Marine

Findings

Abundant coral growth within the Saba Bank is restricted mainly to the two large windward reefs. These two reefs carry a very rich reef fauna.

The rest of the Bank only has a very small growth of corals due to several factors:

• Most of the food supply is probably filtered away by the large windward reefs.
• These reefs are located at a least favorable leeward position.
• These reefs are located at a considerably greater depth.

As in most other atoll lagoons, coral growth in the lagoon area is restricted to small patch reefs; the number of species is not significantly lower than on the reef, but the colonies are smaller in size and number.

The Saba Bank undoubtedly has a volcanic base but no information on this has been collected. This study did uncover some black sand, presumably of volcanic origin, on the southwestern part of the Bank. Geologists believe that a composite volcanic island is buried under the more recent formations.

Only the eastern and largest part of the Saba Bank can be called a living atoll with an open lagoon, while the western part is a bank with drowned fringing reefs.  Whether the western part is included or not, the Saba Bank ranks among the largest atolls in the world.

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.

At St. Eustatius a project has started for the improvement and expansion of the Seaport St. Eustatius. The planned activities related to the project need to be evaluated in order to comply with the legal requirements for a licence from the competent authority Rijkswaterstaat Noordzee in the Netherlands.

A quick scan of the potential environmental impact for the planned activities regarding the St. Eustatius harbour extension was commissioned by Rijkswaterstaat Noordzee. This quick scan was performed within limited time and based upon limited background information. No additional research on site was performed. Consequently, this report provides an environmental impact assessment based only on a review of literature and expert judgement.

Within the project it is foreseen that an estimated 10.000 m3 of sediment will be dredged from the turning basin and dock in the new harbour and from the old harbour. The dredged material will be disposed of in the sheltered inner harbour and south of the breakwater. This deepening of the St. Eustatius harbour and associated activities can potentially negatively impact the environment (directly) through:

1. Destruction of habitat on the dredged site and on the site where the dredge material is deposited
2. The amount of sediment that will be dispersed into St. Eustatius coastal waters, and the cascading impact thereof on marine habitats
3. Noise in marine habitats caused by the placement of piles and moorings

The resulting deepened harbour, the disposal sites and changes in future use may cause long term (indirect) negative impact on the environment due to:

1. Dispersal of the dredge spill deposits, and thereby threatening marine habitats
2. Increased turbidity due to harbour sediment erosion, increased sediment trapping and more shipping movements
3. Changing current and wave patterns, thereby threatening key monuments of human history close to the shoreline
4. The increased risk of spills (fuel, oil, bilge water), introduction of nutrients and marine litter, and introduction of invasive species (bio pollution)

These potential impacts have been investigated in this report and have resulted in the following findings:

The tidal and residual currents around St. Eustatius are weak and estimated to be up to 20 cm/s. Near the harbour area, the residual flow is probably dominantly north. The wave height is low throughout the larger part of the year, except during hurricanes and tropical storms. From December to April cold fronts in Florida regularly generate swells from the north to northeast (“brown seas”). These events occur once or twice a month, last for a day to a week, and may generate swell waves 3 to 5 m high.

The marine substrate in the harbour area consists of a hard substratum overlying a more loosely packed conglomerate including sand and pebbles. This hard substratum consists of large rock fragments and cemented conglomerates. Removing this hard layer makes the underlying softer material available for erosion, especially since the deepened area will be exposed to the winter swells and has a water depth where the swells may break (and hence lead to high near-bed shear stresses). The risk for increased levels of suspended sediment due to erosion is probably small, but depends on the fine silt content of the sediment to be exposed. The available information does not indicate the presence of such fine material in the sediment.

During the dredging works, the sediment spill is expected to be limited. It is assumed dredging will be done during calm conditions. Some sediment will enter the water column during dredging, but due to the low ambient currents most will immediately settle from suspension. If present, silt and flocculated mud will be transported 1-2 km northward. Unflocculated mud can be expected to mix with ambient currents within days, leading to only limited increase in turbidity.

Storage of dredged material occurs in the sheltered inner harbour and south of the breakwater. Little dispersion of this sediment is expected during the dredging and storage activities partly due to the planned placement of bubble screens.

Over longer timescales, the removal of the hard layer will probably lead to higher turbidity in the harbour during storms. The winter storms are associated with southward currents, and therefore some of this sediment may be transported south of the wind breaker.

It is expected that deepening of the harbour will lead to a minor change in alongshore transport in the inner harbour, but will not affect alongshore transport north of the old harbour or south of the breakwater. The wave height near the ruins just south of the old harbour will probably increase due to deepening which may have a small effect on the coast.

Based on the above findings and expert judgement regarding sediment transport and turbidity changes the following conclusions are drawn on the potential impact on the environment:

The sediment that enters the water during dredging works is expected to settle relatively quickly, leading to limited sediment-plumes and turbidity. Therefore, no mayor or irreversible impact from dredging works is to be expected on the surrounding habitats. This is based on the assumption that fine silt is not present at the site. However, if these sediments are present, habitats up to 1-2 km north of the harbour can be affected. The impact is estimated, however, to be limited due to the low expected volumes.

Dredging works will impact living organisms at the dredged site and deposit- sites, covering a total area of approximately 1-2 ha (dredged and dredge-deposit site). Recovery is likely to occur over time if environmental conditions permit. This may take up to several years in case of removal of climax stage ecosystems such as coral reefs and seagrass habitats. 

