What do biologists do when we want to study life from a particular region or environment? We either observe it directly, take samples, or both! The deep-sea is an environment that poses great challenges when it comes to making direct observations, so unless you can take a submersible (like I talked about in my last post) we can’t exactly go bobbing along on the bottom of the beautiful briny sea. And even if you are using a submersible or ROV (remotely operated vehicle), you are often very limited by the amount of samples you can bring up and you have to be able to visually see what you want.
If you want to take a bulk sample to observe critters from a particular substrate, particularly if they live in the sediment and not above it, the best way is to dredge. Basically, you drop down a metal frame with a net attached to it to the depth you want to sample at and then drag it along the bottom for a ways. Then you pull it up, dump the sediment into some bins and take it back to the marine station to sift and sort. Or if you’re on a longer cruise, all this would be done on the ship. Check out the video I took of sinking the dredge below:
We were working out of the Misaki Marine Biological Station by Sagami Bay, so it was convenient to go out to take samples in the bay and out in the open ocean and then sort through them at the station. We dredged from three depths; 50m, 80m, and 300m and each of these had a unique substrate type ranging from sandy to rocky, with different animal communities to go along with each.
We worked late into the night sorting through the sediment looking for live animals and separating the molluscs form the other critters, it was an exhausting day! It was a ot of work, but we found a variety of critters from
clams (to the delight of one of my labmates in particular), sea stars, brittle stars, sea cucumbers, polychaete worms, gastropods, including coiled snails and limpets, a few fish, nudibranchs, and others. Unfortunately, I didn’t find and lepetelloideans (the group of limpets I study), but I did gain a lot just from having the experience of sampling in the field! We also sampled from the shore, but more on that later…