Geest, M. van der

Impact of terrestrial erosion on coral reef health at Bonaire: a plea for nature-inclusive “watershed-to-reef” based coastal management

Coral reefs are rapidly degrading worldwide, due to  a combination of global and local stressors. While gloal stressors, such as ocean warming, cannot be managed, management of local stressors can increase the resilience of coral reefs to these global stressors. One such local stressor is overgrazing- induced terrestrial erosion causing sediment and nutrient run-off to coastal waters, which is associated with coral mortality and changes in benthic community composition. In this study we assessed the link between watershed-specific erosion hazard and coral reef health, using the coral reefs on the west coast of Bonaire, Caribbean Netherlands, as a case study. We first identified watersheds, waterflow and run-off sites into the sea based on a digital elevation model. Next, for each watershed we determined the mean erosion hazard (a proxy for the degree of terrestrial run-off based on slope and ground vegetation cover). Subsequently, we used multiple regression models to investigate whether mean erosion hazard of the nearest upstream watershed, and distance to the nearest upstream run- off point explained variation in marine benthic community composition at two depth zones (~5 m and ~10 m). We found a negative relationship between mean erosion hazard and coral cover (a proxy for coral reef health) at 5 m depth, but no such effect at 10 m depth. In addition, we found a positive relationship between mean erosion hazard and sand cover (a proxy for sediment run-off) for both depth zones, and a small but significant quadratic effect of mean erosion hazard on algae cover (a proxy for nutrient run-off) at 5 m depth. Moreover, distance to the nearest upstream terrestrial run-off point was positively related with coral cover at 10 m depth, and negatively related with sand cover at 10 m depth. Our results provide direct evidence for a negative relationship between watershed-specific erosion hazard and coral reef health, and highlight the need for a nature-inclusive “watershed-to-reef” based coastal management approach that integrates terrestrial and marine conservation to preserve the island's valuable coral reef and related ecosystem services.

 

Publication referenced in BioNews 40 article "Watershed-to-Reef: New Approach for Coral Reef Management"

Date
2020
Data type
Research report
Theme
Research and monitoring
Report number
C055/20
Geographic location
Bonaire

Nexus interventions for small tropical islands: case study Bonaire. Food from the Land.

Like most small tropical islands, Bonaire is largely dependent on imported food. This results in high food prices due to import taxes andtransport costs, and high vulnerability towards price fluctuations andglobal developments, which both present major risks to food security. With many inhabitants living on or below the poverty line, low incomes translate into eating cheap unhealthy food, often causing health issues. While 25% of Bonaire’s surface consists of rural areas suitable for on- land food production, current practices of agriculture are small scale, mainly due to small domestic markets and limited access to freshwater, electricity, human capacity and know-how, while the widely used practice of extensive husbandry results in suboptimal yield and severe grazing- induced erosion issues. Sustainable development of agriculture and husbandry on Bonaire thus provides a great opportunity to increase food security, but requires a holistic (nexus) approach that accounts for the local socio-economic setting and the interlinkages between the water, food, energy and ecosystem domains, to identify trade-offs and seek for synergies among these domains. Several nexus interventions are presented that will aid sustainable development of the agricultural and livestock sector, while simultaneously contributing to water, energy, ecosystem and nutrition security. Identified key nexus interventions are: strong policy aimed at facilitation of fenced livestock keeping, water-saving agriculture, decentralized solar power, development of an agro-business and knowledge centre, and development of educational programmes on sustainable agriculture and healthy diet.

Date
2019
Data type
Research report
Geographic location
Bonaire