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Marine Ecology Progress Series

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MEPS 522:49-65 (2015)  -  DOI:

Organic matter partitioning and stoichiometry in response to rising water temperature and copepod grazing

Antje Biermann1, Aleksandra M. Lewandowska1,2,3, Anja Engel1, Ulf Riebesell1,*

1GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
2German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103 Leipzig, Germany
3Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl-von-Ossietzky University Oldenburg, Schleusenstraße 1, 26382 Wilhelmshaven, Germany
*Corresponding author:

ABSTRACT: Rising ocean temperature is expected to change the balance between production and degradation of organic matter due to different temperature sensitivities of auto- and heterotrophic processes. Copepods are the most prominent zooplankton group, and elevated temperature increases their growth and grazing rates. So far, it is unknown to what extent copepods affect the partitioning and stoichiometry of organic matter in a warmer surface ocean. We therefore conducted a mesocosm experiment with 3 copepod densities and 2 temperature scenarios to determine effects on the pools of dissolved and particulate organic matter and their C:N:P ratios. Here we show that particulate organic C (POC) concentrations decreased with increasing copepod abundance. This effect was more pronounced at elevated temperature, yielding a decrease in the POC to particulate nitrogen ratio (POC:PN) from 26 to 13 and in the POC:particulate organic phosphorus (POP) ratio from 567 to 257, from low to high copepod density. Dissolved organic carbon (DOC) accumulation was positively affected by temperature. However, increasing copepod abundance decreased the accumulation of DOC at elevated temperature. Copepod grazing and egestion enhanced the recycling of N and P, thereby increasing the availability of these nutrients for autotrophs. In concert with temperature-induced shifts in the phytoplankton community composition and size, changes in copepod abundance may therefore have contributed to altering the elemental composition of seston. Our findings suggest combined effects of zooplankton grazing and temperature on the composition and recycling of organic matter that should be taken into account when simulating biogeochemical cycles in a future ocean.

KEY WORDS: Climate change · Ocean warming · Phytoplankton spring bloom · Copepods · Mesocosm study · Organic matter · Transparent exopolymer particles · TEP · Nutrient recycling

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Cite this article as: Biermann A, Lewandowska AM, Engel A, Riebesell U (2015) Organic matter partitioning and stoichiometry in response to rising water temperature and copepod grazing. Mar Ecol Prog Ser 522:49-65.

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