St. Croix, USVI Benthic Composition Assessment and Monitoring Data (2002 - Present)

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Date that the source FGDC record was last modified.

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Site selection begins by stratifying NOAA's nearshore benthic habitat maps into predetermined habitat strata. Utilizing ArcGIS, sites are then randomly selected within strata throughout the region. Using a handheld GPS unit, the boat captain navigates to previously selected sites. A weighted buoy is dropped to mark any site where "live boating" is necessary. Once on site, divers are deployed and maintain contact with each other throughout the entire census. One diver is responsible for collecting data on the benthic composition. The habitat diver follows the belt-transect diver and records data on small-scale benthic habitat composition and structure along the 25m transect. The habitat diver places a 1m2 quadrat divided into 100 (10 x 10cm) smaller squares (1 square equals 1 percent cover) at 5 separate positions. Each position is randomly chosen before entering the water such that there is one random point within every 5m interval along the transect. Percent cover is obtained as if looking at the quadrat in a two dimensional plane (i.e. a photograph) vs. three dimensions where percent cover could add up to greater than 100%.Data are collected on the following: 1) Logistic information - diver name, dive buddy, date, time of survey, site code, and meter numbers at which the quadrat is placed. 2) Habitat structure - to characterize the benthic habitats of the dive site, the habitat diver first categorizes the habitat structure of the site: hard, soft or mangrove. 3) Proximity of structure - on seagrass and sand sites, the habitat diver records the absence or presence of reef or hard structure within 3m of the belt transect. A score of zero (0) indicates that no reef or other hard structure is present; one (1) indicates that a reef or hard structure smaller than 4m2 is present; and (2) indicates that a reef or hard structure larger than 4m2 is present within 3m of the diver. The point-count diver also uses this scoring system to record the absence, presence, and proximity of reef or hard structures within their cylinder. 4) Transect depth profile - the depth at each quadrat position. Depth is measured with a digital depth gauge to the nearest 1ft. 5) Abiotic footprint - defined as the percent cover (to the nearest 1 percent) of sand, rubble, hard bottom, and fine sediments within a 1m2 quadrat. Rubble refers to rocks and coral fragments that are moveable; immovable rocks are considered hard bottom. The percent cover given as a part of the abiotic footprint should total 100 percent. In a seagrass area for example, despite the fact that seagrass may provide 50 percent cover the underlying substrate is 100 percent sand so this is what is recorded. To estimate percent cover, the habitat diver first positions the quadrat at the chosen meter mark along the transect tape. If the meter mark is an odd number, then the quadrat is placed on left side of the tape; if even, it is placed on the right. Next, the habitat diver lays the quadrat along the substrate (regardless of the slope) and estimates percent cover based on a two-dimensional (planar) view (e.g. if bottom is sloping, the quadrat is not held horizontally). Also, the diver should try to use the same planar view for all estimates of percent cover. The habitat diver then estimates, for each quadrat, the height (in centimeters) of the hardbottom from the substrate to get a sense of bottom relief. Note: Height is collected for all hardbottom substrates, excluding rubble; height is not collected for softbottom substrate. (continued...)

