Acid-base regulation in the Dungeness crab (Metacarcinus magister)

Homeostatic regulation allows organisms to secure basic physiological processes in a varying environment. To counteract fluctuations in ambient carbonate system speciation due to elevated seawater pCO2 (hypercapnia), many aquatic crustaceans excrete/accumulate acid-base equivalents through their gills; however, not much is known about the role of ammonia in this response. The present study investigated the effects of hypercapnia on acid-base and ammonia regulation in the Dungeness crab, Metacarcinus magister on the whole animal and isolated gill levels. Hemolymph pCO2 and [HCO3]- increased in M. magister acclimated to elevated pCO2 (330 Pa), while pH remained stable. Additionally, hemolymph [Na+], [Ca2+], and [SO4]2- were significantly increased. When challenged with varying pH during gill perfusion, the pH of the artificial hemolymph remained relatively unchanged. Overall, ammonia production and excretion, as well as oxygen consumption, were reduced in crabs acclimated to elevated pCO2, demonstrating that either (amino acid) oxidation is reduced in response to this particular stress, or nitrogenous wastes are excreted in an alternative form.

稳态调节（Homeostatic regulation）可使生物体在多变环境中维持基本生理过程。为应对海水pCO₂升高（高碳酸血症，hypercapnia）引发的环境碳酸盐系统形态分布波动，诸多水生甲壳动物可通过鳃排泄或积累酸碱当量；但目前关于氨在该调控过程中的作用仍知之甚少。本研究以邓杰内斯蟹（Metacarcinus magister）为对象，从整体动物及离体鳃水平探究了高碳酸血症对其酸碱与氨稳态调节的影响。经330 Pa升高pCO₂环境驯化的邓杰内斯蟹，其血淋巴pCO₂与[HCO₃]⁻浓度均有所升高，而pH保持稳定。此外，其血淋巴中的钠离子（[Na⁺]）、钙离子（[Ca²⁺]）及硫酸根离子（[SO₄]²⁻）浓度均显著升高。在鳃灌流过程中施加不同pH条件时，人工血淋巴的pH相对保持稳定。总体而言，经高pCO₂驯化的螃蟹的氨生成与排泄量及耗氧量均出现降低，这表明：针对该特定胁迫，要么氨基酸氧化水平被下调，要么含氮废物以其他形式被排出。