Coral reefs are increasingly threatened by climate change, especially by thermally driven bleaching events. Southwestern Atlantic reefs (Brazil) have been proposed as potential climate refugia owing to high turbidity, which attenuates light and mitigates thermal stress. In contrast, Northwestern reefs (Bermuda) experience greater light penetration and serve as a comparative system, given their phylogenetic proximity to Brazilian corals. We hypothesized that Brazilian species would differ physiologically under their selective regimes. Indeed, they had higher chlorophyll a packing, sustaining comparable autotrophy and lower oxidative stress. Heterotrophic capacity, however, was similar between regions, challenging the turbidity-feeding paradigm. We also expected that Brazilian species would have greater tolerance to bleaching under simulated climate change. Although corals from both regions bleached, Brazilian representatives increased chlorophyll a packing 3.1-fold and maintained lower oxidative stress, while trophic behaviour remained stable. Calcification persisted under stress, indicating functional resilience across regions. These findings show that symbiosis and oxidative status, rather than trophic strategy, distinguish corals from Brazil, suggesting a compensatory role of chlorophyll a packing and enhanced redox balance under low-light regimes, the latter possibly reflecting relaxed selection and, ultimately, driving convergent physiological evolution. This work offers ecophysiological insight to guide conservation strategies, highlighting refugia as conservation priorities under local-scale stressors.

Most shallow-water octocorals engage in a symbiotic relationship with photosynthetic dinoflagellates of the family Symbiodiniaceae. Their inherently mixotrophic nature, combining autotrophic and heterotrophic feeding, provides a flexible energy acquisition that supports their metabolic demands. This nutritional plasticity depends on the functional integrity of symbiosis, which can be disrupted by thermal stress, potentially disturbing oxidative balance and causing symbiosis breakdown (i.e., bleaching). Although temperature effects are well known in scleractinian corals, octocoral ecophysiological responses remain poorly understood, especially in South Atlantic reefs. In this study, we used two octocoral species, Neospongodes atlantica and Plexaurella grandiflora, to test the hypotheses that elevated temperature (+ 3.5 °C, 14 days) induces bleaching by triggering oxidative stress, and that enhanced heterotrophic feeding occurs after heat stress. Symbiosis was evaluated through symbiont density and chlorophyll-a content; trophic ecology was assessed using fatty acid markers of autotrophy and heterotrophy; and oxidative status was analyzed through total antioxidant capacity and lipid peroxidation. Both species bleached under thermal stress, but via distinct mechanisms. Plexaurella grandiflora showed a reduction in symbiont density, which led to a decline in autotrophic input that was compensated by an increase in heterotrophic feeding. In contrast, N. atlantica decreased chlorophyll-a content, but its trophic balance remained stable. Oxidative status was unaffected in both species, suggesting that bleaching may have mitigated potential oxidative imbalances, or that bleaching occurred independently of oxidative stress—possibly linked to impaired photosynthetic carbon translocation. These findings underscore octocoral susceptibility to warming oceans and reveal species-specific physiological strategies.

The whiteleg marine shrimp Penaeus vannamei, originally from the Eastern Pacific Ocean, now inhabits tropical waters across Asia and Central and Southern America. This benthic species exhibits rapid growth, wide salinity and temperature tolerance, and disease resistance. These physiological traits have led to extensive research on its osmoregulatory mechanisms, including next-generation sequencing, transcriptomic analyses, and lipidomic responses. In crustaceans, osmotic and ionic homeostasis is primarily maintained by the membrane-bound metalloenzyme (Na+, K+)-ATPase. However, little is known about how various ligands modulate this enzyme in P. vannamei. Here, we examined the kinetic characteristics of the gill (Na+, K+)-ATPase to get biochemical insights into its modulation. A prominent immunoreactive band of similar to 120 kDa, corresponding to the (Na+, K+)-ATPase alpha-subunit, was identified. The enzyme exhibited two ATP hydrolyzing sites with K-0.5 = 0.0003 +/- 0.00002 and 0.05 +/- 0.003 mmol L-1 and was stimulated by low sodium ion concentrations. Potassium and ammonium ions also stimulated enzyme activity with similar K-0.5 values of 0.08 +/- 0.004 and 0.06 +/- 0.003 mmol L-1, respectively. Ouabain inhibition profile suggested a single enzyme isoform with a K-I value of 2.10 +/- 0.16 mmol L-1. Our findings showed significant kinetic differences in the (Na+, K+)-ATPase in Penaeus vannamei compared to marine and freshwater crustaceans. We expect our results to enhance understanding of the modulation of gill (Na+, K+)-ATPase in Penaeus vannamei and to provide a valuable tool for studying the shrimp's biochemical acclimation to varying salinity conditions.

