Community structure and biodiversity in marine benthic communities during experiments, 2011

A mesocosm experiment was conducted to quantify the effects of reduced pH and elevated temperature on an intact marine invertebrate community. Standardised faunal communities, collected from the extreme low intertidal zone using artificial substrate units, were exposed to one of eight nominal treatments (four pH levels: 8.0, 7.7, 7.3 and 6.7, crossed with two temperature levels: 12 and 16°C). After 60 days exposure communities showed significant changes in structure and lower diversity in response to reduced pH. The response to temperature was more complex. At higher pH levels (8.0 and 7.7) elevated temperature treatments contained higher species abundances and diversity than the lower temperature treatments. In contrast, at lower pH levels (7.3 and 6.7), elevated temperature treatments had lower species abundances and diversity than lower temperature treatments. The species losses responsible for these changes in community structure and diversity were not randomly distributed across the different phyla examined. Molluscs showed the greatest reduction in abundance and diversity in response to low pH and elevated temperature, whilst annelid abundance and diversity was mostly unaffected by low pH and was higher at the elevated temperature. The arthropod response was between these two extremes with moderately reduced abundance and diversity at low pH and elevated temperature. Nematode abundance increased in response to low pH and elevated temperature, probably due to the reduction of ecological constraints, such as predation and competition, caused by a decrease in macrofaunal abundance. This community-based mesocosm study supports previous suggestions, based on observations of direct physiological impacts, that ocean acidification induced changes in marine biodiversity will be driven by differential vulnerability within and between different taxonomical groups. This study also illustrates the importance of considering indirect effects that occur within multispecies assemblages when attempting to predict the consequences of ocean acidification and global warming on marine communities.本研究开展了一项中型受控生态系统（mesocosm）实验，以定量分析pH降低与温度升高对完整海洋无脊椎动物群落的影响。研究人员采用人工基质单元从潮间带极低潮区采集标准化动物群落，并将其置于8种名义处理组中培养：设置4个pH水平（8.0、7.7、7.3与6.7）与2个温度水平（12℃与16℃），进行交叉实验。暴露培养60天后，群落结构出现显著变化，且多样性随pH降低呈下降趋势；而温度对群落的影响更为复杂。在较高pH水平（8.0与7.7）组中，高温处理组的物种丰度与多样性均高于低温处理组；与之相反，在较低pH水平（7.3与6.7）组中，高温处理组的物种丰度与多样性则低于低温处理组。导致群落结构与多样性变化的物种丧失现象，并非在被检测的各动物门中随机分布。软体动物门（Mollusca）在低pH与高温胁迫下，丰度与多样性下降幅度最大；环节动物门（Annelida）的丰度与多样性基本不受低pH影响，且在高温环境下更高。节肢动物门（Arthropoda）的响应则介于两者之间，在低pH与高温条件下丰度与多样性呈中等程度下降。线虫动物门（Nematoda）的丰度在低pH与高温条件下有所上升，这可能是由于大型底栖动物丰度下降导致捕食、竞争等生态约束得以缓解。这项基于群落的中型受控生态系统研究，佐证了此前基于直接生理影响观测提出的假说：海洋酸化引发的海洋生物多样性变化，将由不同分类群内部及分类群之间的差异化脆弱性所驱动。本研究同时表明，在预测海洋酸化与全球变暖对海洋群落的影响时，需考虑多物种种群组合内发生的间接效应，这一点至关重要。