Habitats

A new study from Wageningen University & Research (WUR) showed that reef sharks utilize different areas of the reef throughout their lifetime. Using baited video cameras, six different species of reef sharks were recorded around the northern Dutch Caribbean islands. These results will impact the design and implementation of shark conservation strategies for years to come.

Reef Sharks

Reef sharks play a critical role within the ocean. As a top predator, reef sharks help maintain the delicate balance within (coral) reef environments. In fact, research has found that reefs with healthy shark populations are more resilient and capable of withstanding the pressures of climate change, pollution, overfishing and diseases.

Juvenile Sharks

Understanding the dynamics of habitat use of local shark populations is critical when designing effective marine conservation strategies. This is exactly what the latest reef shark study from WUR hoped to achieve. Using baited remote underwater video cameras at 376 locations around the reefs of Saba, Saba Bank and St. Eustatius, fish ecologist Twan Stoffers and his colleagues recorded 126 different shark sightings.

Of the six different species recorded in this study, juvenile Caribbean reef sharks (Carcharhinus perezi) and nurse sharks (Ginglymostoma cirratum) were most commonly recorded. Overall, they observed young sharks in shallow, more complex areas of the reef, whereas the larger, more mature, sharks were observed further away from the reef in deeper habitats up to 65 meter depth. Larger nurse sharks were frequently recorded in seagrass beds. The researchers were surprised that hardly any adults were observed over the course of the entire study.

Implications

This knowledge could have an important impact on conservation strategies for reef sharks and other endangered shark species. Since reef sharks use a variety of different habitats (both shallow and deeper water areas), creating an interconnected conservation network is vital for ensuring full protection throughout their life cycle. Sanctuaries such as the Yarari Sanctuary (which includes the marine area around the Caribbean Netherlands) are an important step in creating a network of protected areas. In addition, efforts such as the Caribbean Shark Coalition are important as well, because they work to build capacity for shark and ray research, policy and conservation within the Wider Caribbean Region.

Report your sightings

You can help contribute to the overall understanding of sharks and other species by reporting your nature sightings on sightings and photos on DutchCaribbean.Observation.org or download the free apps (iPhone (iObs) & Android (ObsMapp)).

Species reports by local communities and tourists are invaluable for nature conservation efforts to help increase public awareness and overall species protection.

DCNA, Observation International and Naturalis Biodiversity Center are working together to develop on automated species identification app for your phone for all species on land and in sea. Your uploaded photos are of great value to make this possible. For questions, please contact research@DCNAnature.org

More information

For more information, please find the full report here or follow along on the DCNA’s free digital newsletter BioNews for the latest updates. For questions related to the reef shark study, please contact twan.stoffers@wur.nl

Article published in BioNews 45 and Special Edition BioNews: Tiger Shark Expedition

Recent studies show that late stage pelagic larval fish are not simply drifting with the currents as formerly believed, but are in some cases strong swimmers and more than capable of swimming against the ambient flow. There is evidence that larval fish may select specific habitats in which to settle. Although little is understood about their sensory abilities, both sound and smell have been linked to settlement of coral reef larvae (Leis 1997). On Bonaire, Netherlands Antilles, coral reefs, mangrove forests, and seagrass beds provide refuge and food for young fish. Some fish species are thought to spend the juvenile life stages in mangroves and seagrasses and abundances of certain adult reef fish species have been shown to be greater in coral reefs with surrounding seagrasses and mangroves (Mumby 2004). Larval fish may be able to select environments for settlement based on biological attractions detected by certain senses (Lecchini 2005). This study investigates the potential differences in the larval fish recruiting to mangrove and seagrass habitats with larval fish recruiting to coral reef habitats. Samples of larval fish were taken on the three nights surrounding the November new moon. Light traps and dip nets were used at two different sites, one a mangrove/seagrass habitat, and the other a coral reef habitat. Larger numbers of larval fish and more families were represented in the samples taken in the coral reef habitat than the mangrove/seagrass habitat.

This student research was retrieved from Physis: Journal of Marine Science II (Fall 2007)19: 32-36 from CIEE Bonaire.

