Quantifying the state of the coral reef ecosystem in relation to biophysical benthic and pelagic indicators and biological drivers of change in the Saba National Marine Park, Dutch Caribbean

Student Report

Coral reefs are experiencing large scale degradation. Motivated by the need for regular data monitoring and for quantification of the state and change of benthic and pelagic organisms, the Global Coral Reef Monitoring Network protocol was executed on 18 dive sites in fished and unfished areas around the island of Saba in the Saba National Marine Park (SNMP) in the Dutch Caribbean from March to May 2019. Pictures of the benthos were taken and analysed with the Coral Point Count Excel extension software and fish biomass was calculated through the Bayesian length-weight-relationship. Although considerably below the Caribbean-wide average, coral cover around the island seems to be slowly recovering from past diseases and hurricane events. Coral species richness positively correlates with reef fish density and Serranidae species richness. As in other parts of the Caribbean, macroalgae in the SNMP are rapidly spreading and increasingly compete for space with habitat-providing gorgonians, sponges and other benthic organisms. In contrast to expectations, fish density and biomass continue to increase, even in zones where fishing is allowed. This might be explained by the higher availability of macroalgae that serve as food for various herbivorous fish species, which in turn are, amongst others, the prey of predatory fish and those higher up in the trophic cascade. However, with the exception of the commercially important fish family Lutjanidae all key fish species have declined in average size in recent years. Another finding is the increase of coral diseases. The results indicate the need for further species-specific research in order to identify the factors that are causing the degradation of the reefs in the SNMP. A better understanding of the interactions, ecological roles and functions of benthic and fish communities is therefore essential for the protection of reefs, that are of high value to Saba. The results of this study contribute to the adaptive management of the Saba Conservation Foundation that manages the SNMP. Keywords: GCRMN, Reef Health Index, marine protected area, fish-benthos interaction, macroalgae, herbivory, trophic cascade, fishing, coral disease, Caribbean