Wes Toller; Adolphe O. Debrot; Mark J. A. Vermeij; Paul C. Hoetjes

“ Fish assemblages observed at the Saba Bank reef margin were exceptional in that they did not corroborate the hypothesized relation of habitat complexity to fish abundance and diversity. The fore reef showed the greatest habitat complexity (coral cover, vertical relief and rugosity) yet fish diversity and biomass were similar to or lower than in the adjacent reef flat habitat. The reason for this remains unclear. Commercial trap fishing may have acted selectively to reduce fish density and biomass in the bank's fore reef areas. ”

“ Biomass estimates for Saba Bank ranged between 52 and 83 g/m2 for habitats of the reef zone (FR, ORF and IRF) indicating that these habitat types on the Saba Bank harbor higher fish biomass than most locations in the Caribbean region. Sandin et al. [15] found that within the Caribbean basin, species richness of island fish faunas fits the classical species-area relationship and is governed by island biogeographic factors such as remoteness from source populations and the available number of different habitat types. ”

“ Abstract Saba Bank is a 2,200 km2 submerged carbonate platform in the northeastern Caribbean Sea off Saba Island, Netherlands Antilles. The presence of reef-like geomorphic features and significant shelf edge coral development on Saba Bank have led to the conclusion that it is an actively growing, though wholly submerged, coral reef atoll. However, little information exists on the composition of benthic communities or associated reef fish assemblages of Saba Bank. ”

“ Length data were used to calculate fish biomass using known length-weight relationships for each species [25] . If such data did not exist, the length-weight relationship of a closely related species was used. Species were assigned to trophic guilds according to Froese and Pauly [25] .
To increase the descriptive resolution of species richness of the fish assemblages at each sampling location, belt transect surveys were supplemented by roving diver (RD) surveys to provide a more complete estimate of local species richness. ”

“ All benthic categories considered here (sponges, corals, macro- and coralline algae and gorgonians) except macroalgae and crustose coralline algae decreased in abundance from the fore reef towards the lagoonal area of the central bank (Table 2, Figure 4) . The habitat types thus span a gradient along which most functional benthic groups do occur albeit in increasingly lower abundances. FR harbors the greatest diversity and abundance of benthic life forms and was likely responsible for the high topographical complexity within this habitat type (Table 2) . ”

“ In the 40 RD surveys on Saba Bank, we recorded 63 mid- to large sized groupers, carangids, barracudas and/or (nurse) sharks. The abundance of some predatory fishes stems from the fact that they are not targeted by the commercial fishery. For example, the great barracuda, Sphyraena barracuda, is a large piscivore that is generally not harvested by commercial fishermen because of concerns about ciguatera poisoning. Barracuda were common in visual surveys (>50% of surveys) and observed in all habitat types. ”

“ In the present study, we observed average coral cover in fore reef habitat that was appreciably lower (11.5%) than previously reported. Anecdotal observations suggest that coral cover on Saba Bank has declined during the past five years. In many of our FR surveys, large recently dead (or partially dead) colonies of Montastraea faveolata and Colpophyllia natans were observed. We speculate that the reduced coral cover recorded on Saba Bank in 2007 may be a consequence of declines following the 2005 coral bleaching event that severely impacted reefs in the northern Caribbean [30] . ”

“ Macroalgae dominated benthic cover in all habitats (average cover: 32.5 – 48.1%) but dominant algal genera differed among habitats. A total of 97 fish species were recorded. The composition of Saba Bank fish assemblages differed among habitat types. Highest fish density and diversity occurred in the outer reef flat, fore reef and inner reef flat habitats. Biomass estimates for commercially valued species in the reef zone (fore reef and reef flat habitats) ranged between 52 and 83 g/m2. ”

“ Analysis of species richness (i.e. the number of species observed per RD survey) indicated that fish assemblages differed significantly among habitat types (one-way ANOVA, F4,35 = 14.81, p<0.001) . Average species richness was greatest in FR (28.3 spp./survey) , ORF (28.8 spp./survey) , and IRF (22.4 spp./survey) and lowest in LSB and LHB (10.5 spp./survey and 13.5 spp./survey, respectively) . Post-hoc (Tukey) tests confirmed that species richness was significantly higher in FR, ORF and IRF habitat types than in LSB and LHB habitats. ”

“ We selected this study area as a representative section of the ‘Southeastern Reef’ [1] , [3] – Saba Bank's largest reef system. The study area was a rectangle 7.3 km long by 5.5 km wide totaling 40.2 km2 that extended from the reef edge into the lagoon zone (Figure 2) . Most of the geomorphological reef features known from Saba Bank (see below) are represented within our study area. The sequence of reef structures with different habitat types is oriented perpendicular to the predominant winds and currents coming from the East. See other papers in this volume for further details on Saba Bank. ”

“ For example, Bellwood and Hughes [8] demonstrated that much variation in biodiversity across Indo-Pacific coral reefs can be described simply by the amount of habitable area in the region (i.e. from island to archipelago scale) . ”

“ Depth profile across Overall Bank study area, Saba Bank.A depth profile of the study area (∼8 km in length) was generated in ArcGIS using bathymetric data from the Hydrographic Service of the Royal Netherlands Navy. Names of reef structures and reef zones are from Van der Land [3] . In tropical marine ecosystems, habitat diversity partially underlies the diversity of organisms as local species richness increases with an increasing number of different critical habitat types [7] . ”