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Marine microbial communities in coastal environments are subject to both seasonal fluctuations and anthropogenic alterations of environmental conditions. The separate influences of temperature and resource dependency on phytoplankton growth, community, and ecosystem metabolism are relatively well understood. However, winners and losers in the ocean are determined based on the interplay among often rapidly changing biological, chemical and physical drivers. The direct, indirect, and interactive effects of these conditions on planktonic food web structure and function are poorly constrained. Here, we investigated how simultaneous manipulation of temperature and nutrient availability affects trophic transfer from phytoplankton to herbivorous protists, and their resulting implications at the ecosystem level. Temperature directly affected herbivorous protist composition; ciliates dominated (66%) in colder treatment and dinoflagellates (60%) at warmer temperatures. Throughout the experiments, grazing rates were < 0.1 d 1, with higher rates at subzero temperatures. Overall, the nutrient–temperature interplay affected trophic transfer rates antagonistically when nutrients were amended, and synergistically, when nutrients were not added. This interaction resulted in higher percentages of primary production consumed under nutrient unamended compared to nutrient amended conditions. At the ecosystem level, these changes may determine the fate of primary production, with most of the production likely exported out of the pelagic zone in high-temperature and nutrient conditions, while high-temperature and low-nutrient availability strengthened food web coupling and enhanced trophic transfer. These results imply that in warming oceans, management of coastal nutrient loading will be a critical determinant of the degree of primary production removal by microzooplankton and dependent ecosystem production.
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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 2.6C and chlorophyll > 9 μg L1. Water was incubated in triplicate at 0.5C, 2.6C, and 6C 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.
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- PAR ID:
- 10316322
- Date Published:
- Journal Name:
- Limnology and Oceanography
- ISSN:
- 0024-3590
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/lno.12023
