Meesters, E.H.W.G.

To follow the health of the coral reefs of Bonaire and Curacao a number of locations on each island are photographed each year since 1973. At each location a 3 m square at up to 4 different depths is recorded and analysed.

Please contact Wageningen Marine Research for more information.

The Dutch Caribbean island Bonaire has been protecting its marine resources for more than 35 years and is ranked as one of the Caribbean’s top dive destinations thanks to its easily accessible diving sites, clear waters and the relatively healthy coral reefs around the island. Coral reefs are important for the ecosystem services they provide including jobs and income to local economies from recreation and tourism. They serve as a natural barrier, protecting the coastlines and as a habitat for many economically important species. 

The general consensus is that the extent and biodiversity of Bonaire’s coral reef is decreasing due to local and regional anthropogenic and global climate pressures. However, the last extensive study of the coral coverage of the reef ecosystem was performed in 1985 by Van Duyl who created an underwater atlas of Bonaire and Curaçao. In order to update this atlas of Bonaire’s coral reefs, a hyperspectral mapping exercise was performed in October 2013 using the Wageningen UR Hyperspectral Mapping System (HYMSY) with 101 spectral channels. 

This news article was published in BioNews 27

BioNews is produced by the Dutch Caribbean Nature Alliance and funded by the Ministry of Economic Affairs.

The dissolved organic carbon (DOC) pool on tropical coral reefs is mainly fueled by photosynthates released from benthic primary producers (BPP), such as reef algae and scleractinian corals. DOC concentrations near BPP have repeatedly been observed to be elevated compared to those in the surrounding water column. As the DOC release of BPP increases with increasing light availability, elevated DOC concentrations near them will, in part, also depend on light availability. Consequently, DOC concentrations are likely to be higher on the shallow, well-lit reef terrace than in deeper sections on the fore reef slope. We measured in situ DOC concentrations and light intensity in close proximity to the reef alga Dictyota sp. and the scleractinian coral Orbicella faveolata along a depth gradient from 5 to 20 m depth and compared these to background concentrations in the water column. DOC concentrations near Dictyota sp. were significantly higher at 10 m than at 5 and 20 m depth. Furthermore, at 10 m DOC concentrations near Dictyota sp. were elevated by 15 μmol C L-1 compared to background concentrations in the water column, but not at 5 and 20 m. DOC concentrations near O. faveolata and in the water column did not differ between depths and concentrations near O. faveolata were not elevated compared to background concentrations at any of the tested depths. Our results indicate that DOC concentrations near Dictyota sp. can differ along a depth gradient from 5 to 20 m. However, the occurrence of elevated DOC concentrations did not follow a natural light gradient across depth. Instead, a combination of light availability (including a restriction by photoinhibition) and water movement are proposed to interactively determine the DOC concentrations in the close vicinity of BPP across the reef slope. 

Tropical coral reefs are among the most biologically diverse and economically important ecosystems on earth. Nevertheless, we found dramatic changes in coral communities on the reef slopes of Curaçao and Bonaire since 1973. Cover and abundance declined for virtually all coral species. The data show a shift from communities dominated by framework building species (e.g., Orbicella spp.) to communities consisting of small opportunistic, phenotypically plastic, species, including few remaining structural colonies. Madracis mirabilis, Porites astreoides, Diploria strigosa, and Agaricia lamarcki are at present modest winners in the coral assemblage, although overall cover declined also for these species. Increased frequency and intensity of events inducing coral mortality and ongoing reduction in suitable hard substratum, provided by the remnants of large colony building species, could reduce the chance of these species to remain winners in the longer run. The observed loss in coral cover and the shift from larger structural to smaller opportunistic species reduced reef carbonate production by 67% and therewith, in combination with a trend toward smaller coral colonies, reef complexity. Alarmingly, reefs at upper-mesophotic depths (30–40 m) did not escape the general degradation of the coral community. The negative effects are larger around densely populated areas where local stressors are adding to degradation caused, for instance, by region wide mass bleaching. Without proper conservation and management this already dramatic degradation will continue and turn more and more coral species into losers.

The Coral restoration of Staghorn (Acropora cervicornis) and Elkhorn (A. palmata) as practiced by the Coral Restoration Foundation Bonaire (CRFB) is shown to be highly successful in terms of growth and survival of new colonies, in both nurseries and transplant locations. Coral restoration is expected to contribute to ecosystem services and increase coastal protection, biodiversity, fish biomass, and tourism.

