Population demography

The sea urchin Diadema antillarum is an important herbivore in coral reef ecosystems of the Caribbean. The Caribbean is still recovering from a 1983 mass mortality event that decimated D. antillarum throughout the Caribbean, reducing populations to <3% of former levels (Lessios et al. 2001). By feeding on algae, D. antillarum helps prevent excessive algal growth and is beneficial to juvenile corals (Edmunds and Carpenter 2001). The urchin die off may have precipitated a phase shift in coral reef communities in the Caribbean from coral to algal dominated ecosystems. However, at high densities D. antillarum can have a negative effect, reducing the number of coral recruits (Sammarco 1980; Mumby et al. 2006)

In light of the potential of ecosystem level consequences of D. antillarum population; the purpose of this study was to document the densities in Bonaire to determine if they are over or underpopulated. The range of D. antillarum expected in an area at equilibrium was found to be equal to or greater than 1 m-2 and less than 16 m-2 (Mumby et al. 2006). Using transects, the densities of D. antillarum were counted on the leeward side of Bonaire, Netherlands Antilles at 20 sites. Urchins were found to be extremely patchy and underpopulated (< 1 urchin m-2) for all but one site. Karpata’s population of D. antillarum was within the normal parameters (1< x < 16 urchins m-2). No sites sampled had densities that would indicate overpopulation of D. antillarum (> 16 urchins m-2). 

This student research was retrieved from Physis: Journal of Marine Science I (Fall 2006)19: 38-44 from CIEE Bonaire.

Coral reefs around the world are experiencing high levels of degradation due to temperature changes, increased nutrients and destructive fishing techniques. For example, where there were once large thickets of the branching coral Acropora cervicornis along the coasts of Bonaire, Dutch Caribbean, there is now sand and dead coral. Loss of an entire highly complex habitat has likely altered the local reef fish community. Artificial reefs have been used in the past to test hypotheses about structural complexity and its effects on reef fish communities. However, no studies have sought to discover if artificial reef structures modeled after A. cervicornis would support reef fishes found in the natural branching coral colonies by mimicking the structural complexity provided by the coral. To answer this question, four patches of artificial A. cervicornis were constructed and placed near the reef crest on the leeward side of Bonaire, Dutch Caribbean. Natural thickets of A. cervicornis were used to compare differences in fish species richness, diversity and density. Artificial reef structures were found to support higher diversity but lower abundance of fish. There was no significant difference in species richness between the natural and artificial reef stands. Overall, the artificial reef structures were able to provide some shelter to certain fish species, but were not able to support the fish community that is supported by natural stands of A. cervicornis.

This student research was retrieved from Physis: Journal of Marine Science X (Fall 2011)19: 21-27 from CIEE Bonaire.

Species conservation is becoming an important aspect in marine environments. Climate change and anthropogenic interactions have had a direct impact on the health of local species in all of the world‟s oceans, and coral reef ecosystems are no exception. Studies from around the globe have focused on angelfish demographics. In general, species within the family Pomacanthidae reside in places containing crevices and cliffs but are also seen in sandy areas with reef and seagrass patches. Some species are seen in groups of up to five fish, having one male in a harem of one to four females. Pomacanthidae are also known to predate on sponges and are generally found in areas which contain them. On the fringing reefs in the Dutch Caribbean, the species Pomacanthus paru (French angelfish) have not been extensively studied in terms of population in relation to maximum reef relief. To measure both aspects, 30 m transects were laid out at depths of 3, 6 and 15 m. The number of P. paru individuals as well as seafloor rugosity was documented and compared through statistical analysis during a five week period from September to October 2012. Results showed that most P. paru were found along the deeper transects of 6 and 15 m which had higher rugosity and juveniles were only seen in the less rugose, sandy flats at 3 m. Data collected will aid in providing a baseline for conservation efforts due to the declining state of natural environments, and in turn, the decline of individuals within populations.

This student research was retrieved from Physis: Journal of Marine Science XII (Fall 2012)19: 59-63 from CIEE Bonaire.

When overly abundant, macroalgae can be a major threat to the health of a coral reef ecosystem due to its capability to smother live coral and reduce the rates of recruitment. Several factors can contribute to macroalgal growth, one of the controlling elements being a lack of herbivorous grazing. When grazing pressure is high the ecosystem remains balanced, but when grazing pressure is low reefs can experience macroalgal blooms that have a lasting negative effect. This study examined the indirect causes of macroalgal cover change through assessing damselfish aggression. Stegastes planifrons, also known as the Three Spot Damselfish, are highly aggressive and territorial fish that will defend their territories against a number of intruding species. This study looked at the relationship between damselfish abundance and aggression and the grazing behavior of parrotfish, as well as the relationship between damselfish abundance and macroalgal cover on Bonaire, Dutch Caribbean. Video transects were implemented over the chosen study stations and then analyzed with Coral Point Count (CPCe) software to attain the percentages of macroalgae cover at each station. Aggressive behavior of the three spot damselfish as well as the grazing behavior of parrotfish were observed and recorded using SCUBA diving. It was found that damselfish aggression and parrotfish grazing were negatively correlated, and that parrotfish grazing followed the same trend line as the macroalgae cover. Based on the findings of this study it was concluded that S. planifrons aggression has no considerable effect on the grazing behavior of parrotfish,and it can be assumed that it does not contribute to increased macroalgal cover.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 16-21 from CIEE Bonaire.

Abstract The brittle star Ophiothrix suensonii is a com- mon coral reef sponge commensal with high dispersal potential. Here, we utilize COI sequence data from 264 O. suensonii individuals collected from 10 locations through- out Florida and the Caribbean to investigate dispersal dynamics and demographic history. Locations separated by up to 1,700 km lacked genetic differentiation, confirming the ability for long-range dispersal. However, significant differentiation was detected among other regions. Samples from Utila, Honduras showed the greatest differentiation, suggesting that the circulation of the Mesoamerican gyre could be a significant factor restricting gene flow in this region. Demographic analyses provided strong evidence for a population expansion, possibly out of Florida, through the Caribbean, and into Honduras, which commenced in the early Pleistocene. However, the presence of a clade of rare haplotypes, which split much earlier (mid-Pliocene), indi- cates that O. suensonii persisted long before its recent expansion, suggesting a cyclic history of population con- traction and expansion. Finally, patterns of gene flow are not concordant with contemporary surface currents; rather, they reflect historical movements possibly linked with changes in circulation during periods of Pleistocene climate change.