Coral reefs

Eutrophication status of Lac, Bonaire, Dutch Caribbean Including proposals for measures

Abstract:

Lac is a semi-enclosed lagoon located on the south-eastern side of Bonaire, and contains a diversity of shallow water coral reef associated habitats in close proximity such as mangroves, seagrass beds, Halimeda algal beds, the back reef and sand flats. These habitats support a diversity of fish and invertebrates. The bay has numerous international and national legal protections. The Bonaire National Marine Park regulations and various Island Decrees facilitate from the local perspective. However, despite all regulations, the bay faces several changes, and management and protection of the bay is hampered by a lack of scientific information regarding current environmental status.  

Nutrient poor waters are a requirement for healthy coral reefs. When these become enriched with nutrients, it results e.g. in increased algae and affected reef condition. One area of interest for management is the eutrophication status of Lac. Eutrophication is a pressure that might explain some of observed changes in the bay. However, no baseline on the eutrophication status of Lac exists. IMARES and Environics NV conducted a snapshot assessment of the eutrophication status for current understanding and as a basis for future management. Environics conducted the field measurements at Lac, and most of the data analysis. IMARES analysed geographical data and together with Environics cowrited the report.

The purpose of this baseline study was to assess the trophic status of Lac by analyzing 4 potential indicators of eutrophication simultaneously:

  • Nutrient levels
  • Levels of fecal indicator bacteria (enterococci)
  • Epiphyte loads of seagrasses,
  • Benthic community composition of the back reef

The monitoring was performed at 32 sites within the bay and 1 control site outside the bay in December 2010.

In this study, three of the four observed indicators point towards an ecosystem that is under stress from eutrophication. The levels of nutrients in the bay exceeded thresholds for open coral reef systems due to lack of better. Overall, concentrations show that enrichment with nitrogen was widespread and levels commonly exceeded threshold values. No clear source or “hotspot” could therefore be identified in this study. Phosphate only exceeded threshold values at a few locations, but no clear source was identified. The diffuse enrichment of nutrients across the bay probably results from multiple factors such as water circulation, residence time, freshwater input, rainfall, groundwater contamination, tidal range, and geology. Besides the (semi-) natural conditions the nutrient status is likely to be affected by human impacts as greywater inputs and lacking of proper sewerage. All these factors should be considered regarding the future state and measures to tackle the eutrophication of the bay.  

Enterecocci bacteria were detected at levels above acceptable levels as determined by ISO for bathing waters. The mean levels of enterococci decreased as the distance from shore increases with the highest levels found at groundwater sites and zero enterococci found on the back reef sites. Based on this dispersion we assume that sources of enterococci in this study are most likely birds and cattle (donkey and goat manure). The identification of the true sources of enterococci in Bonaire is however compelling and further study on this aspect is necessary to protect public health.  

The levels of epiphytes on seagrass blades, showed differences in biomass among studied stations. This could mean that seagrass beds in different regions of the bay are experiencing different levels of water column nutrients but no clear relation between nutrient levels and epiphyte cover was observed in this study.

The benthic composition monitoring revealed high abundance of calcareous algae (Ramicrusta sp.). This abundance is likely to be a bloom (pers. observations over time). The bloom of Ramicrusta sp. might be indicative of nutrient enrichment and uptake occurring in Lac. The alga is currently taking over habitat where hard corals lived and changes the benthic composition of the back reef and potentially affecting the integrity of the reef crest. The degradation of the reef crest will diminish the protective role provided by the structure and increase exposure to wave and storm action from the adjacent sea.  

Management Recommendations:

Despite the current eutrophic state of Lac, studies elsewhere indicate that eutrophic bays may begin to recover within months after implementation of proper measures. To do so, natural sources of nutrients should be distinguished from anthropogenic sources. Based on the results of this study and historical accounts of other bays in the Caribbean that have been degraded by eutrophication; the following recommendations for Lac are suggested:

  • a. Reduction of nutrient and fecal bacteria inputs by removing donkeys and goats from the watershed, and ensuring adequate toilet facilities and sewerage at Cai and Sorobon, including greywater disposal.
  • b. Continuation of nutrient monitoring nutrient in order to locate clear sources and fate of the eutrophic state of Lac. We recommend adding urea to the suite of nutrients monitored in this study.
  • c. Implementation of a regular monitoring program to identify sources and fates of fecal bacteria in order to support public health. Effectiveness of above measures can then be assessed as well.
  • d. In general, to understand the outcomes of the water quality management plan it would be of great value to have an understanding of groundwater flows, circulation patterns and residence time of water in Lac.
Date
2011
Data type
Research report
Theme
Research and monitoring
Report number
C093/11
Geographic location
Bonaire

