While we have told you a bit about this project, about connectivity, vertical distributions and Marine Protected Areas MPAs), we have not yet properly introduced you to our target species. So, here is a little bit about our best friends on this trip: Parastichopus tremulus (a sea cucumber), Cidaris cidaris (a pencil urchin), Lophelia pertusa (a reef forming stony coral), and Acanella arbuscula (a bamboo coral). With these beasties come a few others we are getting to know: Madrepora occulata (another stony coral), Solenosmilia variabilis (yet another stony coral), Eunice norvegica (a polychaete worm), and an animal affectionately known as Ophiuroid 1 (a brittle star).
Let’s start with Parastichopus tremulus, aka ‘the pink one’ (among other names used by the ROV pilots – see Amber’s blog post and the most wanted poster). As with most of our animals there is no common name for this species, probably due to the fact that people don’t commonly see them. But let us reassure you, when you have a look down at the seafloor in offshore UK waters you will find that they are indeed pretty common!
This is the main reason for all the species we have chosen. Unfortunately, population genetics requires large sample sizes (we target 20 animals per species per ROV dive) so we need to use animals which are common enough to both find them when we look for them, and to ensure we are not wiping out the population when we sample them!
Parastichopus is an echinoderm, related to sea stars and urchins, we generally see it on flatter seabeds with soft sediment, but they do still turn up in other environments. You have met this guy already in our ROV slurping video. But you may not yet have seen it up close and personal. One of the reasons we use the slurp gun to sample Parastichopus is the fact that they are almost literally a sack of water with a digestive system. As such, they are vulnerable to squeezing and if stressed can eject their entire gut from their body, so we try to just hoover them up rather than risking squeezing them too tight with the ROV claw. You’ll thank us for sparing you from the pictures of dissected and preserved specimens, which do not look appetising at all!
Cidaris cidaris is a pencil urchin, so-called because its spines are so thick and rounded that it looks like a ball of pencils. There are many species of pencil urchin though, so this guy is just known by the ROV pilots as ‘the spikey one’, ‘the mine’, or ‘sputnik’. Cidaris and Parastichopus are often found together in the same environments, although we have had plenty of success in finding Cidaris on steep slopes and in reefy areas too. I am eternally impressed by the places these animals can get themselves into/upto/amongst, and we have had some entertaining issues when testing out the slurp gun sampling method on Cidaris too. Thankfully, we have a clever student on board who suggested a way to extract the spikey ball from the slurp tube with some floating rope – kudos to Nina who outdid the ROV engineers who do this kind of problem solving for a living!
Cidaris also has a body cavity mostly filled with gut, which is pretty hard to get enough unsullied genetic material from. When we dissect the animal we are therefore looking for the gonads, which are found between the gut and the wall of the test (the urchin shell). In larger animals, these are easy to find (there are 5 of them!), but if you have a small specimen in front of you it is quite a challenge, usually resulting in the entire gut being preserved as well.
Now we come to the stony corals. We have a triumvirate we are on the hunt for: Lophelia pertusa is the most widespread in the area and forms most of the reefs that we see around the region, but it is usually accompanied by Madrepora occulata. In our deepest sampling sites, however, it is usually Solenosmilia variabilis which dominates the rocky outcrops and forms the reefs. The trick has been teaching everyone on board how to identify which one you are looking at. They all form a corally matrix made of calcium carbonate, with polyps protruding all over the place. They all can be orange (with Lopehlia and Madrepora also being available in white), and they do easily get confused, especially from afar. The rule of thumb we have all adopted is to look for the zigzags – this is Madrepora, the only animal we are looking for which does have a (ROV pilot friendly) common name: ‘the zigzag coral’. When you are at 1000 m or below, you are in the Solenosmilia danger zone, at which point you are looking for the Y-shaped ends to its branches and its chunkier more robust look…. otherwise it is probably Lophelia. When in the lab we are looking for soft tissues to get genetic material from so we often have a pair of pliers in hand to try and crack the calcium carbonate skeleton open to access the polyps, which retract when disturbed.
Acanella arbuscula is a bit more elusive. Found in deeper waters both on soft sediments and on the edges of reefy areas, this is a very picturesque animal belonging to the Isididae or bamboo corals. Bamboo corals are so-called due to the bamboo-like appearance of their skeletons, which you can see in the laboratory photo above. The black bands are actually areas of soft tissue which allow the animal to flex. The beautiful orange polyps from afar are like a little cloud and close up often seem to house a squat lobster of identical colour. The prominent polyps make this animal easy to preserve, and therefore all the more delightful to be processing in the lab.
Together with these four targeted species (and the two bonus stony corals) there are a couple of other species we have adopted into our study due to their being prolific in our sampling. Both of these animals are considered associates to targeted samples and since we have fished them up in our samples anyway, we might as well make use of them to broaden the study.
Ophiuroid 1 is so-called because it is yet to be formally identified. This brittle star is plentiful in reef samples, especially if any of the dead coral matrix is collected with the live specimen. Generally, these guys are met with disdain in the cold room as the plethora of legs poking out of inaccessible holes can make for a long sample processing session.
However, the bane of all our lives here on board is Eunice norvegica. E. norvegica is related to ragworms and will be found embedded in a stony coral tube, which often requires cracking open with pliers. The issue here is that a) these animals can hold on for dear life with every one of their bristles pulling in the opposite direction to you, and b) they have huge jaws as demonstrated by the picture of Nikolai’s pencil locked in battle!
We have all come to know these animals very well, including many of the crew and non-biologists who regularly pop in for a gander at our beasties. Sadly, none of them survive their trip to the surface but we can guarantee that all are preserved diligently to suit as many scientific purposes as possible. We will make the most of our cruise specimens, and any others who come aboard with them, and hope that we can provide some fantastic science, which will help us learn more about this fascinating realm. We are all keen to help inform future management decisions in the deep sea with the hope to conserving the beautiful environments we have been so privileged to be the first to visit with the ROV and explore in full HD.
Text by Rebecca Ross, PhD student, Plymouth University