The enrichment of coastal environments with nutrients, particularly nitrate, affects coral reef health. Nitrate enrichment can disrupt coral–algae symbiosis and reduce thermal tolerance, raising concerns in the context of global warming. Considering the naturally high nutrient levels along the Brazilian coast, which are further increased by human activity, we investigated whether nutrients impact the symbiosis, oxidative and energy metabolism, and calcification-related markers in the reef-building coral Mussismilia hispida. We also examined whether temperature modulates this effect, and whether corals can recover from stress once returned to normal conditions. This was done after exposure to nitrate enrichment (30 µM), both alone and combined with thermal stress (+ 3.5 °C), followed by a 14-day recovery period. Nitrate alone had no effects in any of the markers evaluated, while elevated temperature induced oxidative stress, leading to bleaching. However, corals maintained high ATP levels, potentially supporting the activity of calcification enzymes. Nitrate did not amplify the effects of temperature. After recovery, corals exposed to elevated temperature, alone or with nitrate, remained bleached, with reduced symbiosis metrics. Our findings highlight the remarkable tolerance of M. hispida to nitrate enrichment, possibly an adaptation driven by the nutritional profile of Southwestern Atlantic Ocean. The results also suggest that it may not rely heavily on symbionts, as energy homeostasis and growth-related markers are maintained even when corals were fully bleached.

The Macrobrachium amazonicum complex is composed of at least the Macrobrachium amazonicum and Macrobrachium pantanalense species, with the latter described from specimens originally identified as part of an endemic M. amazonicum population in the Brazilian Pantanal region. While there may be a reproductive barrier between these two Macrobrachium species, both are phylogenetically close, with small genetic distance. However, there is currently no available biochemical information of Macrobrachium pantanalense (Na+, K+)-ATPase. Here, we report the kinetic characteristics of the gill (Na+, K+)-ATPase in two populations of M. pantanalense from Baiazinha Lagoon (Miranda, MS, Brazil) and Araguari River (Uberlandia, MG, Brazil), and compare them with Macrobrachium amazonicum populations from the Parana-Paraguay River Basin. (Na+, K+)-ATPase activities were 67.9 +/- 3.4 and 93.3 +/- 4.1 nmol Pi min-1 mg-1 protein for the Baiazinha Lagoon and Araguari River populations, respectively. Two ATP hydrolyzing sites were observed for the Araguari River population while a single ATP site was observed for the Baiazinha Lagoon shrimps. Compared to the Araguari River population, a 3fold greater apparent affinity for Mg2+ and Na+ was estimated for the Baiazinha Lagoon population, but no difference in K+ affinity and ouabain inhibition was seen. The kinetic differences observed in the gill (Na+, K+)ATPase between the two populations of M. pantanalense, compared with those of various M. amazonicum populations, highlight interspecific divergence within the Macrobrachium genus, now examined from a biochemical perspective.

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Decapod Crustacea exhibit a marine origin, but many taxa have occupied environments ranging from brackish to fresh water and terrestrial habitats, overcoming their inherent osmotic challenges. Osmotic and ionic regulation is achieved by the gill epithelia, driven by two active ATP-hydrolyzing ion transporters, the basal (Na+, K+)-ATPase and the apical V(H+)-ATPase. The kinetic characteristic of gill (Na+, K+)-ATPase and the mRNA expression of its α subunit have been widely studied in various decapod species under different salinity challenges. However, the evolution of the primary structure has not been explored, especially considering the functional modifications associated with decapod phylogeny. Here, we proposed a model for the topology of the decapod α subunit, identifying the sites and motifs involved in its function and regulation, as well as the patterns of its evolution assuming a decapod phylogeny. We also examined both the amino acid substitutions and their functional implications within the context of biochemical and physiological adaptation. The α-subunit of decapod crustaceans shows greater conservation (∼94% identity) compared to the β-subunit (∼40%). While the binding sites for ATP and modulators are conserved in the decapod enzyme, the residues involved in the α-β interaction are only partially conserved. In the phylogenetic context of the complete sequence of (Na+, K+)-ATPase α-subunit, most substitutions appear to be characteristic of the entire group, with specific changes for different subgroups, especially among brachyuran crabs. Interestingly, there was no consistent separation of α-subunit partial sequences related to habitat, suggesting that the convergent evolution for freshwater or terrestrial modes of life is not correlated with similar changes in the enzyme's primary amino acid sequence.

