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

Biermann, Antje, Lewandowska, Aleksandra M., Engel, Anja and Riebesell, Ulf (2015) Organic matter partitioning and stoichiometry in response to rising water temperature and copepod grazing Marine Ecology Progress Series, 522 . pp. 49-65. DOI 10.3354/meps11148.

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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.

Document Type: Article
Additional Information: WOS:000350667800004
Keywords: Climate change · Ocean warming · Phytoplankton spring bloom · Copepods · Mesocosm study · Organic matter · Transparent exopolymer particles · TEP · Nutrient recycling
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Refereed: Yes
DOI etc.: 10.3354/meps11148
ISSN: 0171-8630
Date Deposited: 05 Dec 2014 10:49
Last Modified: 13 Apr 2017 08:14

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