Emersion Period Research Articles

Structural traits dictate abiotic stress amelioration by intertidal oysters

Abstract Autogenic ecosystem engineers often provide cool microhabitats which are used by associated organisms to reduce thermal extremes. The value of such habitats is, however, dependent on key structural traits of the ecosystem engineer, and the intensity and duration of thermal exposure. Using an experimental mesocosm that mimicked the rocky intertidal environment, we assessed how the spatial configuration of the habitat formed by an autogenic ecosystem engineer, the oyster, influences its capacity to mitigate heat stress experienced by invertebrates during simulated emersion periods on tropical, Hong Kong rocky shores. At the average temperature experienced during summer low tides, oyster habitat ameliorated environmental and organismal temperatures, irrespective of the structural configuration of the oyster bed. As temperatures increased, however, vertically orientated oysters provided microclimates that facilitated cooler invertebrate body temperatures than horizontal beds, which no longer conferred any associational benefit as compared to bare rock surfaces. In the absence of oysters, physiological indicators of stress to associated organisms (i.e., heart rate and osmolality) increased with the intensity and duration of exposure to high temperatures. Such effects were, however, mitigated by association with vertical but not horizontal oyster configurations. In contrast, the osmolality of the oysters was not related to temperature, suggesting they remained in a state of metabolic quiescence throughout emersion. Structural traits such as the spatial configuration of ecosystem engineers are therefore critical to their effectiveness in environmental amelioration. As such, variations in the morphological traits of ecosystem engineers, which have important implications for their ecological role, need to be incorporated into conservation and restoration projects aimed at climate change adaptation. A plain language summary is available for this article.

Microbial decomposition is highly sensitive to leaf litter emersion in a permanent temperate stream

Drought frequency and intensity in some temperate regions are forecasted to increase under the ongoing global change, which might expose permanent streams to intermittence and have severe repercussions on stream communities and ecosystem processes. In this study, we investigated the effect of drought duration on microbial decomposition of Populus nigra leaf litter in a temperate permanent stream (Oliveira, NW Portugal). Specifically, we measured the response of the structural (assemblage composition, bacterial and fungal biomass) and functional (leaf litter decomposition, extracellular enzyme activities (EEA), and fungal sporulation) parameters of fungal and bacterial communities on leaf litter exposed to emersion during different time periods (7, 14 and 21d). Emersion time affected microbial assemblages and litter decomposition, but the response differed among variables. Leaf decomposition rates and the activity of β-glucosidase, cellobiohydrolase and phosphatase were gradually reduced with increasing emersion time, while β-xylosidase reduction was similar when emersion last for 7 or more days, and the phenol oxidase reduction was similar at 14 and 21days of leaf emersion. Microbial biomass and fungal sporulation were reduced after 21days of emersion. The structure of microbial assemblages was affected by the duration of the emersion period. The shifts in fungal assemblages were correlated with a decreased microbial capacity to degrade lignin and hemicellulose in leaf litter exposed to emersion. Additionally, some resilience was observed in leaf litter mass loss, bacterial biomass, some enzyme activities and structure of fungal assemblages. Our study shows that drought can strongly alter structural and functional aspects of microbial decomposers. Therefore, the exposure of leaf litter to increasing emersion periods in temperate streams is expected to affect decomposer communities and overall decomposition of plant material by decelerating carbon cycling in streams.

The regulation of coralline algal physiology, an in situ study of <i>Corallina officinalis</i> (Corallinales, Rhodophyta)

Abstract. Calcified macroalgae are critical components of marine ecosystems worldwide, but face considerable threat both from climate change (increasing water temperatures) and ocean acidification (decreasing ocean pH and carbonate saturation). It is thus fundamental to constrain the relationships between key abiotic stressors and the physiological processes that govern coralline algal growth and survival. Here we characterize the complex relationships between the abiotic environment of rock pool habitats and the physiology of the geniculate red coralline alga, Corallina officinalis (Corallinales, Rhodophyta). Paired assessment of irradiance, water temperature and carbonate chemistry, with C. officinalis net production (NP), respiration (R) and net calcification (NG) was performed in a south-western UK field site, at multiple temporal scales (seasonal, diurnal and tidal). Strong seasonality was observed in NP and night-time R, with a Pmax of 22.35 µmol DIC (g DW)−1 h−1, Ek of 300 µmol photons m−2 s−1 and R of 3.29 µmol DIC (g DW)−1 h−1 determined across the complete annual cycle. NP showed a significant exponential relationship with irradiance (R2 = 0.67), although was temperature dependent given ambient irradiance > Ek for the majority of the annual cycle. Over tidal emersion periods, dynamics in NP highlighted the ability of C. officinalis to acquire inorganic carbon despite significant fluctuations in carbonate chemistry. Across all data, NG was highly predictable (R2 = 0.80) by irradiance, water temperature and carbonate chemistry, providing a NGmax of 3.94 µmol CaCO3 (g DW)−1 h−1 and Ek of 113 µmol photons m−2 s−1. Light NG showed strong seasonality and significant coupling to NP (R2 = 0.65) as opposed to rock pool water carbonate saturation. In contrast, the direction of dark NG (dissolution vs. precipitation) was strongly related to carbonate saturation, mimicking abiotic precipitation dynamics. Data demonstrated that C. officinalis is adapted to both long-term (seasonal) and short-term (tidal) variability in environmental stressors, although the balance between metabolic processes and the external environment may be significantly impacted by future climate change.

