Dispersal of Late Triassic clam shrimps across Pangea linking northwestern Gondwana and central Pangea rift basins.

Clam shrimps are a group of freshwater crustaceans who prospered during the Late Triassic. They were abundant in lacustrine sedimentary records of continental basins distributed throughout Pangea during this time. However, they show significant taxonomic differences between the clamp shrimp faunas from the rift basins of central Pangea and the southern Gondwanan basins. In this contribution, we show new fossil clam shrimp assemblages from the lacustrine sedimentary successions of the Eastern Cordillera of Colombia (the Bocas and Montebel formations), providing information on the Late Triassic species that inhabited the northwestern Gondwana basins. This study demonstrates that the basins of northwestern Gondwana shared Norian clamp shrimp species with rift basins of central Pangea and differed in their faunas with the basins of the southern portion of Gondwana. In addition, the Late Triassic clam shrimps paleobiogeographic distribution reflects the dispersal of this fauna throughout fluvial-lacustrine environments established in the rift valleys along the central Pangea. Therefore, the rift valleys produced during the early fragmentation of central Pangea could have acted as corridors for dispersion. Simultaneously, rift valleys also provided paleobiogeographic barriers that isolated the central Pangea clam shrimp faunas from southern Gondwana.

Metabolic scaling of an invasive mussel depends on temperature and chemical cues from an invasive predator.

Metabolism drives various biological processes, potentially influencing the ecological success and evolutionary fitness of species. Understanding diverse metabolic rates is fundamental in biology. Mechanisms underlying adaptation to factors like temperature and predation pressure remain unclear. Our study explored the role of temperature and predation pressure in shaping the metabolic scaling of an invasive mussel species (Brachidontes pharaonis). Specifically, we performed laboratory-based experiments to assess the effects of phenotypic plasticity on the metabolic scaling by exposing the mussels to water conditions with and without predator cues from another invasive species (the blue crab, Callinectes sapidus) across various temperature regimes. We found that temperature effects on metabolic scaling of the invasive mussels are mediated by the presence of chemical cues of an invasive predator, the blue crab. Investigating temperature-predator interactions underscores the importance of studying the ecological effects of global warming. Our research advances our understanding of how environmental factors jointly impact physiological processes.

When two evils are not equal: Differential biofouling of unionid bivalves by two invasive dreissenid species.

Byssate bivalves are ecosystem engineers with world-wide impact on aquatic communities through habitat forming and biofouling of hard-shelled organisms. In fresh waters, they are represented by invasive Ponto-Caspian dreissenid mussels spreading throughout Europe and North America. They negatively affect globally threatened unionid mussels by fouling, which deteriorates their condition and survival. The appearance of quagga mussels (D. rostriformis bugensis, QM) in areas occupied by zebra mussels (Dreissena polymorpha, ZM) usually has led to the replacement of ZM by QM. We combined long-term field survey (Lake Balaton, Hungary) and experimental data to check differences in fouling of unionid mussels (Unio tumidus and Sinanodonta woodiana) by the two dreissenids, determine their mechanisms and predict environmental consequences of the species replacement. ZM fouled unionids evenly throughout the year, whereas QM exhibited high fluctuations, being common on unionid shells during their recruitment peak (summer), decreasing towards autumn and almost completely absent in spring. Such fluctuations did not occur on stony substrata. This pattern suggests that interspecific differences in fouling did not result from recruitment preferences, but from greater detachment of QM from unionid substratum, whereas ZM more often remained attached to their initial recruitment sites. This was supported by the results of the laboratory experiments, in which dreissenid mussels did not show any consistent preference or avoidance of unionid mussels. Whereas, QM attached less often than ZM to hard objects and showed a higher detachment rate. Furthermore, dreissenids increased detachment after substratum immersion into soft sediments, indicating their capability of coping with suffocation after the burrowing of the living substratum or its siltation. The observed pattern indicates that the replacement of ZM by QM in the dreissenid assemblage may reduce fouling pressure on unionids. On the other hand, unionids may become a refuge for ZM in habitats invaded by competitively superior QM.