Coral reefs and their zonation in the Netherlands Antilles

Although coral reefs are well developed in the Leeward islands of the Netherlands Antilles, they are poorly developed in the Windward group. Coral communities are common in the Dutch Windward islands, but no structural reefs have been observed. Flat, sandy bottoms there seem to prevent reef development, as is also the case on large parts of the southwest coast of Aruba.

The zonation of corals on the reefs, with respect to depth, distance from shore, and conformation to the bottom, resembles that of other Caribbean reefs. Density of living-coral cover ranges in the several zones from nearly zero to almost 100%. Below 20 to 25 m on the forereef slope the corals are areally less abundant than crustose coralline algae. Generic diversity of hermatypic corals is comparable in the Leeward and Windward groups of the Dutch islands, with 24 and 23 genera present, respectively. These numbers are comparable to those of other highly diverse reefs in the Caribbean. The number of species in the Windward group, however, is relatively low. The differences in abundance of coral genera (and species) throughout the Caribbean needs more thorough investigation.

Date
1977
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Aruba
Bonaire
Curacao
Saba
St. Eustatius
St. Maarten
Author

Working paper on the economic valuation of country St. Maarten's coral reef resources

The St. Maarten Nature Foundation conducted an Economic Valuation of St. Maarten’s coral reef ecosystems in the fall of 2010. This attempted to put a monetary estimate on the coral reefs surrounding the island. Coral Reefs are one of the island’s most valuable resources; they provide a livelihood through dive tourism and fishery and provide protection from large, damaging waves caused by hurricanes. In order to properly manage the coral reef ecosystem, an economic valuation is a useful tool to determine what exactly the monetary value of a coral reef is. With an attached value, better management decisions can be made to adequately protect this most precious of resources.

In order to complete the study four questionnaires were distributed. Two dealt specifically with fisheries, one with hotel accommodations, and one with dive tourism. Data was also provided through independent research and stakeholder analysis. Coral reefs have direct and indirect influences on a wide range of economic factors, and the generation of data was crucial to the successful completion of this study. Data was inputted into a computer program created by the United Nations Environment Program and the World Resource Institute (WRI) and which was adjusted by the St. Maarten Nature Foundation to reflect St. Maarten’s unique ecological and economic situation.

The findings of this study have outlined that St. Maarten’s coral reef resources provide important goods and services to the economy of the island. The revenue that the resource is able to generate through coral reef associated tourism and fishery is approximately USD $57,586,976. Although this number is high, and highlights the importance of coral reefs to the island, it also suggests that there is an increased need for conservation in order for this value not to diminish. It is therefore in the best interest of St. Maarten to incorporate environmental economic data to: (1) Establish Marine Protected Area, (2) Incorporate economic valuation into EIAs, (3) Include economic impacts in assessing fines for damages to coral reefs from activities such as anchoring in the reserves, oil spills etc, (4) Weigh revenues from a growing tourism industry against long-term economic losses from environmental impacts, (5) Evaluate distributional effects (“winners” and “losers”) of proposed coastal development projects, (6) Invest in Scientific Research, (7) Increase support from the private and public sector in the proposed Marine Park Management Authority, St. Maarten Nature Foundation. 

Date
2010
Data type
Research report
Theme
Research and monitoring
Geographic location
St. Maarten
Author

Coral reef crisis in deep and shallow reefs: 30 years of constancy and change in reefs of Curacao and Bonaire

Coral reefs are thought to be in worldwide decline but available data are practically limited to reefs shallower than 25 m. Zooxanthellate coral communities in deep reefs (30–40 m) are relatively unstudied. Our question is: what is happening in deep reefs in terms of coral cover and coral mortality? We compare changes in species composition, coral mortality, and coral cover at Caribbean (Curacao and Bonaire) deep (30–40 m) and shallow reefs (10–20 m) using long-term (1973–2002) data from permanent photo quadrats. About 20 zoo- xanthellate coral species are common in the deep-reef communities, dominated by Agaricia sp., with coral cover up to 60%. In contrast with shallow reefs, there is no decrease in coral cover or number of coral colonies in deep reefs over the last 30 years. In deep reefs, non- agaricid species are decreasing but agaricid domination will be interrupted by natural catastrophic mortality such as deep coral bleaching and storms. Temperature is a vastly fluctuating variable in the deep-reef environ- ment with extremely low temperatures possibly related to deep-reef bleaching. 

