Coral reefs

The small island of Bonaire has seen a dramatic increase in visitation due to diving tourism. The economy of Bonaire depends on this influx of visitors and therefore has had an increasing demand for the development of new housing, resorts, and commercial areas. This study examines how the increased human development affects sediment deposition and nutrient load in an area surrounding a combined marina and salina outlet in Bonaire. Sediment load, sediment compositions, and interstitial water quality (water found in the sediment) were analyzed to determine if sediment or nutrient load had an effect on the reef community in the area. The results of this study show no significant trend suggesting reef degradation north of the marina due to point source pollution from the salina outlet. The results, however, only apply to the limited 26 day sampling period. There is a possible seasonal link that could not be explored here without further year-round data collection. These results show that while sediment, nitrogen and phosphate are present in the marine environment north of the marina outlet, it cannot be specifically linked to the marina using data collected in this study. Interstitial water analysis showed no detectable refined oil. The methodology implemented here could be modified to collect additional data in future research.

This student research was retrieved from Physis: Journal of Marine Science XIII (Spring 2013)19: 17-22 from CIEE Bonaire.

Hermodice carunculata the bearded fireworm is abundant in Bonaire‘s coral reefs. The corallivorous fireworm is a voracious eater, and a generalist predator. H. carunculata’s foraging behaviors play a role in coral reef community structure and building. This study looked at the abundance of the bearded fireworm in two environments, coral reefs and sand flats, during dusk and night hours. Within these two substrates size, abundance, and fluorescent color morphologies of the fireworms were studied. Sizes were separated into four length categories: 9 cm. Due to the active nature of fireworms and sampling at night, BlueStar flashlights and yellow barrier filters were used to locate the fireworms in the dark. Field surveys were conducted using 10 m transects and a t-bar to estimate abundance in both environments. Wire box traps were also placed along the coral reef and sand flats to estimate abundance of fireworms in the area. H. carunculata were found to be less abundant on coral reefs at dusk than at night. Furthermore, fireworms in the size class >9 cm were only found on coral reefs, indicating an ontogenetic shift in habitat and size. An ontogenetic shift was also found in the fluorescent color morphologies. Green fluorescence was most abundant in the 0-6 cm size range, and completely absent in the >9 cm size class. The green body with orange bands was an intermediate fluorescent pattern found predominantly in 3-9 cm size range. The orange body with orange bands coloration was found in the largest size class, possibly being the terminal fluorescent phase.

This student research was retrieved from Physis: Journal of Marine Science XIII (Spring 2013)19: 1-9 from CIEE Bonaire.

Coral reef ecosystems provide a number of important ecological services, such as nurseries and protection from storms. This makes their health of vital importance for human populations. Past epidemics in the Caribbean involving high mortality of predominant species, such as long-spined sea urchins (Diadema antillarum) and elkhorn coral (Acropora palmata) have shown the potential of disease to fatally disrupt coral reef ecosystems already under stress. The high prevalence of an unknown disease in ocean surgeonfish (Acanthurus tractus) in the Caribbean, and its apparent ability to infect other fish, including parrotfish and other predominant grazers, is a source of concern since it affects a number of herbivorous fish that are integral to the health of the reefs. This disease is identified by the presence of black spots over the body and fins of infected fish. The number of spots can vary widely. Fin rot and lethargic behavior have been noted in fish with large numbers of spots. Bacterial cultures of swabs from healthy and dark spot epidermis, and necropsy of eight A. tractus specimens were used to attempt to identify the causative agent. This study found smaller bacterial numbers in the dark spot epidermis compared to healthy epidermis cultures, and the presence of encysting organisms embedded in the epidermis directly below black spots in body and fins of A. tractus. Additional encysting organisms were found deeper in the muscle tissue and did not produce a black spot. These encysting organisms are proposed to be digenean trematodes in the metacercariae life stage.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 103-109 from CIEE Bonaire.

