24 hours of plankton!

Today we are staying in the same location and observing how many different sizes of plankton move up and down in the water over the course of a day. Many plankton are known to move up and down on a daily cycle, which we call Diel Vertical Migration or DVM for short. There are pros and cons to being in different depths of the water, and so some plankton find the best balance by moving up and down. For example, a copepod might want to eat a phytoplankton (microscopic plant) and not want to be eaten by a fish. Phytoplankton are usually near the surface of the water where there is the most sunlight with which to grow, but in the surface waters that same sunlight makes it easier for fish to see copepods and eat them. A common compromise for our example copepod would be to feed on the tasty phytoplankton at night in the cover of darkness, and then hide in the deep dark waters in the daytime.

At 9 am, and every 4 hours till tomorrow at 9, we are counting the smallest plankton using two instruments – the LISST and the LOPC. The LISST, Laser In-Situ Scattering Transmisometry, counts and measures the length of all the plankton between 1 and 250 micrometers (millionths of a meter). The LOPC, Laser Optical Plankton Counter, picks up where the LIST leaves off and counts and measures all of the plankton between 100 micrometers and 3 centimeters. Meng Zhou’s team is taking care of these instruments. Both of these instruments are attached to a metal cylindrical cage frame, about 5’ tall and 4’ in diameter. This whole package is on a cable, and we lower it on a winch down to just above the seafloor and then back up to the surface, collecting data all along the way.

In between these repeated samplings for the small creatures, Chris Roman’s group is using the in-situ camera to look for krill and other organisms larger than about 1 cm. So far they haven’t seen much today – but that’s OK because it’s important to know where the animals are not, to understand why they are in the areas that they are.
We also did some more training today – getting ready for our first deployment of small boats tomorrow. Matt, one of our Marine Technicians (MTs), set up the ladder we will use to climb from the ship to the small boat on the hello deck, and we practiced climbing in all of our gear.

The nice thing about staying in one place, is we have a neighborhood of icebergs!

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Categories: Musings of an Oceanographer | Leave a comment

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