Coral overgrowth by an encrusting red alga (Ramicrusta sp.): a threat to Caribbean reefs?

An encrusting red alga (Ramicrusta sp., Peyssonneliaceae) present in Lac Bay, Bonaire, overgrows and kills corals and other sessile organisms. Living coral tissue comprises 7.2 % of the benthic composition of the shallow reef, while Ramicrusta sp. covers 18.7 % of the substratum. Of 1374 coral colonies surveyed, 45.8 % were partially overgrown by Ramicrusta sp., with P. porites, P. astreoides and M. complanata being the most susceptible to overgrowth. Mean Ramicrusta sp. maximum overgrowth rates +/- A SD were 0.08 +/- A 0.05 mm d(-1), 0.07 +/- A 0.03 mm d(-1) and 0.06 +/- A 0.02 mm d(-1) for M. complanata, P. porites and P. astreoides, respectively. None of the 71 coral recruits surveyed were growing on Ramicrusta sp. Ramicrusta sp. is an immediate threat to corals, reduces the area of suitable substratum for coral settlement and may have the ability to influence coral species composition.