Slow‐flow habitats as refugia for coastal calcifiers from ocean acidification

Abstract

The pH of the oceans' surface water is dropping, termed ocean acidification (OA), and the 0.4 unit reduction in pH by 2100 is projected to negatively impact benthic coastal organisms that produce calcium carbonate "skeletons." Research has focussed on identifying species that are susceptible to OA, but there is an urgent need to discover refuge habitats that will afford protection to vulnerable species. The susceptibility of calcium carbonate skeletons to dissolution by OA depends on the pH at their surface, and this is controlled by the interaction between seawater velocity and organismal metabolism. This perspective considers how seawater velocity modifies the responses of calcifying organisms (seaweed, shellfish, and tropical corals) to OA through its action on controlling diffusion boundary layer thickness and thereby the pH and calcium carbonate saturation state (Ω) at the organisms' surface. Evidence is presented to support the idea that slow-flow habitats, such as wave-sheltered bays or the within canopies of seaweed/seagrass beds, might provide inexpensive refugia from OA for vulnerable coastal calcifiers.

Effects of pCO2 on spatial competition between the corals Montipora aequituberculata and Porites lutea

“…DOC and oxygen availability) in seawater between competing corals (Haas et al 2011). The fixation of inorganic CO 2 through photosynthesis of the Symbiodinium within the coral tissue (Muscatine et al 1981) may have further modified the seawater between competing corals, with CO 2 uptake causing a localized increase in seawater pH that could lessen the negative effects of OA on coral growth (see Anthony et al 2013, Hurd 2015.…”

Long photoperiods sustain high pH in Arctic kelp forests

“…Marine macrophytes are autotrophic communities, where photosynthesis exceeds respiration ( 7 ), and their metabolism can create marked pH fluctuations in seagrass meadows ( 8 ) and kelp forests ( 9 , 10 ) with increases of up to 1 pH unit during the day ( 11 ), depending on plant biomass, activity ( 8 , 12 , 13 ), and flow attenuation ( 14 , 15 ). Vegetated habitats may therefore provide refugia for calcifiers from future OA ( 4 , 15 ).…”

Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation?

“…Indeed, during midsummer near the poles where photoperiods exceed 21 h, seaweed productivity can create sustained high pH over the summer period and be particularly suitable habitats for calcifiers . The capacity of seaweed aquaculture to affect pH and provide refugia for calcifiers depend also on flow regimes (Hurd, 2015) and increase where the farms are located in coastal environment with weak currents and/or where the seaweed themselves slow down flow. The capacity of seaweed farms to offer habitat for biodiversity is, however, temporary, as this capacity is lost at harvest.…”