Haemolymph inorganic ion composition of crustaceans from the Southern Ocean@en

Brachyuran and anomuran decapod crabs do not occur in the extremely cold waters of the Antarctic continental shelf whereas caridean and other shrimp-like decapods, amphipods and isopods are highly abundant. Differing capacities for extracellular ion regulation, especially concerning magnesium, have been hypothesised to determine cold tolerance and by that the biogeography of Antarctic crustaceans. Magnesium is known to have a paralysing effect, which is even more distinct in the cold. As only few or no data exist on haemolymph ionic composition of Sub-Antarctic and Antarctic crustaceans, haemolymph samples of 12 species from these regions were analysed for the concentrations of major inorganic ions (Na+, K+, Ca2+, Mg2+, Cl-, SO4 2-) by ion chromatography. Cation relationships guaranteed neuromuscular excitability in all species. Sulphate and potassium correlated positively with magnesium concentration. The Antarctic caridean decapod as well as the amphipods maintained low (6-20% of ambient sea water magnesium concentration), Sub-Antarctic brachyuran and anomuran crabs as well as the Antarctic isopods high (54-96% of ambient sea water magnesium concentration) haemolymph magnesium levels. In conclusion, magnesium regulation may explain the biogeography of decapods, but not that of the peracarids.短尾下目（Brachyuran）与异尾下目（Anomuran）十足目蟹类无法在南极大陆架的极寒水域中存活，而真虾下目（Caridea）及其他虾形十足类、端足类（Amphipoda）与等足类（Isopoda）则在此区域极为繁盛。此前有假说提出，细胞外离子调节能力——尤其是与镁离子相关的调节机制——的差异，决定了南极甲壳动物的耐寒性，并由此影响其生物地理分布格局。已知镁离子具有麻痹效应，且在低温环境下该作用会进一步增强。由于目前针对亚南极与南极甲壳动物血淋巴（haemolymph）离子组成的研究数据极为匮乏甚至空白，本研究对上述区域的12个物种的血淋巴样本进行了分析，采用离子色谱法（ion chromatography）检测了样本中主要无机离子（Na+、K+、Ca²+、Mg²+、Cl-、SO₄²-）的浓度。所有受试物种的阳离子比例均保障了其神经肌肉兴奋性。硫酸盐与钾离子浓度与镁离子浓度呈正相关。南极真虾下目十足类及端足类维持了较低的血淋巴镁离子水平（仅为环境海水镁离子浓度的6%~20%）；而亚南极短尾下目与异尾下目蟹类及南极等足类的血淋巴镁离子水平则较高，可达环境海水镁离子浓度的54%~96%。综上，镁离子调节能力或可解释十足类的生物地理分布规律，但无法阐释囊虾总目（Peracarida）类群的分布格局。