The influence of terrestrial erosion on Acropora palmata occurrence on Saba, Dutch Caribbean
A high influx of sediment resulting from terrestrial erosion, imposes a major threat on coral reef ecosystems worldwide by inducing sedimentation and turbidity. Terrestrial erosion may result from both natural processes and anthropogenic activities. Healthy reefs are important for biodiversity, fisheries, stimulate tourism and provide protection for shorelines. This research examines to what extent terrestrial erosion processes influence the site conditions for elkhorn (Acropora palmata), a major reef building and critically endangered coral species, on Saba in the Dutch Caribbean. This research aims to understand the interaction between terrestrial erosion processes and marine ecosystem vitality and to highlight the relevance of inclusion of both marine and terrestrial processes in conservation and management of vulnerable marine ecosystems. By integrating the slope, soil type, land use and vegetation cover, a potential erosion intensity map was created in ArcMap 10.4.1 which shows the predicted severity of erosion on Saba. With the use of this map 16 sampling sites were selected where the presence of Acropora palmata was examined and several biotic and abiotic parameters, such as presence of wave action, temperature and the size of colonies were measured. The collected data was analysed in R studio with the use of Generalised Linear Models (GLM), Linear Models (LM) and ANOVA. It is found that when the severity of terrestrial erosion increases, the probability of elkhorn occurrence on Saba decreases. Furthermore, it is likely that erosion products entering the reefs result in colony and tissue death. In addition, an interaction was detected which indicated that the more erosion products enter the coral reef ecosystem, the larger the advantage for a colony to be elevated from its surroundings. No effect of terrestrial erosion was detected on the abundance of the species, the colony cross sections and the angle of the most dominant slope the colony had with its substrate. The workflow developed in this research can be applied by research institutes or local governments to assess the effect of terrestrial erosion on coral species in other tropical regions.