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A Deeper View

posted Jun 30, 2012, 5:14 PM by Shannon Casey   [ updated Jul 3, 2012, 8:44 AM ]
How observations with the ROV can expand our research capabilities

The Remotely Operated Vehicle (ROV) is an underwater robot that helps serve as a scientist’s eyes and hands in otherwise inaccessible waters. The ROV is equipped with video cameras and lights and has a manipulator arm that can be used to grab various instruments for collecting organisms. It has a sonar system that helps the ROV driver see in low visibility waters, as well as sensors to measure temperature, salinity, and oxygen. The ROV transmits real-time images through a cable connected to a control room on the ship. This affords scientists the opportunity to stop and make observations when we come across an animal of particular interest.

My fellow Scripps Institution of Oceanography student scientist, Mike Navarro, studies the distribution of squid egg beds in relation to environmental variables. For much of his fieldwork, Mike uses SCUBA to observe and collect squid egg capsules. Many scientists and fisherman think that there may also be squid egg beds in water too deep to be reached by conventional diving. By surveying the seafloor with the ROV to depths of up to 400 m, Mike will be able to safely search for deep egg beds. These seafloor surveys will additionally allow us to make observations on habitat ranges of a number of commercially important species that dwell on the seafloor. In the case that eggs or animals of interest are found, we can even collect the organisms alive and bring them back to the ship’s lab for further study.

My own research is focused on a community of animals that live in deep open ocean waters, specifically the mesopelagic zone, which ranges from from 200-1000m (600-3000 ft). The animals that live there include lanternfish (myctophids), dragonfish, krill, and a number of gelatinous organisms like jellyfish.

Photo: A typical catch from a midwater trawl to 500 m (1500 ft). In this picture, one can see: dragonfish, mytophids (lanternfish), hatchetfish, deep sea smelts, cyclothone (bristlemouths),
krill, and salps. Photo credit: Jim Wilkinson.

Thus far, I have used midwater trawls for direct collection and a scientific echosounder for remote sensing to sample the community. The echosounder works by sending out a sound wave through the water column at a specific frequency. The sound is reflected by anything with a different density than the surrounding water, which includes the seafloor, but also animals. The strength of the reflection can be used to roughly interpret the types of animals that are living in the water. The echosounder is useful because it can be run during an entire cruise without interfering with normal operations, thus allowing me to survey a huge swath of ocean. However, it is hard to interpret what animals are in the water. I generally use net collections to help me interpret the acoustic signal. The net is good at catching fish and other hard-bodied organisms, but many of the delicate gelatinous organisms are not well sampled by the net tow, because they can fall apart. A prime example of this is the siphonophore.

Photo: Siphonophore. Photo credit: Monterey Bay Aquarium Research Institute.

Siphonophores are colonial organisms made up of individual zooids living in a long chain. The colonies often fall apart in the nets, and much of the animal can be lost through the mesh. Since siphonopores have high acoustic reflectance, it is important for my research to get an accurate count of the number of siphonophores that are in the water.  ROV surveys can serve as a complement to acoustic and net sampling, and provide a more accurate picture of what is in the water column.

Further, when animals are collected by net and taken out of their immediate environment, they do not survive well. Observations made by an ROV allow us to observe the animals’ natural behaviors in their own home, which can inform us as to how the animal eats, moves, interacts with other animals, and much more that we can not learn outside of their natural habitat. 

Photos: Top: Vampire squid photographed at depth using an ROV.
Photo credit: Monterey Bay Aquarium Research Institute.
Bottom: Vampire squid collected with midwater trawl. Photo credit: Amanda Netburn.

Finally, ROVs are not only good for biological observations, but also observations of the seafloor itself. A research group onboard the San Diego Coastal Expedition is searching for methane seeps, and will use the ROV to explore potential seep locations (more on methane seeps to come in a few days). We are extremely excited to explore the waters off of San Diego with the ROV in the upcoming days!

--Amanda Netburn, Scripps Graduate Student