Date
2005
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Bonaire
Curacao

An Assessment of the Health and Resilience of Bonaire’s Coral Reefs

Abstract:

From July 19-26, 2010, a dedicated team of researchers completed transect surveys on 25 reefs located on the leeward side of Bonaire and the adjacent Klein Bonaire to characterize the current status, threats, and resilience of Bonaire’s reefs. The assessments focused on corals, fish, algae and motile invertebrates using belt transects, point intercept methods and photographic documentation, incorporating attributes of the Atlantic and Gulf Rapid Reef Assessment (AGRRA) protocol and the IUCN bleaching resilience protocol. The main purpose of this work was to 1) assess changes in reef structure and health since the last region-wide AGRRA assessments (1998-2000) and other surveys (2001, 2005) by Bruckner; 2) identify sites in excellent health, exhibiting a high biodiversity and cover of reef building corals and an intact fish communities; and 3) characterize the health and resilience of these reefs. The intent of this project was to provide critical information that can assist the Bonaire government and Bonaire Marine Park in the conservation and management of their precious resources.

Between 5-15 m depth, cover of living coral was high on all reefs (approximately 50%), with exception of a few sites impacted by white plague outbreaks and shallow areas scoured by strong waves during previous storms. Cover by fleshy macroalgae was generally low, as compared to reefs in other Caribbean localities, although some deeper sites did have high cover of Lobophora and Dictyota spp. (brown macroalgae), and cyanobacterial mats were prominent in several locations (especially on Klein Bonaire); these algae occasionally carpeted the margins of coral colonies and were competing with living corals. Montastraea annularis (complex) were the dominant corals, in terms of living cover, occupying approximately 20-25% of the benthos, and making up over 50% of the total live coral cover. Agaricia, Madracis and Porites spp. were the other dominant corals, in terms of living cover. M. annularis complex was also most abundant taxa (numbers of colonies) at all sites overall, and also the dominant taxa between 5-10 m depth, while Agaricia was slightly more abundant at 15 m depth. While the proportion (number of colonies) of brooding species (especially Agaricia, Porites) was very high, their contribution to living coral cover was less than M. annularis (complex) because most colonies were small in size.

Based on size structure, abundance, levels of recruitment, and coral condition, coral communities could be divided into two primary groups, the M. annularis complex (M. annularis, M. faveolata and M. franksi) and all other species. Corals lumped into “other species” were small to medium- sized (mean=24 cm), and population structure exhibited a monotonic decline in size; most colonies were < 20 cm in diameter and very few colonies were over 60 cm. Although a small proportion of colonies showed active signs of disease and competition from other biotic stressors, these corals had low levels of partial mortality (8%), few completely dead colonies were observed (0.4%), and they were the predominant species colonizing dead skeletal surfaces of other corals as well as reef substrates.

The original size of M. annularis (complex) colonies was significantly larger (58 cm diameter) than all other species, although many had been reduced in size due to partial mortality and skeletal surfaces of colonies often contained numerous smaller tissue remnants. These corals were being affected to the greatest degree by coral diseases (white plague, yellow band disease, black band disease, dark spots disease) and other biotic stressors, including competition and overgrowth by sponges, encrusting gorgonians, hydrozoan corals and a tunicate, predation by snails and parrotfish, and damselfish algal lawns. Colonies of M. annularis (complex) were missing on average 30% of their tissue, although the largest corals (mean size =61 cm; about 50% of all colonies) exhibited significantly higher amounts of partial mortality (mean loss=50%) than smaller (mean=41 cm) corals (mean tissue loss=11%). The extent of partial mortality, large numbers of completely dead colonies (4.5% of 1602 examined corals), ongoing stressors that continue to plague this taxa, and absence of colonies less than 10 cm in diameter (indicative of a lack of recruitment success) is of serious concern for these reefs, as these are the dominant frame-builders and characteristically the longest lived corals in the western Atlantic. The better overall health and high levels of recruitment observed in other taxa, in combination with recent declines in M. annularis complex, may indicate these reefs are undergoing a shift in species assemblages, with communities being replaced by smaller, shorter lived corals.