Habitat selection is critical to the development, growth and reproductive success for most marine animals. Organisms select habitat based on food availability, as in gulls of the North Sea, complexity of structure, as in juvenile fish of seagrass beds, or a combination of both factors as in marine snails of the rocky intertidal zone. Mangrove forests are known to be important habitat and nursery grounds for many endangered and/or economically important species of fish. These habitats are currently under threat by coastal development and overexploitation, therefore, scientifically supported restoration efforts are currently being pursued. The mangroves of Bonaire are threatened by development, causing hypersaline conditions and change in water flow. In this study food availability and composition as well as the structural complexity of the mangrove prop root system were assessed as possible attractants to juvenile fish. Snorkeling observations along permanent transects of the fishes in and amongst the prop roots as well as the algae and invertebrates living on the prop roots were conducted to establish a baseline understanding of the mangrove community (consumers and prey). In order to assess the impacts of consumers on prop root epibiota, consumers were excluded from prop roots using plastic mesh and the regrowth of preferred food species was monitored. The caging experiment showed evidence of the impacts of herbivores in the mangroves as green algae growth increased significantly in their absence and growth of red algae decreased. Artificial mangrove units (AMUs), modeled after prop roots, were also constructed for this study to test the attractiveness of structural complexity to resident fish. Comparisons between the behavior of the fish community of mangrove prop roots and that of AMUs indicated that there is no distinguishable preference between predators and consumers for structurally complex habitat, but that both prefer more complex habitat over simple structure. The data collected concerning preferred food and habitat structural complexity could be used in restoration projects.

This student research was retrieved from Physis: Journal of Marine Science V (Spring 2009)19: 20-26 from CIEE Bonaire.

Biodiversity of coral reef fish species is often related to the structural complexity and diversity of their habitats. This study explores the relationship between fish species richness, habitat diversity (substrate diversity) and habitat complexity (rugosity). Habitat diversity and topographic measures were used to predict reef fish diversity. It was hypothesized that high fish species diversity would show a positive correlation with greater habitat structure, which includes habitat diversity and topographic complexity. Fish species richness was determined at six dive sites in Bonaire, N.A. (Karpata, Andrea II, Cliff, Windsock, Angel City, and Red Slave) using data from 20 randomly chosen expert-level surveys provided by Reef Educational Environmental Foundation (REEF) for 2004 – 2009. Preliminary analysis of REEF data was used to select sites with high and relatively low fish species richness to make comparisons with the habitat structural complexity measurements (substrate diversity and rugosity). Substrate diversity and habitat complexity were measured using a 10 m transect randomly placed at 4 depths (2, 6, 12, and 18 m) at each site. Substrate diversity was determined by measuring the percent cover of the different substrates and then using the Shannon Diversity Index to determine H’. The rugosity of the sample area was measured by fitting a lead line to the reef at each of the determined depths. Overall results suggested that topographical complexity (rugosity) was not related to high fish species richness at dive sites on Bonaire. There was a weak positive correlation between H’ and fish species richness on the reef slope and a weak negative relationship between H’ and fish species richness on the reef flat. The results provide evidence that there are more factors to consider when explaining fish species richness on coral reefs than the structural complexity of the habitat at the scale of this study.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 66-72 from CIEE Bonaire.

Coral reefs are one of the most diverse ecosystems found on earth, and are home to many habitat-specific fish. The Gobiidae family is known to be one of the most habitat-specific groups. Two common gobies found in the Caribbean are Coryphopterus lipernes and Gobiosoma evelynae, and both species rest on live coral heads. This study was conducted to determine if C. lipernes and G. evelynae show a preference for certain coral species and if the presence of disease affects this selection. A benthic survey was performed using video transects and CPC data analysis, allowing calculation of percent frequency for each coral species and frequency of diseased corals. Goby searches were conducted using SCUBA within a depth range of 10 - 15 m along the reef, recording the coral of choice and its disease status. The results showed that C. lipernes selected for 3 coral species and against 5, favoring Colpophyllia natans and Montastraea cavernosa. G. evelynae selected for 3 coral species and against 5, favoring M. cavernosa and Stephanocoenia spp. Both goby species selected significantly against coral disease, C. lipernes had a mean disease selection ratio of 0.39, and G. evelynae showed a complete selection against disease. Coral reefs are important ecosystems that are currently under significant abiotic and biotic stressors. It is important to understand the influence that an increase in disease and reduction in coral abundance may have on habitat-specific fish.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 96-102 from CIEE Bonaire.

