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The intertidal zone is one of the most stressful environments, with extreme shifts in temperature, salinity, pH and oxygen concentration. Marine molluscs, particularly chitons that belong to the category of ecologically significant organisms, survive in this extreme environment, and are ideal systems for studying stress adaptation. Mitochondria are known to be critical for energy homeostasis, and changes in environmental factors result in their dysfunction and consequent injury to the organism. Intertidal organisms are exception in this respect because they are capable of maintaining mitochondrial integrity. Here, we used mitochondrial genetic components from seven chitons of the intertidal zone to infer phylogenetic relationships. Selection analyses on individual protein-coding genes (PCGs) were performed to identify and map potentially adaptive residues in the modelled structures of the mitochondrial respiratory chain complexes. The results showed significant amino acid changes in sites under diversifying selection for all the PCGs, indicating that the mitochondrial genome in chitons is undergoing adaptive evolution. Such sites were observed in the proton pump as well as in the translocation channel of the transmembrane helices and the surrounding loop regions, thus implying functional modification of the mitochondrial proteins essential for survival in the dynamic environment of the intertidal zone. [ABSTRACT FROM AUTHOR]

Increased sedimentation in intertidal areas may stem from anthropogenic sources such as coastal development and natural processes, including discharges by rivers, landslides, and floods. Furthermore, global climate change could eventually lead to environmental hypoxia altering the composition of intertidal communities when hypoxia events surpass the physiological tolerance of intertidal organisms. We measured hemolymph lactate and ammonia (NH3 and NH4+) in the hermit crab Pagurus samuelis (Stimpson, 1857) subjected to shallow burial events and found high lactate and ammonia, indicating a switch to anaerobic respiration. The likelihood of hermit crabs dying during burial increased 31% for every 10 mM increase in lactate. Lactate levels were generally raised by increasing temperature, burial depth, or burial duration. At 20 ºC and 30 ºC, more lactate was detected at 3 cm and 6 cm burial depths than in the control (0 cm). Lactate concentrations were higher at 3 cm burial depth after 6 h than after 2 h. Lactate concentrations were higher at 20 ºC and 30 ºC than at 5 ºC at both 3 cm and 6 cm. A 10 µg ml–1 rise in ammonia concentration was associated with increased probability of death by 21%. Ammonia concentrations were higher at 3 cm than at 6 cm, indicating a shift in ammonia production or excretion at 6 cm. Burial time did not impact ammonia production. Large numbers of hermit crabs survived up to 24 h following lactate (92.9%) and ammonium salt (83.3%) injections. These results provide evidence that neither lactate nor ammonia buildup are principal causes of death following shallow burial. [ABSTRACT FROM AUTHOR]

Intertidal epilithic bacteria communities are important components of coastal ecosystems, yet few studies have assessed their diversity and how it may be affected by changing environmental parameters. Submarine CO2 seeps produce localised areas of CO2-enriched seawater with reduced pH levels. We utilised the seawater pH/CO2 gradient at Levante Bay (Italy) to test the hypothesis that epilithic bacteria communities are modified by exposure to seawater with the varying chemical parameters. Biofilms were sampled from three sites exposed to seawater with different pH/CO2 levels and diversity determined using high-throughput sequencing of 16S rRNA genes. Seawater pCO2 concentrations were increased from ambient at site 1 to 621 μatm at site 2 and 1654 μatm site 3, similar to the predicated future oceans beyond 2050 and 2150, respectively. Alpha diversity of total bacteria communities and Cyanobacteria communities was significantly different between sites ( anova P < 0.05). Comparison between sites showed that bacteria communities and Cyanobacteria communities were significantly different ( anosim P < 0.01; permanova P < 0.01). Proteobacteria, Bacteroidetes and Cyanobacteria dominated all communities; however, there were differences between sites in the relative abundance of specific orders. This study provides the most detailed assessment of intertidal epilithic bacteria diversity and shows that diversity is significantly different along a seawater pH/CO2 gradient. This information supports the evaluation of the impacts of future ocean acidification on coastal marine ecosystems. [ABSTRACT FROM AUTHOR]

