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Will expanding marine vegetation in coastal waters of Greenland provide a refuge from ocean acidification for vulnerable marine life?

The photos show blue mussels among macroalgae, a setup in the laboratory for measuring pH across kelp boundary layers as well as pH loggers deployed in the field over diurnal cycles. Photographer: Carlos Duarte.

Ocean acidification, the progressive decline in pH as anthropogenic CO2 accumulates in ocean waters, is believed to be a major threat to the Arctic ecosystem. However, the pole ward expansion of kelp forests with warming may provide refuges for vulnerable marine life.

Kelp forests are important coastal habitats for many organisms including blue mussel and other bivalves that must deposit calcium carbonate minerals to produce their shells and therefore are favored by pH levels which are sufficiently high to ensure a positive saturation state of carbonate minerals. Kelps forests can exhibit large diurnal excursions in pH as photosynthesis causes increases during the day while respiration causes declines during night. However, long Arctic summer days may maintain pH high during the critical period for growth and development of calcifiers and this effect may provide refuges for bivalves as kelps expand northward in a warmer, high CO2, future.

To test this hypothesis, we conducted a two-week field campaign in Nuuk in late August/early September with the aim of quantifying pH-variability at different spatial scales in a coastal Arctic ecosystem: large-scale variability across a fjord, variability at kelp sites versus bare sites in relation to O2 production/consumption, small-scale variability within kelp forests, and micro-scale variability across boundary layers of algal thalli. Our results were very encouraging. During the few sunny days of the field campaign, diurnal variations in pH of the kelp forest clearly followed diurnal variations in incident light with pH peaks at midday 0.15 units higher than at night. We will conduct a second, crucial expedition and laboratory experiment in June next year, when long days should allow kelps to demonstrate their full power to raise pH and protect molluscs.

Dorte Krause-Jensen, Aarhus University (PI)
Mikael Sejr, Aarhus University
Kitte Linding Gerlich, Aarhus University
Martin Blicher, Greenland Institute of Natural Resources (GINR), Greenland
Lorenz Meire, Greenland Institute of Natural Resources (GINR), Greenland
Ole Geertz-Hansen, Greenland Institute of Natural Resources (GINR), Greenland  
Carlos Duarte, Instituto Mediterráneo de Estudios Avanzados (IMEDEA)/Consejo Superior de Investigaciones Científicas (CSIC), Spain
Iris Hendriks, Instituto Mediterráneo de Estudios Avanzados (IMEDEA)/Consejo Superior de Investigaciones Científicas (CSIC), Spain
Núria Marbà, Instituto Mediterráneo de Estudios Avanzados (IMEDEA)/Consejo Superior de Investigaciones Científicas (CSIC), Spain

For more information, contact Dorte Krause-Jensen

Cf. @duarteoceans for Tweets on the expedition