Lac Bay, Bonaire is the most important mangrove and seagrass area of Bonaire and has been undergoing steady ecological decline in the last decades. Based on an initial assessment of conservation management issue and potential solutions, as, conducted by IMARES in June 2010, the Dutch Ministry of Agriculture, Nature and Food Quality (LNV) asked IMARES to return to Bonaire to work with Stinapa Bonaire to choose narrower priorities and jointly make a short-list of topics as a working document for cooperation and action. In the beginning of September, site visits and discussions were held in Bonaire with the manager of Lac Bay and various stakeholders to identify and agree on priority issues for action. This working report gives the results of that visit.
Four action spear point projects were identified, based on urgency and feasibility based on local Bonaire and Dutch IMARES expertise. The projects are as follows:
1. Mangrove restoration demonstration pilot study
The basic objective is to reestablish water depth and tidal connection in high marsh salt areas that have resulted from infilling with sediment, and restore them as effective mangrove and low marsh fish nursery habitats. By collecting baseline data before the restoration activities take place, it will be possible to monitor and compare and assess changes in fauna and flora at the restoration sites and hence evaluate the effectiveness of the measures implemented.
2. Baseline ecological study of the zonation of aquatic communities
The goal is to complete a scientific description of Lac’s aquatic community zonation as it exists at landscape level today. This will provide the framework against which large-scale community change and effectiveness of mitigation measures can be monitored and evaluated.
3. Recreational and land use survey for Lac Bay and its catchment area
The goal is to identify user problems and potential solutions by mapping and assessing user density and pressures in Lac
4. Study of avifaunal habitat use of Lac Bay
The goal is to identify bird habitat use problems and potential solutions by assessing habitat use of Lac by birds during the migratory season.
(A fifth project for implementation by Stinapa and Dienst LVV was identified)
5. Lac mangrove channel clearing project
Re-establish water flow from the Bakuna dam to Lac using a pipe system.
The Lac mangrove channel clearing project of Stinapa was reviewed and judged to be valuable and important. The baseline study of zonation of aquatic communities (project 2) is urgently needed in this respect to allow short and long-term evaluation of this project which need to become a structural part of Lac Bay management. Routine mangrove channel maintenance was identified as ideal work for involvement of Bonaire youths and volunteers, to rekindle public involvement in caring for Lac and its rich natural and cultural-historical heritage.
A project plan is presented by which all four projects can be delivered by December 2012. These projects can count on government and broad community support. In this all, Stinapa indicated to be willing to provide basic free lodging to interns and scientists at their science accommodations at the entrance of Washington-Slagbaai National Park. The ability and willingness of IMARES to recruit and guide students and interns for these projects was an important selection criterion to help restrain total project costs. The action spear points will, nevertheless, require funding as well as permits from the Island Government of Bonaire. With LNV various funding options were reviewed and discussed, and the need for permits was discussed with DROB (Dienst Ruimtelijke Ontwikkeling en Beheer) Bonaire. DROB envisioned few problems with the required permits. The visit was concluded by the joint resolve to work out ways to maintain momentum and proceed towards the implementation phase.
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.
A semi-detailed landscape-based vegetation map (scale: 1: 37,500) based on field data from 1999 has been available as an update of Stoffers’ 1956 map of the Lesser Antillean island of St. Eustatius, Netherlands Caribbean, but up to now was never finalized or published. In this report we complete the documentation of that map to provide new insights into vegetation change over a period of more than 40 years, and a quantitative reference point for future studies on landscape-level vegetation development for the island.
The principal lower sections of the 21 km2 island of St. Eustatius possess a tropical savannah climate according to the Köppen (1931) classification system, and the documented flora of the island amounts to 505 species. Color aerial photographs (1: 8,000) taken in 1991 and field data from 1999 were used to produce the map. A total of 84 vegetation sample plots were analysed using a stratified random sampling design and TWINSPAN cluster analysis.
