Seawater carbonate chemistry and mussel respiration and calcification rates

Marine habitat‐forming species often play critical roles on rocky shores by ameliorating stressful conditions for associated organisms. Such ecosystem engineers provide structure and shelter, for example, by creating refuges from thermal and desiccation stresses at low tide. Less explored is the potential for habitat formers to alter interstitial seawater chemistry during their submergence. Here, we quantify the capacity for dense assemblages of the California mussel, Mytilus californianus, to change seawater chemistry (dissolved O2, pH, and total alkalinity) within the interiors of mussel beds at high tide via respiration and calcification. We established a living mussel bed within a laboratory flow tank and measured vertical pH and oxygen gradients within and above the mussel bed over a range of water velocities. We documented decreases of up to 0.1 pH and 25 μmol O2/kg internal to the bed, along with declines of 100 μmol/kg in alkalinity, when external flows were  95% of the time. Reductions in pH and O2 inside mussel beds may negatively impact resident organisms and exacerbate parallel human‐induced perturbations to ocean chemistry while potentially selecting for improved tolerance to altered chemistry conditions.

海洋造境物种（Marine habitat-forming species）通常在岩岸环境中扮演关键角色，通过改善伴生生物的生存胁迫条件发挥作用。这类生态系统工程师（ecosystem engineers）能提供栖息结构与庇护场所，例如在低潮时为生物创造躲避热胁迫和干燥胁迫的避难所（refuges）。目前尚未充分探索的是，造境物种（habitat formers）在浸没期间改变间隙海水化学性质的潜力。本研究量化了加州贻贝（Mytilus californianus）密集群落通过呼吸作用和钙化作用（respiration and calcification），在高潮时改变贻贝床内部海水化学性质（溶解氧（dissolved O₂）、pH值及总碱度（total alkalinity））的能力。我们在实验室流水槽（laboratory flow tank）中构建了活体贻贝床，并在不同水流速度条件下，测定了贻贝床内部及上方的垂直pH梯度与氧梯度。研究发现，当外部水流速度<0.5 cm/s（该条件出现频率超过95%）时，贻贝床内部pH值下降幅度可达0.1，溶解氧浓度降低25 μmol/kg，同时总碱度下降100 μmol/kg。贻贝床内部pH值与溶解氧的降低，可能对栖息生物产生负面影响，加剧人类活动引发的海洋化学扰动，同时可能筛选出对化学环境变化耐受性更强的生物。