Variability of size structure and species composition in Caribbean octocoral communities under contrasting environmental conditions
Octocorals have increased in abundance on a number of Caribbean reefs, but this trend has largely been reported with functional group or genus resolution. A species-level analysis of octocoral communities in St. John, US Virgin Islands was conducted to better understand how this taxon will respond to changing conditions based on their synecology at two sites that are 1.5 km apart and differ in physical conditions. East Cabritte is characterized by moderate wave energy, low sedimentation, and clear water, while contrasting conditions characterize Europa Bay. Surveys conducted in 2014 and 2015 showed that the abundance and size of adult octocorals differed between sites, with taller and denser communities at East Cabritte than Europa Bay (mean height of 32 versus 20 cm; 18 versus 8 colonies m−2). Octocoral diversity and evenness were similar between sites, although multivariate octocoral community structure differed between sites regardless of whether octocorals were resolved to genera or species. Genus-resolution masked differences between sites for speciose genera like Eunicea. The broad overlap in species representation at both sites suggests that diversity is less responsive than community structure to differing environmental conditions, perhaps because the ecological niches of these species are broad. With 35 octocoral species, and diversity and abundances comparable to those studied > 40 years ago on shallow Caribbean reefs, the dense octocoral communities appearing on some present-day reefs reflect expanded benthic occupancy by a well-known (rather than a novel) community type.
This research was completed under a permit issued by the VI National Park (VIIS-2011-SCI-0016). Special thanks to W. Goldberg for providing access to the raw data from his studies. We are grateful to E. A. Lenz, A. Ellis and J. Smolenski for analysis of photoquadrats for soft corals, R. Boulon, C. S. Rogers, S. Prosterman, and V. Powell for local support, and the staff of the Virgin Islands Environmental Resource Station for making our visits productive and enjoyable. This is contribution number 262 of the marine biology program of California State University, Northridge.
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Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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