The energy metabolism and transcriptomic responses of the Manila clam (Ruditapes philippinarum) under the low-temperature stress.

Low temperature in winter poses a threat to the Manila clam Ruditapes philippinarum in North China. However, a number of low-temperature-tolerant clams could survive such condition. It is therefore of interest to explore the survival mechanisms underlying the cold tolerance of R. philippinarum. The Zebra II population of R. philippinarum (Zebra II) from North China and the native Putian population from South China were used as experimental materials. Both populations were stressed with low-temperature and the differences in their survival rates, energy metabolism and transcriptional responses were compared. The results shown that after cold treatment at -1.9 °C, survival rate of Zebra II was higher than that of the Putian group. For both groups, the respiration, ammonia excretion, and ingestion rates continuously decreased till 0 with reductions temperature. In addition, RNA-seq revealed that as compared with the Putian group, there were 3682 up-regulated differentially expressed genes (DEGs) and 3361 down-regulated DEGs in Zebra II group. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these DEGs were mostly enriched in the purine, pyrimidine, and pyruvate metabolism pathways in Zebra II under low-temperature stress. Furthermore, qRT-PCR analysis further confirmed that Zebra II responded to low-temperature stress through upregulating genes involved in purine, pyrimidine, and pyruvate metabolism pathways. Taken together, all these results indicated that Zebra II has higher cold tolerance than the Putian group. Therefore, Zebra II is capable for overwintering in the intertidal zone of North China.

Testing the applicability of the Modelling-Ongrowing Fish farms-Monitoring B (MOM-B) investigation system for assessing benthic habitat quality in the manila clam Ruditapes philippinarum aquaculture areas.

The coastal aquaculture areas have been subject to a variety of anthropogenic pressures in recent studies, and reasonable environmental quality assessment is essential for both ecological conservation and production practices. However, there are significant differences between the results produced from various environmental quality assessment regarding the focus of the evaluation and the fundamental methodology. Furthermore, many of these methods are very specific and difficult to adapt to general applications. Here, we utilized the Modelling-Ongrowing fish farms-Monitoring B investigation system (MOM-B), we assessed the benthic habitat quality of benthic bivalve aquaculture areas in the Xiaoqing River estuary located in Laizhou Bay, China. The aim was to validate the accuracy and practicality of this system. The biological, chemical, and sensory parameters of the MOM-B system, temperature, chlorophyll a (Chl-a), food availability, and planktonic larvae were evaluated throughout the investigation area during the summer of 2021. The MOM-B results indicated that the benthic habitat quality in the survey area was good and lightly disturbed, but the quality in the middle tide area began to deteriorate in August, the hottest month of the summer. Environmental factors indicated that the combined effects of high temperatures and fine sedimentation had led to increased environmental stress in the middle tide area. Food availability and population recruitment also suggested that the benthic habitat quality was better in the high tide and low tide areas than in the middle tide area, and more favorable for the survival of Manila clams. The accuracy, sensitivity, and discriminatory ability of the MOM-B system were demonstrated by environmental and biological indicators. This work showed that the MOM-B system is a practical, simple, and sensitive environmental assessment tool that is easy to implement in estuarine and benthic bivalve aquaculture areas. It can be used for long-term continuous monitoring and as an early warning tool for benthic habitat quality.

Elucidating responses of the intertidal clam Ruditapes philippinarum to compound extreme oceanic events.

Ocean acidification and heatwaves caused by rising CO2 affect bivalves and other coastal organisms. Intertidal bivalves are vital to benthic ecosystems, but their physiological and metabolic responses to compound catastrophic climate events are unknown. Here, we examined Manila clam (Ruditapes philippinarum) responses to low pH and heatwaves. Biochemical and gene expression demonstrated that pH and heatwaves greatly affect physiological energy enzymes and genes expression. In the presence of heatwaves, Manila clams expressed more enzymes and genes involved in physiological energetics regardless of acidity, even more so than in the presence of both. In this study, calcifying organisms' biochemical and molecular reactions are more susceptible to temperature rises than acidity. Acclimation under harsh weather conditions was consistent with thermal stress increase at lower biological organization levels. These substantial temporal biochemical and molecular patterns illuminate clam tipping points. This study helps us understand how compound extreme weather and climate events affect coastal bivalves for future conservation efforts.

