Light Show

Right now, I’m sitting on the bridge of the Hugh R. Sharp, watching an amazing light show. It’s about 2:15 am, and we just finished a couple of Tucker trawls before shutting down operations because of the lightning. We’ve had our share of problems so far on this cruise, but overall things have been grand. As I mentioned before the ship’s crew are fantastic, and we’ve got a hardworking group of scientists. Every problem we’ve encountered has been dealt with in one way or another so the really good news is that we’re still doing science and collecting data. Well, not at the moment. At the moment, we’re just enjoying the light show and the snacks in the galley.

So I’ll take a few minutes to describe what we’re doing out here. Basically, we’re looking at how plankton respond to hypoxic conditions in the Chesapeake Bay. The Bay experiences low oxygen in the bottom waters every summer, after plankton blooms exhaust nutrients, sink to the bottom, and are decomposed by bacteria in the water and on the bottom. These conditions would obviously affect the organisms that live directly on the bottom, but we’re interested in the less direct effects that might be experienced by organisms living in the water, either above the low oxygen water or perhaps directly within it. Our target organisms are copepods, tiny crustaceans that live almost anywhere on earth where there is water. In fact, some have suggested that copepods are the most numerous multicellular organism on earth. We’ll save more about copepods for another post, but they are fascinating little critters.

Anyway, copepods are fish food and algae eaters – they sit in the middle of the food chain, but to understand how they are affected by hypoxia, we have to know how other aspects of their environment might be affecting them. So we do collaborative science. We’ve got a world-class team on this project with folks studying fish and jelly fish (copepod eaters), as well as phytoplankton and microzooplankton (copepod food). We’ll try to get these folks to give us some updates on their work in future posts.

So that’s the basic idea, but what are we doing?  Well the first thing we did was map the water conditions in our study region. To do that, we towed an instrument called the Scanfish from the Bay Bridge to the Rappahannock Shoals.  The SF is towed at about 5.5 knots and undulates from within 2 meters of the surface and 3 meters off the bottom, taking measurements every second. We get temperature, salinity, fluorescence (a measure of the amount of algae in the water) and dissolved concentration. Plus, we bolt an optical plankton counter (OPC) to the top of the fish, which gives us an estimate of the sizes and abundance of plankton the entire time the SF is in the water.  Wow, that’s a lot of data already, and we’re only 24 hours into a 7 day cruise.

From the SF data, we determine two stations to do intense process work. These two stations are located at the southern and northern ends of the study region because the low oxygen water starts at the north and progresses southward, generally, every summer. We’re hoping to use the same data collected at the two stations to compare how the zooplankton (and fish, jellyfish, microzooplankton, and phytoplankton) respond to hypoxic and fully oxygenated conditions.

So what are the processes? We’re interested in the condition of the zooplankton, namely their reproductive success, feeding rate, and size. Also, we look at their vertical distribution and movement in the water. Since we’re studying the predators too (jellyfish and fish), we sample their guts to see if they are in fact eating zooplankton and if so, how much. And we look at the composition and general health of their food – the phytoplankton (also referred to as algae interchangeably here) and microzooplankton. Microzooplankton is an operational term that refers to animals and protists that do not get their energy from the sun exclusively (like algae), and which are smaller than .2 mm long. This is a fascinating group of animals that perform some really important functions in the global oceans.

OK, that’s the basic story, and I’ll try to answer any comments and add to it in the coming days.  For now though, I’m going to enjoy this light show.  The storm cell has stalled over us so it looks like we’ll be shut down for a little while longer, and it’s a spectacular show.


About planktoneer

I'm a zooplankton ecologist who studies how individual behaviors and variability affect populations of copepods in marine and estuarine systems.
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1 Response to Light Show

  1. lfreedlander says:

    This information provides excellent background for the purpose of the cruise. Thank you.

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