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Wetlands and Aquatic Research Center - Florida
Cruise Log: 9/22/2009
Mississippi Canyon 751
Martha Nizinski and Amanda Demopoulos
Based on observations from the morning dive, this site was an interesting contrast to what we have seen previously. The bottom was relatively flat and mostly covered with fine sediments. Anemones, in particular the venus fly trap anemone, dominated the benthic faunal assemblage associated with the soft sediment environment. Burrows were scattered all over the bottom and were home to at least one species of crab. We caught a glimpse of one individual, though the crab quickly escaped into the burrow out of sight. Where we did find hard bottom there was very little Lophelia; instead, gorgonians were more common in this area. We also observed some small chemosynthetic sites with characteristic tube worm colonies and bacterial mats. These chemosynthetic sites, however, did not look active. In fact the worms looked to be dead in most cases and no other animals that are usually associated with chemosynthetic sites were visible. Toward the end of the dive we came across a small coral patch and were able to collect specimens of some of our target species, including Callogorgia and scorpion fish. In addition, we collected some different animals, including a sea cucumber and a starfish that we hadn't seen on our previous dives. We also collected a few species of crab that we commonly see at our sites off the southeastern coast of the U.S. but haven't seen in the Gulf recently.
On the second dive at this site, we explored a ridge located directly south of the morning dive. While we were transiting to our first waypoint, we saw giant isopods, Bathynomus, nestled within large burrows. We tried to collect one, but it outsmarted us and dug itself deeper into the mud. In comparison to the first dive we had better luck locating hard corals, although these colonies were small compared to the extensive reefs found at other sites examined on this trip. We saw multiple patches of gorgonians, with several different invertebrate species associated with these small coral areas. Callogorgia (see log 9-19-09) was fairly abundant, plus we saw small colonies of black coral, and other soft corals. Brittle stars were observed in the coral canopy, while Laemonema and Black Bellied Rose Fish were found resting on the bottom or in burrows close to the base of the coral. We were able to collect one of each, using the vacuum suction sampler and manipulator claws. Both specimens are valuable additions to our collections and will be used to help characterize the associated fauna for diversity and food-web studies. Much like the first dive at this site, Lophelia was rarely seen, but small, thin specimens were collected on this dive opportunistically. Chemosynthetic communities were found in close association with the soft corals; tube worms and bacterial mats grew directly next to the soft coral colonies, both using the carbonate rock as a substrate. By the end of the dive, we had collected several specimens of soft and hard corals, some anemones, fish, and multiple species of galatheid crabs.
During both dives, the water column was active with planktonic organisms. There were several different species of midwater fishes and some squids that we observed usually over soft sediments.
Seeing new sites like this one is instructive because it gives us a better idea of what organisms are living in the area. This allows us to assess how unique coral habitats are relative to areas that do not have the structure that corals create. We compare this information with observations we have made at coral sites to help us determine whether the animals we see at these coral sites are always found associated with the coral habitat or whether the animals are using the coral habitat opportunistically. Additionally, exploring sites like this one illustrates the importance of visiting sites more than once and exploring new areas. Coral habitats can be patchy and we shouldn't make broad conclusions about a particular site based on only one dive.
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