In this study I assessed the extent of sedimentation and contamination by human enteric bacteria Enterococci on the reefs of Bonaire, Netherlands Antilles as well as the relationship of these factors to the prevalence of coral disease and bleaching. Largely the effects of sedimentation and enteric bacteria from wastewater run-off in Bonaire have been relatively unknown. Because of the lack of wastewater treatment in Bonaire, runoff contamination by sewage and nutrient fluxes is common. Assessment sites for this study were chosen based on the intensity of nearby anthropogenic activity. These sites were defined as “More Impacted” (MI, n=2) and “Less Impacted” (LI, n=2). Water and sediment samples were acquired at 12 m on a weekly basis for the assessment of enterococcal concentration using the Enterolert™ fluorescing substrate system and determination of sediment particle size distributions. In addition, the frequency of coral disease and extent of coral bleaching were assessed using Coral Point Count software on data acquired along two 10 m video transect lines laid at 12m for each site over 4 weeks. Overall sediment particle size analysis yielded statistically significant differences between LI and MI particle size distributions, with more fine grained sediments at MI sites and more coarse grained sediments at LI sites. Finer grains suggest greater human impact. Enteric bacteria were found at several sites over time and their concentrations show a positive correlation between human presence and higher bacteria counts. Bleaching and disease did not show any correlation with sediment particle sizes or presence of enteric bacteria.
Anthropogenically induced stressors are degrading coral reefs globally. Nutrients and bacteria present in wastewater increase the frequency and severity of coral disease. As a result of the lack of sewage treatment and poor sewage containment in Bonaire, N.A., the surrounding coastal marine environment is likely the endpoint of sewage-contaminated groundwater, especially near resort areas where water use is high and only a small portion of sewage is trucked away. This study compared the frequency of coral disease at three sites adjacent to resorts (with >100 beds) with three sites in the same region of the leeward coast that are not adjacent to resorts. Because areas where groundwater is entering the near-shore environment have not been identified; physical parameters of the seawater (temperature, specific conductivity, dissolved oxygen, and pH) at the six sites were measured using a YSI multiparameter probe held directly above the substrate in areas 100 m wide along depths of 3, 6, 9, 12, and 18 m. To detect the presence of enterococci, a fecal indicator bacteria, six water samples were collected at 3, 9, and 18 m isobaths, 0.5 m below the surface and above the substrate. Additionally, water samples were collected twice at 3, 6, 9, 12, and 18 m to determine ammonia concentrations at each site. To determine the frequencies of disease in hard coral (≥20 cm) and soft corals (sea fans, sea rods, sea plumes), three 10 x 1 m transects were surveyed at 3, 6, 9, and 18 m at all sites. The relationship between depth and specific conductivity, temperature, dissolved oxygen, and pH were similar for all sites except 18th Palm. Significantly higher concentrations of ammonia were found at resort sites (p=0.016). Enterococci was detected at the three resort sites in greater concentrations than at non-resort sites. Disease in hard and soft corals did not differ between site types. This study suggests that coral reefs adjacent to resorts have greater concentrations of ammonia and enterococci, common wastewater indicators. Although the frequencies of soft and hard coral disease were not significant between sites, the abundance of hard corals was significantly lower at resort than at nonresort sites (p=0.010). Soft corals were less abundant at resort sites than at non-resort sites, but the difference was not statistically significant (p=0.059).
This student research was retrieved from Physis: Journal of Marine Science VII (Spring 2010)19: 1-11 from CIEE Bonaire.
The main conclusion from this study is that at the moment tourists and locals use Lac Bay and its catchment area at levels and in ways that are not sustainable.
- Recreational use is concentrated on and around the Sorobon Peninsula. The major activities are beach and sports-related (sunbathing and windsurfing). The main water based activities are windsurfing and swimming/wading.
- The social carrying capacity for the present kind of visitor and present kind of usage begins to become an issue around 250 beach visitors. Average visitor numbers on cruise days is 359 (highest is 760) and on weekends is 260.
- There is a large difference in visitor numbers between cruise days and non- cruise days, with cruise days having the highest.
- Awareness of Lac Bay’s regulations and zoning plan is low, resulting in certain activities taking place in sensitive zones.
- Fresh water surface-flow to the bay is affected by approximately 54 dams or more, and groundwater flow by many (uncounted) wells
- 213 kunukus (farms on Bonaire) are present in Lac Bay and its catchment area.
Livestock densities within the natural areas surrounding Lac Bay are not sustainable. They exceed the ecological carrying capacity of the area.
- Develop and implement a set of measures that can be used to preserve and enhance the Lac visitor experience in accordance with social carrying capacity.
- Develop sunbathing and water sport possibilities elsewhere on Bonaire to distribute user densities from Lac Bay.
- Develop and implement a set of measures that can be used to preserve and enhance the natural values of Lac Bay.
- Improve the implementation of the zoning plan.
- Organize several facilities at Sorobon more properly.
- Create a visitor centre at Sorobon.
- Reduce livestock densities in the Lac Bay catchment area.
Key recommendations for further study:
- Research on up to what extend tourists facilities are contributing to the eutrophication at Lac.
- Research on the effect of sunscreen on coral bleaching at Lac.
- Further research to obtain a clear overview of land use in Lac’s catchment area.
