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
Coral reefsare experiencing large scale degradation. Motivated by the need for regular data monitoring and forquantification of the state and change of benthic and pelagic organisms,the Global Coral Reef Monitoring Networkprotocolwas executed on 18 dive sites in fished and unfished areasaround 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 andanalysed with the Coral Point Count Excel extension software and fish biomass was calculated through the Bayesian length-weight-relationship. Although considerablybelow the Caribbean-wide average, coral cover around the island seems to be slowlyrecoveringfrom past diseasesand hurricane events. Coral species richnesspositively correlates with reef fish density and Serranidae species richness. As in other parts of the Caribbean, macroalgae in the SNMP arerapidly spreadingand increasingly competefor space with habitat-providing gorgonians, sponges and other benthic organisms. Incontrast toexpectations, fish density and biomass continue to increase, evenin zones where fishing is allowed. This mightbe explained by the higher availability of macroalgae that serve as food for variousherbivorous fish species, which in turn are, amongst others, the prey of predatory fish and thosehigher up in the trophic cascade. However, with the exception ofthe commercially important fish family Lutjanidae all key fish species have declinedin average size in recent years. Another findingis the increase of coral diseases. The results indicate the need for further species-specific research in order to identify the factorsthat arecausing the degradation ofthe reefs in the SNMP. A better understandingofthe 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