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The bottom of the food chain

NIWA scientist David Bowden explains the importance of the benthic food web and where phytoplankton is being eaten in the water column of the Ross Sea. NIWA scientist Julie Hall talks about the bottom of the food chain in the Antarctic waters, the bacteria, phytoplankton and zooplankton.

Points of interest

• In what way does the food chain operate differently in the Ross Sea?
• Julie refers to an unusual place where phytoplankton can be found. Where is this?

Transcript

DAVE BOWDEN

The Ross Sea has a peculiar shelf environment in terms of what happens with primary production. Where as in the rest of the world on the shelf you’d expect a lot of, a lot of organisms in the water column feeding on the primary production, so zooplankton, planktiferous fish and the meso-zooplankton. What we’re seeing in the Ross Sea rather than that, is that most of that primary production is going – boom - straight down to the sea bed and it’s, that primary production hitting the sea bed in one big lump that’s feeding the benthic communities that we’re seeing here. So we see a lot of animals there, a lot of sponges, a lot of bryozoans, crinoids all the animals that feeding on suspended matter that’s falling from the upper water column and animals that are feeding on the phytoplankton once it’s hit the bottom – so they’re picking it up off the sea bed, they’re pulling it from the water column, that’s where the life is going on, on the sea bed.

It differs a great deal from what’s going on in other shelf areas that we see. We don’t fully understand exactly what’s going on and it’s becoming clear that a large part of that primary production isn’t being eaten by the animals we’re seeing here – the big ones we’re seeing in the camera - there’s a big proportion of it is consumed by microbes, by the bacterial loop, by all the microscopic single cell organisms that are actually degrading the organic matter on the sea bed.

JULIE HALL

The bottom of the food web is made up of microscopic organisms, we have the bacteria, the phytoplankton and the zoo plankton. The phytoplankton are the grass of the sea, they take the sunlight and the nutrients, photosynthesise to produce food that can be then used by other organisms. The phytoplankton are eaten by the zooplankton. We have a whole range of sizes of zooplankton – some eating the phytoplankton, some eating each other - till we get from the microscopic to the macroscopic that you can see with the naked eye.

Also in the Ross Sea area where you get icebergs and ice you get algae that grow on the icebergs and you see these yellow bands which is the algae – those are also eaten by the zooplankton.

Now in the Ross Sea we also see another phenomenon and that is where we have the phytoplankton in the surface waters. Some of that is not eaten by the zooplankton in the water column, but sinks to the bottom and that can be quite a high proportion in the Ross Sea and that then forms food for the organisms that are living on the sea floor.

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