The Effects of Feeding Activity on the Bioenergetics of a Pelagic Calanoid Copepod, Pleuromamma xiphias

Diel vertical migration (DVM) is a daily cycle in which animals move up and down in the water column. DVM plays an important role in biogeochemical fluxes throughout the oceans. Metabolism of migrating animals also changes on a daily cycle, but these effects are poorly quantified. The copepod, Pleuromamma xiphias, is a known vertical migrator and a major contributor to nitrogen and carbon fluxes. Specific dynamic action (SDA) is the increase in metabolism shortly after the ingestion of food. It has been observed in many organisms, including other copepods. The objective of this pilot study was to observe how much of the daily variation in metabolism of P. xiphias is due to SDA with different trials of feeding and starving. Live P. xiphias (n = 55) were collected at “Station Leo” which is 3 – 5 miles off the coast of St. George’s Island, Bermuda. The copepods were initially fed for 24 hours in 1L bottles inoculated with the flagellate algae, Rhodomonas lens. The copepods were then split between various lengths of either continual feeding trials or long and short starving trials. Oxygen consumption and ammonium excretion were measured while the copepods were still alive. The copepods were frozen in liquid nitrogen after respirometry and brought back to the lab at Woods Hole Oceanographic Institute to measure glutamate dehydrogenase activity as a proxy for excretion. We observed some trends of a decrease in metabolic activity with an increase in starving period. The largest differences were observed between fed and long-starved copepods that were sampled in the morning, most likely representing SDA after feeding at night. These results encourage continued experimentation with a larger sample size, more replicates, more precise measurements, and changes to food source and lighting conditions.