Available Data

Benthic Cover

At each site, benthic cover surveys are conducted annually along six 10 m long permanent transects marked with steel or brass rods. Video sampling consists of one diver traversing each transect videotaping the benthic cover using a high definition digital video recorder.

After taping, images from each transect are captured and imported into RStudio where twenty randomly allocated points are superimposed on each image. Analysis consists of identifying the substrate located under each point. For each transect, the percent cover of coral, epilithic algae (EAC), macroalgae, sponges, gorgonians, and sand/sediment are calculated by dividing the number of random dots falling on that substrate type by the total number of dots for that transect.

The TCRMP benthic cover data set is available for download here.

Coral Health & Algae Heights

At each site, coral health surveys are conducted annually along six 10 m long permanent transects marked with steel or brass rods. All coral colonies located directly under the transect lines are assessed in situ for signs of mortality and disease following a modified Atlantic and Gulf Rapid Reef Assessment protocol (Kramer et al. 2005). Partial mortality of coral colonies is broken into two categories: recent partial mortality and old partial mortality.

Diseases are conservatively categorized into recognized Caribbean scleractinian diseases and syndromes that include bleaching, black band disease, dark spots disease, white plague, and yellow band (blotch) disease (following Bruckner 2007). Bleaching is assessed as abnormal paling of the colony, and, when present, the severity of the bleaching (paling or total whitening) and the area of the colony affected are assessed. A major bleaching event occurred between September and December 2005, affecting all monitoring sites, and a mild bleaching event occurred between September and October 2010. For each transect, the prevalence of coral impairment categories is calculated as the number of colonies with partial mortality, disease, or bleaching divided by the number of colonies assessed.

After the completion of coral health, algae heights are measured along the same permanent transects. Heights are recorded perpendicular to the growth substrate without disturbing the algae every 50 cm. Heights are differentiated to genus with the exception of turf algae and crustose coralline algae which are recorded as such.

The TCRMP coral health data set is available for download here, while the algae heights data may be downloaded here.

Fish Census

Fish surveys have been historically conducted at 14 sites around St. Croix and 10 sites around St. Thomas and, starting in 2012, are conducted at 32 of the 33 monitoring site. Ten replicate belt transects and three replicate roving dive surveys are conducted at each site. Belt transects are 25 x 4 m and are conducted in 15 minutes per replicate. Roving replicates are also 15 minutes. All fish encountered are recorded except blennies and most gobies. Divers also assess the abundance of Diadema antillarum sea urchins along the 25 x 2 m belt transects. The mean number of sea urchins per 50 m² is calculated for each site.

The TCRMP fish census data set is available for download here. The Diadema antillarum data set may be downloaded here.