Physiological and transcriptomic analysis provides new insights into osmoregulation mechanism of Ruditapes philippinarum under low and high salinity stress.

The Manila clam (Ruditapes philippinarum) is a commercially important marine bivalve, which inhabits the estuarine and mudflat areas. The osmoregulation is of great significance for molluscs adaptation to salinity fluctuations. In this study, we investigated the effects of low salinity (10 psu) and high salinity (40 psu) stress on survival and osmoregulation of the R. philippinarum. The results of physiological parameters showed that the ion (Na+, K+, Cl-) concentrations and Na+/K+-ATPase (NKA) activity of R. philippinarum decreased significantly under low salinity stress, but increased significantly under high salinity stress, indicating that there are differences in physiological adaptation of osmoregulation of R. philippinarum. In addition, we conducted the transcriptome analysis in the gills of R. philippinarum exposed to low (10 psu) and high (40 psu) salinity challenge for 48 h using RNA-seq technology. A total of 153 and 640 differentially expressed genes (DEGs) were identified in the low salinity (LS) group and high salinity (HS) group, respectively. The immune (IAP, TLR6, C1QL4, Ank3), ion transport (Slc34a2, SLC39A14), energy metabolism (PCK1, LDLRA, ACOX1) and DNA damage repair-related genes (Gadd45g, HSP70B2, GATA4) as well as FoxO, protein processing in endoplasmic reticulum and endocytosis pathways were involved in osmoregulation under low salinity stress of R. philippinarum. Conversely, the ion transport (SLC6A7, SLC6A9, SLC6A14, TRPM2), amino acid metabolism (GS, TauD, ABAT, ALDH4A1) and immune-related genes (MAP2K6, BIRC7A, CTSK, GVIN1), and amino acid metabolism pathways (beta-Alanine, Alanine, aspartate and glutamate, Glutathione) were involved in the process of osmoregulation under high salinity stress. The results obtained here revealed the difference of osmoregulation mechanism of R. philippinarum under low and high salinity stress through physiological and molecular levels. This study contributes to the assessment of salinity adaptation of bivalves in the context of climate change and provides useful information for marine resource conservation and aquaculture.

Mesocosm study of PAC-modified clay effects on Karenia brevis cells and toxins, chemical dynamics, and benthic invertebrate physiology.

Modified clay compounds are used globally as a method of controlling harmful algal blooms, and their use is currently under consideration to control Karenia brevis blooms in Florida, USA. In 1400 L mesocosm tanks, chemical dynamics and lethal and sublethal impacts of MC II, a polyaluminum chloride (PAC)-modified kaolinite clay, were evaluated over 72 h on a benthic community representative of Sarasota Bay, which included blue crab (Callinectes sapidus), sea urchin (Lytechinus variegatus), and hard clam (Mercenaria campechiensis). In this experiment, MC II was dosed at 0.2 g L-1 to treat bloom-level densities of K. brevis at 1 × 106 cells L-1. Cell removal in MC II-treated tanks was 57% after 8 h and 95% after 48 h. In the water column, brevetoxin analogs BTx-1 and BTx-2 were found to be significantly higher in untreated tanks at 24 and 48 h, while in MC II-treated tanks, BTx-3 was found to be higher at 48 h and BTx-B5 was found to be higher at 24 and 48 h. In MC II floc, we found no significant differences in BTx-1 or BTx-2 between treatments for any time point, while BTx-3 was found to be significantly higher in the MC II-treated tanks at 48 and 72 h, and BTx-B5 was higher in MC II-treated tanks at 24 and 72 h. Among various chemical dynamics observed, it was notable that dissolved phosphorus was consistently significantly lower in MC II tanks after 2 h, and that turbidity in MC II tanks returned to control levels 48 h after treatment. Dissolved inorganic carbon and total seawater alkalinity were significantly reduced in MC II tanks, and partial pressure of CO2 (pCO2) was significantly higher in the MC II-only treatment after 2 h. In MC II floc, particulate phosphorus was found to be significantly higher in MC II tanks after 24 h. In animals, lethal and sublethal responses to MC II-treated K. brevis did not differ from untreated K. brevis for either of our three species at any time point, suggesting MC II treatment at this dosage has negligible impacts to these species within 72 h of exposure. These results appear promising in terms of the environmental safety of MC II as a potential bloom control option, and we recommend scaling up MC II experiments to field trials in order to gain deeper understanding of MC II performance and dynamics in natural waters.