Mass bleaching events are growing in duration and intensity. Besides causing extensive mortality, the progressively shorter time between events disrupts the ability of reefs to recover. The unique reefs of the Southwestern Atlantic are often considered climate refugia as they have suffered less bleaching-related mortality when compared to Indo–Pacific and Caribbean reefs. However, their recovery capacity still requires investigation. In 2019, an unprecedented heatwave triggered the most severe bleaching episode recorded for Southwestern Atlantic reefs. Therefore, this study aimed to (i) document the bleaching incidence and mortality during the heatwave, and (ii) assess coral recovery over 3 years. We measured bleaching incidence and monitored coral cover through surveys in three Southern Bahia (central Brazilian coast) reefs before, during and after thermal stress. Our findings show that coral assemblages were exposed to a 5-month-long thermal anomaly, experiencing thermal stress peaking at 14.1 ºC-weeks. Roughly 70

Weakly osmoregulating crustaceans use intracellular free amino acids (FAA) to attenuate cell volume changes consequent to alterations in hemolymph osmolality. Whether semiterrestrial, strong hyper/hypo-osmoregulators exhibit this ability is unknown. We investigate FAA mobilization in muscle tissue of 10 fiddler crabs from the genera Minuca, Leptuca, and Uca distributed along the Atlantic coast of South America. Crabs were subjected to severe hypo- or hyper-osmotic challenge at their lower or upper critical salinity limits for 5 days; reference crabs were held in isosmotic media. Hemolymph osmolality was measured, chela muscle FAA were identified and quantified, and percent contribution to intracellular osmolality (%FAA) was calculated. At isosmoticity, total FAA were nominally twofold higher in Minuca species (≈116 mmol/kg wet mass) compared to Uca (≈60 mmol/kg wet mass). Glycine, alanine, arginine, and taurine constituted >80% of the total FAA pool. On hyperosmotic challenge, hemolymph osmolalities ranged from 843 to 1282 mOsm/kg H2 O. FAA increased, although %FAA remained unaltered. Hypo-osmoregulating crabs thus can mobilize FAA, likely owing to a lesser ability to secrete salt near their upper critical limits. On hypo-osmotic challenge, osmolalities were regulated more tightly, between 475 and 736 mOsm/kg H2 O. Total FAA and %FAA showed little change, probably due to the crabs' strong hyper-osmotic extracellular regulatory ability, FAA consequently playing a diminished role in isosmotic intracellular regulation (IIR). Total FAA responses to hyper/hypo-osmotic challenge are thus asymmetrical. The lack of phylogenetic signal in FAA mobilization suggests that closely related fiddler crabs do not share similar strategies of IIR.

The Southwestern Atlantic (SWA) corals are more tolerant to global warming than those from the Caribbean Sea, possibly due to their higher heterotrophy and flexibility of symbiotic associations in nutrient-rich waters. Increased heterotrophy promotes greater energy gain via increased mitochondrial respiration, which can be used to face unfavorable conditions. Citrate synthase (CS) is a pacemaker enzyme of cellular respiration, and its activity can be used as a proxy for maximum aerobic capacity, thus being a potential predictor of organism tolerance against climate change. Therefore, we hypothesized that endemic coral species from SWA would have higher CS activity than those of pan-Caribbean distribution after exposure to a simulated scenario of moderate climate change (seawater temperature increase: + 2.5 °C; seawater acidification: − 0.3 pH unit), according to IPCC. Seven species of scleractinian corals and one hydrocoral species were biochemically evaluated in a phylogenetic perspective. Favia gravida, Mussismilia harttii, Montastraea cavernosa, Porites astreoides and Siderastrea stellata were unresponsive regarding CS activity, whereas Millepora alcicornis, Mussismilia hispida and Porites branneri showed a compensatory effect. Regardless of their phylogenetic relationships, endemic SWA coral species revealed higher CS activity than those of pan-Caribbean distribution. We suggest that the unique evolutionary history of SWA endemic species contributes to their biochemical tolerance to climate change, thus supporting the hypothesis of SWA as a refuge for reef life. Although CS is not a suitable biomarker for assessing the putative effects of climate change owing to its species-specific responses, it is an informative metric to indicate stress tolerance of species with different biogeographic origins. This idea becomes particularly evident for SWA reefs, where such a comparative, biochemical approach highlights the greater tolerance of endemic species at the subcellular level of organization.

