Seawater carbonate chemistry and benthic marine community during experiments, 2011

Ocean acidification is predicted to impact all areas of the oceans and affect a diversity of marine organisms. However, the diversity of responses among species prevents clear predictions about the impact of acidification at the ecosystem level. Here, we used shallow water CO2 vents in the Mediterranean Sea as a model system to examine emergent ecosystem responses to ocean acidification in rocky reef communities. We assessed in situ benthic invertebrate communities in three distinct pH zones (ambient, low, and extreme low), which differed in both the mean and variability of seawater pH along a continuous gradient. We found fewer taxa, reduced taxonomic evenness, and lower biomass in the extreme low pH zones. However, the number of individuals did not differ among pH zones, suggesting that there is density compensation through population blooms of small acidification-tolerant taxa. Furthermore, the trophic structure of the invertebrate community shifted to fewer trophic groups and dominance by generalists in extreme low pH, suggesting that there may be a simplification of food webs with ocean acidification. Despite high variation in individual species' responses, our findings indicate that ocean acidification decreases the diversity, biomass, and trophic complexity of benthic marine communities. These results suggest that a loss of biodiversity and ecosystem function is expected under extreme acidification scenarios.

海洋酸化（Ocean acidification）预计将影响全球所有海域，并对多样的海洋生物造成冲击。然而，不同物种对酸化的响应差异，使得我们难以明确预测其对生态系统层级的影响。本研究以地中海海域的浅海水CO₂喷口（shallow water CO₂ vents）作为模式系统，探究岩礁群落中底栖无脊椎动物群落对海洋酸化的生态系统级响应。我们对沿连续pH梯度分布的三个特征鲜明的pH区间（背景pH、低pH、极低pH）内的原位（in situ）底栖无脊椎动物群落（benthic invertebrate communities）开展了调查，这些区间的海水pH均值与波动幅度均存在显著差异。研究发现，极低pH区间内的类群数量更少、分类均匀度（taxonomic evenness）更低，生物量也显著下降。但各pH区间的个体总数并无显著差异，这表明小型耐酸化类群（acidification-tolerant taxa）的种群爆发（population blooms）可实现密度补偿（density compensation）。此外，极低pH区间内的无脊椎动物群落营养结构（trophic structure）发生转变：营养类群数量减少，且以广食性物种（generalists）占据主导，这提示海洋酸化可能导致食物网结构简化。尽管单个物种对酸化的响应存在高度异质性，本研究结果仍表明，海洋酸化会降低底栖海洋群落的多样性、生物量与营养复杂性（trophic complexity）。上述结果预示，在极端酸化情景下，海洋生物多样性（biodiversity）与生态系统功能（ecosystem function）或将出现丧失。