Community structure

Beach environments are considered nutrient poor systems that support limited abundances of life due to the lack of attainable nutrients. Since the surrounding environment is nutrient limited, plants and organisms residing in sandy beach communities take advantage of available nutrients whenever possible, for example, nests laid on the beach. This study assessed whether nesting hawksbill sea turtles (Eretmochelys imbricata) are transporters of nutrients from ocean systems to nutrient-poor beaches of Bonaire, N.A. It was hypothesized that nitrogen (N) and phosphorus (P) levels would be elevated, infaunal organisms would be more abundant, and plant cover would be higher in nest plots compared to areas without nests. To determine the input of nutrients from nesting and the potential effects of nutrient enrichment on the plants and infauna, five experimental arrays, including nest, mechanically disturbed (no nutrient addition), and undisturbed treatments were sampled from September to October 2009 on Klein Bonaire. Five days following hatching events, sediment cores were taken to assess concentrations of N and P, as well as to determine the abundance of infauna. Plant percent cover was also determined for each plot. Nutrients did not differ significantly among plot type, with both N and P consistently at low concentrations. For all nest plots, 2.5 X more taxonomic groups, including known predators, were detected than in undisturbed or mechanically disturbed plots. No plants were found in any plot type for the duration of the study. This study suggests that hawksbill sea turtle nests are not strong drivers of coastal community structure in Bonaire. It is believed that the CaCO3 composition of the sand and the limestone base of the island do not allow for nutrient retention and thus excess nutrients are not available for exploitation by beach plants or infauna.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 14-19 from CIEE Bonaire.

Human activity and higher frequencies of disturbance have increased coral reef degradation and created barren substrates with the opportunity for primary colonization. The pioneer microorganisms determine the subsequent community composition, as many organisms require specific substrates and environmental conditions to recruit. Considering that coral recruits more effectively on hard substrates (including crustose coralline algae, polychaete tubes, and other encrusted invertebrates), examining colonization on artificial substrates is increasingly important for coral recruitment. This study documented the pioneer species and early succession on introduced substrates on the fringing reef in Kralendijk, Bonaire, Dutch Caribbean. Ceramic tiles were used as the artificial substrate, and data was collected and analyzed weekly over a period of four weeks. Tiles were placed in three different environments in the reef ecosystem: the sand flat, reef crest, and reef slope. Tiles were analyzed in the laboratory using stereomicroscopy for organism colonization. Turf algae, and brown and green algal filaments were present on all tiles over the experimental time period, but there was no fleshy macroalgal growth. Strong increasing trends of invertebrate abundance and diversity occurred in all environments over the four-week research period. Microfauna including polychaetes, oligochaetes, bivalves, gastropods, crustaceans, bryozoans and foraminiferans were the main pioneer organisms observed. According to other studies, these organisms are also present on artificial substrates over the time period of two to five months. Therefore, these benthic invertebrates likely dominate substrates for several months before further succession occurs allowing organisms such as crustose coralline algae and coral recruits to settle.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 23-30 from CIEE Bonaire.

Abstract:

Ecological studies have rarely been performed at the community level across a large biogeographic region. Sponges are now the primary habitat-forming organisms on Caribbean coral reefs. Recent species-level investigations have demonstrated that preda- tory fishes (angelfishes and some parrotfishes) differentially graze sponges that lack chemical defenses, while co-occurring, palatable species heal, grow, reproduce, or recruit at faster rates than defended species. Our prediction, based on resource allocation theory, was that predator removal would result in a greater proportion of palatable species in the sponge community on overfished reefs. We tested this prediction by performing surveys of sponge and fish community composition on reefs having different levels of fishing intensity across the Caribbean. A total of 109 sponge species was recorded from 69 sites, with the 10 most common species comprising 51.0% of sponge cover (3.6–7.7% per species). Nonmetric multidimensional scaling indicated that the species composition of sponge communities depended more on the abundance of sponge-eating fishes than geographic location. Across all sites, multiple-regression analyses revealed that spongivore abundance explained 32.8% of the variation in the proportion of palatable sponges, but when data were limited to geographically adjacent locations with strongly contrasting levels of fishing pressure (Cayman Islands and Jamaica; Curaçao, Bonaire, and Martinique), the adjusted R2 values were much higher (76.5% and 94.6%, respectively). Overfishing of Caribbean coral reefs, particularly by fish trapping, removes sponge predators and is likely to result in greater competition for space between faster-growing palatable sponges and endangered reef-building corals.