Staghorn fields once covered the bottom of the shallow reefs of Bonaire for up to 70%. Most of Bonaire’s Staghorn and Elkhorn populations have been decimated by white band disease (WBD), leaving the shallow terraces around this popular diving destination as biologically barren sandy plains. The CRFB restoration project attempts to restore these populations by actively (with help from volunteers) rebuilding the once so attractive Staghorn fields. The coral restoration project of CRF Bonaire needed scientific assessment of important aspects of the restoration methodology such as growth, regeneration and survival of CRFB’s corals recruits.

Fragments are created from mother colonies by cutting and these cuts are short‐term wounds that need to be regenerated by the living tissue on both the ‘parent’ and the fragment. Results of a series of field experiments in the CRFB coral nurseries indicated that recovery of cut fragments was 99.6% (n=234). Time until recovery of tissue was extremely fast within approximately 1 week. Full pigmentation and apical polyp formation was generally achieved within two weeks and depended on the origin of parental colonies and the current growing location.

Over 200 colonies were transplanted from the nurseries on to attachment structures at different locations on the reef to determine growth rates and potential effects of location, attachment structure, and parental origin (genetic identity). Transplant sites (several kms apart) differing in environmental conditions and type of attachment structure were not found to impact transplant growth which was exceptionally high (almost 14 cm per year per branch tip and). An average fragment of 25 gram will grow to approximately 12 times its weight within one year. Nursery grown Staghorn fragments developed more side branches compared to their wild counterparts. While the exact mechanism behind side branch formation is not yet understood, several possible explanations are provided. The results of this research generate many follow‐up suggestions and exciting ideas for future coral restoration practices.

Results show clearly that current restoration practices by CRFB of transplanting Staghorn colonies to different locations is likely to be an excellent way to restore the Staghorn fields of Bonaire and probably in the wider Caribbean. Parental origin of the transplanted fragments significantly affected damage regeneration and growth rate, opening up the possibilities for active selection of specific genotypes to increase transplantation success. However, genetic diversity of the population should be studied and safeguarded. The measured survival, regeneration, and growth rates indicate that current restoration practices of CRFB are highly sustainable and may create viable clusters of Staghorn colonies which may initiate the regrow of Staghorn corals into thick fields. Coral restoration through fragmentation can create a very large number of viable fragments in a very short time (one fragment can be cut into two fragments within 6 months without influencing survival rate). It is recommended to also monitor the long‐term development of these restored Staghorn colonies in order to determine the recovery of the total community associated with these colonies. 

Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2, has attained international conservation status due to the rich diversity of species that reside on the bank. In order to assess the role of Saba Bank as a potential reservoir of diversity for the surrounding reefs, we examined the population genetic structure, abundance and health status of two prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongia muta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1-5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) on Saba Bank and around Saba Island, and compared with published data across the wider Caribbean. Our data indicate that there is genetic connectivity between populations on Saba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean, ranging in distance from 100s–1000s km. The genetic diversity of Saba Bank populations of M. cavernosa (π = 0.055) and X. muta (π = 0.0010) was comparable to those in other regions in the western Atlantic. Densities and health status were determined along 11 transects of 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa (0.27 ind. m-2, 95% CI: 0.12–0.52) were average, while the densities of X. muta (0.09 ind. m-2, 95% CI: 0.02–0.32) were generally higher with respect to other Caribbean locations. No disease or bleaching was present in any of the specimens of the coral M. cavernosa, however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth (48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta (83.5%) showed signs of presumed bleaching. The combined results of apparent gene flow among populations on Saba Bank and surrounding reefs, the high abundance and unique genetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to replenish genetic diversity or as a storehouse of diversity that can be utilized if needed for restoration practices.

In 2014 a part of the Curacao reef was captured by underwater photography. From this photo collection a 3D model and an ortho-photo of that part of the reef was constructed. The ortho-photo shows a unique view on the reef that cannot be captured in a single underwater photograph.

Please contact the DCBD administratorfor more information.

To follow the health of the coral reefs of Bonaire and Curacao a number of locations on each island are photographed each year since 1973. At each location a 3 m square at up to 4 different depths is recorded.

