Corals

Yellow band disease (YBD) is a bacterial infection affecting corals of the Montastrea annularis species complex. Recent mortality rates of M. annularis spp. on Bonaire have risen due to YBD and other biotic and abiotic factors. The loss of staghorn coral, Acropora cervicornis, the preferred habitat of the threespot damselfish, Stegastes planifrons, has caused the damselfish to inhabit M. annularis spp. Unfortunately, M. annularis spp. are slower growing corals that take longer to reach reproductive maturity and are thus less able to withstand S. planifrons biting their tissues and creating algal gardens on exposed skeleton. This weakens the coral and makes it more susceptible to diseases like YBD. The objective of this study was to examine the relationship between S. planifrons gardening and YBD. Sample sites of healthy and diseased colonies of M. annularis spp. were established across depths at Yellow Sub dive site in Kralendijk, Bonaire. Sites were monitored for damselfish inhabitants and signs of coral biting. Pictures were taken of each site to chart the progress of the disease over the course of the study, and ImageJ was used to determine percent cover of healthy versus unhealthy coral. No significant relationship was found between S. planifrons activity and YBD, although S. planifrons seemed to select healthy colonies. The increase of damselfish populations and their detrimental effects on Bonaire’s reef calls attention to the need for fishing regulations of predatory species and a heavier focus on the conservation of A. cervicornis thickets.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 83-87 from CIEE Bonaire.

A coral is made up of key associations between endosymbiotic zooxanthellae, protists, bacteria, archaea, viruses, and fungi. These microbe-coral interactions can be very beneficial, some associations providing key functions in reproduction, nutrition, and antimicrobial protection. However, as a coral becomes thermally stressed, the ability to regulate microbe growth in its surface mucus layer becomes diminished and opportunistic pathogens are able to colonize. Corals may be able to adapt for the changing reef ecosystem by selecting for more beneficial associations: one of the facets of the coral probiotic hypothesis. The invasive azooxanthellate coral Tubastraea coccinea is able to colonize very shallow, hot and turbid areas that are not favorable for settlement by other species. However, not much is known about T. coccinea other than its invasive nature in the Caribbean. The purpose of this investigation was to determine if the surface microbial communities of T. coccinea are one of the factors aiding its survival. Culturing on Thiosulfate Citrate Bile Salt plates was used to visualize and compare the overall culturable Vibrio spp. communities present in T. coccinea and other widespread shallow corals. At each site, the numbers of Vibrio spp. were not significantly different between the three species, but numbers of a gram-positive bacteria, Enterococcus spp., were found to be significantly higher in T. coccinea.

This student research was retrieved from Physis: Journal of Marine Science XII (Fall 2012)19: 73-79 from CIEE Bonaire.

The study of introduced species has gained popularity in recent years. A species introduced to a new area can have negative effects on the native ecosystems, as well as positive interactions with local fauna. The success of an exotic species depends on many factors. Those that are most successful at expanding possess mechanisms of reproduction, settlement, and distribution that aid in competing for space and resources. Tubastraea coccinea, also known as orange cup coral, is native to the Indo-Pacific and was introduced in Bonaire in the 1940s. Little is known about the effects T. coccinea has on the local marine community. It has a very opportunistic nature and has become a dominant scleractinian coral in the subtidal zones occupying shallow, heavy surged waters. T. coccinea is an azooxanthellate coral, which explains its ability to occupy habitats not desirable by other corals requiring sufficient nutrients and sunlight for photosynthesis. The purpose of this investigation was to determine the distribution and abundance of T. coccinea along various sites in Bonaire and observe its habitat preferences. Six sites in Kralendijk, Bonaire were surveyed by snorkelers, who counted various sized colonies and substratum occupancy. T. coccinea was found at all six surveyed sites, being most abundant at sites with very shallow shores and heavy surge. It preferred man-made pilings underneath docks as its habitat. This confirms that T. coccinea is established in Bonaire. By observing the distribution and preferences, the successful nature of T. coccinea throughout the Caribbean can be better understood.

This student research was retrieved from Physis: Journal of Marine Science XIII (Spring 2013)19: 10-16 from CIEE Bonaire.

