Blog entry by Lisa Skein & Luis Greiffenhagen
A few days ago, stationed above the “western middle branch” of the Whittard Canyon, the ROV went down once more. This time, the objective was to perform a photogrammetry survey of a very special section of a vertical canyon wall. What makes this particular wall so special is that it’s covered by incredible densities of Acesta excavata, or fire clams as they are commonly referred to.
First discovered in 2012, the “Acesta wall” has been shown to be home to many other deep sea organisms. This is partly because the outer surfaces of the clams’ shells, in addition to all the little crevices between multiple clams, provide additional habitat for other organisms that may not otherwise have been able to live in that particular spot. In addition, because of the clams’ feeding activity, there are more nutrients in the area that can be used by other organisms. These other organisms can, in turn, be eaten by other organisms. What you end up with is an entire ecosystem. For this reason, Acesta clams (up to 15cm in diameter), are referred to as ecosystem engineers. Other well-known species that also have this effect include corals, mangrove trees, mussels, and kelps.
Indeed, during our recent ROV dive in this habitat, we observed many different deep-sea species on and around the wall. This included species like flytrap anemones, cerianthid anemones, deep sea oysters, cold water corals, sea urchins, starfish, crabs, conger eels and probably many more that we haven’t yet spotted from the latest photos and videos. They can all find their ecological niches within this habitat, giving the Acesta wall the function of a marine animal forest.
Why go back to known sites, when so many areas have not been seen before?
When doing deep-sea research, it may be tempting to continuously go to new areas that have never been looked at before. This we do, yes, but it’s also important that we revisit sites like the Acesta wall. Solid scientific research relies quite a lot on repeated observations of whatever it is you’re measuring or trying to figure out. For this reason, the Acesta wall has been revisited a few times since its discovery. This is being done to collect more data on the organisms that live there, to document if and how they change over time, and in trying to understand why they are so abundant in this particular part of the larger Whittard Canyon. To get to grips with all of this, it’s also important to understand how the water moves, what nutrients it carries, how the surrounding areas look, and so on. These are all questions we are trying to answer during this research expedition.
On this particular night, our aim was to perform a photogrammetry survey on a 10 x 100m area of the Acesta wall. Photogrammetry is a technique that can be used to provide a complete panorama of a large area by stitching together multiple images. To do this, the ROV performs several continuous photographic lines over a specific area, making sure that there are overlapping sections across all the lines. These overlapping sections are then used to stitch together the entire picture, giving scientists a pretty good view of the entire wall in this case.
The discovery and further study of habitats like these are important not only because it advances our understanding of deep-sea habitats, but it also helps us and decision-makers to make informed decisions about which areas are important when it comes to conservation planning.
