We are now within the Celtic sea, the French part of it at least. I didn’t know there was a French part of the Celtic sea but it turns out there is, and I am in it.
The ROV has been in the water again conducting transect surveys at Petite Sole; flying along at about 2m above the seabed and plotting the changes in habitat as we go. We have also had another session of sampling. These dives are a little more complex than just completing our animal shopping list. A big focus of this current work is the gene flow of these corals. Corals can reproduce asexually: colonies grow larger or fragments break off and then start new colonies, but these methods likely mostly affect a localised area. Corals also reproduce sexually and there is a juvenile stage that can be carried by the water currents. We can get some idea how this happens by comparing the reefs genetically and looking at the degree of “relatedness”. This required a much stricter sampling plan with the ROV. Sample boxes were selected and specific locations randomly generated within them. At each of these locations a sample of the two main reef forming species is taken. Later it is hoped that we will be able to look into how these colonies have spread over the area.
I am also able to finally start talking about the lander…..since it has finally started working! I have never had it give me this much trouble in the past. The fault was frustrating since it only happened under pressure. On the deck everything worked fine, no matter how hard I tested it, but once it was down to more than 100m depth the camera would stop functioning. I had to resort to excessively sealing all the connectors again to get it working.
I also discovered how strong the currents are down there! It has been noted for some time that the corals are associated with high water flow; it brings them their food and prevents sediment building up and choking them. We are currently in Spring tides, where the sun and the moon pull in unison and you get really big tides. At the seabed I was recording a flow of 40cm/second, about 4 times what I am used to seeing. I can remember sitting watching the ROV footage and all those particles rushing past the camera in the current. Then thinking of my lander, with all its floats, looking like a kite. I was right to worry. When the lander returned it had been on an adventure and conducted a transect of its own. All was not lost though, on its travels it discovered a beautiful coral area that we did not know existed. We now have a whole new site we can investigate.
The lander was deployed again, this time will much more ballast (100kg more!) and seemed to stay put. I will have to use this amount from now on it seems, at least until these big tides pass. We finally got some nice images of fish feeding.