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Seafloor Characterization of the U.S. Caribbean
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Day 11: 03/31/2006:

Three transects were preformed today: two deep transects over mud and a shallow transect down a rock precipice. The first transect targeted a steep slope with high-frequency downslope-upslope oriented channels. From the bathymetric data they appeared to be caused by mass slumping at a very steep grade. The second transect targeted deeply carved wide channels. The third transect, was very similar to the last transect completed on day 10. It began at 20 m over colonized hard bottom, descended down a 200 m vertical precipice, and ended at the precipice’s bottom on a 45 degree slope.

Although the first dive was relatively deep (500 m) several sharks and large snappers were seen in a relatively small area. Before the ROV began recording data a hammerhead shark appeared, minutes later another shark (taxa unknown) with large dark eyes was spotted and minutes after that three snappers huddled next to a large boulder. For some reason, the location where the ROV touched down had a large amount of biomass. The only distinguishing feature was the boulder. Interestingly, although some boulders were sites for many corals and sponges this boulder was relatively barren. Why were there fish and sharks but no coral or sponges?

The second transect was relatively uneventful, except for some peculiar crabs that looked like spiders. The ROV had spotted the spider-crabs before, but they were on the solid surfaces and this time one was hovering in the water above the seafloor. The hovering crab seemed to be dangling from threads, just like a spider would from its web. We had not ever heard of this phenomenon before so we deduced that the unfortunate crab had probably been taken by jellyfish tentacles.

A third transect over colonized hard bottom was performed during the crepuscular period when fish and invertebrates are most active on the reef. Hundreds of fish swam around sponges and coral on the colonized hard bottom, but their numbers dwindled as the ROV descended the precipice. Only a few sporadic sightings of fish were seen below 40 m, but sponges and coral were still prevalent. At approximately 80 m the sponges and coral sightings faded too. Near the bottom of the precipice, at a depth of 200 m, a school of squid swam around the ROV. They were probably attracted by the ROV’s lights thinking it was the moon. The ROV was swarmed by about twenty of them and they constantly squirted ink into the water reducing visibility. Soon after the squids retreated the transect was terminated and the ROV ascended.

[A white lobster pokes its head from a hole - its home. Many similar holes were seen during every ROV transect, but only rarely did we capture images of the lobsters too.]

A white lobster, Acanthacaris ceaca, pokes its head from a hole - its home. Many similar holes were seen during every ROV transect, but only rarely did we capture images of the lobsters too. According to Mary Wicksten, a professor of invertebrate zoology at Texas A&M University, A. ceaca is one of the largest varieties of blind lobster in the Atlantic.

[Many black durgon (Melichthys niger) swim above colonized hard bottom in front of a transect at 20 m. The bottom is covered in waving gorgonians, rough sponges and colorful stony corals.]

Many black durgon (Melichthys niger) swim above colonized hard bottom in front of a transectFebruary 15, 2007ges and colorful stony corals.


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