Comparative transcriptomics revealed parallel evolution and innovation of photosymbiosis molecular mechanisms in a marine bivalve.

Photosymbioses between heterotrophic hosts and autotrophic symbionts are evolutionarily prevalent and ecologically significant. However, the molecular mechanisms behind such symbioses remain less elucidated, which hinders our understanding of their origin and adaptive evolution. This study compared gene expression patterns in a photosymbiotic bivalve (Fragum sueziense) and a closely related non-symbiotic species (Trigoniocardia granifera) under different light conditions to detect potential molecular pathways involved in mollusc photosymbiosis. We discovered that the presence of algal symbionts greatly impacted host gene expression in symbiont-containing tissues. We found that the host immune functions were suppressed under normal light compared with those in the dark. In addition, we found that cilia in the symbiont-containing tissues play important roles in symbiont regulation or photoreception. Interestingly, many potential photosymbiosis genes could not be annotated or do not exhibit orthologues in T. granifera transcriptomes, indicating unique molecular functions in photosymbiotic bivalves. Overall, we found both novel and known molecular mechanisms involved in animal-algal photosymbiosis within bivalves. Given that many of the molecular pathways are shared among distantly related host lineages, such as molluscs and cnidarians, it indicates that parallel and/or convergent evolution is instrumental in shaping host-symbiont interactions and responses in these organisms.

Toxicology assessment of deep-sea mining impacts on Gigantidas platifrons: A comparative in situ and laboratory metal exposure study.

Deep-sea toxicology is essential for deep-sea environmental impact assessment. Yet most toxicology experiments are conducted solely in laboratory settings, overlooking the complexities of the deep-sea environment. Here we carried out metal exposure experiments in both the laboratory and in situ, to compare and evaluate the response patterns of Gigantidas platifrons to metal exposure (copper [Cu] or cadmium [Cd] at 100 µg/L for 48 h). Metal concentrations, traditional biochemical parameters, and fatty acid composition were assessed in deep-sea mussel gills. The results revealed significant metal accumulation in deep-sea mussel gills in both laboratory and in situ experiments. Metal exposure could induce oxidative stress, neurotoxicity, an immune response, altered energy metabolism, and changes to fatty acid composition in mussel gills. Interestingly, the metal accumulating capability, biochemical response patterns, and fatty acid composition each varied under differing experimental systems. In the laboratory setting, Cd-exposed mussels exhibited a higher value for integrated biomarker response (IBR) while in situ the Cu-exposed mussels instead displayed a higher IBR value. This study emphasizes the importance of performing deep-sea toxicology experiments in situ and contributes valuable data to a standardized workflow for deep-sea toxicology assessment.

Does the incorporation of shell waste from aquaculture in the construction of marine facilities affect the structure of the marine sessile community?