Four main and 16 sub-landscape types were distinguished based on geology, geomorphology and different mixes and expressions of the component vegetation types. The five principal landscape types are in descending order of importance: H1, H2, M4, M9 and C, and covered some 67 % of the seminatural habitat of the island. H1 and H2 are the Pisonia-Justicia hills and Pisonia-Bothriochloa hills and are limited to The Mountains area. Analysis of the sampling data resulted in the distinction of 13 (semi)natural vegetation types. The three principal vegetation types were, the Pisonia-Justicia type, Pisonia-Ayenia type and Bothriochloa-Bouteloua type which together accounted for 38 % of total (semi)natural vegetation cover. The following well-developed vegetation types of St. Eustatius represent primary climax communities: Types 1, 2, 3, 5 and 7, all found in and around the Quill in the southwestern part of the island. A comparison of the vegetation types in the present study with those of Stoffers (1956) showed that only one vegetation type closely resembles one in Stoffers’ study. Major changes have taken place in certain types of the natural vegetation of the island in the intervening five decades.
The majority of the central sections of the island around Oranjestad the so-named “Cultuurvlakte”, amounting to approximately 25 % of the surface of the island, have suffered intensive disturbance due to past agriculture, livestock husbandry and invasive species and were not mapped. Only a small remnant portion of the semi-natural lowlands vegetation (L1 and L2) was left in the coastal reaches of Billy’s Gut. Nevertheless, this area is heavily affected by grazing and the invasive vine Antigonon leptopus.
A comparison with the 1950s vegetation map by Stoffers shows that the rarest and most valuable elfin woodland vegetation of the rim of the Quill crater had been largely lost and that the areas he described as “Montane thickets” (Type 2) had declined and been degraded. We speculate that these losses may be most directly attributable to the impact of recent hurricanes and/or grazing by introduced livestock. On the lower slopes of the Quill, several areas mapped by Stoffers as farmland had been abandoned and have evidently regenerated into mixed deciduous and evergreen thorny woodlands.
The vegetation of the Mountains area showed some recovery since the 1950s. There were more evergreen bushes, and less Acacia and Leucaena than Stoffers described. The vegetation Stoffers described for the lowlands had more Acacia than we found but the invasive Antigonon has since dramatically increased as a ubiquitous and often dominant species. The former importance of Opuntia prickly pear cacti in disturbed vegetations has dramatically declined since the 1950s. We ascribe this to the likely effect of the invasive parasitic insect Cactoblastis cactorum. In the 1980s and 1990s many Opuntia cacti were seen affected by this insect (G. Lopes, pers. comm.).
Our field data show that all wilderness areas of St. Eustatius remained heavily affected by grazers. This reduces the resilience of natural vegetations and interferes with natural succession by imparting heavy losses to hardwood seedlings and saplings (see e.g. Melendez-Ackerman et al. 2008), by reducing plant biomass (which increases exposure to wind and sun), and by favoring hardy invasive plant species. In Curaçao, large scale reduction in densities of feral grazers in the Christoffelpark since 1993 has led to rapid recovery of several rare plant species and vegetation types. The problem of feral livestock remains severe. Therefore the number one priority for terrestrial conservation in St. Eustatius will be to reduce feral grazer densities and impacts in key wilderness areas.
Parts of the natural areas of both The Mountains and the Quill are protected by law, but goats and other roaming livestock are omnipresent in all habitats and continue to have evident impacts on the vegetation. Aside from generally reducing the resilience of the vegetation to major disturbance, intensive impact in the herbaceous layers likely affects regeneration of rare hardwood species directly through selective predation and indirectly by overall desiccation and increased exposure to the elements. Goats have a broad diet in the region and species eaten include canopy, mid-canopy and understory species (Melendez-Ackerman et al. 2008). Vegetation degradation further also affects the competitive balance towards (unpalatable) invasive species such as Antigonon leptopus, Pedilanthus tithymaloides, and Leucaena leucocephala, which have expanded massively into natural habitat in the last 50 years. Not only is general vegetation degradation suggested as a problem to endangered breeding seabirds, but goats likely also directly trample nesting burrows of seabirds (Collier & Brown 2009).
