Quantification of the effects of ocean acidification on benthic foraminifera

Abstract

The global ocean has experienced an alteration of its seawater chemistry due to the continuing uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere. This ongoing process called Ocean acidification (OA) has reduced seawater pH levels, carbonate ion concentrations (CO₃⁻²) and carbonate saturation state (Ω) with implications for the diversity and functioning of marine life, particularly for marine calcifiers such as foraminifera. The vulnerability of this ubiquitous calcifying group to future high 𝘱CO₂ /low pH scenarios has been assessed naturally and experimentally in the last decades. However, little is known about how benthic foraminifera from coastal environments such as intertidal environments will respond to the effects of OA projected by the end of the century. This research aimed to quantify the effects of OA on a series of biological parameters measured on the benthic foraminifera 𝘌𝘭𝘱𝘩𝘪𝘥𝘪𝘶𝘮 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 and 𝘏𝘢𝘺𝘯𝘦𝘴𝘪𝘯𝘢 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢 through a laboratory-based experimental approach where future scenarios of a high CO₂ atmosphere and low seawater pH were explored. Experimental evidence revealed that survival rates, test weight and size-normalized weight (SNW) of 𝘌. 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 were negatively affected by OA. Whereas 𝘏. 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢 was positively affected (i.e. enhanced growth rates) showing a species-specific response to OA at 13°C. However, the combined effect of OA and temperature (15°C) reduced survival and growth rates for 𝘌𝘭𝘱𝘩𝘪𝘥𝘪𝘶𝘮 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 and 𝘏𝘢𝘺𝘯𝘦𝘴𝘪𝘯𝘢 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢. Test morphology (i.e. test surface and feeding ornamentation) of live 𝘌. 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 and 𝘏. 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢 were severely affected after 6 weeks by OA, negatively influencing the uptake of 13C-labelled diatoms of 𝘕𝘢𝘷𝘪𝘤𝘶𝘭𝘢 𝘴𝘱., notably for 𝘌. 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪. Test dissolution rates were enhanced by OA and negatively affected foraminiferal morphology of recently dead assemblages with implications for net accumulation and preservation. These results imply that the long-term storage of inorganic carbon and cycling of carbon in coastal benthic ecosystems will be considerably altered by future OA.