Corals are the building blocks of coral reefs as they provide countless marine organisms with protection and habitat. However, coral diseases are currently threatening coastal environments by causing tissue loss and, in some cases, death of corals. This destroys the habitats utilized by marine organisms and the biodiversity of given areas. Many factors contribute to the prevalence of coral diseases, but very little is known about the overall impact of anthropogenic stressors on diseases. Dark spots disease (DSD) is a common coral disease found in the Caribbean and was the subject of this study. Dark spots disease prevalence and severity was quantified utilizing video transects and a severity index approximately one kilometer north of downtown Kralendijk on the west coast of Bonaire, Dutch Caribbean. This data was then analyzed for any trends with regards to spatial location and depth. It was observed that DSD is typically more common and severe at deeper depths of 15 m than at shallower depths of 8 m, although no trends were observed in regards to spatial location and DSD distribution. Gaining a better understanding of DSD distribution paves the way for future studies to potentially understand causative agents of DSD; therefore, allowing for more preventative measures and mitigation processes to conserve the health of coral reefs.

This student research was retrieved from Physis: Journal of Marine Science XV (Spring 2014)19: 79-85 from CIEE Bonaire.

Environmental changes and deterioration have increased coral disease outbreaks, creating a Caribbean hot spot of high disease prevalence and virulence. Dark spots disease (DSD) has an unknown causative agent, although it is suspected to be a result of a biotic pathogen. Variation with anthropogenic stressors and DSD has been limited in research; therefore, the purpose of this study was to determine if a correlation existed between DSD prevalence and nutrient enrichment, in the form of nitrogen concentration. It was hypothesized that DSD prevalence and nitrogen concentration would be highest at shallower depths and that there would be a positive correlation between DSD prevalence and nitrogen concentration. In Kralendijk, Bonaire, sites were surveyed for DSD to calculate the prevalence and water samples were collected to determine the concentration of nitrogen. The results indicated no significant effect of depth and site on DSD prevalence as well as no significant effect of depth on nitrogen concentration. There was a significant effect of site on nutrient concentration as indicated by the significantly higher nitrogen concentration. The pooled data illustrated a weak positive relationship and correlation between DSD prevalence and nitrogen concentration with insignificant results, but one site illustrated a moderately strong positive relationship and correlation with statistical significance. The significant results at that site suggest some correlation between DSD prevalence and nitrogen concentration which requires further investigation ex situ to establish a stronger correlation or possible causation.

This student research was retrieved from Physis: Journal of Marine Science XV (Spring 2014)19: 36-44 from CIEE Bonaire.

Diseases, pathogens, and parasites in marine ecosystems are difficult to research and understand. Tracking the health of ecosystems, such as tropical coral reefs, is important for protecting these sensitive ecological areas. On the coral reefs surrounding Bonaire and other Caribbean islands, a dark spot ailment has been observed on ocean surgeonfish, Acanthurus tractus. This condition has been found to be a parasite, although its exact taxonomic identity is still unknown. The study of this parasite has become the point of interest for many researchers because dark spots have now been observed on other herbivorous fish in this region. The current frequency of the parasite on ocean surgeonfish and other species of surgeonfish is not known. These herbivorous fish are crucial to a healthy and sustainable coral reef ecosystem; a large change to the health of the population of these fishes could potentially affect the entire system. The purpose of this research was to find the prevalence of this parasite in species of surgeonfish through repetitive transects of counting infected individuals on the reefs of Bonaire. Additionally, collection and excision of parasites from their hosts allowed for a hypothesized genus of the infecting organism. The proportion of the density of ocean surgeonfish infected with this black spot causing parasite was 63% and it was found that the proportion of density for the degree of infection for ocean surgeonfish differed significantly among the population. Furthermore, through individual samplings of ocean surgeonfish, the lowest possible taxonomic description of this parasite was found to be the genus Paravortex.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 1-9 from CIEE Bonaire.

Coral reef environments exhibit numerous ecological interactions between different organisms. The habitat structure of a healthy coral reef is composed of many different coral species, with various fish species inhabiting the reef. Coral reef studies often focus on a large spatial scale rather than smaller local scale environments within the reef. The objective of this study was to compare fish populations associated with the microhabitat surrounding individual coral heads of two different species. The purpose of this study was to determine if there were differences in fish abundance, fish species richness, and fish diversity between two massive stony corals, Diploria strigosa and Orbicella annularis. These two corals are common on many Caribbean reefs but are morphologically different; therefore, it was hypothesized that they would show differences between their associated fish assemblages. By conducting fish count observations on both D. strigosa and O. annularis, I was able to compare means between the coral associated fish populations using statistical tests. No statistically significant differences were found between these two coral species for mean fish abundance, species richness, or diversity. One possible explanation is that the larger scale reef environment and processes may have a significant effect on local fish populations found on individual coral heads. By studying the microhabitats of coral species and the associated fish assemblages, we can gain a better understanding of fish population dynamics of coral reefs across larger ecological scales—both regionally and globally

This student research was retrieved from Physis: Journal of Marine Science XVIII (Fall 2015)19: 61-69 from CIEE Bonaire.