Consequently, priorities for nature conservation are to:
- Reduce grazer densities in all areas,
- Protect the most sensitive vegetations using total grazer exclusion, and
- Experiment with methods to spur vegetation recovery, including erosion control, propagation of rare and endangered species and reforestation with indigenous species
- Establish permanent plots in areas with the most sensitive vegetations in order to better understand causal factors of short- and longer term changes.
This report is part of the Wageningen University BO research program (BO-11-011.05-004) and has been financed by the Ministry of Economic Affairs, Agriculture and Innovation (EL&I) under project number 4308202004.
The endangered Lesser Antillean Iguana, Iguana delicatissima, is an emblematic species for the island of St. Eustatius and in Caribbean Netherlands it is only found on St. Eustatius. In this study we conducted an extensive population survey for the iguana and compared densities in different areas to densities documented most recently in 2004. We conducted 39 field surveys and spent a total of 80 hours and 21 minutes searching for iguanas. We covered 63,672 m of trails and tracks and found only 22 iguanas. An overall average of 3.70 hours were searched for each iguana found. Due to the low encounter rates, detailed estimation and comparison of population densities remain problematic. Overall population density was 0.35 iguanas per hectare which represents 0.5-1% of densities documented elsewhere in healthy populations. Current population densities have declined across all habitats since the 2004 survey. Iguana encounter rates and densities in natural habitat were highest for the region where the northern hills abut onto the central plain. Island-wide, those areas provide the best combination of sun, shelter, food and potential for nesting sites. The population of the Lower Town sector, indicated in 2004 as the most dense and promising subpopulation, has all but disappeared. Island-wide, the residential estate subdivisions remains the second-most important area for the iguana.
We conclude that even though several valuable conservation measures are in place (e.g. establishment of legally protected parks, designation as a legally protected species and a successfully-run awareness campaign), the status of the iguana has not improved significantly in the last 8 years. Our results show that compared to 2004 when the population was estimated to number 425 (275-650) animals, current population size certainly lies on the low side of this range. This is far below the required minimum viable population size of 5000 animals and means that the iguana is critically endangered on St. Eustatius. It is readily vulnerable to extirpation on the island. Human hunting is likely a minor problem, shelter and food availability on the island are abundant, and invasive predator densities in the wild are relatively low. Of the 28 documented instances of death or endangerment of iguanas during the study period, most were attributable to anthropogenic causes. Suitable nesting sites for the iguana appear very limited, especially due to a combination of geology and vegetation. Therefore, lack of nesting sites and high iguana mortalities due to anthropogenic causes are suggested as the two core factors limiting recovery of the iguana on St. Eustatius .
The following management measures are proposed:
1. Protect current populations by:
- Prevention of introduction of invasive species
(Train and equip border officials to prevent potential entry of the mongoose and the Green Iguana from neighbouring islands),
- Enforcement and upgrading of legal protection
(Implement enforcement and upgrade protective legislation),
- Development and protection of additional nesting sites
(Develop and maintain new additional nesting habitat, a measure that is both easy and inexpensive),
- Establishment of an “iguana-friendly yard” programme
(Establish a programme to promote “iguana-friendly” gardens, as the main means of reducing cumulative mortality).
2. Increase the biological knowledge about the iguana by conducting studies for a better knowledge of the critical biological parameters,
3. Create public awareness for the plight of the species,
4. Establish a small, local husbandry project.
(Development of an in situ husbandry and breeding project could serve a pivotal role in bolstering the other core program themes and especially offers a relaxed setting in which islanders can experience the iguana as the gentle and beautiful animal that it is).
This report is part of the Wageningen University BO research program (BO-11-011.05-004) and was financed by the Ministry of Economic Affairs, Agriculture and Innovation (EL&I) under project number 4308701004.
Based on the goals set forth in the Dutch Biodiversity Policy Programme, The Netherlands has a traditionally strong commitment to protect biodiversity and marine mammals both internationally and in its own national and Kingdom waters. Last year the responsible ministry, namely the Netherlands Ministry of Economic Affairs, Agriculture and Innovation (EL&I), developed a management plan for the biological resources of the recently declared Dutch Caribbean Exclusive Economic Zone. The Dutch Caribbean EEZ was formally declared on June 10, 2010, and amounts to more than 90,000 km2 of diverse tropical marine habitats. One of the key ambition coming forth from that plan was to develop a Dutch Caribbean Marine Mammal Sanctuary (MMS). This report provides the necessary review and background on which to base such an endeavour.
