Fkt230918 - Vertical Reefs of the Galapagos

Corals can form colorful oasis teaming with life not only in shallow waters, but in deeper water as well. They provide suitable habitat for a range of species, and if you follow our expedition, you will see that the more we zoom in on coral colonies, the more associated species we can observe. However, discovering the location of those deep-water reefs is a lot more difficult, especially since the majority of the ocean remains unmapped. Deep-water corals tend to like topographic reliefs like mounds or canyons, but with poor maps of the seafloor even these relatively large features cannot always be resolved.

As most of our mapping tools look downward from the surface, one specific relief that is especially favoured by corals, but difficult the map, are vertical walls. We hypothesize that current dynamics in the vicinity of these walls are favourable to bring the food particles that deep-water corals eat as well as provide the exposed bedrock on which larvae can settle before growing into large colonies over many decades. Cliff environments are of particular interest as, owing to their complex topography, they provide a natural protection for vulnerable coral species against trawling activities, potentially allowing larvae to help recolonize surrounding damaged habitats. However, as you may see during our expedition, not all walls are necessarily covered by the same coral species or even colonized by corals at all. In order to understand this variation, we need to take an interdisciplinary approach and examine a range of possible factors such as hydrodynamics, geology and geomorphology as well as climatic history.

During this cruise, we collected lava samples to understand the lava flows that created the Galápagos Islands as well as collect coral fossil to reconstruct the conditions of past water masses. We mapped these environments across a range of resolutions using techniques from shipboard multibeam sonars (5-50m resolution) to multibeam sonars (~25cm) and underwater laser scanners (~mm) mounted on the remotely operated vehicle SuBastian. We used a current-temperature-depth (CTD) sensor and acoustics Doppler current profilers (ADCP) to measure the physical properties of the water column and the currents in the vicinity of cliff faces.

For this expedition, we had the privilege of working around the Galápagos Islands, an ideal location as cosmopolitan CWC species are known to be present in an active and complex geological and oceanographic environment. Moreover, the oceanographic complexity of the region is important for understanding past and future climatic conditions. Luckily, in this region, these ecosystems have been protected and as such remain near pristine. This now allows us to observe natural patterns in order to help establishment the ecological baselines that are often missing from better studied, but more impacted, systems (e.g. North Atlantic).