(continued from above) 6) Biotic footprint - defined as the percent cover (to the nearest 0.1 percent) of algae, seagrass, live corals, sponges, gorgonians, and other biota (tunicates, anemones, zooanthids, and hydroids) within a 1m2 quadrat. The remaining cover is recorded as bare substrate to bring the total to 100 percent. Again, the diver must use a planar view to estimate percent cover of the biota. Seagrasses and gorgonians should not be stacked upright. For example, e.g., if a single seagrass blade crosses 10 squares, then total seagrass coverage should be the sum of the area taken up by that blade in all 10 squares instead of the area covered if the blade was held upright. Species covering less than 0.1 percent of the area are not recorded. Taxa are identified to the following levels: stony coral-species, algae-morphological group (macro, turf, crustose, rhodolith, filamentous, cyanobacteria), sponge-morphological group, and gorgonians-morphological group. When estimating percent cover, it is important to realize there is a balance between precision and time. For stony corals, the approximate area covered by living coral tissue is recorded. Coral skeleton (without living tissue) is usually categorized as turf algae or uncolonized substrate. Data on the condition of coral colonies are also recorded. When coral is noticeably bleached, the percentage of bleached coral is estimated to the nearest 0.1 percent. Diseased/dead coral refers to coral skeleton that has recently lost living tissue because of disease or damage that is still visible, and has not yet been colonized by turf algae. Turf algae include a mix of short (less than 1cm high) algae that colonizes dead coral substrate. 7) Maximum canopy height - for each soft biota type (e.g., gorgonians, seagrass, algae), structure is recorded to the nearest 10cm. 8) Number of individuals - for sponges, gorgonians and "other" biota type (non-encrusting anemones and non-encrusting hydroids), the number of individuals at the quadrat level are recorded. 9) Rugosity - measured by placing a 6-m chain at two randomly selected positions along the 25m belt transect. The chain is placed such that it follows the substrate's relief along the centerline of the belt transect. Two divers measure the straight-line horizontal distance covered by the chain. The chain is placed on top of any hard substrate encountered, but not on top of soft corals or sponges since we are measuring hard bottom rugosity. Data on rugosity are collected for reef sites only. Rugosity measurements typically are made by the point-count and belt-transect divers while awaiting the completion of other benthic habitat measurements by the habitat diver. Upon completion of the dive, the rugosity data are transferred from the fish data sheet to the habitat data sheet by the habitat diver. 10) Abundance and maturity of queen conchs (Strombus gigas) - a count of the total number of conch encountered within the 25m x 4m belt transect are enumerated. The maturity of each conch is determined by the presence or absence of a flared lip and labeled mature or immature, respectively.If conch abundance is counted by a fish diver, the data are then reported to habitat diver. The decision of who will collect conch data should be made prior to entering the water. 11) Abundance of spiny lobsters (Panilaurus argus) - a count of the total number of lobsters encountered within the 25m x 4m belt transect. No measurements are taken. If lobster abundance is counted by a fish diver, the data are then reported to habitat diver. The decision of who will collect lobster data should be made prior to entering the water. (continued...)

(continued from above) 12) Abundance of long-spined urchin (Diadema antillarium) - a count of the total number of urchins encountered within the 25m x 4m belt transect. No measurements are taken. If urchin abundance is counted by a fish diver, the data are then reported to habitat diver. The decision of who will collect urchin data should be made prior to entering the water. 13) Marine debris - type of marine debris within the transect is noted. The size of marine debris and the area that it is affecting is also recorded along with a note identifying any flora or fauna that has colonized it. Data Caveats: Over time, some changes were made to the stratified random site selection process as follows: 1) Habitat strata initially consisted of hard bottom, sand, and seagrass. Sand and seagrass strata were subsequently combined into one soft bottom strata at all three locations (Puerto Rico, St. Croix, and St. John). This action was taken after the February 2002 mission to Puerto Rico. 2) A small subset of sites were resampled during each mission through June 2002 in Puerto Rico and October 2002 in St. Croix. These station names contain the letter 'P' indicating they are permanent stations. 3) The sample area in St. Croix has increased over time. Initially, samples were collected within historic Buck Island National Monument boundaries as well as outside up to a distance of 0.5 km from those boundaries. In February 2002 the sampling effort was increased to include the entire expanded monument boundaries. Finally in April 2003 the effort was increased again to include areas outside of the Monument for control sites. This area is now almost entirely enclosed within the East End Marine Park of St. Croix. 4) The habitat map utilized to stratify the samples in St. Croix was changed from the original habitat map created with a 1 acre minimum mapping unit to one with a 100m2 minimum mapping unit beginning with the April 2003 mission. 5) In 2007, algae data collection changed from identification of each alga to the genus level to grouping algae into six morphological groups: macro, turf, crustose, filamentous, rhodolith, and cyanobacteria for more efficient data collection. Marine debris data collection began in 2007. (end continuation)