Populations of Diadema antillarum have had low densities ever since its mass mortality event in 1983. A slow population density increase has resulted from fertilization complications due to extensive distance between individuals. The relationships between D. antillarum and their competitors and predators as a cause for the lack of population recovery has not been directly studied. The correlation of D. antillarum density with the abundance of predators, competitors, and microalgae, was studied to determine additional possible explanations for the low density of individuals. There were three dives during the day at six sites. The day dives included observational fish counts and transects and quadrates to assess percent algae cover in a 10 m2 . While the night dives include observation counts of all of the urchins in the 10 m2 . No increase was found in Diadema antillarum density compared with a study in 2009 (0.005 individuals per m 2 ). No significant correlation was determined between D. antillarum density and predator density. A weak, positive correlation between competitor density and D. antillarum density was determined. In contrast, a strong, positive correlation between percent algae cover and D. antillarum density was found This study revealed additional pressures on D. antillarum population (e.g. competitors, percent algae cover), which could account for the slow recovery of local D. antillarum population in Bonaire.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 25-32 from CIEE Bonaire.

Coral reefs are being threatened by both anthropogenic and environmental factors. One prominent factor is the loss of herbivores on coral reefs due to overfishing and disease. Herbivores play a key role in coral reef ecosystems by grazing away competing algae that threaten coral survivorship and recruitment. The loss of Diadema antillarum in the Caribbean due to an unknown pathogen has been detrimental; however, there is another species of sea urchin emerging in the reef environment: Tripneustes ventricosus. Little is known about the environmental factors that influence the abundance and distribution of T. ventricosus in the reef environment. This study seeks to quantify the distribution and abundance of a particular population of T. ventricosus on the back reef found along the waterfront of Kralendijk, Bonaire, Dutch Caribbean. It also examines the effects of benthic composition and competition on the distribution of T. ventricosus. In order to examine these factors, 30-m transects were laid at three different distances from the waterfront wall at five sites. Quadrats were placed at 5-m intervals along each transect. Within each quadrat, algal, benthic, and sea urchin composition was observed and recorded. Water samples were taken from each site to test nitrogen concentration. The diversity and abundance of algae and substrate type appear to be factors influencing T. ventricosus’ distribution and abundance; competition did not appear to be a factor. The area of the abundance of T. ventricosus seems to have ideal conditions for T. ventricosus, and many other urchins, including D. antillarum, that were observed at this site indicating that it may be an ideal place for sea urchins in general.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 14-24 from CIEE Bonaire.

Coral reefs harbor a vast amount of global diversity relative to their size, and are an important economic resource to coastal communities. Over the past few decades, many coral reefs have undergone a phase shift from a substrate dominated by coral to one dominated by algae, largely due to anthropogenic stress. Herbivorous fishes play a major role in topdown control of algal growth and composition; however, depletion of biomass due to overfishing and habitat degradation has threatened the top-down control of fish herbivory on algal composition. This experiment compared endolithic turf algae (TA) composition on coralline rubble under complete fish exclusion, large fish exclusion (>13 cm), and no fish exclusion treatments. There was a significant increase in growth, richness, and percent cover of TA in response to reduced herbivory. The greatest compositional shift occurred in complete fish exclusion treatments. Crustose coralline algae (CCA), important in coral recruitment and growth, significantly increased in cover under every treatment except complete fish exclusion. This illustrates the importance of large-bodied herbivorous fish in controlling TA growth and maintaining bare substrate to facilitate coral recruitment and growth. This study provided insight into how Caribbean reefs go through initial stages of a phase shift from a coral dominated benthos to one dominated by taller, denser algae. Finally, it illustrates how Bonaire’s reef, currently regarded as one of the most intact in the Caribbean, could change in composition if large herbivorous fish are removed from the ecosystem.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 55-65 from CIEE Bonaire.

Global climate change is having widespread effects on the world’s oceans. Particularly vulnerable to changing global conditions are coral reefs, which boast high biodiversity levels though they comprise a small percentage of the oceans. Sea level rise decreases light availability to corals and their symbiotic photosynthetic zooxanthellae, which are responsible for fixing the carbon that corals use to create their carbonate skeleton. Studies have shown how changing light availability with depth can be used as an indicator of coral species diversity. Species richness and diversity of corals is greatest at intermediate depths, with decreasing diversity at greater depths. This study investigated the relationship between coral species diversity and light intensity at depths of 12, 18, and 24 m on the fringing reef ecosystem off the western coast of Bonaire, Dutch Caribbean. Light intensity data were based on theoretical values provided by Beer-Lambert’s law, and video transects were conducted to determine composition of the substrata and to calculate coral species diversity and richness. Strong correlations were found between decreasing coral species diversity with depth (p = 0.041) and percent coral cover and decreasing percent cover of macroalgae and cyanobacteria with depth (p = 0.000, F = 37.60, df = 1). This indicates that while species diversity of corals decreases with lowered light intensity, corals are better able to outcompete macroalgae in environments with decreased light availability. This information is useful in understanding how reefs will respond to environmental changes brought on by sea level rise.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 48-54 from CIEE Bonaire.

