So, what exactly is it that I’m doing out here?
For one, I’m learning a lot about the animals that live on the seafloor and in seafloor sediment (aka “mud”), but for my own research- I’m sticking to the animals that live in the water column- animals that spend all or part of their lives entirely in the open ocean. On this cruise, I am studying these so-called midwater animals using two methods: 1) a midwater trawl (see picture) and 2) video surveys using a Remotely Operated Vehicle (ROV) (see picture).
The net is really good at catching relatively hard-bodied animals like fishes and crustaceans (there are a lot of shrimp-like animals such as krill and copepods living in the open ocean environment), but can be pretty rough on the gelatinous animals, like jellyfish. Some of these animals are so watery that they collapse or fall apart in the net. Some are made of colonies of animals that are too small to be captured in the net.
Video is a great way to see these animals without harming them, and also allows me to see at exactly what depth each animal is, so I can match its location to its environment (temperature, salinity, oxygen). As a marine ecologist, I am interested in how the animals use their environment, and in particular, here off the coast of California, I am interested in how and why some animals can live at extremely low oxygen levels that exist in deep open ocean waters.
I did my first midwater ROV dive yesterday, and it was absolutely amazing! The whole 8 hours that I spent in the ROV control room, I felt like I had been transported into the deep open ocean! The ROV drivers, Drew and Jay, did a fantastic job holding the ROV steady while I took notes on every organism that we passed at depths from 100 to 750 meters (about 300 to 2250 feet).
Controlling the ROV with what is basically a video game joystick, the drivers said they felt like they were living out their fantasies of flying around in outer space. Out in the seemingly barren ocean, there is a steady fall of “marine snow,” small bits of organic matter derived from dead organisms (animals big and small, and phytoplankton) and, well, a lot of feces. Marine snow slowly rains down to the seafloor where it is a super important food source to animals and bacteria. A friend recently discovered that even vampire squids feed on marine snow as it passes by them (see article here).
But it is in between the marine snow where the real excitement happens. The animals of the deep are both strange and beautiful:
Larvaceans are open ocean tunicates (related to seasquirts - edited typo/error here). A bizarre creature, the animal itself resembles a tadpole, and builds a mucous “house” through which it filters food. Larvaceans regularly abandon their houses after they clog, but they are able to rebuild them rapidly.
Salps are another kind of tunicate that live in the open ocean. Salps can become extremely abundant- crazy extremely abundant. Last spring and summer there was a huge salp bloom off of the west coast of the US- you could scarcely glance at the water without seeing one. The reason remains unknown, and the bloom has since dissipated. This salp was one of just a few that I saw on the ROV dive:
Comb jellies (ctenophores) have 8 rows of ciliated cells (cilia are tiny little hair-like cells). When they move, they appear iridescent. Most species of comb jellies are transparent. Animals in the deep sea tend to be either transparent, red or black, because all of these colorings make them effectively invisible in the deep.
Siphonophores are related to jellyfish. They are colonial animals that can form chains many meters long. We saw a ton of siphonophores on the dive.
The fish that we saw all look about like this guy below. I saw a good many of them, but they quickly darted out of the way of the camera before I could take a good look (or snap a good photo). Oh well!
For background on the San Diego Coastal Expedition, please visit Sam Diego Seaflex.
Previously in this series: