Superoxide dismutase measurements as a complement to tackle the responses of Cnemidocarpa verrucosa sp. A to sedimentation due to rapid climate change

Rapid regional warming causes glacial retreat and melting of ice caps along the West Antarctic Peninsula, in consequence, sediment discharge into marine coastal areas reduces food availability and impairs respiratory performance of benthic filter-feeders. Here we analyzed the response of a highly abundant Antarctic ascidian Cnemidocarpa verrucosa sp. A to experimental changes in sedimentation rates through enzymatic measurements: Caspase and Superoxide Dismutase. Experimental work was carried out at Dallmann laboratory, Carlini Station in Potter Cove (58°40'W; 62°14'S), South Shetland Islands, Antarctica; during the summer campaign 2015/2016. Animals were collected by SCUBA diving at 20-30 m water depth (58°39'37,86W; 62°14'6, 153S), placed in containers with seawater from the sampling site, and immediately transferred to the experimental facilities of the laboratory. Specimens were placed in a 100 L container after cleaning their tunics from large epibionts. Both species were kept in an open flow system with unfiltered natural seawater (0 ± 1 °C) directly pumped from the cove for ten days, to allow for recovery from sampling and acclimation to the experimental system. Thereafter, specimens (n=10) with similar body sizes (approximately 10cm high) were selected, and 1-2 individuals were placed randomly in six aquaria (8 L), with individual closed circulation systems (EHEIM universal 300 Water Pump (300l/h)) and a venturi to assure constant aeration inside the aquaria. The six aquaria were placed in a 90 L running seawater bath (open system) for the incubation experiments in order to keep constant temperature (1.76 ± 0.37 °C). Treatment was applied to three aquaria which consisted in applying a single pulse of 200 mg L-1 of sediment per experimental aquarium. The experiment was stopped when turbidity was no longer observed in the water (36 h after exposure). The control treatments were maintained in seawater without sediment addition. Sediment used for the treatment was obtained using a grab sampler at 20 m depth in Potter Cove, from the surface bottom sediments of the inner cove (around 15 m depth, close to the mouth of the major creek), dried at 70 °C and sieved through a 50 μm mesh, following the protocol of Torre et al. (2012). After exposure, animals were dissected on ice, branchial basket, mantle, and gut were separated and frozen at -80ºC. […]快速的区域气候变暖导致西南极半岛（West Antarctic Peninsula）沿线的冰川退缩与冰盖消融，进而使得入海近岸海域的沉积物输入量降低了食物可获得性，并损害了底栖滤食性动物（benthic filter-feeders）的呼吸功能。本研究通过酶活性测定手段，分析了丰度极高的南极被囊动物（ascidian）——疣齿褶海鞘A种（Cnemidocarpa verrucosa sp. A）对沉积物沉积速率实验性变化的响应，所测定的酶包括半胱氨酸天冬氨酸蛋白酶（Caspase）与超氧化物歧化酶（Superoxide Dismutase）。 实验于2015/2016年夏季科考期间，在南极洲南设得兰群岛（South Shetland Islands）波特湾（Potter Cove）的卡尔尼站（Carlini Station）达尔曼实验室（Dallmann laboratory）开展。研究人员通过水肺潜水（SCUBA diving）在20~30米水深（坐标：58°39'37.86W; 62°14'6.153S）采集实验动物，将其置于采样现场采集的海水容器中，并即刻转运至实验室的实验设施内。 在清除其被囊（tunics）表面的大型附生生物（epibionts）后，将实验个体放置于100 L的容器中。将两类物种置于开放式流水系统中，使用直接从波特湾抽取的未过滤天然海水（水温0 ± 1 ℃）饲养10天，以使实验动物从采样胁迫中恢复，并适应实验系统环境。随后，选取10只体型相近（体长约10 cm）的个体，随机将1~2只个体放入6个8 L的水族箱中，每个水族箱配备独立的封闭循环系统（伊罕通用300水泵（EHEIM universal 300 Water Pump），流量300 L/h）及文丘里管（venturi）以保证水族箱内持续通气。 将6个水族箱放置于90 L的循环流水水浴槽（开放式系统）中开展孵化实验，以维持恒定水温（1.76 ± 0.37 ℃）。对其中3个水族箱施加实验处理：向每个实验水族箱单次脉冲式添加200 mg·L⁻¹的沉积物。当水体中不再观测到浑浊现象时（暴露36 h后），终止实验。对照组仅维持在未添加沉积物的海水中。 实验所用沉积物通过采泥器（grab sampler）于波特湾20 m水深处采集，取自内湾（约15 m水深，靠近主要溪流入海口）的表层底泥，经70 ℃烘干后通过50 μm筛网（mesh）筛分，遵循Torre等人（2012）的实验方案。暴露处理结束后，在冰面上对实验动物进行解剖，分离鳃篮（branchial basket）、外套膜（mantle）与肠道（gut），并将组织样品冷冻保存于-80 ℃环境中。[…]