The growth of the human population causes significant harm to ecosystems, directly affecting the biological diversity of coastal areas by replacing natural habitats with artificial structures such as breakwaters, ports, and marinas. The hard substrate from those marine facilities lacks the topographic complexity of natural habitats. Because of that, artificial habitats usually do not support a diverse community to the same extent as rocky shores in the surroundings. To address this issue and bring a strategic solution to the improper disposal of shell waste from aquaculture farms, we evaluated how increasing the environmental heterogeneity of walls by incorporating mussel and oyster shells on artificial concrete affected the diversity of sessile organisms from the subtidal zone. Adding shells to concrete positively affected ascidians' richness. Substrates with added shells supported more species than flat substrates in total. They promoted species that did not occur on flat substrates that simulated the traditional walls of marinas and harbors. However, it did not affect the number of bryozoans and the average species richness. Consequently, incorporating shells resulted in communities with completely distinct structures from those on flat substrates. Adding shells affected the community structure, reducing the dominance by the exotic bryozoan Schizoporella errata, and promoting the occurrence of other groups, such as ascidians. Using shell residues from aquaculture on marina walls adds substrate for colonization. Still, it is also likely to provide refuges for fragile and vulnerable organisms, like crevices and pits in natural habitats. Because of that, the increment in diversity was mostly group-specific and restricted to ascidians. This research reinforces the importance of creating complex artificial coastal structures, inspired by the blue economy, for a more heterogeneous coverage of sessile communities and reduced presence and dominance of exotic species. Thus, the strategy tested here, besides the effects on the sessile community, also supports efforts to reduce inappropriate waste disposal in the environment.

Hyposalinity stress reduces mussel byssus secretion but does not cause detachment.

Environmental stressors such as salinity fluctuations can significantly impact the ecological dynamics of mussel beds. The present study evaluated the influence of hyposalinity stress on the detachment and survival of attached mussels by simulating a mussel farming model in a laboratory setting. Byssus production and mechanical properties of thread in response to varying salinity levels were assessed, and histological sections of the mussel foot were analyzed to identify the changes in the byssus secretory gland area. The results showed that hyposalinity stress (20 and 15 psu) led to a significant decrease in mussel byssus secretion, delayed initiation of new byssus production, and reduced plaque adhesion strength and breaking force of byssal threads compared to the control (30 psu) (p < 0.05). The complete suppression of byssal thread secretion in mussels under salinity conditions of 10 and 5 psu, leading to lethality, indicates the presence of a blockade in byssus secretion when mussels are subjected to significant physiological stressors. Histological analysis further demonstrated a decrease in the percentage of foot secretory gland areas in mussels exposed to low salinities. However, contrary to expectations, the study found that mussels did not exhibit marked detachment from ropes in response to the reduced salinity levels during one week of exposure. Hyposalinity stress exposure reduced the byssal secretion capacity and the mechanical properties of threads, which could be a cause for the detachment of suspension-cultured mussels. These results highlight the vulnerability of mussels to hyposalinity stress, which significantly affects their byssus mechanical performance.

The long-lived deep-sea bivalve Acesta excavata is sensitive to the dual stressors of sediment and warming.

Human influence in the deep-sea is increasing as mining and drilling operations expand, and waters warm because of climate change. Here, we investigate how the long-lived deep-sea bivalve, Acesta excavata responds to sediment pollution and/or acute elevated temperatures. A. excavata were exposed to suspended sediment, acute warming, and a combination of the two treatments for 40 days. We measured O2 consumption, NH4+ release, Total Organic Carbon (TOC), and lysosomal membrane stability (LMS). We found suspended sediment and warming interacted to decrease O:N ratios, while sediment as a single stressor increased the release of TOC and warming increased NH4+ release in A. excavata. Warming also increased levels of LMS. We found A. excavata used protein catabolism to meet elevated energetic demands indicating a low tolerance to stress. A. excavata has limited capacity for physiological responses to the stressors of warming and sediment which may lead to decreased fitness of A. excavata.

Influencing intertidal food web: Implications of ocean acidification on the physiological energetics of key species the 'wedge' clam Donax faba.

