Fish assemblages

The implementation of artificial reefs is one effort used to mitigate the rate of decline of coral reefs and the deterioration of fish communities. Artificial reefs add support to struggling reefs habitats by providing additional or varied structural relief, sometimes mimicking specific coral structure types. The purpose of this study is to assess the effectiveness of branching artificial reef (BAR) habitat deployed in November 2011 by comparing the fish density and biomass, and species richness and diversity of the BAR to those of habitats in which it was placed. Three plots of BAR habitat were compared to three plots of rubble habitat and three plots of fore-reef habitat. BAR plots were found to have significantly lower fish density, fish biomass, and species richness than the fore-reef, but no statistical difference in species diversity. When compared to the rubble, BAR habitat showed significantly higher species richness, but no significant difference in density, biomass, or diversity. A comparison of family and fish phase community composition revealed that BAR habitat supports significantly more initial phase Scaridae than either adjacent habitat. It was concluded that BAR habitat adds little in the way of a complementary habitat to the terrace-fore-reef zone. The results from this study suggest that no further implementation of this form of artificial reef should be carried out along the rubble terraces of Bonaire. However, further monitoring of the BAR habitat and research into a branching structure with greater complexity, more interstitial matrix and constructed from calcareous material may be useful.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 88-95 from CIEE Bonaire.

Saba Bank is a large and completely submerged carbonate platform in the northeastern Caribbean Sea located approximately 4 km southwest of Saba Island, Netherlands Antilles. Zonation patterns of reef-like bathymetric features, together with observations of significant shelf edge coral reef development, suggest that Saba Bank is an actively growing coral reef atoll. Little quantitative data exists to evaluate the composition and distribution of marine benthic communities or fish assemblages of Saba Bank. In the present study, habitat surveys were conducted to investigate the abiotic characteristics, benthic community composition, and fish assemblage structure of habitats from an eastern portion of Saba Bank known as Overall Bank. A random stratified sampling design was developed that utilized remote sensing data for bathymetry and ocean color superimposed on reef zones. Five sampling strata, which putatively delineated five distinct marine habitat types, were identified along a shelf edge-to-lagoon gradient. Survey results indicate that the proposed strata correspond to distinct marine habitat types in terms of substrate composition, benthic cover, and dominant macro algae. Significant coral cover was restricted to the outer reef edge in the fore reef habitat (11.5 %) and outer reef flat (2.4 %), declining to near absence in the lagoon habitats towards the bank center. Macro algae dominated benthic cover in all habitats (32.5 – 48.1 % cover) with the composition of dominant algal genera differing among habitats. Gorgonians reached their highest density and greatest average colony height in the fore reef zone. Gorgonian colony height was also pronounced in softbottom habitats of the lagoon. Fish assemblage structure showed patterns that were concurrent with observed habitat zonation. Highest fish densities were observed in the outer reef flat, fore reef, and inner reef flat zones. Fish abundance and diversity was low in the lagoon zone and lowest over softbottom habitats within the lagoon. The greatest diversity of fishes (average number of species per survey, cumulative number of species) occurred in the fore reef zone and outer reef flat zone. Fish biomass followed the same pattern of distribution, with the greatest weight occurring in the outermost zones and least in the lagoon. Queen conch were most frequently encountered in the softbottom lagoon zone and estimates of average conch density were between 42 and 60 individuals per hectare. Abundance of spiny lobster was not adequately surveyed by the methods employed in this study and recommendations are made for improved field assessment of lobster stocks. Collectively, the results of this study indicate that the benthic communities of Saba Bank follow predictable patterns of distribution, diversity, and abundance across a gradient from shelf edge to lagoon. Recommendations for future research are given. 

Abstract:

We conducted an ichthyological survey during the dry season of 2006 on the semi-arid islands of Aruba, Bonaire and Curaçao to provide information on species composition, richness and dis- tribution in natural and non-natural aquatic habitats. The dry season species assemblages (N = 9 species) comprised less species than the wet seasons, and these data refine our knowledge of the indigenous fish fauna and its refuge localities during phases of drought and ensuing high salinity. A hierarchical cluster analysis reveals that the three islands have different species compositions with Curaçao being the most diverse, probably due to its having the most habitats and freshwaters present throughout the year. Species richness was unrelated to salinity and species diversity was highest in canalised streams. In the dry season fewer amphidromous species are present than in the wet season. We found no significant effect of human-induced changes on the presence or absence of fish species in the Netherlands Antilles. The presence of exotic species (including Xiphophorus helleri on Aruba, a first record for this island, and Oreochromis mossambicus and Poecilia reticulata occurring on all three islands) did not have a clear effect on the presence of indigenous species, nor did human alteration of the habitats have an influence on the occurrence of fish species.