Effects of acute ocean acidification on spatially-diverse polar pelagic foodwebs:Insights from on-deck microcosms

The polar oceans are experiencing some of the largest levels of ocean acidification (OA) resulting from the uptake of anthropogenic carbon dioxide (CO2). Our understanding of the impacts this is having on polar marine communities is mainly derived from studies of single species in laboratory conditions, while the consequences for food web interactions remain largely unknown. This study carried out experimental manipulations of natural pelagic communities at different high latitude sites in both the northern (Nordic Seas) and southern hemispheres (Scotia and Weddell Seas). The aim of this study was to identify more generic responses and greater experimental reproducibility through implementing a series of short term (4 day), multilevel (3 treatment) carbonate chemistry manipulation experiments on unfiltered natural surface ocean communities, including grazing copepods. The experiments were successfully executed at six different sites, covering a diverse range of environmental conditions and differing plankton community compositions. The study identified the interaction between copepods and dinoflagellate cell abundance to be significantly altered by elevated levels of dissolved CO2 (pCO2), with dinoflagellates decreasing relative to ambient conditions across all six experiments. A similar pattern was not observed in any other major phytoplankton group. The patterns indicate that copepods show a stronger preference for dinoflagellates when in elevated pCO2 conditions, demonstrating that changes in food quality and altered grazing selectivity may be a major consequence of ocean acidification. The study also found that transparent exopolymeric particles (TEP) generally increased when pCO2 levels were elevated, but the response was dependent on the exact set of environmental conditions. Bacteria and nannoplankton showed a neutral response to elevated pCO2 and there was no significant relationship between changes in bacterial or nannoplankton abundance and that of TEP concentrations. Overall, the study illustrated that, although some similar responses exist, these contrasting high latitude surface ocean communities are likely to show different responses to the onset of elevated pCO2.

极地海洋正经历着全球最为显著的海洋酸化（OA）过程之一，这一现象源于其对人为二氧化碳（CO₂）的吸收。目前学界对海洋酸化对极地海洋生物群落的影响认知，主要来自实验室条件下的单物种研究，而其对食物网相互作用的潜在影响仍鲜为人知。本研究针对北半球（挪威海）与南半球（斯科舍海、威德尔海）的多个高纬度海域的自然浮游生物群落开展了实验操控研究。本研究的目标是，通过对包含植食性桡足类（copepods）在内的未过滤自然表层海洋群落开展一系列短期（4天）、多水平（3种处理组）的碳酸盐化学操控实验，以识别更具普适性的响应模式，并提升实验可重复性。本实验在6个不同海域顺利完成，涵盖了多样的环境条件与不同的浮游生物群落组成。研究发现，溶解态二氧化碳（pCO₂）浓度升高会显著改变桡足类与甲藻细胞丰度之间的相互作用：在全部6组实验中，相较于环境背景条件，甲藻的丰度均出现下降。其余所有主要浮游植物类群均未出现类似的变化模式。上述变化模式表明，当处于pCO₂升高的环境中时，桡足类对甲藻的取食偏好性会显著增强，这意味着食物质量的改变与取食选择性的偏移，可能是海洋酸化带来的主要后果之一。本研究同时发现，当pCO₂浓度升高时，透明胞外聚合物颗粒（TEP）的丰度通常会上升，但这一响应取决于具体的环境条件组合。细菌与超微型浮游生物对pCO₂升高则表现出中性响应，且细菌或超微型浮游生物的丰度变化与透明胞外聚合物颗粒的浓度变化之间，未呈现显著关联。总体而言，本研究表明：尽管部分响应模式具有相似性，但这些特征各异的高纬度表层海洋群落，对pCO₂升高的响应可能存在显著差异。