Our updated review establishes beyond doubt that the Dutch Caribbean EEZ has a rich and diverse marine mammal fauna which merits more extensive protection. Even though the fauna is only poorly known, based almost exclusively on incidental sightings and strandings, it amounts to a minimum of 19 marine mammal species, and possibly up to more than 30. Without exception, all documented species appear on protected species lists of one or more treaties ratified by the Kingdom, and/or its constituent countries. Large differences are apparent between the leeward and windward sectors of the Dutch Caribbean EEZ, both in terms of species composition and conservation issues. Throughout the region, cetaceans are playing an increasingly important role in island economies as an important natural attraction for eco-based recreation and tourism, and in this respect the Dutch Caribbean also possesses major potential.
We here propose the establishment of a MMS as the cornerstone to sustainable conservation and management of these charismatic animals. Ecological arguments for the establishment of habitat protection by means of the concept of sanctuaries are outlined, as are the many environmental issues that would eventually need to be addressed within the sanctuary.
Favourable pre-conditions for the establishment of a MMS in the Dutch Caribbean include the fact that
- a) all cetaceans are already have a legal status in the Dutch Caribbean EEZ which calls for actual protection,
- b) the most deleterious fishing practices are already significantly limited and controlled within Kingdom waters,
- c) the key enforcer, namely the Coastguard, is already strongly present (largely due to other reasons),
- d) the islands generally have a strong tradition of marine protected areas in coastal habitat,
- e) the incremental costs for research and enforcement needed to establish a sanctuary is modest,
- f) public support is high, thanks to the generally high level of development and awareness of the public,
- g) indigenous fishery practices do not conflict with cetacean conservation, and
- h) whale watching interests are only in their infancy.
Steps to establish a Marine Mammal Sanctuary (MMS) should include:
- Legal designation of the sanctuary is the first and most important step that provides the framework for all broader (international cooperation) and in-depth (knowledge and conservation development) initiatives.
- Once established, the fuller implementation of an MMS should be seen as a gradual process, involving development of knowledge, policy, rules and regulations, as well as public and stakeholder participation
The following key action points are proposed to establish a Marine Mammal Sanctuary:
- a) Legal designation of the EEZ (one or both sectors) as MMS, along with establishment of legal guidelines for interacting with cetaceans (whale watching).
- b) Establish bonds of cooperation with sister sanctuaries in the region (France, USA, Dominican Republic), (e.g. regional stranding and sightings data network).
- c) Conduct baseline quantitative surveys of cetacean distribution and assessments in light of sources of deleterious sound sources and risks of vessel strikes.
- d) Review and adapt existing national and insular legal frameworks to improve these, preferably by developing separate and standardized marine mammals legislation.
- e) Develop information systems to promote the development of a whale (cetacean) watching industry.
- f) Train and equip marine parks and island veterinarians to conduct elementary autopsies and collect basic stranding specimens for analysis of causes of mortality, contamination levels and genetics, and link them to international academic institutions who will accept and analyse the specimens in regional context.
- g) Develop species action plans (e.g. humpback).
- h) Conduct cetacean surveys and management reviews every 5 years to assess marine mammal status and conservation progress.
The marine exotic species of the Dutch Caribbean are less well-known than its terrestrial exotics. So far, only 27 known or suspected marine exotic species, some of which are also invasive are documented for one or more islands of the Dutch Caribbean. Four of these were documented only once or were only present for a certain period of time and are no longer present. Six of the species are marine epidemic diseases. As very little is known about these diseases, they might actually be native, but based on the literature and their ecological signature we regard them as special cases of invasive species.