Fish communities on Bonaire were relatively high in diversity, with a dominance by herbivores (especially parrotfishes and damselfishes). Many species of important predatory fishes were present, including the dominant western Atlantic species of snapper, grouper, jacks and grunts, although these predatory fishes may be declining as the size structure was dominated by small and medium-sized fish. In particular, grouper over 30 cm total length were very rare. Large- sized groupers are the most important members of the family, as these species change sex (large individuals are females) and the larger fish produce an exponentially higher number of offspring.

In general, Bonaire’s reefs show signs of high resilience and a good ability to recover from acute disturbances. Reefs had high coral cover, low levels of disease, high levels of recruitment, and low amounts of fleshy macroalgae. There are minor problems that need to be addressed through management actions and conservation strategies. This could include 1) a program to eradicate lionfish before their numbers get out of control (these species were seen, but they appear to be rare as compared to other Caribbean Islands); 2) community-based efforts to remove an encrusting tunicate, coral-eating snails, and three-spot damselfish; 3) a nursery/restoration program to propagate A. cervicornis and A. palmata and reintroduce these corals into their former habitat; 4) steps to increase the abundance of herbivorous sea urchin (Diadema antillarum) populations; 5) elimination of fishing on herbivores (parrotfish caught along the shoreline using handlines) and top predators (groupers); and 6) better sewage treatment and other strategies to reduce run-off and nutrient input from hotels located along the coastline. 

Date
2010
Data type
Research report
Theme
Research and monitoring
Geographic location
Bonaire

Scuba diver behaviour and the management of diving impacts on coral reefs

Coral reefs worldwide are attracting increasing numbers of scuba divers, leading to growing concern about damage. There is now a need to manage diver behaviour closely, especially as many dive companies offer unlimited, unsupervised day and night diving from shore. We observed 353 divers in St. Lucia and noted all their contacts with the reef during entire dives to quantify rates of damage and seek ways of reducing it. Divers using a camera caused significantly more contacts with the reef than did those without cameras (mean 0.4 versus 0.1 contacts min-1), as did shore versus boat dives (mean 0.5 versus 0.2 contacts min-1) and night versus day dives (mean 1.0 versus 0.4 contacts min-1). We tested the effect of a one-sentence inclusion in a regular dive briefing given by local staff that asked divers to avoid touching the reef. We also examined the effect of dive leader intervention on rates of diver contact with the reef. Briefing alone had no effect on diver contact rates, or on the probability of a diver breaking living substrate. However, dive leader intervention when a diver was seen to touch the reef reduced mean contact rates from 0.3 to 0.1 contacts min-1 for both shore and boat dives, and from 0.2 to 0.1 contacts min-1 for boat dives. Given that briefings alone are insufficient to reduce diver damage, we suggest that divers need close supervision, and that dive leaders must manage diver behaviour in situ.

Date
2004
Data type
Scientific article
Theme
Research and monitoring

Synthesis of coral reef health indicators for the Western Atlantic: Results of the AGRRA program (1997-2000)

Abstract:

The Atlantic and Gulf Rapid Reef Assessment (AGRRA) sampling strategy is designed to collect both descriptive and quantitative information for a large number of reef vitality indicators over large spatial scales. AGRRA assessments conducted between 1998 and 2000 across a spectrum of western Atlantic reefs with different histories of disturbance, environmental conditions, and fishing pressure were examined to reveal means and variances for 15 indicators. Twenty surveys were compiled into a database containing a total of 302 benthic sites (249 deep, 53 shallow), 2,337 benthic transects, 14,000 quadrats, 22,553 stony corals. Seventeen surveys contained comparable fish data for a total of 247 fish sites (206 deep, 41 shallow), 2,488 fish transects, and 71,102 fishes. Shallow (≤ 5 m) reefs were dominated by A. palmata, a good proportion of which was standing dead, while deep (>5m) reefs were nearly always dominated by the Montastraea annularis species complex. Fish communities were dominated by acanthurids and scarids with seranids making up less than 1% of the fish seen on shallow reefs and 4% on deep reefs.

