Assessment of Prymnesyophyta (Haptophyta) Abundance by CARD-FISH in the Sargasso Sea

Phytoplankton are central to oceanic primary productivity and the marine food web, playing a critical role in the biogeochemical cycling of carbon (C) through their photosynthetic uptake of atmospheric CO₂. The phytoplankton group, prymnesiophytes, include coccolithophores that are easily identifiable in their calcifying state. However, increasing evidence suggests that many prymnesiophytes undergo complex life cycles, alternating between haploid and diploid stages that may exclude calcification. This complicates their identification using traditional light microscopy or scanning electron microscopy (SEM) during their non-calcifying phases. To overcome these limitations, fluorescence in situ hybridization (FISH) coupled with catalyzed reporter deposition (CARD-FISH), was used to target Eukaryotes, Chlorophytes, non-Chlorophytes and Prymnesiophytes regardless of calcification status. Surface, Deep Chlorophyll Maximum, and Lower Photic Zone samples were collected from the Sargasso Sea during the Fall of 2020. Prymnesiophyte abundance was compared to the total eukaryotic phytoplankton community and concurrent SEM analyses. While CARD-FISH produced results consistent with SEM at the surface, it underestimated Prymnesiophyte abundance—by ~50%—in deeper waters. These regions are characterized by a high diversity of rare and uncultured species with sequences unavailable during probe design. This underestimation suggests that the molecular diversity of Prymnesiophytes in the Sargasso Sea, and likely the broader phytoplankton community, is higher than previously anticipated.

Presentation Preference: Oral

Primary Presenter: Josué Millán, Indiana State University (josue.g.millan@gmail.com)

Authors:

Josué Millán, Indiana State University - North Carolina Central University  (Jmillan1@sycamores.indstate.edu)

Rachel Parsons, Bermuda Institute of Ocean Sciences – Arizona State University, Julie Ann Wrigley Global Futures Laboratory  (rachel_parsons@asu.edu)

José Vargas-Muñiz, Virginia Polytechnic Institute and State University  (jvm15@vt.edu)

Leocadio Blanco-Bercial, Bermuda Institute of Ocean Sciences – Arizona State University, Julie Ann Wrigley Global Futures Laboratory  (leocadio@asu.edu)

Amos Winter, Indiana State University  (amos.winter@indstate.edu)