Baseline survey of anthropogenic pressures for the Lac Bay ecosystem, Bonaire

Findings:

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).

Recreational use

• 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.

Anthropogenic impacts

• 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.

Management Recommendations:

• 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.