Please contact the DCBD administratorfor access to the raw digital photographs.

The Caribbean islands of Bonaire, Saba, St.Eustatius, Aruba, Curacao and St. Maarten are part of the Kingdom of the Netherlands. The islands have a rich biological diversity and a variety of globally threatened ecosystems. These ecosystems are important for their services such as the production of food, coastal protection, tourism attraction, erosion control, medicine, carbon sequestration and climate change resilience, water and air purification and/or retention, and non-material benefits such as heritage and recreational experiences. Robust monitoring indicators are needed to assess ecosystem health in relation to environmental change and socio-economic stressors and exploitation.
The Kingdom of the Netherlands has ratified international treaties and conventions, signed regional agreements and implemented national law for the protection of nature and biodiversity in the Dutch Caribbean. These treaties call for reporting on status and trends of biodiversity.
Currently considerable effort is being invested in collecting baseline data and local monitoring to support local policy on and management of nature and biodiversity. These activities partially overlap with the demands of treaty reporting requests, but do not provide all the data necessary to satisfy the needs of either the reporting obligations or the local policy and management needs. The main issues are that:
• Existing monitoring programmes on the islands do not cover all required biodiversity and nature topics;
• Several existing monitoring programmes are based on methods that cannot be used to generate the indicators required.
This report concludes that monitoring all the separate species identified would require considerable resources. Monitoring in the Dutch Caribbean cannot be compared to the Netherlands which has a long history of monitoring the natural environment and many periodic reviews of the efficacy of monitoring techniques. Holistic monitoring of ecosystems using key indicators is a good alternative to detailed monitoring as the ecosystem health implicitly considers all dependent species. However, some additional species monitoring is necessary of keystone species, endangered species, commercially important species and invasive species.
It is recommended to :

• Keep supporting the foolowing current activities: Maintain existing monitoring on: turtle nests, coral, cover, shark and ray densities, flamingo counts, yellow-shouldered amazon roost counts and terns. Adjust the existing monitoring for: fish densities and population structure, bird species richness, red billed tropic bird, Lesser Antillean Iguana;
• Set up ecosystem/habitat monitoring;
• Set up vegetation monitoring;
• Link forest and migratory bird monitoring to vegetation monitoring;
• Link bird of prey monitoring to flamingo monitoring on Bonaire;
• Collect data on pressures and abiotic conditions from other sources ;
• Stimulate the use of volunteers for monitoring

Abstract

The importance of mangrove and seagrass lagoonal habitats as nursery areas for many reef-associated fish species is well established in the scientific literature. However, few studies have examined the relative use by nursery species of different sub-habitats within such systems. Here, we investigated fish community structure of a variety of interconnected sub-habitats of the tropical lagoon of Lac Bay in Bonaire, Dutch Caribbean. Visual census was used to test the degree to which these sub-habitats may differ in their use by fishes of different species and life stages. We quantitatively sampled the fish species abundance, composition, and size structures at a total of 162 sites distributed among nine different sub-habitats that are common to mangrove and seagrass ecosystems. Fish community variables differed consistently among sub-habitats and were mainly influenced by the presence of mangrove root structure or seagrass cover. Mangrove fringe sub-habitats were a premier habitat since multiple life stages of a variety of species showed highest densities and biomass there. Several reef fish species had a distribution pattern suggesting a unique stepwise post-settlement life cycle migration in which larger juveniles and/or subadults appear to move from the open bay environment (seagrass beds or bay mangrove fringe) to the interior mangrove fringes along mangrove pools before later departing to the adult habitat of the coral reef. In the case of the well-lit and well-circulated central bay sub-habitat, the limiting factor to fish abundance and diversity appeared to be the paucity of three-dimensional shelter due to the lack of Thalassia seagrass beds. In the warm and hypersaline backwaters, physiological tolerance limits were likely a key limiting factor. Long-term changes driven by mangrove expansion into this non-estuarine lagoon have been steadily reducing the net coverage of clear bay waters, while the surface of shallow, muddy, and hypersaline backwaters, unusable by key nursery reef fish species, has been increasing by an almost equal amount. Our study shows how fish density varies along the full gradient of sub-habitats found across a tropical bay to provide insight into the potential consequences for nursery habitat function when the availability and quality of these sub-habitats change in response to the long-term dynamic processes of mangrove land reclamation and climate change.