Ocean acidification has become increasingly severe in coastal areas. It poses emerging threats to coastal organisms and influences ecological functioning. Donax faba, a dominant clam in the intertidal zone of the Bay of Bengal, plays an important role in the coastal food web. This clam has been widely consumed by the local communities and also acts as a staple diet for shorebirds and crustaceans. In this paper, we investigated how acidified conditions will influence the physiology, biochemical constituents, and energetics of Donax faba. Upon incubation for 2 months in lowered pH 7.7 ± 0.05 and control 8.1 ± 0.05 conditions, we found a delayed growth in the acidified conditions followed by decrease in calcium ions in the clam shell. Although not significant, we found the digestive enzymes showed a downward trend. Total antioxidant was significantly increased in the acidified condition compared to the control. Though not significant, the expression level of MDA and antioxidant enzymes (SOD, CAT, GST, GPX, and APX) showed increasing trend in acidified samples. Among nutrients such as amino acids and fatty acids, there was no significant difference between treatments, however, showed a downward trend in the acidified conditions compared to control. Among the minerals, iron and zinc showed significant increase in the acidified conditions. The above results suggest that the clam growth, and physiological energetics may have deleterious effects if exposed for longer durations at lowered pH condition thereby affecting the organisms involved in the coastal food web.

Genome-wide sequencing reveals geographical variations in the thermal adaptation of an aquaculture species with frequent seedling introductions.

Climate change and human activity are essential factors affecting marine biodiversity and aquaculture, and understanding the impacts of human activities on the genetic structure to increasing high temperatures is crucial for sustainable aquaculture and marine biodiversity conservation. As a commercially important bivalve, the Manila clam Ruditapes philippinarum is widely distributed along the coast of China, and it has been frequently introduced from Fujian Province, China, to other regions for aquaculture. In this study, we collected four populations of Manila clams from different areas to evaluate their thermal tolerance by measuring cardiac performance and genetic variations using whole-genome resequencing. The upper thermal limits of the clams showed high variations within and among populations. Different populations displayed divergent genetic compositions, and the admixed population was partly derived from the Zhangzhou population in Fujian Province, implying a complex genomic landscape under the influence of local genetic sources and human introductions. Multiple single nucleotide polymorphisms (SNPs) were associated with the cardiac functional traits, and some of these SNPs can affect the codon usage and the structural stability of the resulting protein. This study shed light on the importance of establishing long-term ecological and genetic monitoring programs at the local level to enhance resilience to future climate change.

Clearance rates of sand-burrowed and laterally pressed unburrowed Pismo clam Tivela stultorum (Mawe 1823) in a laboratory open-flow system.

Pismo clam extraction is currently banned in Mexico to help the recovery of natural populations. Thus, the primary objective of this study was to gain insight on its basic biology and husbandry protocols. Growth and clearance rate (CR) of sand-burrowed and sediment-free, laterally pressed adult Pismo clams were quantified in the laboratory as a function of burrowing condition, flow, temperature, and microalgal concentration using open-flow chambers. After 40 days, clams remained healthy regardless of burrowing condition and showed a hyperbolic CR response pattern to increased flow, with CR directly proportional to flows lower than 1000 ml min-1. Maximal asymptotic CR values (300 to 400 ml min-1 org-1) were observed from 1000 to 2000 ml min-1. No significant CR differences were observed between burrowed and laterally pressed clams, yet microalgal concentration effects were detected, with constant maximal CRs of ∼250 ml min-1 in the range of 50 to 200 cells µl-1 and decline at higher concentrations. Maintenance protocols of laterally pressed organisms were validated in the laboratory with both weight and CR data. To our knowledge, this is the first study providing whole-body physiological data translated into effective husbandry protocols for Pismo clams. This approach represents a fresh perspective to traditional research areas, opening the possibility for continued experimentation under controlled conditions.

Behavioral responses of intertidal clams to compound extreme weather and climate events.

Rapidly increasing concentration of carbon dioxide (CO2) in the atmosphere not only results in global warming, but also drives increasing seawater acidification. Infaunal bivalves play critical roles in benthic-pelagic coupling, but little is known about their behavioral responses to compound climate events. Here, we tested how heatwaves and acidification affected the behavior of Manila clams (Ruditapes philippinarum). Under acidified conditions, the clams remained capable of burrowing into sediments. Yet, when heatwaves attacked, significant decreases in burrowing ability occurred. Following two consecutive events of heatwaves, the clams exhibited rapid behavioral acclimation. The present study showed that the behavior of R. philippinarum is more sensitive to heatwaves than acidification. Given that the behavior can act as an early and sensitive indicator of the fitness of intertidal bivalves, whether, and to what extent, behavioral acclimation can persist under scenarios of intensifying heatwaves in the context of ocean acidification deserve further investigations.