Many fish prefer to live in certain habitats based on protection, shade cover, rugosity, and foraging return. Haemulidae, also known as grunts, are a family of fishes that are prevalent on Bonaire and can be found throughout tropical coral reef ecosystems. This study utilized in situ observations to investigate the preferred habitats of solitary grunts compared to colonial grunts based on the amount of the of protection and shade cover that the habitat provided. Three types of grunts were focused on in this study: blue striped grunts (Haemulon sciurusnch), French grunts (Haemulon flavolineatu), and smallmouth grunts (Haemulon chrysargyreum). The results of this study demonstrated that solitary smallmouth grunts utilized habitats that provided the most protection. Further, solitary smallmouth grunts were found in habitats shaded by coral more than the other grunt species. French grunts were found in overall shade cover more than both smallmouth grunts and blue striped grunts. This study showed that blue striped grunts rely mainly on their size for protection, smallmouth grunts on schooling, and French grunts on habitat. A general knowledge of grunts habitat preferences is beneficial because many reefs worldwide are currently degrading. If the reefs continue to degrade, grunts could be in danger because of their specific habitat preferences, based on both their species and social status. Preserving the complexity of coral reef habitats is crucial for some grunts, such as French and smallmouth grunts, but it is not crucial for other grunts, such as blue striped grunts.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 34-42 from CIEE Bonaire.

With the exception of Elysia crispata, shell-less Sacoglossa species (Order: Mollusca), have been widely studied. Within the Caribbean, these small bodied organisms occur in low population densities, making them hard to find and, in turn, difficult to study. This project served to assess E. crispata abundance, ecology and life history traits on the island of Bonaire. Data collected for this study was conducted by observations from ten 40 m2 transects located at depths of 2.2 m, 7.9 m and 10.7 m. A pair of surveyors recorded the number of individuals found, size of individuals, substrate individuals were located on, and color intensity of individuals within each transect. Overall abundance of individuals found at the study sites were much higher than anticipated. Of the 275 individuals found, the highest population densities were found in shallow transects. The average size of individuals was between 3.0 ± 2.6 cm to 5.0 ± 3.8 cm (mean ± SD) in length, with no correlation between size of individual and coloration. Overall abundance of smaller individuals found on shallower transects could indicate higher densities of preferred substrate within these areas. Roughly 94% of individuals were found on various compositions of turf algae. These results implied that E. crispata were biased towards occupying substrates with turf algae compositions as opposed to other available substrates.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 26-33 from CIEE Bonaire.

Processes affecting reef ecosystems have three levels of organization: macroscale, mesoscale and microscale. These processes are conducive to interspecific competition amongst various coral and aggressive invertebrate species. Surveys of these organisms’ distribution, abundance and ecological description of their intra/interspecific competition have been conducted throughout the Caribbean. Previous research has found that scleractinian corals in reef slope ecosystems are frequently outcompeted by sessile aggressive invertebrates, such as Clionid sponges, encrusting bryozoans, encrusting gorgonians and overgrowing mat tunicates. Furthermore, interspecific spatial competition between corals and aggressive invertebrates has been observed to increase in frequency with depth. This project analyzed the distribution and abundance of coral-aggressive invertebrate spatial competition along a fringing reef ecosystem on the west coast of Bonaire. Belt transects were laid out between 200 m north and south of the GPS coordinates N 12°09.6 12’ W 068° 16.9 15’, at two depths (10 and 15 m) along the reef slope. Instances of spatial competition involving individuals at least 10 cm in length were photographed for further analysis. Five coral species and 25 aggressive invertebrate species were encountered in a total of 216 coral-aggressive invertebrate interactions. Quantitative data analysis showed that the orange lumpy encrusting sponge (Scopalina ruetzleri) was the most abundant aggressor at 15 and 10 m, although mean total area covered by coralaggressive invertebrate interactions and their frequency did not increase with depth. Findings could be used as a baseline for future scientific marine research, potentially on growth rate of competing species and the underlying mechanisms responsible for their interspecific spatial competition.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 17-25 from CIEE Bonaire.