concern that climate changes and sea level rise may negatively impact some species. There has been a gradual loss of park islands and vegetation through erosion, from eleven islands in 1829 to seven in 2018. The remaining seven islands have shorelines that are forecast to have moderate to high vulnerability to further erosion. DRTO provides essential habitats for several hundred species of coral reef fishes.

Natural resource condition assessment: Dry Tortugas National Park

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