In addition to these documented species, 76 other exotic species that have already been observed elsewhere in the Caribbean may already be present or can be expected to arrive in the Dutch Caribbean in the near future. The marine communities of the Dutch Caribbean have suffered major changes based on a handful of marine exotic and/or invasive species, particularly in the special case of (opportunistic) pathogens. In certain cases experience shows that after decades, the affected systems/species may show slow signs of recovery from initial impacts (e.g. the green turtle fibropapillomas), while in other cases the impact may be long-lasting and recovery doubtful (e.g. sea fan mortality).
Compared to terrestrial exotic species, eradication and control have been proven difficult or impossible for marine exotics. Therefore, management practices aimed at controlling unwanted species introductions should focus on preventing the arrival of such species by ships-- that transport exotics in their ballast water or as fouling communities on their hulls-- and (accidental) introductions from aquaculture or the aquarium trade. Busy harbors can be expected to be the areas where most marine exotics likely establish first.
Because of dispersal of marine exotics is facilitated by ocean currents, local approaches to prevent their arrival or reduce their numbers will be less effective compared to similar efforts for terrestrial species. In the case of marine exotics and invasives, it is paramount that prevention, control and management efforts should be regionally integrated. We conclude this report by listing a number recommendations on how to develop effective management approaches with which to address the impacts and risks associated with marine exotic species.
This research is part of the Wageningen University BO research program (BO-11-011.05-004) and has been financed by the Ministry of Economic Affairs, Agriculture and Innovation (EL&I) under project number 4308202004.
While the scarcity of up-to-date data on beach litter contamination in the Caribbean has been stressed in several recent studies, we here point to the even greater paucity of published work on litter in mangroves and on the shallow tropical seafloor. During collection of baseline data on beach litter contamination on the Southeastern Caribbean island of Bonaire we also collected preliminary data that may serve to highlight the need for further studies on these largely neglected litter issues.
Marine litter contamination is a wide-spread problem and considered to be one of the most serious threats to sustainable use of the region’s marine and coastal resources. Mangrove litter and shallow submerged litter contamination figure significantly in Bonaire and we have made practical recommendations to help address these problems in a separate report to government. In presenting this synopsis here, we aim to draw scientific attention to these largely neglected facets of the litter problem and hope to see further studies to assess the extent of these problems in the Wider Caribbean.
The main conclusion of this study is that the shallow, warm and saline back-water habitat which is continuing to increase in importance within Lac Bay is unable to support meaningful mangroves, seagrass or algal meadows, nor the key nursery species. As the natural process of land reclamation by mangroves carries on, the bay’s important nursery habitats will come under additional salinity stress and likely continue to decrease in coverage and quality at an accelerated rate.
Distribution of sea grass and algal beds in Lac Bay
- The valuable seagrass and mangrove habitats of Lac are currently trapped in an enclosed bay.
- High light-intensity and well-circulated shallow habitats that fringed the mangroves of the central bay have the richest assemblages with the highest biotic coverage.
- Isolated mangrove pools have the lowest total cover, species richness and biodiversity of all habitats.
- Biotic diversity and cover decrease towards the deeper parts of the bay.
- There is an alarmingly rapid invasion of the bay by the invasive seagrass H. stipulacea.
Fish species utilization of contrasting habitats in Lac Bay
- Fish community variables differ consistently among habitats and are influenced by the percent cover of seagrass vegetation or presence of mangrove-root structure.
- Mangrove fringe habitats are a premier habitat since multiple life stages of a variety of species showed highest densities there. Mangrove fringing open waters had highest overall fish densities and species diversity.
- The various vegetated sub-habitats all play a unique role for different size-classes of different fish species.
- Management action is needed to stem further erosion of nursery habitat quality and ensure that a tipping-point is not reached beyond which recovery may be difficult or impossible.
- Measures should be taken to help restore water depth and circulation to relieve the bay’s ecosystem of thermal and salinity stress caused by the shallow backwaters. This includes excavating accumulated erosional and biogenic sediments as well as dredging to restore former feeder channels by removal of mangrove overgrowth (as already started by Stinapa).
- Further studies to assess the impacts of the invasive seagrass H. stipulacea on the bay’s flora and fauna.