Smith A, Erber J, Watson A, Johnson C, Gato W E, George S B
B iology Department, Georgia Southern University, Statesboro, GA 30460, USA.
Department of Chemistry and Biochemistry, Georgia Southern University, Statesboro, GA 30460, USA.
Integr Org Biol. 2024 Aug 21;6(1):obae031. doi: 10.1093/iob/obae031. eCollection 2024.
Salt marsh ecosystems are heavily reliant on ribbed mussel () populations to aid in rapid recovery from droughts. The focus of this study was thus to document the effects of rising temperatures on ribbed mussel populations in a Georgia salt marsh. Seven lab and eight field experiments were used to assess the effects of current air temperatures on mussels at two high marsh (HM) sites with short and sparse cordgrass and one mid marsh (MM) site with tall and dense cordgrass. Field results in 2018 and 2019 indicate that ribbed mussels were experiencing extremely high temperatures for prolonged periods of time at the landlocked high marsh (LHM) site. In 2018, the highest temperature (54°C) and longest high temperature events, HTEs (58 days), that is, consecutive days with temperatures ≥40°C, were recorded at this site. When laboratory temperatures were increased from 20 to 36°C, mean heart rates increased by an average of 19 bpm for mussels from both high and MM sites respectively. When field temperatures rose from 20°C in April to 40°C in September 2019, mean heart rates increased by an average of 10 bpm for HM mussels and by 26.3 bpm for MM mussels. Under identical laboratory and field conditions, mean heart rates for mussels from the LHM site with the highest temperatures, increased by <1 bpm and 3.7 bpm respectively. Evidence of the potential role of shade on mussel aggregates was provided by examining whether mussels from the edge of mussel aggregates with little to no cordgrass for shade were more stressed than those living at the center of mussel aggregates. In the absence of shade, mean body temperatures for mussels at the edge of mussel aggregates were up to 8°C higher than for those living in the center underneath a dense tuft of cordgrass. Despite high body temperatures, mean heart rates and Hsp70 gene expression were lower for mussels living at the edges. This agrees with the strategy that during prolong exposure to high temperatures, mussels may reduce their heart rate to conserve energy and enhance survival. Alternatively, heat-stressed mussels at the edges of aggregates may not have the resources to express high levels of Hsp70. Increase in the frequency, intensity, and duration of HTEs may stress the physiological and biochemical function of mussel populations to the limit, dictate mussel aggregate size, and threaten the functionality of SE salt marshes.
盐沼生态系统严重依赖条纹贻贝种群来帮助从干旱中快速恢复。因此，本研究的重点是记录温度上升对佐治亚州盐沼中条纹贻贝种群的影响。通过七个实验室实验和八个野外实验，评估当前气温对两个高沼（HM）站点（短叶和稀疏的互花米草）和一个中沼（MM）站点（高且茂密的互花米草）中贻贝的影响。2018年和2019年的野外结果表明，在内陆高沼（LHM）站点，条纹贻贝长时间经历极高的温度。2018年，该站点记录到最高温度（54°C）和最长高温事件（HTEs，即连续58天温度≥40°C）。当实验室温度从20°C升高到36°C时，来自高沼和中沼站点的贻贝平均心率分别平均增加了19次/分钟。当2019年4月野外温度从20°C上升到9月的40°C时，高沼贻贝平均心率平均增加了10次/分钟，中沼贻贝增加了26.3次/分钟。在相同的实验室和野外条件下，来自温度最高的LHM站点的贻贝平均心率分别增加了不到1次/分钟和3.7次/分钟。通过检查来自贻贝聚集边缘几乎没有或没有互花米草遮荫的贻贝是否比生活在贻贝聚集中心的贻贝压力更大，提供了遮荫对贻贝聚集潜在作用的证据。在没有遮荫的情况下，贻贝聚集边缘的贻贝平均体温比生活在密集互花米草簇下中心位置的贻贝高8°C。尽管体温很高，但生活在边缘的贻贝平均心率和热休克蛋白70（Hsp70）基因表达较低。这与以下策略一致，即在长时间暴露于高温期间，贻贝可能会降低心率以保存能量并提高存活率。或者，聚集边缘受热应激的贻贝可能没有资源来高水平表达Hsp70。高温事件的频率、强度和持续时间增加可能会使贻贝种群的生理和生化功能压力达到极限，决定贻贝聚集大小，并威胁盐沼生态系统的功能。