Intertidal marine sediment harbours Actinobacteria with promising bioactive and biosynthetic potential

Actinobacteria are the major source of bioactive natural products that find their value in research and drug discovery programmes. Antimicrobial resistance and the resulting high demand for novel antibiotics underscore the need for exploring novel sources of these bacteria endowed with biosynthetic potential. Intertidal ecosystems endure regular periods of immersion and emersion, and represent an untapped source of Actinobacteria. In this study, we studied the diversity and biosynthetic potential of cultivable Actinobacteria from intertidal sediments of Diu Island in the Arabian Sea. A total of 148 Actinobacteria were selectively isolated using a stamping method with eight isolation media. Isolates were grouped into OTUs based on their 16S rRNA gene sequence, and categorized within actinobacterial families such as Glycomycetaceae, Micromonosporaceae, Nocardiaceae, Nocardiopsaceae, Pseudonocardiaceae, Streptomycetaceae, and Thermomonosporaceae. The biosynthetic potential of the Actinobacteria, necessary for secondary metabolite biosynthesis, was screened and confirmed by extensive fingerprinting approaches based on genes coding for polyketide synthases and nonribosomal peptide synthetases. The observed biosynthetic potential was correlated with the antibacterial activity exhibited by these isolates in laboratory conditions. Ultimately, the results demonstrate that intertidal sediment is a rich source of diverse cultivable Actinobacteria with high potential to synthesize novel bioactive compounds in their genomes.

Seasonality and vertical distribution of epiphytic diatoms on the pneumatophore surface of mangrove Avicennia officinalis L.

Mangrove pneumatophores (respiratory roots) form a unique habitat about which very little ecological information is available. In this study, epiphytic diatoms on the pneumatophore surface of Avicennia officinalis (L.) were investigated with a focus on their seasonal and vertical distribution. The results indicated that among the seasons, highest diatom abundance was observed in monsoon. Vertically, maximum abundance was observed on 0–5 cm of the pneumatophore during post-monsoon and pre-monsoon and then gradually decreased upwards, but during monsoon, 5–10 cm section hosted maximum abundance. There was a seasonal and vertical variation on the diatom abundance and their interactive effect. This is because diatoms probably avoid the basal section (0–5 cm) of the pneumatophore during monsoon due to excessive sediment burial caused by intense riverine flux and settlement of suspended material. Overall it was found that vertically, diatoms (>70%) are mainly concentrated on the lower 0–10 cm of the pneumatophore, probably because this section remains moist during emersion period (low tide). Among the diatoms, Melosira nummuloides and Bacillaria paradoxa exhibited dominance during the monsoon, whereas Thalassiosira spp., Navicula spp., and Nitzschia spp.were prevalent during post- and pre-monsoon. To the best of our knowledge, this is the first study describing the composition of epiphytic diatoms from the pneumatophore surface of A. officinalis. Keeping in mind that these aerial roots together greatly enhance the surface area for attachment of epiphytic diatoms, their cumulative primary production would probably surpass that of mangroves on a quantitative basis and needs future investigation.

Limited proteomic response in the marine snail Melarhaphe neritoides after long-term emersion.

