Relative roles of endolithic algae and carbonate chemistry variability in the skeletal dissolution of crustose coralline algae

[摘要] The susceptibility of crustose coralline algae (CCA) skeletons todissolution is predicted to increase as oceans warm and acidify. Skeletaldissolution is caused by bioerosion from endolithic microorganisms and bychemical processes associated with undersaturation of carbonate minerals inseawater. Yet, the relative contribution of algal microborers and seawatercarbonate chemistry to the dissolution of organisms that cement reefs underprojected pCO₂ and temperature (pCO₂-T) scenarios have not beenquantified. We exposed CCA skeletons (Porolithon onkodes) to four pCO₂-T treatments(pre-industrial, present-day, SRES-B1 "reduced" pCO₂, andSRES-A1FI "business-as-usual" pCO₂ emission scenarios) under natural lightcycles vs. constant dark conditions for 8 weeks. Dissolution rates ofskeletons without photo-endoliths were dramatically higher (200%) thanthose colonized by endolithic algae across all pCO₂-T scenarios. Thissuggests that daytime photosynthesis by microborers counteract dissolutionby reduced saturation states resulting in lower net erosion rates overday–night cycles. Regardless of the presence or absence of phototrophicmicroborers, skeletal dissolution increased significantly under the springA1FI "business-as-usual" scenario, confirming the CCA sensitivity tofuture oceans. Projected ocean acidity and temperature may significantlydisturb the stability of reef frameworks cemented by CCA, but surficialsubstrates harbouring photosynthetic microborers will be less impacted thanthose without algal endoliths.

[学科分类] 地球化学与岩石