Seawater carbonate chemistry and Posidonia oceanica epiphytic community composition and mineralogy

• Main Authors: Cox, T Erin, Nash, Merinda C, Gazeau, Frédéric, Deniel, M, Legrand, Erwann, Alliouane, Samir, Mahacek, Paul, Le Fur, Arnaud, Gattuso, Jean-Pierre, Martin, Sophie
• Format: Dataset
• Language: English
• Published: PANGAEA 2017
• Subjects: Alkalinity; total; Aragonite; Aragonite saturation state; Asymmetry; Benthos; Bicarbonate ion; Calcite saturation state; Calcium carbonate mass; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; Community composition and diversity; Coverage; Entire community; EXP; Experiment; Field experiment; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Magnesium carbonate; magnesite; Mediterranean Sea; Mesocosm or benthocosm; OA-ICC; Ocean Acidification International Coordination Centre; Other studied parameter or process; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); pH; standard deviation; Salinity; Soft-bottom community; Temperate; Temperature; water; Time point; descriptive; Treatment; Type; Villefranche_eFOCE; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.880301; https://doi.org/10.1594/PANGAEA.880301

Alterations in seagrass epiphytic communities are expected under future ocean acidification conditions, yet this hypothesis has been little tested in situ. A Free Ocean Carbon Dioxide Enrichment system was used to lower pH by a ~0.3 unit offset within a partially enclosed portion (1.7 m3) of a Posidonia oceanica meadow (11 m depth) between June 21 and November 3, 2014. Leaf epiphytic community composition (% cover) and bulk epiphytic mineralogy were compared every 4 weeks within three treatments, located in the same meadow: a pH-manipulated (experimental enclosure) and a control enclosure, as well as a nearby ambient area. Percent coverage of invertebrate calcifiers and crustose coralline algae (CCA) did not appear to be affected by the lowered pH. Furthermore, fleshy algae did not proliferate at lowered pH. Only Foraminifera, which covered less than 3% of leaf surfaces, declined in manner consistent with ocean acidification predictions. Bulk epiphytic magnesium carbonate composition was similar between treatments and percentage of magnesium appeared to increase from summer to autumn. CCA did not exhibit any visible skeleton dissolution or mineral alteration at lowered pH and carbonate saturation state. Negative impacts from ocean acidification on P. oceanica epiphytic communities were smaller than expected. Epiphytic calcifiers were possibly protected from the pH treatment due to host plant photosynthesis inside the enclosure where water flow is slowed. The more positive outcome than expected suggests that calcareous members of epiphytic communities may find refuge in some conditions and be resilient to environmentally relevant changes in carbonate chemistry.