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Marine Ecology Progress Series

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MEPS 605:103-110 (2018)  -  DOI:

Ocean warming, but not acidification, accelerates seagrass decomposition under near-future climate scenarios

Brendan P. Kelaher1,*, Melinda A. Coleman1,2, Melanie J. Bishop3

1National Marine Science Centre and Marine Ecology Research Centre, Southern Cross University, PO Box 4321, Coffs Harbour, NSW 2450, Australia
2NSW Fisheries, Department of Primary Industries, PO Box 4321, Coffs Harbour, NSW 2450, Australia
3Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia
*Corresponding author:

ABSTRACT: The majority of marine macrophyte production is not consumed by herbivores but instead is channeled into detrital pathways where it supports biodiversity and drives coastal productivity, nutrient cycling and blue carbon sequestration. While it is clear that detrital pathways will be affected by ocean climate change, the relative importance of changing temperature or pH, or their interactions, has not been assessed. We used outdoor mesocosm experiments to assess the relative importance of ocean warming, acidification and latitude of litter origin on the decomposition and biomechanical properties of seagrass Zostera muelleri. Seagrass, collected from 2 sites at each of 2 latitudes (29° and 35°S), was subjected to an orthogonal combination of current and predicted future ocean warming (+3°C) and acidification (-0.3 pH unit). Elevated temperatures resulted in a 15% greater loss of seagrass detrital mass. Mass loss of seagrass detritus was also greater in seagrass from higher than from lower latitudes. The stiffness (Young’s modulus) of decomposing seagrass was greater at 22°C than at 25°C. Elevated sea temperatures also weakened decomposing seagrass, but the magnitude of these effects was greater for Z. muelleri originating from higher than from lower latitudes. Overall, ocean warming is likely to have a much larger influence on seagrass decomposition than ocean acidification. As climate changes, however, if seagrass from higher latitudes takes on similar characteristics to seagrass currently growing at lower latitudes, there may be a negative feedback against the impacts of ocean warming on decomposition, moderating changes in associated primary and secondary productivity that supports coastal fisheries and ecosystem processes.

KEY WORDS: Ocean climate change · Ocean warming · Acidification · Seagrass · Decomposition · Eelgrass · Zostera

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Cite this article as: Kelaher BP, Coleman MA, Bishop MJ (2018) Ocean warming, but not acidification, accelerates seagrass decomposition under near-future climate scenarios. Mar Ecol Prog Ser 605:103-110.

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