Dataset: Coral reefs in the US Virgin Islands

Location: St. John, US Virgin Islands (18.315°N, 64.716°W), Multiple field expeditions to the USVI between 2011 and 2021.

Material and methods

Sampling was accomplished photographically using digital cameras on a frame that held the camera perpendicular to the reef to record 0.5 × 0.5 m photoquadrats. Photographs were taken with a Nikon D90 camera in 2011 (12.3 MP, fitted with a Nikkor DX 18-70 lens), a Nikon D7000 in 2015 (16.2 MP, fitted with a Nikkor DX 18-70 lens), and a Nikon D810 in 2015–2021 (36.3 MP, fitted with a Nikkor FX 18-35 lens). Cameras were fitted with two strobes (Nikon SB105) and the pictures provided a resolution of objects > 5 mm diameter.

Two sampling regimes were employed. First, sampling in the core area of the time-series project (1992-present on the south shore of St. John) took place between White Point and Cabritte Horn (1.3 km), and sampled 6 permanently marked sites (five at 9 m depth, one at 7 m depth) that were randomly selected in 1992. Along one 40 m transect at each site, photoquadrats were recorded at 40 positions that were randomized annually. Each sampling generated ~ 240 photoquadrats from which 40 were drawn randomly to characterize the fringing reefs along this stretch of shore (hereafter referred to as the Pooled Random Sites, PRS*) and support a balanced statistical contrast with the other 11 sites (described below). Sampling at the core sites in July/August 2011, 2015, 2019, and 2020 are used in the present analysis. Although the core sites were sampled in August 2020, they are contrasted with the January 2021 sampling of the other sites and considered together as “2021 sampling”.

In 2011, the sampling included 11 additional sites at 10 m depth that were scattered around St. John and St. Thomas to provide a contrast of shores (n = 3 sites shore-1) and islands (n = 6 sites island-1). These sites were selected haphazardly to sample fringing reefs at a landscape scale commensurate with the linear distance occupied by St. John and St. Thomas (~ 40 km). Logistical constraints prevented permanent marking of the sites, but they were relocated using GPS and landscape and seascape features. It therefore was possible to revisit the sites over time, but identical areas of reef were not sampled on each occasion. Sampling of the sites around both islands and their shores occurred in June 2011, June 2015, August 2019 (two sites on the south shore of St. John), and January 2021.

Coral reef benthic community structure was analyzed using CoralNet software with manual annotation of 200 dots randomly located on each image, and the results were expressed as percentage cover. Analyses resolved scleractinians to the lowest taxonomic level possible, macroalgae (mostly Dictyota, Lobophora, Padina, Sargassum, Halimeda, and peyssonellid algal crust), and crustose coralline algae, algal turf, and bare space combined (CTB) because they could not reliably be distinguished in photoquadrats. Scleractinians subsequently were pooled to Orbicella spp., Montastraea cavernosa, Agaricia spp., Colpophyllia natans, Pseudiploria spp., Diploria spp., Meandrina sp., Porites spp., Siderastrea spp, and “other” corals.

See Edmunds & Smith (2022) for statistical analyses that used these data.  Statistical software used: Systat 13, PRIMER 6.

Issue note: Some sampling non-consecutive in date columns.