Prior to the 2017 hurricanes, six shallow (8-15 m depth) reef sites had been selected from the Virgin Islands Territorial Coral Reef Monitoring Program\u2019s (TCRMP) permanent monitoring sites to study variation in sponge communities in St. Thomas. These sites included Black Point (N18\u00b0\u00a020.665\u2019, W64\u00b0\u00a059.107\u2019), Coculus Rock (N18\u00b0\u00a018.734\u2019, W64\u00b0\u00a051.613\u2019), and Magens Bay (N18\u00b0 22.459\u2019, W64\u00b0 56.077\u2019), which are in embayments with heavily developed watersheds. Buck Island (N18\u00b0 16.717\u2019, W64\u00b0 53.925\u2019) and Savana Island (N18\u00b0\u00a020.437\u2019, W65\u00b0\u00a004.939\u2019) are located near undeveloped offshore cays. Botany Bay (N18\u00b0\u00a021.433\u2019, W65\u00b0\u00a002.071\u2019) is a nearshore site in a bay with a low level of watershed development. For this study, we used three randomly selected transects out of the six permanently established 10 m TCRMP transects at each site. The same three transects at each site were re-surveyed repeatedly in August 2015, August 2016 (pre-hurricanes) and December 2017 (10 weeks post-hurricanes).\u00a0
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Sponge assemblages were surveyed on each transect using multiple measures. Sponge density was quantified by a diver\u00a0in situ\u00a0by counting every sponge individual (i.e., ramet) within 0.5 m of each transect (resulting in 0.5 x 10 m belt transects) for all sites except Black Point, where 0.5 m on both sides of the transects (1 x 10 m belt transects) were surveyed. Density (sponges/m2) was calculated as the total number of individual sponges per transect, divided by the transect area (Gochfeld et al. 2020).
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To determine whether different sponge morphologies were differentially affected by hurricanes, each sponge from each transect was assigned to a broad morphological category (sensu\u00a0Wulff 2006). These categories included excavating sponges (\"excavating\"); low relief encrusting sponges (\"encrusting\"); thicker cushions, massive, tube, vase, or other amorphous shapes of medium relief (\u201cmassive\u201d); and upright, branching and rope sponges (\u201cupright\u201d). These groupings differ slightly from those used by Wulff (2006), but represent the morphotypes found within our transects in St. Thomas. The percent of the entire sponge community represented by each morphological category was calculated as the number of individuals in each category divided by the total number of individuals for each transect and multiplied by 100 (Gochfeld et al. 2020).
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Percent cover of sponges was determined from videos of the three transects at each site following established methods from the Virgin Islands Territorial Coral Reef Monitoring Program (Smith et al. 2016). A diver swam at uniform speed while videoing the substrata from a height of approximately 0.4 m (the height of a guide wand). Consecutive, non-overlapping images, each approximately 0.64 x 0.48 m in planar area, were captured for each transect, for an average of 21 images per transect. Twenty random points were superimposed on each image (average of 1282 points per site, per sampling period) and the benthic cover underneath each point was identified to the lowest identifiable taxonomic level and used in the calculation of percent cover by transect. Specific sponges were not identified in the benthic cover analysis and were instead grouped into the overarching category of \u201cSponge\u201d. The number of points per image required to adequately characterize the percent cover of each of the benthic categories (sponges, hard corals, macroalgae, epilithic algal community [EAC; i.e., diminutive turf algae and other low complexity filamentous algal communities; Smith et al. 2016], non-living substrata, calcareous algae, cyanobacterial mats, gorgonians, zoanthids and other/unknown living substrata) was determined by visual inspection of the running means. For all categories, the mean value stabilized at no more than 17 points per image per transect, indicating that the 20 points analyzed per image was sufficient to accurately reflect percent cover at these sites (Gochfeld et al. 2020).
This dataset includes\u00a0sponge density and morphology and percent cover of sponges and associated benthic community determined from videos along transects at six sites at\u00a0the Virgin Islands Territorial Coral Reef Monitoring Program site, pre- and post-hurricane, 2015-2017.
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These data were published in Gochfeld et al (2020).
To test for hurricane effects on various metrics of the sponge community, repeated measures analyses of variance (ANOVA) were performed on sponge density and sponge volume, with site as a random factor, using the lmer function in the lme4 package in R (Bates et al. 2015). Square-root transformations were performed to meet the assumptions of parametric analysis. For significant effects, post-hoc comparisons were performed using the lumens function with the Tukey correction specified in R. To characterize hurricane effects on sponges with differing morphologies, a repeated measures ANOVA was also performed on arcsine transformed proportions to test for the main effect of year, using site as a random factor, followed by least square means post-hoc tests where warranted (Gochfeld et al. 2020).
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Sponges, hard corals, macroalgae, EAC and non-living substrata represented over 90% of the overall benthic substrata. Percent cover of these major benthic community constituents were compared individually among years using repeated measures ANOVAs as described above, following logarithmic or square root transformation if necessary. Post-hoc comparisons among years were performed using least square means as described above. Other benthic constituents were either of such low representation or did not meet the assumptions of parametric analysis even after transformation, and were not analyzed independently (Gochfeld et al. 2020).
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BCO-DMO Processing:
\n- added conventional header with dataset name, PI name, version date
\n- modified parameter names to conform with BCO-DMO naming conventions
\n- added lat, and lon columns
\n- joined tables of density, morphology, and benthos percent cover into single table
\n- changed\u00a0calcareous_agale to calcareous_algae
\n- rounded percent cover values to 2 decimal places