Recruitment of scleractinians onto the skeletons of corals killed by blackband disease

To determine what happens to scleractinian corals that have been killed by black band disease (BBD), massive corals with BED were monitored for 11 yea rs on a shallow reef (<10 m depth) in St. John, US Virgin Islands. Small qu adrats (0.039 m(2)) were used to compare the rates of scleractinian recruit ment to the skeletons of corals killed by either BED or physical disturbanc e (Hurricane Hugo 1989). Coral recruitment was also quantified on the adjac ent fringing reef using larger quadrats (0.25 m(2)) to detect possible bias es associated with using small, permanent quadrats to assess recruitment to BED-killed corals. Of 28 tagged colonies with BED in 1988, 43% were lost t o Hurricane Hugo in 1989, 7% were lost to unknown causes between 1991 and 1 992, and 14 were monitored annually for 11 years; of these, 71% were dead a nd still in their original growth position in 1998. Between 1988 and 1997, corals recruited to the BED-killed surfaces at a rate of 1.1 +/- 0.3 recrui ts 0.039 . m(-2) . decade(-1) (mean +/- SE, n = 14), although mortality red uced the density to 0.3 +/- 0.2 recruits 0.039 m by 1997. The rate of recru itment and the taxonomic composition of the coral recruits to BED-killed co rals were indistinguishable statistically from those to corals killed by Hu rricane Hugo. This demonstrates that BED creates space that is functionally the same as other dead coral surfaces in providing a substratum for coral recruitment. However, because coral recruits are dispersed widely, clumped in distribution and temporally variable in density on the fringing reef as a whole, it is unlikely that they will be found on monitored coral colonies that have been killed by BED. While this hypothesis is consistent with the higher density of recruits on the fringing reef compared with EBD-killed c orals, further studies are required to investigate alternative explanations such as the role of substratum age in favoring recruitment to surfaces oth er than those killed recently by BBD.