The injection of anthropogenically-produced CO2 into the atmosphere will lead to an increase in temperature and a decrease in pH at the surface of the oceans by 2100. Marine intertidal organisms possess the ability to cope in the short term with environmental fluctuations exceeding predicted values. However, how they will cope with chronic exposure to elevated temperature and pCO2 is virtually unknown. In addition, individuals from the same species/population often show remarkable levels of variation in their responses to complex climatic changes: in particular, variation in metabolic rates often is linked to differences in individuals’ performances and fitness. Despite its ecological and evolutionary importance, inter-individual variation has rarely been investigated within the context of climatic changes, and most investigations have typically employed orthogonal experimental designs paired to analyses of independent samples. Although this is undoubtedly a powerful and useful approach, it may not be the most appropriate for understanding all alterations of biological functions in response to environmental changes. An individual approach arguably should be favored when trying to describe organisms’ responses to climatic change. Consequently, to test which approach had the greater power to discriminate the intensity and direction of an organism’s response to complex climatic changes, we investigated the extracellular osmo/iono-regulatory abilities, upper thermal tolerances (UTTs), and metabolic rates of individual adults of an intertidal amphipod, Echinogammarus marinus, exposed for 15 days to combined elevated temperature and pCO2. The individual approach led to stronger and different predictions on how ectotherms will likely respond to ongoing complex climatic change, compared with the independent approaches. Consequently, this may call into question the relevance, or even the validity, of some of the predictions made to date. Finally, we argue that treating individual differences as biologically meaningful can lead to a better understanding of the physiological responses themselves and the selective processes that will occur with complex climatic changes; selection will likely play a crucial role in defining species’ responses to future environmental changes. Individuals with higher metabolic rates were also characterized by greater extracellular osmo/iono-regulative abilities and higher UTTs, and thus there appeared to be no evolutionary trade-offs between these functions. However, as individuals with greater metabolic rates also have greater costs for maintenance and repair, and likely a lower fraction of energy available for growth and reproduction, trade-offs between life-history and physiological performance may still arise. [ABSTRACT FROM PUBLISHER]

Within intertidal sediments, much of the dissolved organic carbon (DOC) consists of carbohydrate-rich extracellular polymeric substances (EPS) produced by microphytobenthic biofilms. EPS are an important source of carbon and energy for aerobic and anaerobic microorganisms owing to burial of microphytobenthos and downward transport of their exudates. We established slurries of estuarine biofilms to determine the fate of organic carbon and EPS fractions, differing in size and complexity, under oxic and anoxic conditions. DOC and hot-water-extracted organic matter (predominately diatom chrysolaminarin) were utilised rapidly at similar rates in both conditions. Concentrations of insoluble, high-molecular-weight EPS were unchanged in oxic microcosms, but were significantly degraded under anoxic conditions (39% degradation by day 25). Methanogenesis and sulphate reduction were major anaerobic processes in the anoxic slurries, and 16S rRNA gene pyrosequencing revealed that Desulfobacteraceae (relative sequence abundance increased from 1.9% to 12.2%) and Desulfobulbaceae (increased from 1.5% to 4.3%) were the main sulphate reducers, whilst Clostridia and Bacteroidetes were likely responsible for anaerobic hydrolysis and fermentation of EPS. We conclude that a diverse consortium of anaerobic microorganisms (including coexisting sulphate reducers and methanogens) degrade both labile and refractory microphytobenthic-derived carbon and that anaerobic degradation may be the primary fate of more structurally complex components of microphytobenthic EPS. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) has emerged as a fundamental signal molecule involved in the responses of plant to stress. A role for NO in the regulation of methionine sulfoxide reductase (MSR) mRNA expression and high light acclimation was studied in a green macroalga Ulva fasciata Delile. Transfer from darkness to high light (&geq;1,200 μmol photons m−2 s−1) inhibited photosynthesis and growth but increased NO production and UfMSRA and UfMSRB transcripts. Treatment with an NO scavenger, 2-(4-carboxy- phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO), at 1,200 μmol photons m−2 s−1 caused a further growth inhibition accompanied by an inhibition of the increase of UfMSRA and UfMSRB transcripts by high light, while treatment with an NO generator, sodium nitroprusside (SNP), alleviated the growth inhibition and enhanced UfMSRA and UfMSRB expression. Exposure to moderate light (300 μmol photons m−2 s−1) conditions also increased UfMSRA and UfMSRB transcripts, which were not affected by cPTIO treatment but were enhanced by SNP treatment. So, NO does not mediate the up-regulation of UfMSR genes by transfer to moderate light possibly as a precautionary mechanism in the sense of increasing light intensities in the daytime. In conclusion, NO production can be induced in U. fasciata upon exposure to high light for up-regulation of UfMSRA and UfMSRB expression but the level of NO production is not sufficient for acquisition of full tolerance to high light stress. Enhanced NO production by an exogenously applied NO generator can effectively trigger the high light acclimation process, including UfMSRA and UfMSRB expression. [ABSTRACT FROM AUTHOR]

Some mitochondrial introgression is common between closely related species, but distinct species rarely show substantial introgression in their entire distribution range. In this study, however, we report a complete lack of mitochondrial divergence between two sympatric species of flat periwinkles ( Littorina fabalis and Littorina obtusata) which, based on previous allozyme studies, diverged approximately 1 Ma. We re-examined their species status using both morphology (morphometric analysis) and neutral genetic markers (microsatellites) and our results confirmed that these species are well separated. Despite this, the two species shared all common cytochrome-b haplotypes throughout their NE Atlantic distribution and no deep split between typical L. fabalis and L. obtusata haplotypes could be found. We suggest that incomplete lineage sorting explains most of the lack of mitochondrial divergence between these species. However, coalescent-based analyses and the sympatric sharing of unique haplotypes suggest that introgressive hybridization also has occurred. [ABSTRACT FROM AUTHOR]