Seawater carbonate chemistry and net calcification of Porites, Zoanthus growth and maximum PSII efficiency of Porites and Zoanthus@en

Ocean acidification (OA) threatens the persistence of reef-building corals and the habitat they provide. While species-specific effects of OA on marine organisms could have cascading effects on ecological interactions like competition, few studies have identified how benthic reef competitors respond to OA. We explored how two common Caribbean competitors, branching Porites and a colonial zoanthid (Zoanthus), respond to the factorial combination of OA and competition. In the laboratory, we exposed corals, zoanthids and interacting corals and zoanthids to ambient (8.01 ± 0.03) and OA (7.68 ± 0.07) conditions for 60 days. The OA treatment had no measured effect on zoanthids or coral calcification but decreased Porites maximum PSII efficiency. Conversely, the competitive interaction significantly decreased Porites calcification but had minimal-to-no countereffects on the zoanthid. Although this interaction was not exacerbated by the 60-day OA exposure, environmental changes that enhance zoanthid performance could add to the dominance of zoanthids over corals. The lack of effects of OA on coral calcification indicates that near-term competitive interactions may have more immediate consequences for some corals than future global change scenarios. Disparate consequences of competition have implications for community structure and should be accounted for when evaluating local coral reef trajectories.海洋酸化（Ocean Acidification，OA）威胁着造礁珊瑚的存续及其所提供的栖息环境。尽管海洋酸化对海洋生物的物种特异性效应可能对竞争等生态相互作用产生级联影响，但目前鲜有研究阐明底栖珊瑚礁竞争者对海洋酸化的响应模式。本研究探究了两种常见的加勒比海珊瑚礁竞争者——分枝微孔珊瑚（Porites）与群居花虫珊瑚（Zoanthus）对海洋酸化与竞争的析因组合的响应情况。实验室内，我们将单独培养的珊瑚、花虫珊瑚，以及共培养的珊瑚与花虫珊瑚分别置于环境对照（pH 8.01 ± 0.03）与海洋酸化（OA，pH 7.68 ± 0.07）条件下培养60天。海洋酸化处理对花虫珊瑚及珊瑚的钙化速率无显著影响，但降低了微孔珊瑚的PSII最大光化学效率。与之相反，种间竞争相互作用显著降低了微孔珊瑚的钙化速率，但对花虫珊瑚的影响极小甚至无显著影响。尽管60天的海洋酸化暴露并未加剧这一种间竞争相互作用，但能够提升花虫珊瑚生存表现的环境变化，可能进一步强化其相对于珊瑚的竞争优势。海洋酸化对珊瑚钙化速率无显著影响这一结果表明，相较于未来全球变化情景，近期的种间竞争相互作用可能对部分珊瑚产生更为直接的生态后果。种间竞争所带来的差异化影响后果对珊瑚礁群落结构具有重要意义，在评估当地珊瑚礁的发展轨迹时应予以考虑。