Isotopic turnover experiments

Amanda Ziegler
PD fellow
UiT The Arctic University of Norway

Stable isotopes of carbon and nitrogen are commonly analyzed to study the diets of various organisms. The amount of these isotopes can inform ecologists about the structure of the food web; in other words, we can find out what different animals eat.

On the seafloor, organisms rely on the slow rain of organic particles from above as food. In the Arctic, the extreme changes from summer to winter dramatically alter how much food is available throughout the year for seafloor organisms. So, the question is, what are they eating throughout the year and does this change dramatically with the seasons and in different places?

To measure changes in an organism’s diet through time using stable isotopes, we must first know how long it takes the isotopes from the food to be incorporated into the tissue of the organism. This is called isotopic turnover and it tells us how long the isotopic signature of the organism represents its diet. Isotopic turnover rates are lacking for most benthic organisms, especially in the Arctic where collecting seafloor organisms is particularly difficult during much of the year.

A postdoctoral fellow in the Nansen Legacy will answer some of these questions and improve our understanding of how isotopes are incorporated into benthic organisms through controlled feeding experiments of some key Arctic taxa. These organisms will be kept in aquaria under controlled environmental conditions and fed isotopically-labelled food. The isotopic signature of the food and the organisms will be measured over time until the isotopes have been completely incorporated into the organism’s tissue. The length of time that this takes is the turnover time.