Spatial and temporal patterns of coral black band disease in relation to a major sewage outfall

Abstract

Spatial and temporal patterns of coral black band disease (BBD) prevalence were examined during the summers of 2004 to 2008 at 10 reef sites located along a sewage gradient on either side of a major marine outfall on Bermuda's south shore. The gradient was identified by cur- rent meter and drogue deployments and confirmed by a water quality monitoring using fecal indi- cator bacteria (gastrointestinal enterococci) as a sewage marker. BBD prevalence was also exam- ined at 22 locations across the Bermuda platform in different physiographic reef zones, identified by reef survey techniques and analysis of community composition. BBD prevalence was generally low and was recorded in Diploria strigosa > Montastraea franksi > M. cavernosa = D. labyrinthi- formis > Porites astreoides and the hydrocoral Millepora alcicornis. Most occurrences were in D. strigosa, and BBD prevalence was highest on the outer rim reef (range: 0.3 to 1.9%), followed by the outer lagoonal patch reefs (range: 0.05 to 0.8%) and the deeper terrace reefs (range: 0.1 to 0.2%). BBD prevalence levels decreased over the study period, and BBD was only rarely observed in D. labyrinthiformis, which appears to be immune to infection in Bermuda. The BBD prevalence in D. strigosa was lower on reefs regularly exposed to sewage than on the near pristine outer rim reef sites, which experience the exceptional water quality characteristics of the oligotrophic North Atlantic gyre.