Rocky intertidal organisms are commonly exposed to environmental gradients, promoting adaptations to these conditions. Emersion time varies along the intertidal range and in the supralittoral zone is frequently larger than a single tidal cycle, even lasting for weeks. The planktonic-dispersing gastropod Melarhaphe neritoides is a common species of the high shore, adapted to reduce water loss in order to survive during long-term emersion. In this study, we investigated the molecular response, at the proteome level, of M. neritoides collected in high-shore tide pools to a series of emersion periods, from 8 to 24 days, in laboratory conditions. We compared this response to individuals maintained submerged during this period, because this was their original habitat. We also included a reversion treatment in the study, in which emersed individuals were returned to the submerged conditions. Although we detected an increase in overall protein concentration with longer emersion periods, contrary to general expectation, the two dimensional electrophoresis (2DE)-based proteomic analysis did not show significant differences between the treatments at the level of individual protein spots, even after an emersion period of 24 days. Our results suggest that the metabolism remains unaltered independent of the treatment carried out or the changes are very subtle and therefore difficult to detect with our experimental design. We conclude that M. neritoides could be equally adapted to emersion and submersion without drastic physiological changes.

Stress response according to transport protocol in Norway lobster, <i>Nephrops norvegicus</i>

The Norway lobster, Nephrops norvegicus, is a valuable and commonly exported European decapod crustacean, which experiences stress from point of capture and onward transport. Stressors such as air exposure duration (i.e. emersion period) and air temperature have been studied previously. We investigated whether mortality could be reduced by decreasing road vibrations during transport, and how physiological stress measurements were influenced in a transport simulation experiment, reflecting a typical short road journey along a supply chain. Baseline haemolymph samples were taken from lobsters sampled immediately after commercial capture using static traps (lobster pots). Individuals were emersed for one hour, either immobile or with continuous shaking; the latter to simulate conditions occurring during transport. Both treatments significantly increased Total Haemocyte Counts (THC) and serum glucose, lactate and ammonium concentrations compared to baseline animals. Individuals subjected to continuous shaking showed higher glucose and ammonium concentrations compared to individuals maintained immobile. We conclude that shaking appears to influence the physiological responses of N. norvegicus in addition to the effects of emersion alone, and the reduction of road vibrations (e.g. via simple cushioning) can reduce post-transport mortality.

Regulation of Intertidal Microphytobenthos Photosynthesis Over a Diel Emersion Period Is Strongly Affected by Diatom Migration Patterns.

Changes in biomass and photosynthesis of a diatom-dominated microphytobenthos (MPB) intertidal community were studied over a diel emersion period using a combination of O2 and scalar irradiance microprofiling, variable chlorophyll (Chl) fluorescence, and pigment analysis. The MPB biomass in the photic zone (0–0.5 mm) of the sediment exposed to low irradiance (150 μmol photons m-2 s-1) showed a >2-fold increase during the first hours of the emersion period, reaching >0.2 mg Chl a cm-3. Concentrations of Chl a started to decrease half-way through the emersion period, almost 2 h before tidal inundation. Similarly, O2 concentrations and volumetric gross photosynthesis in the photic zone increased during the first half of the emersion period and then decreased toward the timing of incoming tide/darkness. The results suggest that intertidal MPB community-level photosynthesis is mainly controlled by changes in the productive biomass of the photic zone determined by cell migration. A diel pattern in the photosynthesis vs. irradiance parameters α (photosynthetic efficiency at limiting irradiance) and ETRmax (photosynthetic capacity at saturating irradiance) was also observed, suggesting photoacclimation of MPB. Under high light exposure (2000 μmol photons m-2 s-1), lower α, ETRmax and sediment O2 concentrations were observed when cell migration was inhibited with the diatom motility inhibitor latrunculin A (Lat A), showing that migration is also used by MPB to maximize photosynthesis by reducing exposure to potentially photoinhibitory light levels. A higher de-epoxidation state in sediment treated with Lat A indicates that the involvement of the xanthophyll cycle in physiological photoprotection is more relevant in MPB when cells are inhibited from migrating. In the studied diatom-dominated MPB intertidal community, cell migration seems to be the key factor regulating photosynthesis over a diel emersion period and upon changes in light exposure.

Cheating the Locals: Invasive Mussels Steal and Benefit from the Cooling Effect of Indigenous Mussels.

