Habitat characterization of the Tortugas Ecological Reserve south using photographic and quadrat methods

Florida Keys National Marine Sanctuary - Tortugas Ecological Reserve

Once in the field, the boat captain navigates to previously selected station locations using a GPS. On-site, divers are deployed on the exact station GPS numbers and maintain contact with each other throughout the entire dive. Upon arrival at the bottom, one diver is responsible for swimming out the 30 m transect tape along a predetermined random compass heading obtained from a data sheet. From 2007-2009, the procedure used was photographic transects done in the following manner: As this diver swims out the tape, the second diver takes photographs of the bottom around the tape, approximately 0.5m above the seafloor, with a digital camera in an underwater housing. The photographs are taken every 5 m along the tape (i.e., at 0, 5, 10, 15, 20, 25 and 30 m. When the first diver who swims out the tape gets to the end of the 30 m distance, he lays down the tape and swims back to the photographer and stays with him/her, as called for by the diver buddy system. Once the photographic transect is finished, diver #1 reels the tape back in, taking the two divers back to their starting point. Only one photographic transect is done per station. Images were analyzed later by determining the percentage of total area that belonged to each of four functional habitat types: coral, octocoral, sponge and macroalgae. In 2011, the procedure was changed from photographic transects to a quadrat characterization approach, completed as follows: Diver #1 swam out a 30 m transect tape as was done in previous years. Diver #2 followed behind, deploying a 0.25 m2 quadrat beside the transect tape at 0, 10, 20, and 30 m along the length of the tape. Total percent cover of abiotic substrate, defined as sand, hardbottom and rubble, was estimated within each quadrat. Biotic cover was estimated within four general functional habitat groups: coral, octocoral, sponge and macroalgae. Abiotic cover within each quadrat always totaled 100%, as the underlying substrate was quantified. Biotic cover did not necessarily total 100%, as there were often regions of uncolonized substrate. As time permitted, divers also recorded the dominant species within each quadrat to the finest taxonomic level. The habitat is never altered in any manner by lifting or moving structure, and the photographer made every effort in the early years to include the measuring tape in the photograph, as it is an aid to estimating the amount of total area in the image. Sometimes it is necessary for the photographer to turn the tape over so that the measuring marks appear in the photograph. On-site, no attempt to avoid structural features within a habitat such as a sand patch or large coral head should be made as these are real component of the habitats. The only instance when the transect should deviate from the designated path is to stay above 130 ft (limitations imposed by diving). The typical photographic transect should take only approximately 15 minutes regardless of habitat type, and the typical quadrat transect should take approximately 20 minutes.