Stoichiometry of growth under variable scenarios of nutrient limitation: Differential homeostasis of body composition among growth phenotypes of the Manila clam.

Fast- and slow-growing phenotypes from two separate breeding families of the Manila clam (Ruditapes philippinarum) were alternatively fed two monoalgal diets with high and low N content (C:N ratios of 4.9 and 13.5, respectively). After 35 days of food conditioning, clams were sacrificed, and the soft body was dissected out into five different tissue fractions to determine the corresponding ponderal ratios (tissue wt./body wt.) and a separate analysis of the elemental composition of these tissues. Previously reported C and N balances performed with the same conditioning diets were integrated and compared with tissue composition of the same phenotypes in order to assess the efficacy of mechanisms elicited to compensate for N deficit. Broad differences in dietary N content resulted in only minor changes in whole-body C:N composition which suggests a noticeable degree of homeostatic regulation of nutrient balances. This regulation was found to be stricter in fast-compared to slow-growing phenotypes and differed among the various body tissues. Using the threshold element ratio approach, physiological mechanisms were identified that partly compensate for large stoichiometric mismatches between low-N food and body tissues.

Increased seawater temperature triggers thermal, oxidative and metabolic response of Ostrea edulis, leading to anaerobiosis.

Bivalves are among the marine organisms most influenced by climate change. Despite the flat oyster's Ostrea edulis high economic value, its culture is developed on a very small scale, since this species possesses a strong susceptibility to abiotic stressors. Due to climate change, temperature is one of the most critical environmental parameters for the welfare of the Mediterranean basin's marine inhabitants. The present study's purpose was to investigate the physiological performance of the Mediterranean's native O. edulis as it faces exposure to different temperatures. Since juveniles are more susceptible to abiotic stressors, this experimental procedure was focused on young individuals. The seawater temperatures studied included a standard control temperature of 21 °C (often observed in several marine areas throughout the Mediterranean), as well as increased seawater temperatures of 25 °C and 28 °C, occasionally occurring in shallow Mediterranean waters inhabited by bivalve spat. These were selected since the tissues of O. edulis becomes partly anaerobic in temperatures exceeding 26 °C, while cardiac dysfunction (arrhythmia) emerges at 28 °C. The results demonstrate that temperatures above 25 °C trigger both the transcriptional upregulation of hsp70 and hsp90, and the antioxidant genes Cu/Zn sod and catalase. Enhancement of thermal tolerance and increased defense against increased ROS production during thermal stress, were observed. As the intensity and duration of thermal stress increases, apoptotic damage may also occur. The increased oxidative and thermal stress incurred at the highest temperature of 28 °C, seemed to trigger the switch from aerobic to anaerobic metabolism, reflected by higher pepck mRNA expressions and lower ETS activity.

Effects of cadmium exposure on haemocyte immune function of clam Ruditapes philippinarum at different temperatures.

Haemocytes are crucial for the immune defence of mollusks. It is important to explore the immune performance of haemocytes of mollusks under the stress of heavy metals with global warming. In order to study the effects of cadmium (Cd) exposure and temperature stress on the haemocyte immune function of clam Ruditapes philippinarum, clams were exposed to different Cd concentrations (0.05, 0.10 and 0.25 mg/L) at 20 °C, 25 °C and 30 °C respectively. Haemocyte mortality, reactive oxygen species (ROS) and superoxide dismutase (SOD) activity were measured at day 1, day 3, day 5 and day 7. The results showed that the changes of the three indexes were not obvious when exposed to 0.05 mg/L of Cd at 20 °C, while significant differences were observed with the increase of temperature, Cd concentration and exposure time. Under a condition of relative high temperature coupling with high concentration of Cd, the clams were significantly influenced, showing an obvious synergistic effect. Selected indexes reflect the clam's response to the combined stress of temperature and Cd. Moreover, R. philippinarum might be an ideal biological index species to the Cd pollution.