Benthic Communities

Summary

Habitat mapping is crucial for understanding habitat connectivity and for spatial planning, environmental management, conservation, and targeted research, including long-term change monitoring. However, such information has been lacking for many Dutch Caribbean islands, especially regarding marine habitats. This study used 2144 georeferenced images from different surveys to develop habitat models predicting the distribution of habitat types within the Saba Bank National Park. The habitat models link environmental factors to species or habitat occurrence, enabling predictions in unsurveyed areas with known covariates. Machine learning techniques (Random Forests, Gradient Boosting, and weighted K Nearest Neighbor) were applied to interpret and predict ten habitat types over the Bank. Three models were created for each technique: 1) utilizing only geographic coordinates; 2) incorporating covariables such as depth, distance to the edge of the Bank, Topographic Position Index (TPI), and Terrain Ruggedness index (TRI); 3) a combination of the previous two models. All models performed well, accurately predicting habitat types between 67 and 74% of the georeferenced images. However, the most natural representation occurred with models combining geographic and covariate variables. Predicted habitats include coral reef, patch reef, gorgonian reef, sargassum fields, cyanobacteria-dominated fields, Lobophora fields, Neogoniolithon- Lyngbya habitat, other macroalgae fields, sand with a mix of species, and bare sand. Habitat distribution appears to be related to the main currents in the area and depth, with coral reefs occurring mainly along the southern and eastern edge of the Bank, with gorgonians and other soft corals dominating there the shallow areas. Macroalgae, including fields of Sargassum, dominate the back-reef area. Extensive sand plains dominate the center of the Bank, and along the north-western and northern edge of the Bank, between 40 and 60m depth Lobophora fields can occur. In the south-eastern back reef area a number of mounds built up by the coralline alga Neogoniolithon occur. The Luymes Bank, the northeastern part of the Saba Bank, was the only area that was not correctly predicted, indicating that additional field-based observations are needed to refine results in this area.
 

An unidentified benthic cyanobacterial species has been documented growing on the reef system of Bonaire, N.A. Despite their role as nitrogen fixers in marine environments, cyanobacteria may cause diseases or release toxins on coral reefs. This study used line-intercept transects at 7 sites and photographic mapping at one site on Bonaire to determine the distribution and growth patterns of the cyanobacteria. The cyanobacteria showed greatest concentration at depths of 30-18 m, with largest average patch size occurring at 27-18 m. It grows almost exclusively on old dead coral, and appears to overgrow live coral only in rare cases. Patch dynamics are quite stable against competitive substrates such as live coral, but if ideal substrates are present patches as large as 100 cm2 may form over two weeks. Further study is needed to determine the long-term effects of the growth of the cyanobacteria on live coral.

This student research was retrieved from Physis: Journal of Marine Science II (Fall 2007)19: 37-40 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.

Suspension feeders perform a crucial role in uniting the benthic and pelagic environments in coral reef ecosystems. Of suspension feeders, sponges are one of the most highly abundant, widespread, and efficient filter-feeding organisms. However, suspension feeding in sponges is not completely understood. Previous studies have looked at the effect of temperature on pumping rate as well as the effect of particle size on retention rate. The purpose of this study was to investigate the depth-dependence of pumping rates and filtration efficiencies in two Caribbean reef sponges, Aplysina archeri and Aplysina lacunosa, at two depth profiles. Videos were taken of sponges pumping fluorescein dye to obtain pumping rates, and turbidity measurements were taken of both inhalant and exhalant water samples that were collected in situ via syringes in order to estimate filtration efficiency. The results revealed a species-specific interaction with depth for both pumping rate and filtration efficiency. Aplysina lacunosa was found to have both a faster pumping rate and increased filtration efficiency at the shallower depth, while no differences were observed across depths for A. archeri. Additionally, correlations were found between pumping rate and filtration efficiency for both species, suggesting the development of distinct filter-feeding strategies. Aplysina lacunosa had a positive correlation between pumping rate and filtration efficiency, while the correlation in A. archeri was found to be negative. Understanding the effect of depth on the filter-feeding mechanism of sponges is important to understanding the greater implications of the benthic-pelagic coupling process of sponges and suspension feeders in general.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 6-12 from CIEE Bonaire.

Free-living marine nematodes are a functionally and morphologically diverse group of animals. They have important ecological functions, many of which are not currently well understood, and may be bioindicators of climate change and pollution. Nematode abundance is impacted by many factors; the focus of this paper is to study the effects of sediment composition on nematodes. Within a study site on the west side of the island of Bonaire in the Dutch Caribbean, three stations with different sediment compositions and mean grain sizes were selected. Endobenthos samples were taken at each station and abundance of nematodes was recorded and compared between the stations. Mean grain size was not found to have a correlation with the density of nematodes, non-nematode organisms, or total organisms across the study stations. The overall average density of nematodes found at the site (1.71 ± 0.32 nematodes per cm3 , ± SD) is lower than values found in comparable studies, which could be related to pollution or change in temperature affecting the endobenthic community in the study site. This data may have been insufficient to support the hypothesis due to having a small sample size and too narrow a range of mean grain size between the stations. Despite this, this paper provides the first published data on nematode communities in Bonaire, and is an important foundation for future study of the ecological functions of marine nematodes in this area.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 1-8 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.