Direct impact on marine mammals due to pile driving and placement of moorings are considered to be negligible as the migrating season has already passed and noise levels are considered to be relatively low.

During the deposition of the dredged sediment at the two locations, no impact on surrounding habitats is expected due to the minor dispersion and mitigation measures taken (bubble sheets).

Unless added measures are taken it is expected that the dredge deposit on the south side of the breakwater and south of the old harbour will erode and will be dispersed during storm conditions. The rate at which this deposit will erode, and how much that contributes to overall turbidity during the storm-event, cannot be predicted based on available information.

An adverse impact of the deposited sediment over longer timescales on surrounding habitats cannot be excluded. Erosion of the southern deposit during storm events or hurricanes is likely to occur. This means that it cannot be ruled out that an extra total volume of 7000m3 sediment can be transported towards the southern reserve during a single hurricane event, potentially smothering coral and seagrass habitats. This might lead to severe impact on some species of corals and sea grasses. A significant part of the southern reserve is covered with these species. Current species coverage and abundance is not known, and therefore impact cannot be quantified.

Besides the intrinsic ecological value of the habitats of the southern reserve, the southern reserve holds many important dive sites. The environmental quality of the southern reserve habitats is therefore of high importance to the sustainable economic development and prospects of St. Eustatius. Any risk of deterioration of the southern reserve through resuspension of the dredged material and deposition within the southern reserve should be considered with caution and necessary preventive actions should be taken.

Potential indirect impacts on historical monuments could occur as a result of slightly increased wave heights in the harbour but are expected to be minor.

Indirect impact due to more extensive use of the harbour is expected to be a risk, but hard to quantify. Maintenance dredging is not expected, and if needed, the impact due to sediment suspension will no doubt be less than that of the dredging related to this extension, thus limited (assuming calm conditions and no silt content). Risk of bio-pollution is likely. In order to assess actual impact and proper measures, monitoring should be considered. 

Preventive actions should focus on the deposited sediment in the southern corner of the breakwater and lack of information on silt and mud content. Suggestions are to:

• Retrieve information on silt, mud and chalk content in the dredging area
• Make sure sediment deposits cannot erode towards southern reserve. Proper constructions
• should be considered with the contractor and island bureau
• Halt dredging and deposit activities temporarily in case of elevated seawater temperatures
• and during rough seas (to avoid multiple stress)
• Monitor surrounding habitat quality (reefs and seagrass) over time
• Monitor future use and related pressures and mitigate as considered needed 

This document serves as a reference for the controlling and management of the invasive Indo-Pacific lionfish (Pterois miles and P. volitans complex). Lionfish are expected in St. Eustatius waters in the near future and can have serious detrimental affects to the island’s marine environment, particularly to the populations of both ecologically and economically important fish species. Coral reef ecosystems can also experience degradation due to predatory stress caused by lionfish on coral reef grazers such as parrotfish (Scaridae).

The invasive lionfish also poses a threat to public health; the species has fourteen venomous spines over the length of its body which can inflict a painful sting. Particularly vulnerable to lionfish envenomations are those stakeholders of the Marine Park who have the potential of coming in close contact with the species such as fishers and divers. Recreational beach goers also face the potential of being envenomated. Envenomations can be particularly dangerous to infants, the elderly, individuals with a compromised immune system and those sensitive to the venom.

Due to the nature of the invasion of aquatic species in general and lionfish more specifically, it must be realized that a complete eradication of the species is impossible, therefore this plan will seek to actively manage lionfish in Statia territorial waters. The goals and objectives of this management plan are to adequately control the impact the species will have on the ecosystem level and with regards to the risk it poses to the community and to the local economy. Management goals and objectives are coordinated and communicated with different agencies to ensure local and regional cooperation, education of and outreach to stakeholders, research and management option development on the nature of the infestation, and a species control mechanism which will seek to limit the effects of species arrival.

Management actions should be clear in both the management of the species on a local level and contributing species information on a regional and international level. Management actions in this plan are divided into two stages; pre species arrival and post species arrival actions. Actions within the two stages can belong to phase one management actions, which are the first actions to be implemented, or phase two actions, which follow phase 1 actions and are continuous. Some management actions belong to both phase one and phase two management actions. The proposed management actions for the controlling of lionfish in the St. Eustatius National Marine Park include education and outreach on the nature and threats of the invasion, coordination with other agencies and organizations on management options, infestation research and development such as stomach content analysis and genetic sampling, planning and assessment in the form of lionfish action protocols and lionfish sweeps, and specimen control mechanisms such as species collection and eventual culling.

Appreciation is expressed to all those who assisted with technical support regarding this Response Plan, particularly the insight gained during the Lionfish Workshop hosted by the Bonaire National Marine Park in cooperation with the Reef Environmental Education Foundation and funded by the Dutch Caribbean Nature Alliance, and various workshops given by Chris Flook of the Bermuda Museum and Zoo. 

Lionfish, Pterois volitans and P. miles, are native to the Indo-Pacific and have recently invaded the Western Atlantic Ocean. Strategies for control of this invasion have included limited removal programs and promotion of lionfish consumption at both local and commercial scales. We demonstrate that lionfish meat contains higher levels of healthy n-3 fatty acids than some frequently consumed native marine fish species. Mean lionfish fillet yield was 30.5% of the total body wet weight, a value that is similar to that of some grouper and porgy species. A sensory evaluation indicated that lionfish meet the acceptability threshold of most consumers.