Palaemonid shrimps inhabit osmotic niches from marine to continental waters. They hyper-regulate hemolymph osmolality and ionic concentrations in dilute media, hypo-regulating in concentrated media. Their gill epithelia express ion transporters like the Na+-K+-2Cl(-) symporter (NKCC) thought to play a role in salt secretion. To examine Cl- hypo-regulatory capability and phylogenetic correlations between gill NKCC mRNA levels and protein expression, we used palaemonids ranging from marine tide pools through estuaries (Palaemon) to coastal and continental fresh waters (Macrobrachium). We established the species' upper critical salinity limits (UL50) and short- (24 h) and long-term (120h) hypo-regulatory abilities at salinities of 80% of their UL50's (80%UL50). The Palaemon species exhibited the highest UL50's and greatest hypo-regulatory capabilities; among the Macrobrachium species, UL50's were higher in the diadromous than in the hololimnetic species. While basal transcript levels of gill NKCC mRNA were highest in P. pandaliformis, levels were unaffected by salinity or exposure time in all species. However, gill NKCC protein abundance increased after 120-h exposure at the 80%UL50 in all Macrobrachium species, except M. potiuna. Unexpectedly, hemolymph hyper-osmoregulatory capability in acclimatization media correlated with gill NKCC protein synthesis, while gill NKCC mRNA expression correlated with hemolymph hyper-Cl- regulation in Macrobrachium. These findings, together with the evolutionary history of osmoregulation in this shrimp clade, suggest a role for the gill NKCC symporter in both salt uptake and secretion. The evolution of NKCC protein expression responsiveness, unlike hemolymph hypo-regulation and NKCC mRNA expression, may have been driven by environmental salinity during niche radiation. Summary statement: While mRNA expression of the gill Na+-K+-2Cl(-) symporter is unchanged during acclimation of palaemonid shrimps to saline media, protein expression is up regulated, revealing a role in chloride secretion.

Temperature is an important abiotic factor that drives the evolution of ectotherms owing to its pervasive effects at all levels of organization. Although a species' thermal tolerance is environmentally driven within a spatial cline, it may be constrained over time due to differential phylogenetic inheritance. At the limits of thermal tolerance, hemolymph oxygen is reduced and lactate formation is increased due to mismatch between oxygen supply and demand; imbalance between enzyme flexibility/stability also impairs the ability to generate energy. Here, we characterized the effects of lower (LL50) and upper (UL50) critical thermal limits on selected descriptors of aerobic and anaerobic metabolism in 12 intertidal crab species distributed from northern Brazil (≈7.8°S) to southern Patagonia (≈53.2°S), considering their phylogeny. We tested for (i) functional trade-offs regarding aerobic and anaerobic metabolism and LDH kinetics in shaping thermal tolerance; (ii) influence of shared ancestry and thermal province on metabolic evolution; and (iii) presence of evolutionary convergences and adaptive peaks in the crab phylogeny. The tropical and subtropical species showed similar systemic and kinetic responses, both differing from the sub-Antarctic crabs. The lower UL50's of the sub-Antarctic crabs may reflect mismatch between the evolution of aerobic and anaerobic metabolism since these crabs exhibit lower oxygen consumption but higher lactate formation than tropical and subtropical species also at their respective UL50's. LDH activity increased with temperature increase, while Km Pyr remained fairly constant; catalytic coefficient correlated negatively with thermal niche. Thermal tolerance may rely on a putative evolutionary trade-off between aerobic and anaerobic metabolism regarding energy supply, while temperature compensation of kinetic performance is driven by thermal habitat as revealed by the LDH affinity/efficiency equilibrium. The overall physiological evolution revealed two homoplastic adaptive peaks in the sub-Antarctic crabs with a further shift in the tropical/subtropical clade. The physiological traits at UL50 have evolved in a phylogenetic manner while all others were more plastic. Thus, shared inheritance and thermal environment have driven the crabs' thermal tolerance and metabolic evolution, revealing physiological transformations that have arisen in both colder and warmer climes, especially at higher levels of biological organization and phylogenetic diversity.

