Assessment of natural resource conditions in and adjacent to Dry Tortugas National Park

Jeffrey, Christopher; Hile, Sarah; Addison, Christine; Ault, Jerald; Currin, Carolyn; Field, Don; Fogarty, Nicole; Luo, Jiangang; McDonough, Vanessa; Morrison, Doug; Piniak, Greg; Ransibrahmanakul, Varis; Smith, Steve; Viehman, Shay

Dry Tortugas National Park (DRTO), located in the Straits of Florida west of Key West, is relatively comprises seven small islands and extensive shallow water coral reefs. Significant natural resources include coastal and oceanic waters, coral reefs, reef fisheries, seagrass beds, and sea turtle and bird nesting habitats. Oceanographic conditions and circulatory patterns near DRTO are determined primarily by the convergence of several ocean current systems that profoundly affect the region’s ecology. The convergent current systems enable connectivity among reefs in the Florida Keys and along the Florida mainland. Coral communities are prominent and biologically productive natural resources . Historical reports from the 1800s suggest that live coral was widely distributed and abundant on hardbottom substrates in the Tortugas region. Live coral is now significantly less abundant and less widely distributed. Long-term declines in living coral is unexplained, but may be the result of episodic events (e.g., hurricanes and diseases) and human-associated stressors. Seagrass and algal communities are extensive and important components of marine ecosystems in the Tortugas region, and their primary productivity contributes substantially to the nutrients and trophic energy. Seagrass monitoring data indicate a loss 29% of seagrass between 2003−2007, which was attributed to hurricanes in 2004 and 2005. Fish assemblages are prominent components of DRTO coral reef ecosystems and part of a larger species complex whose home ranges extend beyond park boundaries to areas subject to commercial and recreational fishing. DRTO has been closed to commercial fishing since its implementation in 1935; however, park waters supported recreational fisheries until 2007 when implementation of a protected area within the park prohibited fishing. Reef fish monitoring since 1999 suggest that several metrics (e.g., species richness, fish size, fish abundance) of reef fish assemblages improved compared with areas in the region that are open to fishing. Historical information on sea birds and sea turtles indicate that the park supports resident and migratory individuals. Turtle abundance in the Tortugas region is substantially lower now compared to pre-European times. Sea birds forage and breed in the park, which the National Audubon Society lists as one of the important birding areas in Florida. The major threats and stressors to marine natural resources in the Tortugas region include climate change (increased sea surface temperature, sea level rise and ocean acidification); extreme events (tropical storms and coral disease epidemics); and resource extraction (recreational overfishing, habitat destruction from fishing gear, and boat groundings and anchor damage). Few studies have directly assessed the effects of stressors on marine natural resources in the Tortugas region, which makes it difficult to differentiate among causes of local resource degradation in the coral reef ecosystem. During the last century, natural stressors, such as hurricances, coral bleaching episodes, and anomalous hydrodynamic circulatory patterns, acted synergistically to reduce coral cover and abundance. Anthropogenic stressors, such as resource extraction, contributed to loss of live coral cover and declines in species diversity, coral reef health, and abundance of natural resources. The most likely anthropogenic stressors to natural resources are recreational activities. Continued increases in human visitation will result in increased levels of recreational activities, which could have profound negative effects on the region’s natural resources.

Assessment of natural resource conditions in and adjacent to Dry Tortugas National Park

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