Collecting corn-bale animals and the last logs
October 27, 2013
Our day started a little later this morning, since we didn’t need to deploy any elevators over the side of the ship. The remotely operated vehicle (ROV) launch proceeded as scheduled at 6:30 a.m., and we were viewing the bottom at 3,200 meters just before 8:30 a.m.
We immediately began collecting the remaining 17 logs that Jenna Judge had placed on the seafloor two years ago. These included wood from several different species of trees and shrubs. Some of the wood appeared to have been colonized by many deep-sea animals, while others had very few. It will take some time for Jenna to analyze these samples before we’ll have the final word on whether limpets and deep-sea animals favor certain types of wood over others.
Once we had completed the log collections, we headed south about 900 meters to return to the corn bale to collect more samples of seafloor animals. We stopped about 500 meters from the bale to collect squat lobsters in a ‘control’ area assumed to be unaffected by the bale. Using the suction sampler, the pilots were able to quickly capture about 10 of these small crabs.
We continued toward the bale, running a benthic video transect for the last 250 meters. We’ll use this video to measure the abundance of all identifiable benthic organisms in relation to distance from the bale. During this cruise, we have run several such transects near and far from the bale, and radiating outward from it. After compiling the data from these videos, we’ll be able to find out if there were any changes in the abundance of seafloor animals near the bale.
After we arrived at the corn bale, we parked the ROV directly in front of the bale and used the suction sampler to capture many small animals on and at the base of the bale. These included squat lobsters, polychaete worms, snails, and limpets.
We want all of these specimens for a few purposes. First, we cannot identify all of these species from video alone, particularly for deep-sea animals—species unknown to science are commonly discovered on these dives. So, we need specimens for morphological and molecular analyses to determine the actual identities of the species we are viewing. Second, we are keenly interested in just how much energy these animals may be getting from the corn bale, compared to the normal deep-sea food sources. We’ll analyze stable carbon and nitrogen isotopes in muscle tissue from the animals to help understand that, and may use other methods, such as fatty acid analyses.
After we finished collecting animals near the corn bale, we began another video transect moving away from the bale toward the northeast. This continued only for about 60 meters and the video monitors suddenly went black! We waited for a few minutes while the pilots tried to troubleshoot the problem. Fortunately they still had control of the ROV and some other cameras worked, even though the main cameras had failed. In the end, we decided to abort the dive, and the ROV started to ascend toward the surface.
We also sent acoustic commands to release the benthic elevator, which was full of Jenna’s logs. The elevator worked perfectly and sent a signal to us indicating that it had released its extra weights. We tracked the elevator for several minutes and determined that it was indeed rising toward the surface. By measuring the rate of ascent, we estimated it would hit the surface at about 4:15 this afternoon.
Once the ROV arrived at the surface, we gathered our samples and began to sort them. All of the squat lobsters that we captured on the bottom are closely related and look very similar on the video monitors. But upon inspection under a microscope, we estimated that there were at least four species and probably five or six present. It will take more careful analysis to be certain. However, we know for sure that the crabs we captured at the control site away from the bale were all the same species, and were different from any species found on the bale.
The Western Flyer is now heading back to the urchin-caging study sites closer to Moss Landing, where we dove on the first day of the cruise. Tomorrow morning we will dive again at this site during our last dive of the cruise. The winds are picking up and are supposed to increase to 20-30 knots overnight. We hope conditions are good enough for a dive in the morning.
— Jim Barry