Seawater carbonate chemistry and vertical movement of stone crab larvae

Anthropogenic activities are increasing ocean temperature and decreasing ocean pH. Some coastal habitats are experiencing increases in organic runoff, which when coupled with a loss of vegetated coastline can accelerate reductions in seawater pH. Marine larvae that hatch in coastal habitats may not have the ability to respond to elevated temperature and changes in seawater pH. This study examined the response of Florida stone crab (Menippe mercenaria) larvae to elevated temperature (30°C control and 32°C treatment) and CO2-induced reductions in pH (8.05 pH control and 7.80 pH treatment). We determined whether those singular and simultaneous stressors affect larval vertical movement at two developmental stages. Geotactic responses varied between larval stages. The direction and rate of the vertical displacement of larvae were dependent on pH rather than temperature. Stage III larvae swam upwards under ambient pH conditions, but swam downwards at a faster rate under reduced pH. There was no observable change in the directional movement of Stage V larvae. The reversal in orientation by Stage III larvae may limit larval transport in habitats that experience reduced pH and could pose challenges for the northward dispersal of stone crabs as coastal temperatures warm.

人类活动正导致海洋温度升高与海水pH值下降。部分沿海生境正经历有机径流量增加，若此情况与植被岸线丧失同时发生，将进一步加速海水pH值的下降。在沿海生境中孵化的海洋幼体，或许无法应对温度升高与海水pH值变化。本研究针对佛罗里达石蟹（Florida stone crab, Menippe mercenaria）的幼体，探究其对温度升高（对照组30℃、处理组32℃）以及二氧化碳诱导的pH值降低（对照组pH 8.05、处理组pH 7.80）的响应。本研究旨在明确上述单一及复合胁迫因子，是否会对两个发育阶段幼体的垂直运动产生影响。幼体的趋地性响应随发育阶段不同而存在差异。幼体垂直移动的方向与速率，取决于pH值而非温度。在正常pH条件下，Ⅲ期幼体向上游动；而在pH降低的环境中，其则以更快的速率向下游动。Ⅴ期幼体的定向运动未出现可观测到的变化。Ⅲ期幼体的运动方向反转，可能会限制其在pH降低的生境中的扩散，同时随着沿海温度升高，也会对石蟹向北扩散造成阻碍。