Testing Antarctic resilience: the effects of elevated seawater temperature and decreased pH on two gastropod species

Ocean acidification has been hypothesized to increase stress and decrease shell calcification in gastropods, particularly in cold water habitats like the western Antarctic Peninsula (WAP). There is limited information on how calcified marine benthic invertebrates in this region will respond to these rapidly changing conditions. The present study investigated the effects of elevated seawater temperature and decreased pH on growth (wet mass and shell morphometrics), net calcification, and proximate body composition (protein and lipid) of body tissues in two common benthic gastropods. Individuals of the limpet Nacella concinna and the snail Margarella antarctica collected from the WAP were exposed to seawater in one of four treatment combinations: current ambient conditions (1.5°C, pH 8.0), near-future decreased pH (1.5°C, pH 7.8), near-future elevated temperature (3.5°C, pH 8.0), or combination of decreased pH and elevated temperature (3.5°C, pH 7.8). Following a 6-week exposure, limpets showed no temperature or pH effects on whole body mass or net calcification. Despite no significant differences in whole body mass, the shell length and width of limpets at elevated temperature tended to grow less than those at ambient temperature. There was a significant interaction between the sex of limpets and pH. There were no significant temperature or pH effects on growth, net calcification, shell morphologies, or proximate body composition of snails. Our findings suggest that both gastropod species demonstrate resilience to initial exposure to temperature and pH changes predicted to occur over the next several hundred years globally and perhaps sooner along the WAP. Despite few significant impacts of elevated temperature or decreased pH, any response to either abiotic variable in species with relatively slow growth and long lifespan is of note. In particular, we detected modest impacts of reduced pH on lipid allocation in the reproductive organs of the limpet N. concinna that warrants further study.

海洋酸化已被提出假说，会加剧腹足类（gastropods）的生存压力，并降低其贝壳钙化程度，尤其在南极半岛西部（WAP）这类冷水生境中。目前针对该区域钙化海洋底栖无脊椎动物如何响应这些快速变化的环境条件的相关研究信息十分有限。本研究探究了海水温度升高与pH降低对两种常见底栖腹足类的生长（湿重与贝壳形态计量指标）、净钙化率以及体组织近似体成分（蛋白质与脂质）的影响。研究对象为采自南极半岛西部（WAP）的康氏帽贝（Nacella concinna）及南极玛雷螺（Margarella antarctica）个体，将其置于四种处理组合之一的海水中进行暴露实验：当前环境条件（1.5℃，pH 8.0）、未来近期pH降低组（1.5℃，pH 7.8）、未来近期温度升高组（3.5℃，pH 8.0），以及pH降低与温度升高的联合处理组（3.5℃，pH 7.8）。经过6周的暴露实验后，康氏帽贝的整体湿重与净钙化率未表现出显著的温度或pH效应。尽管整体湿重无显著差异，但温度升高组帽贝的贝壳长度与宽度的生长量低于环境温度组个体。帽贝的性别与pH之间存在显著的交互作用。对于南极玛雷螺而言，其生长、净钙化率、贝壳形态特征以及体组织近似体成分均未表现出显著的温度或pH效应。本研究结果表明，两种腹足类物种在暴露于未来数百年全球预计将出现的温度与pH变化（甚至南极半岛西部可能更早出现此类变化）时，均表现出一定的恢复力。尽管温度升高或pH降低对其产生的显著影响较少，但对于生长速率相对缓慢、寿命较长的物种而言，其对任一非生物变量的响应都值得关注。尤为值得注意的是，我们在康氏帽贝（N. concinna）的生殖器官中检测到pH降低对脂质分配产生的微弱影响，这一发现有待进一步研究。