AGRRA benthic and fish indicators on deep reefs showed the highest variation at the smallest spatial scale (~<0.1 km), with recent mortality and macroalgal canopy height displaying the largest area and subregional scale (~1-100 km) variation. A mean live coral cover of 26% for the 20 survey areas was determined for the deep sites. Significant bleaching and disease-induced mortality of stony corals associated with the 1998 (El Niño-Southern Oscillation) ENSO event were most apparent in the western Caribbean and Bahamas subregions and the Montastraea annularis complex was the most heavily impacted.

The overall low number of sightings for larger-bodied groupers and snappers (~< 1/100 m2) as a whole suggest that the entire region is overfished for many of these more heavily targeted species. More remote reefs showed as much evidence of reef degradation as reefs more proximal to human coastal development. Characterizing present-day reef condition across the region is a complex problem since there are likely multiple sources of stress operating over several spatial and temporal scales. Not withstanding the many limitations of this analysis, the value of making multiple observations across multiple spatial scales that can approximate the “normal” state for the region today is still very high. 

Date
2003
Data type
Scientific article
Theme
Research and monitoring
Author

Functional Valuation of Ecosystem Services on Bonaire

Abstract:

My thesis research builds on the ‘movement’ to value nature. This movement as I call it started as early as 1970 with a theory to quantify and monetize nature (Hueting, 1970). References to the concept of ecosystem services date back to the mid 1960s and early 1970s (de Groot et al., 2002). A Phd research into the value of nature by De Groot (1992) emphasized the need to “ecologize” economic valuation of ecosystem services by integrating ecological information.

In 2005 the Millenium Ecosystem Assessment (MEA) report used the ecosystem services approach to highlight the importance and drivers of changes of ecosystem service delivery (MEA, 2005). The Economics of Ecosystem services and Biodiversity (TEEB) platform built on the framework of MEA, but specified ecosystems in underlying functions, processes and structures to “ecologize” economic benefits of biodiversity and costs of biodiversity losses (TEEB, 2010a).

Valuation of ecosystem services can be done at three levels, monetary, quantitative and qualitative. Qualitative describes benefits in a non-numerical scale, quantitative measures benefits and changes based on numerical data and monetary builds on quantitative value and attaches a monetary value (White et al., 2011). This research is a semi-quantitative analysis of the functional value of coral reef habitats on Bonaire to support ecosystem services. It is part of an economic valuation study of marine and terrestrial ecosystem services on Bonaire. The economic valuation study estimated a monetary value of selected ecosystem services. My research measured the functional value, defined as the ecological importance of a habitat, on an ordinal scale with four levels (0-3).

The TEEB theoretical framework was applied by studying the underlying ecological functions, processes and structures of coral reefs that determine the capacity to deliver coral reef ecosystem services through a literature review. The functional group approach was used as a measure of the importance of habitats based on the level of representation of fish and coral functional groups. The methodology to analyze the functional value was inspired by a study of Harborne (2006) that established the functional value of Caribbean coral reef, seagrass and mangrove habitats to ecosystem processes.

My research applied this method using Bonaire as case study and adapted the method to determine the functional value of habitats to ecosystem services instead of ecosystem processes. This way the study of Harborne has been taken a step further by making the link between the economic analysis focussing on ecosystem services and the ecological analysis focussing on ecosystem functioning. The other adaptations made were the spatial scale, the habitat types and the data collection method. Harborne determined the value by doing a meta-analysis of empirical literature on processes in ten coral reef, seagrass and mangrove habitat types.

For my research primary data of fish and benthic functional groups were collected at over hundred locations along the entire leeward coast of Bonaire to value just two coral reef habitat types.

Outcome of this research are matrices presenting relationships between socio-economic services and ecological functions, processes and fish and benthic species representing a functional role. Another outcome are maps presenting the functional value of each location to support twelve ecosystem services based on the primary data collected. These maps were analyzed taking into account resource use on Bonaire and show which area are of high importance for each service.

This research is innovative in its attempt to link the economic value of ecosystem services with an ecological value of habitats to support these ecosystem services. In addition the survey of benthic cover and fish biodiversity and abundance has not been done at such a large scale according to our knowledge since the mapping of Bonaire in 1985 (Van Duyl, 1985).

Date
2011
Data type
Research report
Geographic location
Bonaire