title: Effect of Inorganic and Organic Carbon Enrichments (DIC and DOC) on the Photosynthesis and Calcification Rates of Two Calcifying Green Algae from a Caribbean Reef Lagoon.
abstract: Coral reefs worldwide are affected by increasing dissolved inorganic carbon (DIC) and organic carbon (DOC) concentrations due to ocean acidification (OA) and coastal eutrophication. These two stressors can occur simultaneously, particularly in near-shore reef environments with increasing anthropogenic pressure. However, experimental studies on how elevated DIC and DOC interact are scarce and fundamental to understanding potential synergistic effects and foreseeing future changes in coral reef function. Using an open mesocosm experiment, the present study investigated the impact of elevated DIC (pHNBS: 8.2 and 7.8; pCO2: 377 and 1076 μatm) and DOC (added as 833 μmol L-1 of glucose) on calcification and photosynthesis rates of two common calcifying green algae, Halimeda incrassata and Udotea flabellum, in a shallow reef environment. Our results revealed that under elevated DIC, algal photosynthesis decreased similarly for both species, but calcification was more affected in H. incrassata, which also showed carbonate dissolution rates. Elevated DOC reduced photosynthesis and calcification rates in H. incrassata, while in U. flabellum photosynthesis was unaffected and thalus calcification was severely impaired. The combined treatment showed an antagonistic effect of elevated DIC and DOC on the photosynthesis and calcification rates of H. incrassata, and an additive effect in U. flabellum. We conclude that the dominant sand dweller H. incrassata is more negatively affected by both DIC and DOC enrichments, but that their impact could be mitigated when they occur simultaneously. In contrast, U. flabellum can be less affected in coastal eutrophic waters by elevated DIC, but its contribution to reef carbonate sediment production could be further reduced. Accordingly, while the capacity of environmental eutrophication to exacerbate the impact of OA on algal-derived carbonate sand production seems to be species-specific, significant reductions can be expected under future OA scenarios, with important consequences for beach erosion and coastal sediment dynamics.
authors.affiliation: Leibniz Center for Tropical Marine Ecology (ZMT), Bremen, Germany.
authors.forename: Friedrich W
authors.initials: FW
authors.lastname: Meyer
authors.affiliation: Laboratory of Photobiology, Unidad Académica de Sistemas Arrecifales Puerto Morelos (ICMyL), Universidad Nacional Autónoma de México (UNAM), Cancún, Mexico.
authors.forename: Nadine
authors.initials: N
authors.lastname: Schubert
authors.affiliation: Edinburgh Napier University, School of Life, Sport and Social Sciences, EH11 4BN Edinburgh, United Kingdom.|St Abbs Marine Station, St Abbs, Berwickshire, TD14 5QF, United Kingdom.
authors.forename: Karen
authors.initials: K
authors.lastname: Diele
authors.affiliation: Leibniz Center for Tropical Marine Ecology (ZMT), Bremen, Germany.
authors.forename: Mirta
authors.initials: M
authors.lastname: Teichberg
authors.affiliation: Leibniz Center for Tropical Marine Ecology (ZMT), Bremen, Germany.|Faculty of Biology & Chemistry, University of Bremen, Bibliothekstraße 1, Bremen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Wild
authors.affiliation: Laboratory of Photobiology, Unidad Académica de Sistemas Arrecifales Puerto Morelos (ICMyL), Universidad Nacional Autónoma de México (UNAM), Cancún, Mexico.
authors.forename: Susana
authors.initials: S
authors.lastname: Enríquez
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic / Q000502:physiology*; D002244:Carbon / Q000378:metabolism*; D017554:Carbon Compounds, Inorganic / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D017691:Caribbean Region; D000460:Chlorophyta / Q000737:chemistry / Q000378:metabolism*; D057894:Coral Reefs; D006863:Hydrogen-Ion Concentration; D009930:Organic Chemicals / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D012623:Seawater
chemical_list: D017554:Carbon Compounds, Inorganic; D009930:Organic Chemicals; D002245:Carbon Dioxide; D002244:Carbon