The main conclusion from this study is that the combined levels of anthropogenic impact on the bay currently exceed sustainable levels. Lac Bay is experiencing a long-term decline in productive habitat area all the while non-sustainable grazing of vegetation, eutrophication, seagrass trampling and high levels of litter contamination have been documented.
Lac catchment area
- The Lac catchment area was mapped using satellite imagery combined with field verification and gave a preliminary estimated size of about 22.6 km2 of surrounding lands. This area consists of a mix of semi- natural deciduous and dry-evergreen vegetation types and at least 213 small part-time farms.
- There are at least 52 dams that obstruct or retard water flow and many wells from which groundwater can be or is being extracted.
- Extensive livestock husbandry (goat and sheep) occurs at densities higher than 1 animal per hectare. Such densities well exceed densities that permit ecological recovery (0.1 animal per hectare).
- The Lac lagoon is intensively used for recreation. From 9 in the morning to 4:30 pm practically every day anywhere from 100 - 400 people are present on or along the shorelines of the bay at any given moment. Highest numbers occur during cruise ship days.
- The majority of recreational use of Lac is concentrated on and around the Sorobon Peninsula.
- The major recreational activities at Lac are sunbathing, windsurfing and swimming or wading. Little current use is directed towards nature activities
- Usage patterns and awareness differ importantly between the four different user-categories of cruise tourists, stay-over tourists, foreign residents and inhabitants born on Bonaire.
- The inner borders of the seagrass exclosures display much bare space due to trampling.
- As there is no sewage treatment and as the available toilets and cesspits are generally defunct, beach visitation definitely result in nutrient enrichment in the waters of the bay
- Beach litter contamination is a matter of concern along mangrove shores at entrance of the bay and the lagoon-bottom immediately off the public beach of Sorobon.
- High levels of uses pose issues of disturbance for birds and sea turtles.
- Additional problems are the rapid invasion of the exotic seagrass, Halophila stipulacea and a bloom of an encrusting (possibly invasive) calcareous alga (Ramicrusta sp.) that is smothering live corals at the seaward side of the bay.
- Develop sunbathing and water sport possibilities elsewhere on Bonaire to distribute user densities away from Lac.
- Upgrade user facilities and infrastructure at Lac. These include toilets and septic system, garbage disposal, organized parking, shade, signage and markers for the various management zones.
- Implement a Visitor Centre to provide visitor service (products and added value-information) and enforcement.
- Reduce grazer densities in the watershed and/or around the bay.
- Discourage/prohibit the use of throw-away food and beverage packaging at Lac and participate actively in the regional Marine Litter Action Plan developed by UNEP.
- Design a boom system to herd and trap contaminants entering Lac before they penetrate the mangrove fringes.
- Organize regular beach clean-ups in Lac.
Research to address knowledge gaps
- Further map and quantify anthropogenic effects in the watershed area (pollution, water diversion and extraction, forestation, grazing, farming, erosion) and their effects on Lac (in terms of sedimentation, reduced freshwater influx, nutrient loading).
- Document traffic levels on Kaminda di Sorobon and its effects in terms of disturbance, road-kills and littering.
- Study the concentration and effects of litter-derived contaminants on the environment and biota of the bay.
- Study the distribution and habitat selection of sea turtles in the bay as related to diet, food availability, water temperature, disturbance and other factors.
- Study the use of more and/or larger exclosures to improve seagrass coverage in the Sorobon area.
Doel en achtergrond werkbezoek
Sinds 10 oktober 2010 maken Bonaire, Sint Eustatius en Saba deel uit van Nederland. Rijkswaterstaat heeft wettelijke verantwoordelijkheden voor deze eilanden. Hieronder valt het opzetten van een operationele maritieme incidentenorganisatie. Gezien de enorme olie-overlagbedrijven op Sint Eustatius en Bonaire, de economische afhankelijkheid van de eilanden van duik toerisme en gezien de biodiversiteit in (de zeeën rond) Caribisch Nederland is dit geen overbodige luxe. RWS Noordzee zet de incidentenorganisatie op. De landelijke coördinatiecommissie milieuincidenten (LCM) ondersteunt hierbij. Doel van de reis naar Caraïbisch Nederland (CN) was om te komen tot een advies over de olie-bestrijdingsmogelijkheden, waaronder mechanisch opruimen en het gebruik van detergenten.
Bij oliebestrijding is de keuze voor de wijze van bestrijding belangrijk. Het standaard uitgangspunt van de oliebestrijding is het verwijderen van de gemorste olie uit het milieu (mechanisch opruimen). Gedurende de reis is geïnventariseerd welke middelen beschikbaar zijn en wat noodzakelijk is om de opruimcapaciteit op het afgesproken niveau te brengen (tier 1, 16 m3).
Er zijn situaties waarbij de inzet van detergenten kwetsbare kustzones kan beschermen. Om het gebruik van detergenten te ondersteunen is een beslisboom detergenten beschikbaar. Voor het Caraïbisch beheergebied moet deze beslisboom worden aangepast. Voor het toepassen van detergenten is het van belang inzicht te hebben in de verspreiding van olie op zee. In Europees Nederland wordt gebruik gemaakt van het operationele model oilmap. Voor CN is het van belang dat dit model ook ingezet kan worden.
Het advies is gericht op het beperken van de belangrijkste risico’s en op maatregelen die op korte termijn gerealiseerd kunnen worden.