The implementation of artificial reefs is one effort used to mitigate the rate of decline of coral reefs and the deterioration of fish communities. Artificial reefs add support to struggling reefs habitats by providing additional or varied structural relief, sometimes mimicking specific coral structure types. The purpose of this study is to assess the effectiveness of branching artificial reef (BAR) habitat deployed in November 2011 by comparing the fish density and biomass, and species richness and diversity of the BAR to those of habitats in which it was placed. Three plots of BAR habitat were compared to three plots of rubble habitat and three plots of fore-reef habitat. BAR plots were found to have significantly lower fish density, fish biomass, and species richness than the fore-reef, but no statistical difference in species diversity. When compared to the rubble, BAR habitat showed significantly higher species richness, but no significant difference in density, biomass, or diversity. A comparison of family and fish phase community composition revealed that BAR habitat supports significantly more initial phase Scaridae than either adjacent habitat. It was concluded that BAR habitat adds little in the way of a complementary habitat to the terrace-fore-reef zone. The results from this study suggest that no further implementation of this form of artificial reef should be carried out along the rubble terraces of Bonaire. However, further monitoring of the BAR habitat and research into a branching structure with greater complexity, more interstitial matrix and constructed from calcareous material may be useful.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 88-95 from CIEE Bonaire.

Herbivores are important structuring agents for ecosystems worldwide. While effects of grazing by herbivorous fish are well studied, their roles in organismal dispersal have only recently become a topic of interest. Location preference and range of defecation may indicate the importance of their contribution to organism spreading. This study therefore examined the distribution and frequency of defecation of the princess parrotfish (Scarus taeniopterus) and queen parrotfish (Scarus vetula) between coral reef and sand flat habitats. Observations were performed using SCUBA in Bonaire, Dutch Caribbean. Target species were observed for 20-minute trials in each habitat. Defecation frequency, bite frequency, maximum distance between defecations, and location of defecation were recorded and averaged for each species in each habitat, and compared between species and habitats through two-way analysis of variance (ANOVA). Additionally, unique food sources observed during trials were sampled and examined in the lab. S. taeniopterus individuals were found to defecate significantly less and have smaller maximum distance between defecations within the reef habitat than the sand habitat, while S. vetula did not show significant behavioral changes for any of the variables between the two habitats. Lab results also suggest that S. taeniopterus may be opportunistic omnivores. This study offers insight to behavioral plasticity and specificity to habitat type, and provides a broader understanding of dietary plasticity and ecological roles for S. taeniopterus and S. vetula.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 1-13 from CIEE Bonaire.

Various marine organisms are known to consciously select specific types of habitat that provide maximum shelter from potential predators. Reef fish such as Haemulon chrysargyreum (smallmouth grunts) are commonly seen congregating in groups around the coral structures in Bonaire. Observing schooling fish can provide pertinent information on the refuge provided by structurally complex and diverse ecosystems. This study assessed the habitat preference of H. chrysargyreum based on species of coral, complexity of sites, and substrate type. Levels of phosphate, nitrate, and ammonia were also analyzed in the areas occupied by shoaling H. chrysargyreum to see if they provide a significant input of nutrients into the coral reef ecosystem. The results of this study demonstrate that H. chrysargyreum prefer areas of medium to high complexity accompanied with a soft substrate (sand, rubble) and an overhanging structure. Nutrient level analysis was inconclusive and, therefore, requires further studies. This research sought to identify certain species of coral and structures that are used by H. chrysargyreum for habitation. Such knowledge can aid conservation efforts by honing in on specific areas that schooling fish utilize for shoaling and feeding. Additionally, data from this study provided preliminary assessment for future studies on the potential nutrient input of H. chrysargyreum to the marine ecosystem.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 52-63 from CIEE Bonaire.

Stenorhynchus seticornis (Yellowline arrow crab) is a decapod crustacean native to the Western Atlantic in tropical and subtropical climates. Stenorhynchus seticornis is abundant in the Caribbean and has been studied associating with many different species from different phyla. Bonaire is a small island in the Southern Caribbean where S. seticornis is common, however no research on S. seticornis has been published on Bonaire. This study provides new information on S. seticornis and its ecological role on the reefs of Bonaire. This study examined the habitat type, habitat substrates, behaviors, and inter-species associations of S. seticornis by surveying at two depths, 8 and 14 m. Stenorhynchus seticornis was observed more frequently at 14 m (n = 53) compared to 8 m (n = 27). There was a higher frequency of inter-species associations and more total species observed associating at 14 m compared to 8 m. The majority of S. seticornis at 8 m were observed on sand under ledges, while at 14 m S. seticornis were recorded primarily on turf algae in crevices. The predominant behavior of S. seticornis at 8 and 14 m were eating and hiding respectively. The data collected contributes new information about S. seticornis, which is an abundant crustacean in Bonaire and is not fully understood. The results suggest that S. seticornis associates across many phyla and could serve an important role in the larger coral reef ecosystem. 

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 35-41 from CIEE Bonaire.

Marine habitat map of Saba (GIS)
 

See this report for more info.