Title: 40 YEARS OF BENTHIC COMMUNITY CHANGE AT THE FORE-REEF SLOPE (10 – 40 M) OF THE CARIBBEAN REEFS IN CURAÇAO AND BONAIRE: THE RISE OF CYANOBACTERIAL MATS

Abstract: In the past decades benthic sessile communities of tropical coral reefs have undergone significant changes worldwide. Generally, there was a shift from stony corals to fleshy macroalgae. Long-term studies documenting changes in other benthic reef groups, however, are scarce. We have studied change in dominant benthic groups at 4 reef sites in the Caribbean islands of Curaçao and Bonaire over a time-span of 40 years. Permanent 3 x 3 m quadrats at 10, 20, 30 and 40 m depth have been photographed at intervals since 1973. The temporal and spatial dynamics in cover of dominant benthic groups [corals, macroalgae, sponges, cyanobacteria, algal turf and crustose coralline algae (CCA)] were assessed based on image point-analyses. Our results show a strong decrease in the cover of calcifying groups averaged over all sites and depths from 32.9% [1973] to 9.2% [2013] for coral and for CCA from 6.4% to 0.95%. Initially, coral cover is replaced by turf algae (24.5% to 45.3%) and fleshy macroalgae (0% to 12%). These new dominants are however largely reduced from 2000 to 2013 (10.8% and 2.2%, resp.), signalling the rise of benthic cyanobacterial mats (BCM). BCM become the most dominant component increasing from a mere 0.1% [1973] to 22% [2013]. This is accompanied by a small increase in sponge cover (0.5% to 2.3%). Strikingly, the observed pattern of degradation and phase change was seen down to mesophotic depths of 40 m. These results suggest that reefs dominated by algae may be less stable than previously thought and that the next phase may be the domination by slimy cyanobacterial mats.

Authors: De Bakker DM, Van Duyl FC, Nugues MM, Bak RP, Nieuwland G, Meesters EH

Presentation: Oral

Session: 17

Date: 06/23/16

Time: 17:15

Location: 313 A

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