Herbivorous consumption of primary production is a key transformation in global biogeochemical cycles, directing matter and energy either to higher trophic levels, export production, or remineralization. Grazing by microzooplankton is often poorly constrained, particularly in dynamic coastal systems. Temperate coastal areas are seasonally and spatially variable, which presents both challenges and opportunities to identify patterns and drivers of grazing pressure. Here we report on two winter and one summer week‐long cruises (2018–2019), as part of the new Northeast U.S. Shelf Long‐Term Ecological Research program. During both seasons, coastal waters were colder and fresher, and had higher phytoplankton biomass than waters at the shelf break. The phytoplankton community was dominated by large cells in winter and by small cells in summer. Phytoplankton growth rates ranged from < 0.5 d−1in winter and up to 1.4 d−1in summer and were strongly correlated to temperature, to light availability, and to phytoplankton community size‐structure. Grazing rates were not correlated with total chlorophyll
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.
more » « less- NSF-PAR ID:
- 10388555
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 68
- Issue:
- S1
- ISSN:
- 0024-3590
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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