By Veronica Radice, Catlin Oceans Scholar
The under-described deep reefs of the Maldives are beckoning to be explored. To enhance the Catlin Seaview Survey’s shallow water studies in the Maldives, the deep team is diving to 30 meters to compare coral communities over a depth gradient. Our surveys at 10 and 30 meters encompass several research projects, which are the main focus of my PhD research. Down below, and on deck, I am lucky to have the unwavering support of my teammates Craig Heatherington and Kelly Latijnhouwers.
The bleaching events that struck the Maldives over the last two decades did not spare the corals of the deep. Seawater temperatures rose sharply, even at 30 meters. Extensive post-bleaching assessments in the shallow waters ensued, however, investigation of the deep reefs are lacking. In order to understand how the deep reefs were impacted, and which corals are likely to survive a subsequent bleaching event, we need to study the coral community over depth. Deep reefs are particularly important as they are hypothesized to act as a “refugia” for shallow-water corals by having the potential to seed shallow water reefs.
I believe corals are among the most complex living organisms. The coral ‘holobiont’, i.e. the coral as a whole, consists of the coral animal ‘host’, photosynthetic algae (zooxanthellae), bacteria, and fungi. All of these components interact within the coral tissue, calcium carbonate skeleton, and surface mucus layer. You may be surprised that the composition of these different players change. Location, depth, and time are all factors that affect the composition of these coral associates.
The integral association of the coral and photosynthetic algae, which provides food to the coral through photosynthesis, changes over depth. Just as you and I prefer comfortable temperatures, so do the algae. The algae are tolerant of certain environmental conditions, and when the conditions become too harsh, the algae exit the coral. When this happens, corals may rely more on another feeding strategy – heterotrophy – by capturing external food sources, such as plankton, floating in the water column.Here in the Maldives I am collecting small fragments of coral specimens, as well as seawater samples, from 10 and 30 meters depth. Back in Australia, I will study the coral feeding strategies and their associations with the photosynthetic algae and bacteria. To better understand the environmental conditions, we’ve deployed temperature and light loggers at 10 and 30 meters at three sites in North Ari atoll. This research will add to the growing amount of information on deep coral communities, and explore whether or not they represent important refugia against global climate change.