THE INTERACTIVE EFFECTS OF TEMPERATURE AND NUTRIENTS ON A SPRING PHYTOPLANKTON COMMUNITY

A complex interplay of environmental variables impacts phytoplankton community composition and physiology. Temperature and nutrient availability are two principal factors driving phytoplankton growth and composition, but are often investigated independently and on individual species in the laboratory. To assess the individual and interactive effects of temperature and nutrient concentration on phytoplankton community composition and physiology, we altered both the thermal and nutrient conditions of a cold-adapted spring phytoplankton community in Narragansett Bay, Rhode Island, when surface temperature was 2.6°C and chlorophyll > 9 μg L⁻¹. Water was incubated in triplicate at −0.5°C, 2.6°C, and 6°C for 10 d. At each temperature, treatments included both nutrient amendments (N, P, Si addition) and controls (no macronutrients added). The interactive effects of temperature and resource availability altered phytoplankton growth and community structure. Nutrient amendments resulted in species sorting and communities dominated by larger species. Under replete nutrients, warming tripled phytoplankton growth rates, but under in situ nutrient conditions, increased temperature acted antagonistically, reducing growth rates by as much as 33%, suggesting communities became nutrient limited. The temperature–nutrient interplay shifted the relative proportions of each species within the phytoplankton community, resulting in more silica rich cells at decreasing temperatures, irrespective of nutrients, and C : N that varied based on resource availability, with nutrient limitation inducing a 47% increase in C : N at increasing temperatures. Our results illustrate how the temperature–nutrient interplay can alter phytoplankton community dynamics, with changes in temperature amplifying or exacerbating the nutrient effect with implications for higher trophic levels and carbon flux.

Presentation Preference: Oral

Primary Presenter: Stephanie Anderson, University of Rhode Island (sianderson@uri.edu)

Authors:

Stephanie Anderson, University of Rhode Island  (sianderson@uri.edu)

Gayantonia Franzè, Institute of Marine Research Norway  (gayantonia.franze@hi.no)

Joshua Kling, University of Southern California  (joshuakling13@gmail.com)

Paul Wilburn, Michigan State University  (paul.wilburn@nasa.gov)

Colin Kremer, University of Connecticut  (colin.kremer@uconn.edu)

Susanne Menden-Deuer, University of Rhode Island  (smenden@uri.edu)

Elena Litchman, Carnegie Science  (elitchman@carnegiescience.edu)

David Hutchins, University of Southern California  (dahutch@usc.edu)

Tatiana Rynearson, University of Rhode Island  (rynearson@uri.edu)