The indigenous South African mussel Perna perna gapes during periods of aerial exposure to maintain aerobic respiration. This behaviour has no effect on the body temperatures of isolated individuals, but when surrounded by conspecifics, beneficial cooling effects of gaping emerge. It is uncertain, however, whether the presence of the invasive mussel Mytilus galloprovincialis limits the ability of P. perna for collective thermoregulation. We investigated whether varying densities of P. perna and M. galloprovincialis influences the thermal properties of both natural and artificial mussel beds during periods of emersion. Using infrared thermography, body temperatures of P. perna within mixed artificial beds were shown to increase faster and reach higher temperatures than individuals in conspecific beds, indicating that the presence of M. galloprovincialis limits the group cooling effects of gaping. In contrast, body temperatures of M. galloprovincialis within mixed artificial mussel beds increased slower and exhibited lower temperatures than for individuals in beds comprised entirely of M. galloprovincialis. Interestingly, differences in bed temperatures and heating rates were largely dependent on the size of mussels, with beds comprised of larger individuals experiencing less thermal stress irrespective of species composition. The small-scale patterns of thermal stress detected within manipulated beds were not observed within naturally occurring mixed mussel beds. We propose that small-scale differences in topography, size-structure, mussel bed size and the presence of organisms encrusting the mussel shells mask the effects of gaping behaviour within natural mussel beds. Nevertheless, the results from our manipulative experiment indicate that the invasive species M. galloprovincialis steals thermal properties as well as resources from the indigenous mussel P. perna. This may have significant implications for predicting how the co-existence of these two species may change as global temperatures continue to rise.

Hygric stresses and strategies in maintaining the association between crayfish and ectosymbiotic worms across vastly different environments

Crayfish and their ectosymbiotic worms may be a valuable model system for studying strategies to maintain symbiotic relationships strained by host-induced environmental shifts. Ectosymbiotic branchiobdellidan worms are thought to be dependent on crayfish hosts for reproduction. However, many crayfish species leave surface waters to excavate and reside in subterranean burrows. During this semi-terrestrial phase, crayfish are frequently out of water, subjecting their associated worms to desiccation. Water balance characteristics of Cambarincola mesochoreus, an ectosymbiont of Procambarus clarkii, were examined to elucidate strategies for surviving emersion while maintaining host associations. Emersed worms were characterized by a high water loss rate and low tolerance for dehydration. A lack of direct water contact eventually prompted a coiled, immobile dormant state where water loss was temporarily suppressed. This dormant state was broken by addition of water and re-entered by subsequent emersion. Neither group effects by clustering of many worms, nor water vapor absorption were utilized as mechanisms to increase desiccation hardiness. When crayfish leave surface or subterranean water, worm survival while maintaining host contact is likely facilitated by facultative quiescence. However, this strategy only allows for survival during relatively short-term, cyclic bouts of emersion. Survival of longer-term emersion periods would require worms to leave hosts and remain behind in surface or subterranean water. These strategies likely incur counterbalancing trade-offs: increased mortality but maintenance of host association versus increased survival but temporary or permanent loss of host association and sites for reproduction.

Abiotic factors influencing biomass accumulation of green tide causing Ulva spp. on Pyropia culture rafts in the Yellow Sea, China

Annually recurrent green-tides in the Yellow Sea have been shown to result from direct disposal into the sea of fouling Ulva from Pyropia aquaculture. The role abiotic factors play in Ulva biomass accumulation on rafts was studied to find ways to mitigate this problem. Dissolved inorganic nitrogen (DIN) was very high at all sites, but the highest Ulva biomass was associated with the lowest DIN and anthropogenic N. Under luxuriant background nutrient conditions, variability in temperature and periods of emersion, rather than pH, light and salinity determined Ulva biomass. Two dominant species of Ulva displayed differing tolerances to temperature and desiccation which helped explain why Ulva prolifera dominates floating green-tides. Rather than trying to mitigate green-tides only by reducing nutrient pollution, an earlier harvest of Pyropia in southern Jiangsu Province especially before temperatures increase greatly above 10°C during April, could reduce the biomass of U. prolifera disposed from rafts.

Spatial and temporal variability of CO2 fluxes at the sediment–air interface in a tidal flat of a temperate lagoon (Arcachon Bay, France)

This study aimed to explore the spatial and temporal variability of benthic metabolism in a temperate mesotidal lagoon. This was achieved by measuring fluxes of CO2 in static chambers during emersion, both under light and dark conditions. Three sample sites were selected according to their tidal level (upper or mid), their sediment type (sand or mud) and the presence/absence of the seagrass Zostera noltei. The three sites were investigated at three seasons (end of winter, spring and beginning of autumn). At each site and each season, three benthic chambers were used simultaneously in successive incubations over the emersion period. The sediment chlorophyll-a content varied seasonally in the upper sands (reaching 283mg.m−2 in spring) but not in the mid muds (averaging 142mgm−2 in bare muds and 186mgm−2 in muds covered by seagrass). The maximum sediment CO2-uptake under light was 9.89mmolm−2h−1 in the mid-bare muds, in early autumn. The maximum sediment CO2-release under darkness was 6.97mmolm−2h−1 in the mid muds covered by seagrass, in spring. Both CO2-fluxes measured in the light and in the dark increased over periods of emersion. This increase, not related to light nor temperature variations, could be explained by changes in the amount and chemistry of pore water during the air exposure of sediments. The benthic trophic state index, based on the maximum light CO2-flux versus maximum dark CO2-flux ratio, assigned to each site at each season indicated that the sediments were net autotrophic in spring in upper sands and in mid muds covered by seagrass and highly autotrophic in other cases. The most autotrophic sediments were the mid-level bare muds whatever the season. The relevance of this index is discussed compared to carbon annual budget.