Dissolved organic carbon (DOC) release of three algal and two coral species was determined at three light intensities (0, 30–80, and 200–400 μmol photons m−2 s−1) in ex situ incubations to quantify the effect of light availability on DOC release by reef primary producers. DOC release of three additional algal species was quantified at the highest light intensity only to infer inter-specific differences in DOC release. For species tested at different light intensities, highest net release of DOC occurred under full light (200–400 μmol photons m−2 s−1). DOC released by benthic algae under full light differed (up to 16-fold) among species, whereas DOC release by scleractinian corals was minimal (Orbicella annularis Ellis and Solander, 1786) or net uptake occurred (Madracis mirabilis Duchassaing and Michelotti, 1860) independent of light availability. DOC concentrations and light intensities were also measured in situ near seven benthic primary producers, sediment, and in the water column at nine sites evenly distributed along the leeward coast of Curaçao. In situ DOC concentrations increased with light availability, although the magnitude of this positive effect differed among species and bottom types tested. In situ DOC concentrations were on average lower in November–December [87 (SD 45) μmol L−1] compared to May–June [186 (SD 136) μmol L−1], which can, at least partly, be explained by the lower light availability in the latter period. Our results suggest that DOC release by Caribbean benthic primary producers varies considerably among species and depends on light availability in reef algae. 

Aim

Coral assemblages on Caribbean reefs have largely been considered to be biogeographically homogeneous at a regional scale. We reassess this in three taxa (corals, sponges and octocorals) using three community attributes with increasing levels of information (species richness, composition and relative abundance) across hierarchical spatial scales, and identify the key environmental drivers associated with this variation.

Location

Caribbean Basin.

Methods

We assessed reefs along 546 transects positioned within the same forereef habitat (Orbicella reef) in 11 countries, using a consistent methodology and surveyors. Spatial variability in richness, composition and relative abundance was assessed at four hierarchical spatial scales – transects (metres), sites (kilometres), areas (tens of kilometres) and regions (hundreds of kilometres) – using permutational multivariate analysis of variance (PERMANOVA). The relevance of contemporary environmental factors in explaining the observed spatial patterns was also assessed using PERMANOVA.

Results

Consistent with previous studies, species richness of coral assemblages, commonly the focus of biogeographical studies, showed little variance at large spatial scales. In contrast, species composition and relative abundance showed significant variability at regional scales. Coral, sponge and octocoral assemblages each varied independently across spatial scales. Rugosity and wave exposure were key drivers of the composition and relative abundance of coral and octocoral assemblages.

Main conclusions

Caribbean reef assemblages exhibit considerable biogeographical variability at broad spatial scales (hundreds of kilometres) when more responsive community attributes were used. However, the high degree of variability within sites (kilometres) highlights the relevance of local ecological drivers such as rugosity and wave exposure in structuring assemblages. The high levels of within-site variability that is not explained by environmental variables may suggest a previously unrealized contribution of anthropogenic disturbance operating at local scales throughout the region.

Abstract:

Emerging infectious diseases are a worldwide problem and are believed to play a major role in coral reef degradation. The study of coral diseases is difficult but the use of culture-independent molecular techniques has been, and will continue to be, useful in a system where a limited number of visible signs are commonly used to define a “coral disease”. We propose that coral “diseases”, with rare exception, are opportunistic infections secondary to exposure to physiological stress (e.g. elevated temperature) that result in reduced host resistance and unchecked growth of bacteria normally benign and non-pathogenic. These bacteria are from the environment, the host, or the coral mucus layer and become opportunistic pathogens. While difficult and time consuming, we do not advocate abandoning the study of disease-causing pathogens in corals. However, these studies should include comprehensive efforts to better understand the relationship between coral diseases and environmental changes, largely anthropogenic in nature, occurring on coral reefs around the world. These environmental insults are the cause of the physiological stress that subsequently leads to coral mortality and morbidity by many mechanisms including overwhelming infections by opportunistic pathogens.