Dry Tortugas National Park: a Unique Setting for USGS Marine Research
This is the first in a series of articles looking at Coral Reef Ecosystem Studies research projects taking place in Dry Tortugas National Park. Stay tuned for the next edition of Sound Waves in which we look at ocean acidification and coral calcification.
About 70 miles west of Key West, at the terminus of the Florida Keys, lies a cluster of tiny islands. These islands and the 100 square miles of surrounding water constitute Dry Tortugas National Park. Protected by the U.S. National Park Service since 1935, this isolated area in the southeastern Gulf of Mexico is rich in marine life, making it a valuable location for scientific research. Scientists from the USGS Coral Reef Ecosystem Studies (CREST) Project in St. Petersburg, Florida, conduct field studies in the Dry Tortugas to monitor and study the health of shallow-water reef environments and to improve our understanding of global issues such as climate change and ocean acidification.
The various research activities and remote location of the National Park require detailed coordination and logistical planning. Research teams spend days traveling and rely on the National Park Service for accommodations—often on board the 110-ft M/V Fort Jefferson, operated by Captains Clayton "Blue" Douglass, Janie Douglass, and John Spade. With the excellent support of the vessel's crew, scientists eat, sleep, and work round the clock setting up equipment, collecting data, and conducting surveys for as much as two weeks at a time.
"Tortugas work takes a lot of logistical planning," said USGS research ecologist Kristen Hart. "We use the National Park Service ship a lot. We work with the captains; we plan out our schedules, and they work to accommodate our needs and crazy work hours. We often need to have all our equipment and permits in place, sometimes months in advance."
The Dry Tortugas offers a unique research setting away from human activities. This makes it an ideal control site to compare to other areas where significant local-scale impacts on natural resources have taken place. Scientists with the CREST program have been working in the area for several years. Current tasks include research on coral calcification rates, monitoring coral reef community metabolism, investigating coral disease causes and processes, using historical coral core data to assess past ocean chemistry and temperature, and mapping and monitoring benthic habitats. This last task is overseen by USGS oceanographer Dave Zawada.
Detailed maps are essential to efforts for conserving and managing ecosystems. Characterizing the composition and condition of benthic habitats provides a basis for assessing changes and monitoring the progress of restoration efforts. To collect such data, Zawada developed and operates a noninvasive observing system called the Along-Track Reef-Imaging System (ATRIS), which simultaneously acquires geo-located, color digital images and water-depth measurements. ATRIS can be deployed either from an adjustable pole mounted to the side of a boat ("shallow" configuration) or from a towed vehicle at depths of 27 m ("deep" configuration). The same camera and acquisition software are used for both operating modes.
"ATRIS provides us with information about the condition and type of substrate. From transects over an area, we can start to obtain estimates of the percent coverage and abundance of corals, sponges, vegetation, and other organisms on the sea floor. We can also get information pertaining to the physical state of the habitat," said Zawada.
ATRIS images can be combined to create an image mosaic, allowing comparisons to previous ATRIS datasets of the same area to track changes over time. This capability is particularly useful with the possibility of oil impacting marine habitats. In 2009, Zawada and his team used ATRIS to map 163 km of sea floor in Dry Tortugas National Park, yielding nearly 460,000 color digital images. Should oil from the Deepwater Horizon leak reach the Park, this pre-event image collection establishes a baseline for evaluating oil impacts.
In the Dry Tortugas, ATRIS images are also being used to study and monitor the foraging, grazing, and transiting of threatened and endangered sea turtles. Green, hawksbill, and loggerhead sea turtles are being tagged and tracked to determine spatial and temporal habitat-use patterns. ATRIS data are used to determine the amount of time sea turtles spend in and around various habitats and zones. Blood and tissue samples are also collected from turtles to gain important dietary and genetic material. Together, the information is used to track the whereabouts and conditions of these endangered marine species.
Zawada and Hart recently submitted their first manuscript, using ATRIS to map areas Hart had determined were core-use zones for loggerhead females during the time in between successive nests, called the internesting period. Females usually lay a nest every two weeks during a nesting season, which typically occurs from May through early August in the Dry Tortugas. This year, Zawada and Hart will continue their ongoing research, making observations and captures near the end of the nesting season in late July.
in this issue:
Marine Research in Dry Tortugas National Park