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TAXON-SPECIFIC PHYTOPLANKTON MORTALITY DUE TO MICROZOOPLANKTON GRAZING IN THE SOUTHERN CALIFORNIA CURRENT DURING THE 2014 BLOB AND 2016 EL NIÑO (E)

The dilution method is commonly used to measure rates of phytoplankton growth and mortality due to microzooplankton (<200 µm) grazing. Here, we present results of dilution experiments conducted on two cruises in the southern California Current, as part of the California Current Ecosystem Long Term Ecological Research (CCE LTER) program, during the anomalously warm years of 2014 (the Blob) and the 2016 El Niño. Experimental bottles were incubated in situ in the mixed layer, attached to a drifter line, for 24 h. Community phytoplankton mortality rates due to grazing were determined using fluorometric chlorophyll and flow cytometry. Relative growth and mortality rates of key phytoplankton taxa from the results of 16S/18S rDNA metabarcoding. Grazing mortality was comparable in both warm years, with 20-32% of daily phytoplankton growth consumed by microzooplankton in coastal areas and 80-128% offshore. This is slightly lower than previously measured coastal grazing rates of ~40% in the El Niño neutral year of 2006 (Landry et al. 2009). A likely reason for this could be mesozooplankton grazing on microzooplankton. Size-fractioned experiments targeting nanozooplankton (<20 µm) grazing found rates similar to that of the whole microzooplankton community, indicating that the smallest protists played a major grazing role. Relative phytoplankton growth and mortality estimates from molecular analyses showed unique patterns among diatoms, dinoflagellates, and prasinophytes. The use of size-fractioned dilution treatments and molecular analyses provided insights into complex trophic interactions that would otherwise have been hidden in the community-level growth and grazing rates.

Authors

Freibott, A., UC San Diego, Scripps Institution of Oceanography, USA, afreibott@ucsd.edu

Valencia, B., UC San Diego, Scripps Institution of Oceanography, USA, bellival@ucsd.edu

Rabines, A., UCSD, JCVI, USA, arabines@jcvi.org

McCrow, J. P., JCVI, USA, jmccrow@jcvi.org

Selph, K. E., University of Hawaii at Manoa, USA, selph@hawaii.edu

Allen, A. E., UCSD, JCVI, USA, aallen@ucsd.edu

Landry, M. R., UCSD, Scripps Institution of Oceanography, USA, mlandry@ucsd.edu

Details

Poster presentation

Session #:053
Date: 03/03/2017
Time: 15:30 - 16:30
Location: Poster/Exhibit Hall

Presentation is given by student: Yes

PosterID: 429