Sommer, B.

The coastal deposits of Bonaire, Leeward Antilles, are among the most studied archives for extreme-wave events (EWEs) in the Caribbean. Here we present more than 400 electron spin resonance (ESR) and radiocarbon data on coarse-clast deposits from Bonaire’s eastern and western coasts. The chronological data are compared to the occurrence and age of fine-grained extremewave deposits detected in lagoons and floodplains. Both approaches are aimed at the identification of EWEs, the differentiation between extraordinary storms and tsunamis, improving reconstructions of the coastal evolution, and establishing a geochronological framework for the events. Although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive-related processes, insufficient separation, superimposition or burying of coarse-clast deposits and restricted dating accuracy limit the use of both fine grained and coarse-clast geoarchives to unravel decadal- to centennial-scale events. At several locations, distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin. Coastal landforms on the western coast have significantly been influenced by (sub)-recent hurricanes, indicating that formation of the coarse-clast deposits on the eastern coast is likely to be related to past events of higher energy.

We assessed the status of coral reef benthic communities at Bonaire, Netherlands Antilles, in December 2008 and January 2009 through ~5 km of photo transects taken at depths of 5, 10, and 20 m at 14 locations around the island. Univariate and multivariate analyses detected significant variation in benthic communities among depths and locations, as well as between leeward and windward sides of the island. Mean percentage cover of scleractinian corals ranged between 0.2% and 43.6% at the study sites and tended to be lowest at 5-m depth. The survey recorded 40 scleractinian coral species from 19 genera, within 10 families. Faviidae were by far the most abundant scleractinian family at all depths (predominantly Montastraea spp.), followed by Agariciidae at 20 and 10 m, and by Astrocoeniidae at 5-m depth. Macroalgal cover exceeded scleractinian coral cover at nearly all sites, averaging 34.9% (all samples pooled), compared with a pooled mean coral cover of 15.4%. Windward reefs were characterized by prolific growth of the brown algae Sargassum spp., and leeward reefs by growth of turf algae, Dictyota spp., Trichogloeopsis pedicellata (Howe) I. A. Abbott & Doty, and Lobophora variegata (Lamouroux) Womersley ex Oliveira. Damage from recent hurricanes was evident from the presence of toppled and fragmented corals, the movement of sand, and exposure of cemented Acropora cervicornis (Lamarck, 1816) rubble on the shallow reef platform. The combination of algal dominance and low to moderate coral cover are symptomatic of partly degraded reef systems, particularly as they coincide with elevated nutrients and reduced herbivory.