Acclimation to tidal conditions alters the physiological responses of the green shore crab, Carcinus maenas, to subsequent emersion

Impact of marine heatwaves on Carcinus maenas crabs: Physiological and biochemical mechanisms of thermal stress resilience

Marine heatwaves (MHWs), characterized by prolonged periods of elevated sea temperatures, pose significant threats to marine ecosystems, particularly affecting the physiology and behavior of marine organisms, including crustaceans. This study investigates the physiological and biochemical responses of males and females of Carcinus maenas crabs, after an acute exposure to an MHW, focusing on energy metabolism, oxidative status, and potential neurotoxicity. Specimens were exposed to controlled laboratory conditions simulating a temperature increase from 17 °C to 23 °C, and responses were analyzed in gills and hepatopancreas. Results revealed sex-specific differences in thermal stress resilience, with males showing higher glycogen storage in gills after MHW exposure, while females exhibited a significant reduction in glycogen reserves and an increase in antioxidant enzyme activity. Superoxide dismutase and glutathione reductase activities were notably elevated in females subjected to MHW, suggesting a more robust antioxidant response to counteract oxidative stress. Additionally, acetylcholinesterase activity, an indicator of neurotoxicity, was significantly reduced in females post-MHW, hinting at potential neurotoxic effects. Despite these biochemical changes, lipid peroxidation levels remained stable across both sexes and tissues, indicating that short-term MHW exposure did not cause significant oxidative damage to cell membranes. This study highlights the importance of considering sex differences in assessing the impacts of climate change-induced stressors on marine organisms, as males and females display distinct metabolic and physiological strategies for coping with thermal stress.

Effects of hypo-osmotic shock on osmoregulatory responses and expression levels of selected ion transport-related genes in the sesarmid crab Episesarma mederi (H. Milne Edwards, 1853)

This study examined the osmoregulatory responses to hypo-osmotic shock in the commercially and ecologically important crab Episesarma mederi (H. Milne Edwards, 1853). After the acclimation for one week at a salinity of 25 PSU, Adult males E. mederi were immediately exposed to salinities of 5 PSU and 25 PSU (the control group). The time course of changes in haemolymph osmolality, gill Na+/K+ ATPase (NKA) activity, oxygen uptake rates, and mRNA expression levels of ion-transport related genes, including the NKA-α subunit, V-type H+ATPase (VT) and Na+/K+/2Cl-(NKCC), were determined. The results showed that E. mederi was a strong hyperosmoregulator after exposure to 5 PSU, achieved by modulations of NKA activity in their posterior gills rather than the anterior gills. The crabs acclimated to 5 PSU increased oxygen uptake, especially during the initial exposure, reflecting increased energetic costs for osmotic stress responses. In the posterior gills, the NKA activities of the crabs acclimated to 5 PSU at 3, 72 and 168 h were significantly higher than those in the control group. Elevated NKA-α subunit expression levels were detected at 6 h and 12 h. Increased expression levels of VT and NKCC were identified at 6 h and 12 h, respectively. Our results indicate that elevated gill NKA activity at 3 h could result from enzyme activity and kinetic alterations. On the other hand, the gill NKA activity at 72 and 168 h was sustained by elevated NKA-α subunit expression. Hence, these adaptive responses in osmoregulation enable the crabs to withstand hypo-osmotic challenges and thrive in areas of fluctuating salinity in mangroves and estuaries.

Latitudinal variation and plasticity in response to temperature in Geukensia demissa

As global temperatures warm, species must adapt to a changing climate or transition to a different location suitable for their survival. Understanding the extent to which species are able to do so, particularly keystone species, is imperative to ensuring the survival of key ecosystems. The ribbed mussel Geukensia demissa is an integral part of salt marshes along the Atlantic coast of North America. Spatial patterns of genomic and phenotypic divergence have been previously documented, although their link with coastal environmental variation is unknown. Here, we study how populations of G. demissa in the northern (Massachusetts) and southern (Georgia) portions of the species range respond to changes in temperature. We combine assays of variation in oxygen consumption and RNA transcriptomic data with genomic divergence analyses to identify how separate populations of G. demissa may vary in distinct thermal environments. Our results show differences in constitutive oxygen consumption between mussels from Georgia and Massachusetts, as well as shared and disparate patterns of gene expression across temperature profiles. We also find that metabolic genes seem to be a strong component of divergence between these two populations. Our analysis highlights the importance of studying integrative patterns of genomic and phenotypic variation in species that are key for particular ecosystems, and how they might respond to further changes in climate.

Exercise and emersion in air, and recovery in seawater in the green crab (Carcinus maenas): metabolic, acid-base, cardio-ventilatory, and ionoregulatory responses

In nature, the green crab exhibits emersion and terrestrial activity at low tide. Treadmill exercise in air (20-23°C) of crabs acclimated to 32ppt seawater (13°C) revealed an inverse relationship between velocity and duration: 2.0 BL sec−1sustainable for several minutes, and 0.25 BL sec−1 for long periods. Fatigue was not due to dehydration. Physiological responses over 18-h recovery in seawater after near-exhaustive exercise (0.25 BL sec−1, 1h) in air were compared with responses after quiet emersion (1h) in air. Exercising crabs exhibited transient scaphognathite slowing and progressive increases in heart rate, whereas emersed crabs exhibited persistent inhibition of ventilation and transient heart slowing. Upon return to seawater, all these rates increased above both control and treatment levels. Post-exercise disturbances were more marked and/or longer lasting (e.g. EPOC, hyperventilation, tachycardia, metabolic acidosis, lactate elevation, ionic disturbances) than those after simple air exposure. However, an increase in net acidic equivalent excretion to the environment occurred after emersion but not after exercise. Instead, post-exercise crabs relied on carapace buffering, signaled by elevated haemolymph Ca2+ and Mg2+. Prolonged lowering of haemolymph PCO2 associated with hyperventilation also played a key role in acid-base recovery. EPOC after exercise was 3-fold greater than after emersion, sufficient to support control M˙O2for>14h. This reflected clearance of a large lactate load, likely by glycogen re-synthesis rather than oxidation. We conclude that the amphibious green crab uses a combination of aquatic and terrestrial strategies to support exercise in air, emersion in air, and recovery in seawater.