Science Serving Maryland's Coasts

Erin Kithcart, East Stroudsburg University

Class Year: 

Project Title: 

Effects of Grazing by Acartia tonsa on the Structures of Alkenones used as Tracers in Paleo Sea Surface Temperatures

Long-chain alkenones are found in many sediments throughout the oceans. They are considered exclusive to the prymnesiophytes, to which Isochrysis galbana (a coastal species) and Emiliania hmleyi (an ocean coccolithophore) both belong. The ratios of unsaturated alkenones found in sediments has been used to establish an index, Uk37, which can be used to determine the temperature at which an alkenone was formed. Since it is unlikely that anything reaches the ocean floor without going through some sort of biological process (such as digestion), researchers must determine if the ratios of alkenones found in these algae remain the same after they have gone through digestion. The focus of this study was to determine if the ratios of the alkenones found in I. galbana and E. huxley remained the same in the fecal pellets of the copepods (Acartia tonsa) which had been feeding upon the algae. Both L. galbana and E. huxleyi were grown in 15 psu at 18°C. Algal and fecal pellet samples were extracted and analyzed with a gas chromatograph. The abundance of the alkenones was reduced in the fecal pellet sample, but the ratios of the alkenones with relation to one another remained the same. When plotted on the individual Uk'37 regression lines for E. huxteyi and I. galbana from a previous study done at Chesapeake Biological Laboratory, the index from each respective experiment predicted the correct temperature at which the algal cultures were grown. This indicates that grazing has no effect on the ratios of alkenones, and that the Uk37 index is a reliable source in predicting sea surface temperatures.