From 19-27 October 2013, IMARES Wageningen UR organized a research expedition to the Saba Bank, to investigate its ecological functioning. Thirty-three 50m long transects resulted in more than 2000 images of the reef, and over 5000 fish counts of almost 100 fish species.
Photo: Divers at the Saba Bank (© Franck Mazéas)
A preliminary comparison with the data from 2011 shows a reduction in snappers, groupers, and grunts, while there were noticeably more sharks. There were fewer algae on the bank than in 2011, possibly indicating a healthier reef, though there appeared to be a gradient in increased algae cover towards the island of Saba. It is unclear if this is related to anthropogenic activities on the island or to natural causes.
Lots of data to be analysed
The international team of marine biologists investigated the coral reef structure as well as the spatial variation in species assemblages and population genetic connectivity of corals, fish, and sponges on the Saba Bank. The data from the fish survey, benthic images, and population connectivity study will now be further analysed in The Netherlands; results are expected by the mid of 2014.
Largest submarine atoll
The Saba Bank is the largest submarine atoll in the Caribbean Sea spanning an area of 2000km2. It houses an expansive coral reef ecosystem with a rich diversity of species and as such is also an important source of commercial fish for the nearby islands. The Saba Bank furthermore forms the largest protected area of the Kingdom of the Netherlands, after the Dutch part of the Wadden Sea in Europe. As there are no large land masses nearby, the Saba Bank can be considered as relatively pristine. Environmental threats such as climate change, sea surface temperature increase and acidification, however, also threaten the Bank’s coral reefs.
The second Expedition
The expedition is a follow up of a survey of the Bank in 2011 and is part of the “The Saba Bank Research Program 2011-2016” initiated by the Dutch Ministry of Economic Affairs (EZ). The Saba Bank is a Marine Protected Area and by the CBD (the Convention of Biological Diversity) acknowledged as an Ecological and Biological Significant Area. The research is part of the implementation of the Exclusive Economic Zone management plan for the Dutch Caribbean. On board of the “Caribbean Explorer II”, an international team of marine scientists surveyed different aspects of the coral reef ecosystem.The expedition was funded by the Dutch Ministry of Economic Affairs and the World Wide Fund for Nature.
Photos of corals, algae and sponges
Erik Meesters, expedition leader (IMARES), Jean Philippe Marechal (OMMM Martinique), Franck Mazéas (DÉAL Guadeloupe) recorded the cover of major benthic groups and coral recruits with the use of underwater cameras. Corals, algae and sponges form essential components of the biodiversity of the Bank. Together they create and maintain the coral reef ecosystem which forms the Saba Bank, one of the major hotspots of biodiversity in the Caribbean.
An important factor for coral-reef resilience is the connectivity between and within coral reefs in different regions. A key question is how populations of reef organisms on the Saba Bank are connected with populations in the region and in the Wider Caribbean. In order to answer this, Lisa Becking (IMARES and Naturalis Biodiversity Center) and Didier de Bakker (University of Amsterdam) investigated the population genetic structure of two common benthic species (barrel sponge and great star coral), an invasive species in the Caribbean (lionfish) and two commercially relevant fish (silk snapper and red hind). Geographical surveys of genetic variation provide an indirect means of tracing movements made between marine populations by larvae and other propagules.
Video monitoring of pelagic and benthic fish
Ingrid van Beek (IMARES), Steve Pointek (STENAPA St. Eustatius), Erik Boman (LVV St. Eustatius), and Fleur Holtrop (Van Hall Larenstein) assessed the pelagic and benthic fish communities by underwater visual census and video monitoring. Great numbers of fish species inhabit the reefs and algal plains of the Saba Bank and these fish communities provide important information on the status of the ecosystem.
Joe Phillipson (CAH Vilentum) studied reef complexity. The topographic complexity of the reef has direct consequences for the biomass and diversity of fish living on a reef. Phillipson assessed the complexity at the sites using a variety of methods.
Sponges as vacuum cleaners
Sponges are essential, yet often neglected, components of the reef as vacuum cleaners of pathogens from the water and as producers of food and nutrients for other reef organisms. Fleur van Duyl and Ben Mueller (Royal Netherlands Institute for Sea Research (NIOZ), The Netherlands) have examined water quality and the diet of dominant sponges in the Saba Bank to obtain insight into nutrient and carbon processes. Simply put, they would like to find out what the sponges are eating.
Interaction algae and corals
Maggy Nugues (CRIOBE France) studied competitive interactions between algae and corals and will identify the macroalgae on the Bank that are the most damaging to corals, as well as the most susceptible coral species. Algae form an important component of the Bank, however, under adverse conditions they may outcompete corals in terms of growth and thus cause coral mortality by overgrowing neighbouring coral colonies.
Filmed by National Geographic TV
The work of the researchers, both above and under water, was recorded on film by Willem Mouissie (Mouissie Corporation) and Javier Boezem, as part of the series Marine Life for National Geographic TV.