International Journal of Molecular Ecology and Conservation 2024, Vol.14, No.5, 208-217 http://ecoevopublisher.com/index.php/ijmec 209 2 Climate Change Stressors Affecting Crustaceans 2.1 Rising ocean temperatures and thermal stress Rising ocean temperatures pose a significant threat to crustaceans, impacting their thermal tolerance and adaptive capacity. Studies on the tidepool copepod Tigriopus californicus reveal that local adaptation to temperature is pronounced, with limited potential for further adaptation to increasing temperatures. This is evidenced by the lack of increased thermal tolerance after several generations of selection, indicating that existing genetic variation may be insufficient to cope with future thermal stress (Kelly et al., 2012). Similarly, the invasive green crab Carcinus maenas demonstrates rapid adaptation to temperature changes, facilitated by a genomic island of divergence that correlates with cold tolerance. This adaptation is crucial for the species' survival across diverse thermal environments, highlighting the role of genetic mechanisms in thermal stress resilience (Tepolt and Palumbi, 2020). The Antarctic krill Euphausia superba also faces challenges due to rising temperatures, as it exhibits low genetic variation and evolutionary rates, suggesting limited adaptive potential to rapid climate change. This lack of genetic diversity may hinder the species' ability to cope with thermal stress, potentially affecting its survival and distribution in warming oceans (Choquet et al., 2023). These findings underscore the importance of understanding genetic adaptation and plasticity in crustaceans to predict their responses to climate-induced thermal stress. 2.2 Ocean acidification and its effects on shell formation Ocean acidification, resulting from increased CO2 levels, affects crustaceans by altering the availability of carbonate ions necessary for shell formation. The estuarine oyster Crassostrea ariakensis provides insights into how genetic divergence and phenotypic plasticity contribute to adaptation under such conditions. The species exhibits strong selection signals in genes responding to salinity and temperature stress, which are crucial for maintaining shell integrity in acidified waters (Li et al., 2021). This genetic adaptation is vital for the survival of crustaceans in environments where ocean chemistry is rapidly changing. Moreover, the evolutionary genomics of species' responses to climate change highlights the need for integrating genetic data into models predicting species' responses to ocean acidification. By understanding the genetic basis of adaptation, researchers can better predict how crustaceans will cope with changes in ocean chemistry, which is essential for developing conservation strategies (Waldvogel et al., 2020; Aguirre-Liguori et al., 2021). These studies emphasize the critical role of genomic research in addressing the challenges posed by ocean acidification on crustacean shell formation. 2.3 Hypoxia and low oxygen environments Hypoxia, or low oxygen levels, is another stressor affecting crustaceans, particularly in deep-sea environments. The squat lobster Shinkaia crosnieri, inhabiting both hydrothermal vents and cold seeps, provides a model for studying adaptation to hypoxic conditions. Transcriptomic analyses reveal that stress response and immune-related genes are up-regulated in hydrothermal vent populations, suggesting that these genetic adaptations are crucial for surviving in low oxygen environments (Cheng et al., 2019). This genetic resilience is essential for crustaceans living in habitats where oxygen levels are variable and often depleted. The ability of crustaceans to adapt to hypoxia is also linked to their evolutionary history and genetic diversity. Species with low genetic variation, such as the Antarctic krill, may struggle to adapt to hypoxic conditions, potentially leading to population declines (Choquet et al., 2023). Understanding the genetic mechanisms underlying hypoxia tolerance is vital for predicting the impacts of climate change on crustacean populations and their ecosystems. 2.4 Salinity changes and their impact on osmoregulation Salinity changes, driven by climate change, affect crustaceans' osmoregulatory abilities, which are crucial for maintaining cellular homeostasis. The estuarine oyster Crassostrea ariakensis demonstrates how genetic adaptation to salinity stress is facilitated by the expansion of solute carrier gene families, which play a significant role in osmoregulation (Li et al., 2021). This genetic adaptation is essential for crustaceans inhabiting estuarine and coastal environments where salinity levels fluctuate.
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