CAN ZOOPLANKTON UTILIZE DISSOLVED AMINO ACIDS AS A NUTRIENT SOURCE?

In the marine food web, crustaceans are best known for their role as consumers of primary producers and other organisms; however, there is growing evidence that some species are capable of dissolved nutrient uptake in the form of amino acids. This leads us to hypothesize that copepods, the most abundant and widespread marine crustacean, may also be able to actively utilize amino acids from their environment via absorption or other uptake pathways.  Here we explore how zooplankton contribute to marine biogeochemical cycles by acting as both a source, returning nutrients to the environment via excretion, and as a sink, via amino acid uptake, for dissolved nutrients. In parallel but separate 24-hour incubations, we measured 1) the amount of ammonium excreted and 2) the absorption of amino acids by Calanus sp. collected from the Gulf of Maine. To test copepod absorption of amino acids, Calanus sp. were collected and incubated in seawater with dual isotopically-labeled (15N and 13C) amino acids; then their level of isotopic enrichment was analyzed and compared to unexposed (control) Calanus sp. incubated over the same 24 hour period. Our results showed that ammonium excretion ranged broadly from 0.03 to 0.13µmols per individual per 24 hours. We also discovered that Calanus sp. are capable of absorbing amino acids and that the carbon to nitrogen ratio of the absorbed substrate (1.1:1) was lower than the initial substrate (4:1), indicating preferential uptake of nitrogen. This establishes a previously unrecognized source of nutrients for copepod metabolism. 

Presentation Preference: Poster

Primary Presenter: David Gonzalez, California State University Dominguez Hills (dgonzalez386@toromail.csudh.edu)

Authors:

Collen McBride, Memorial University of Newfoundland  (cemcbride@mun.ca)

David Gonzalez, California State University Dominguez Hills  (dgonz3014@gmail.com)

Karen Stamieszkin, Bigelow Laboratory for Ocean Sciences  (kstamieszkin@bigelow.org)

Rachel Sipler, Bigelow Laboratory for Ocean Sciences  (rsipler@bigelow.org)