Description: The data describes fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA) in mmol m⁻² h⁻¹ measured in a red sea mangrove and adjacent coral lagoon (negatives fluxes are uptake of TA or DIC by the sediment). The incubations were conducted in a mono-specific Avicennia marina mangrove forest of the central Red Sea (22° 20' 23" N, 39° 05' 22" E). The incubations were conducted during the last 2 hours of the rising tide, around solar noon and at night within the same day. The Incubations were conducted from April 2018 to May 2019. In April/May 2018, day and night incubations were done 15 days apart.

Description: Ocean acidification (OA) is generally assumed to negatively impact calcification rates of marine organisms. At a local scale however, biological activity of macrophytes may generate pH fluctuations with rates of change that are orders of magnitude larger than the long-term trend predicted for the open ocean. These fluctuations may in turn impact benthic calcifiers in the vicinity. Combining laboratory, mesocosm and field studies, such interactions between OA, the brown alga Fucus vesiculosus, the sea grass Zostera marina and the blue mussel Mytilus edulis were investigated at spatial scales from decimetres to 100s of meters in the western Baltic. Macrophytes increased the overall mean pH of the habitat by up to 0.3 units relative to macrophyte- free, but otherwise similar, habitats and imposed diurnal pH fluctuations with amplitudes ranging from 0.3 to more than 1 pH unit. These amplitudes and their impact on mussel calcification tended to increase with increasing macrophyte biomass to bulk water ratio. At the laboratory and mesocosm scales, biogenic pH fluc- tuations allowed mussels to maintain calcification even under acidified conditions by shifting most of their calcification activity into the daytime when biogenic fluctuations caused by macrophyte activity offered temporal refuge from OA stress. In natural habitats with a low biomass to water body ratio, the impact of biogenic pH fluctuations on mean calcification rates of M. edulis was less pronounced. Thus, in dense algae or seagrass habitats, macrophytes may mitigate OA impact on mussel calcification by raising mean pH and providing temporal refuge from acidification stress.

Description: Salinity, oxygen and pH conditions in the microhabitat patches of Fucus, Zostera and sand at daytime and nighttime in the months august and september 2013 as sampled by regular SCUBA dives.

Description: Shell length increase of mussels exposed in natural micrahabitats (Fucus, Zostera, sand) was monitored by SCUBA over 30 days.