Physiological knowledge gained from questions focused on the challenges faced and strategies recruited by organisms in their habitats assumes fundamental importance about understanding the ability to survive when subjected to unfavorable situations. In the aquatic environment, salinity is particularly recognized as one of the main abiotic factors that affects the physiology of organisms. Although the physiological patterns and challenges imposed by each occupied environment are distinct, they tend to converge to osmotic oscillations. From a comparative perspective, we aimed to characterize the osmoregulatory patterns of the bivalve mollusks Corbicula largillierti (purple Asian cockle), Erodona mactroides (lagoon cockle), and Amarilladesma mactroides (white clam) - inhabitants of different osmotic niches - when submitted to hypo- and/or hyperosmotic salinity variations. We determined the hemolymph osmotic and ionic concentrations, tissue hydration, and the intracellular isosmotic regulation (IIR) from the use of osmolytes (organic and inorganic) after exposure to species-specific salinity intervals. Additionally, we incorporated phylogenetic perspectives to infer and even broaden the understanding about the patterns that comprise the osmoionic physiology of Bivalvia representatives. According to the variables analyzed in the hemolymph, the three species presented a pattern of osmoconformation. Furthermore, both ionic regulation and conformation patterns were observed in freshwater, estuarine, and marine species. The patterns verified experimentally show greater use of inorganic osmolytes compared to the participation of organic molecules, which varied according to the osmotic niche occupied in the IIR for the mantle, adductor muscle, and gills. This finding widens the classic vision about the preferential use of certain osmolytes by animals from distinct niches. Our phylogenetic perspective also indicates that environmental salinity drives physiological trait variations, including hemolymph osmolality and the ion composition of the extracellular fluid (sodium, chloride, magnesium, and calcium). We also highlight the important role played by the shared ancestry, which influences the interspecific variability of the hemolymph K+ in selected representatives of Bivalvia.

Ocean warming is one of the greatest global threats to coral reef ecosystems; it leads to the disruption of the coral–dinoflagellate symbiosis (bleaching) and to nutrient starvation, because corals mostly rely on autotrophy (i.e., the supply of photosynthates from the dinoflagellate symbionts) for their energy requirements. Although coral bleaching has been well studied, the early warning signs of bleaching, as well as the capacity of corals to shift from autotrophy to heterotrophy, are still under investigation. In this study, we evaluated the bleaching occurrence of the scleractinian coral Mussismillia harttii and the hydrocoral Millepora alcicornis during a natural thermal stress event, under the 2015–2016 El Niño influence in three reef sites of the South Atlantic. We focused on the link between peroxynitrite (ONOO−) generation and coral bleaching, as ONOO− has been very poorly investigated in corals and never during a natural bleaching event. We also investigated the natural trophic plasticity of the two corals through the use of new lipid biomarkers. The results obtained first demonstrate that ONOO− is linked to the onset and intensity of bleaching in both scleractinian corals and hydrocorals. Indeed, ONOO− concentrations were correlated with bleaching intensity, with the highest levels preceding the highest bleaching intensity. The time lag between bleaching and ONOO− peak was, however, species-specific. In addition, we observed that elevated temperatures forced heterotrophy in scleractinian corals, as Mu. harttii presented high heterotrophic activity 15 to 30 days prior bleaching occurrence. On the contrary, a lower heterotrophic activity was monitored for the hydrocoral Mi. alicornis, which also experienced higher bleaching levels compared to Mu. hartii. Overall, we showed that the levels of ONOO− in coral tissue, combined to the heterotrophic capacity, are two good proxies explaining the intensity of coral bleaching.

The antioxidant defense system (ADS) protects organisms against the potential oxidative stress induced by environmental features, underlying processes of habitat diversification. The anomurans Aegla constitute the most threatened freshwater decapods of South America, occupying pristine habitats with narrow distribution. Using phylogenetic comparative methods, we addressed: Is the variability of habitat physicochemical parameters and tissue ADS phylogenetically structured? How do environmental features correlate with ADS? How do they vary among species? Several physicochemical parameters of water, as well as metals in sediments, were measured in ten aeglid species’ habitats. Additionally, metal accumulation and ADS parameters [metallothionein-like proteins (MTLP), antioxidant capacity against peroxyl radicals (ACAP), and glutathione system (GSH-GSSG)] were evaluated in hepatopancreas. Water conductivity and pH showed phylogenetic signal, while all other physicochemical traits demonstrated plastic variability. Metals were present at natural concentrations, which are corroborated by the relative stable GSH/GSSG ratio, and by their absence of correlation with bioaccumulation levels and MTLP, both phylogenetically structured. However, metal variability across species’ niches is associated with ACAP, a potential biomarker tool. Thus, the physiological sensitivity of aeglids is environmentally driven but also phylogenetically constrained, unraveling the importance of systematic framework for cross-species investigations and future monitoring strategies of these conspicuous freshwater animals.