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Dry Tortugas Cruise Day 3 - August 27, 2007
Photo credit: Kim Foley
Our cruise provides coastal managers with scientific information and tools to make informed stewardship decisions about one of NOAA’s protected areas—the Florida Keys National Marine Sanctuary’s Tortugas Ecological Reserve. The 800 nm² Tortugas Ecological Reserve (TER) was designated in July 2001 to protect fish and coral reefs from fishing. It is NOAA’s responsibility to ensure that the closure is doing what it was designed to do—protect and rebuild fish stocks. In doing this, NOAA strives to balance society’s environmental, social, and economic goals.
Today we completed an additional six dives, collecting data that will allow us to compare fish and fish habitat between areas within and outside protected areas. We also collected data on algae and seagrass communities to
Brian Degan reel in the transect tape
after completing a survey.
Photo credit: Vanessa McDonough
By 8:10 am, the Nancy Foster’s capable crew had launched the first of our dive teams in a small boat, and the other teams followed in quick succession. The sun was shining at the surface, but down at 100 feet the visibility was limited to 35 feet. As we approached the reef, a group of about 30 grouper scattered. These slow growing, large fish are named for their habit of gathering in groups to mate, often a few days before or after full moons in the summer. With the full moon only two days away, it is likely that we had interrupted such a gathering.
Our bottom time is limited at 100 ft, so we immediately went to work. A diver laid out a 30 meter transect tape, recording the types and sizes of fish observed one meter to either side of the tape, and
takes benthic photos, and Brett Harrison
videos the transect.
Photo credit: Kim Foley
Between dives, all three boats and their dive teams returned to the Nancy Foster. The scientists downloaded photos, entered data, and prepared the cameras, tanks, and data sheets for the second dive. Our second dive was on the edge of ‘The River’, a wide swath of sand that runs between the two bank formations in Dry Tortugas. The reef topography was low with but a few coral heads or soft corals growing higher than one meter above the sand. Fish were mostly small, as is often the case when there is not a lot of physical structure. A curious black grouper watched us work, swimming
attach a temperature logger.
Photo credit: Kim Foley
We also deployed a temperature logger that will provide a long term record of water temperatures. Prolonged periods of warm water can cause corals to expel their symbiotic algae. Commonly called bleaching, this phenomenon is expected to occur more frequently with rising sea surface temperatures. Bleaching is a growing threat to U.S. coral reef ecosystems.
With another six reef sites examined, the scientists turned their attention to the soft sediment communities in TER. Unlike the reefs, which are dominated by the hard structures for which they are named, the soft sediment communities are dominated by low relief algae and seagrass. Outside TER, these areas are trawled for the pink shrimp that live close to the bottom. While we need to dive on the reef to accurately record the abundant and diverse species found there, the soft sediment communities are simple enough that observations with a video camera can be used to observe major changes in these communities. Working aboard the ship, rather than by SCUBA, allows us to cover larger areas more quickly. We also used a beam trawl to sample the fish and invertebrate populations.
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Today’s website contributor, Ruth Kelty, surveying fish. Photo credit: Kim Foley |