Tiny “aliens” in the tows

Good evening everyone,

Today at noon the Gordon Gunter reached its first Georges Bank station, tucked away on the southwest corner of this area. Even before reaching it, we were greeted with a typical Georges Bank warm-weather phenomenon, fog. We’ve been surrounded by it most of the day, but along with it the water has been very calm, so it hasn’t hindered our progress at all.

Plankton catches in the eastern part of the Southern New England area have changed from the ones we had further south in the Mid-Atlantic Bight area. For one thing we started seeing considerable amounts of Calanus finmarchicus copepods, easily recognized by the reddish oils they form for food storage and visible in their clear bodies. What is always amazing is the patchiness of these concentrations. One station may have large numbers of these animals, while an adjacent station just a few miles away will have almost nothing in it even after a comparable tow for the same amount of time! Also present in some of the Southern New England plankton tows were Phronima amphipods. This two-centimeter-long crustacean takes up residence inside another planktonic organism, a salp. It devours the salp’s inner tissues then anchors itself  inside the clear outer barrel-shaped salp body which it swims along and uses as a nursery for its young. The distinct profile of this tiny amphipod is said to have been the inspiration for the much larger and more menacing creature in the movie Alien!

PlanktonComparison rd.jpg

Comparison of catches from plankton tows at two adjacent stations just a few miles apart in Southern New England waters: large  numbers of Calanus finmarchicus copepods in one, and almost nothing in the other! Photo by Jerry Prezioso, NEFSC/NOAA Fisheries

Another change has been visible in the imagery coming from the Imaging FlowCytoBot (IFCB) unit. We are seeing mostly diatoms now as opposed to the dinoflagellates we had earlier in the trip. These microscopic planktonic algae are easily recognized from the distinctive shapes of the clear silica shells they form to encase themselves in, and which have been visible all day today on the computer monitor hooked up to the IFCB.

Phronima rd.jpg

A Phronima amphipod removed from its salp dwelling, caught in a recent plankton tow in southern New England waters.  Photo by Jerry Prezioso, NEFSC/NOAA Fisheries

Diatoms2 rd.jpg

Today’s images of diatoms from the monitor of the laptop connected to the Imaging FlowCytoBot unit, which samples the surface water the ship is sailing through. Photo by Jerry Prezioso, NEFSC/NOAA Fisheries

Looking ahead to the remaining time we have for this cruise, it is apparent that Georges Bank will be the last area we’ll be able to survey. With a favorable forecast for the next few days I’m optimistic that we’ll get to most of it, and perhaps leave some easily-reached stations on the northern edge for the next leg to sample when they start work in the Gulf of Maine.

Jerry Prezioso
Chief Scientist
GU1608 Ecosystem Monitoring Survey

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