Agnes' experiment

Some of you might think that we are just hiking and being tourists in Hamilton. This is not completely true, the only reason for living here this spring was to carry out an experiment on the fate of algae on intertidal sandflats. Yes, this could have been done at many other places in the world, for example in Holland, but New Zealand seemed much more exciting to us. And the reason for doing it in Hamilton at Waikato University, was that one of my collaborators in NZ has a new PhD student here, who had set up a big experiment during her time as Master student and who was now interested in using this set-up for testing the questions I got funding to study. A good opportunity for both of us we thought, but everything seemed at risk when the biggest oil-spill in NZs history happened at our study site – Tauranga harbor, in the northern part of what is called The Bay of Plenty.

Visa tauranga på en större karta

The field site at low tide

Luckily the oil didn’t reach our sandflat and a few weeks ago when all the preparations were done we could finally collect our animals and bring them back to the laboratory. Yesterday we terminated the experiment, so all that is left is to arrange to ship the samples down to Dunedin where I will spend several months analyzing the data. So – what is the experiment about?

Very shortly - it is about the fate of algae. One of the most abundant species on sandflats is the alga sea lettuce, and the animals living in the sediment (clams, cockles, bristle worms, amphipods – in Swedish - musslor, havsborstmaskar, märlkräftor) are suspected to be more or less dependent on this alga for food. By feeding on algae they also contribute to complete breakdown of the algae, i.e. the nutrients in algae that are not taken up by animals are released to the water and can be taken up by algae again. Without breakdown no new growth! In the experiment we are tracing carbon and nitrogen using stable isotopes (nitrogen and carbon which is heavier than normal) to quantify how much of the algae is taken up by different species of fauna and how much is left in the sediment.

Sea lettuce in the lab, incubated with stable isotopes of carbon and nitrogen, to be given to the animals soon.

When the tide is low we walk on the sandflat and select sites with high and low density of the species we are interested in. All of them are hiding in the sediment but we can estimate what is in the sediment by looking at the feeding tracks on the sediment surface.

This is how it looks like when 4 clams has been feeding on the sediment surface (they uses their siphons to vaccum-clean the sediment surface for small edible particles, for example algae that has been broken down to small pieces).

And this is how it looks like when all the cores have been transported to the laboratory. We let the animals feed on the isotope labeled sea lettuce for about 10 days. Will be interesting to see how different communities process the alga.

It took ages to make the pumps imitate the tides...