Coral Reefs

Findings:

• Ramicrusta overgrows 14 of Lac’s species of scleractinian corals including Acropora, Agaricia, and Diploria, as well as three species of gorgonians.
• Ramicrusta grows upward from the base of coral and causes the death of grown tissues.
• Complete overgrowth by the crustose calcareous algae may happen after several months.

Management Recommendations:

N/A

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 ± SD were 0.08 ± 0.05 mm d-1, 0.07 ± 0.03 mm d-1 and 0.06 ± 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. 

Coral reefs are thought to be in worldwide decline but available data are practically limited to reefs shallower than 25 m. Zooxanthellate coral communities in deep reefs (30–40 m) are relatively unstudied. Our question is: what is happening in deep reefs in terms of coral cover and coral mortality? We compare changes in species composition, coral mortality, and coral cover at Caribbean (Curacao and Bonaire) deep (30–40 m) and shallow reefs (10–20 m) using long-term (1973–2002) data from permanent photo quadrats. About 20 zoo- xanthellate coral species are common in the deep-reef communities, dominated by Agaricia sp., with coral cover up to 60%. In contrast with shallow reefs, there is no decrease in coral cover or number of coral colonies in deep reefs over the last 30 years. In deep reefs, non- agaricid species are decreasing but agaricid domination will be interrupted by natural catastrophic mortality such as deep coral bleaching and storms. Temperature is a vastly fluctuating variable in the deep-reef environ- ment with extremely low temperatures possibly related to deep-reef bleaching.