Drying responses of microbial litter decomposition and associated fungal and bacterial communities are not affected by emersion frequency

Leaf-litter decomposition is driven by microbial and invertebrate communities and is likely to be severely affected by climate change and increased water abstraction and diversion. The occurrence, frequency, and severity of drying events are increasing in rivers worldwide. These events are a major threat to aquatic microbial communities and their contribution to riverine biogeochemical processes. A growing body of evidence suggests a dramatic reduction in litter processing rates and microbial activity during emersion. We hypothesized that leaf-litter decomposition would be less affected by high than low emersion frequency (characterized by longer emersion periods between immersion events, assuming a constant emersion duration). We exposed Alnus glutinosa L. litter to high-, medium-, and low-frequency emersion–immersion cycles in the Albarine River (eastern France). After 28 d of incubation, we quantified leaf mass loss and the biomass, extracellular enzyme activity (cellobiohydrolase), and structure (molecular fingerprint) of the fungal and bacterial communities that developed on the leaves. Leaf-litter decomposition was negatively affected by drying, but we found no effect of emersion frequency. Cellobiohydrolase activity and fungal and bacterial biomass did not vary with emersion frequency, and microbial biomass was dominated by fungi in all treatments at the end of the incubation period. Fungal and bacterial community structures were relatively insensitive to emersion frequency. Emersion duration had a larger effect on microbial community composition and leaf-litter decomposition than emersion frequency. We found no evidence of a link between the composition of microbial communities and their enzymatic activity or their ability to decompose leaf litter. Our findings suggest some degree of functional redundancy in microbial communities affected by drying stress during early stages of leaf-litter decomposition.

Metabolic activity of intertidal Fucus spp. communities: evidence for high aerial carbon fluxes displaying seasonal variability

Semi-sheltered rocky shores are characterized by a typical succession of Phaeophycean-dominated communities where canopy-forming algae are assumed to be very productive. However, metabolic activity of whole communities, integrating the main interactions that occur in these assemblages, still needs to be investigated more deeply, especially when communities are emerged. Thus, the metabolism of the mid-intertidal Fucus vesiculosus and Fucus serratus communities was surveyed once a month throughout a year in the Bay of Morlaix (France). In situ measurements of primary production and respiration were taken at the onset of emersion periods, using benthic chambers coupled to CO2 infrared gas analyzers. Benthic measurements were taken successively on whole communities and after canopy removal, to assess the contribution of the canopies to the communities’ carbon fluxes. Concurrently, nitrogen and organic carbon contents of the two Fucus species were evaluated monthly. Both communities exhibited high metabolic activity year-round (community gross primary production: 400–1000 mgC m−2 h−1; community respiration: 100–500 mgC m−2 h−1), with canopies accounting for 77–97 % of the global CO2 fluxes. However, this relative canopies’ contribution to global CO2 fluxes did not follow seasonal fluctuations, whereas both metabolic activities and nitrogen and carbon contents did, confirming the importance of light and temperature in the regulation of metabolic processes. A nutrient limitation was also suggested to occur in summer, when seawater was nutrient-depleted. Finally, the F. vesiculosus community, located upper on the shore, exhibited lower photosynthetic activity than the F. serratus community, being consistent with the vertical zonation rules of intertidal habitats.

Plant–water relations of intertidal and subtidal seagrasses

AbstractThis work represents the first contribution to (i) examine the changes in plant‐water relations of an inter‐tidal seagrass during air exposure (Zostera noltii), and (ii) compare the water status descriptors between inter‐tidal‐ and subtidal‐adapted species (Cymodocea nodosa,Zostera marina). Two different morphotypes ofZ. noltiithat develop in the highest and lowest inter‐tidal levels in the Portuguese lagoon of Ria Formosa were exposed to natural emersion periods under laboratory conditions, and the evolution of leaf water relations and osmolytes (ions, proline and non‐structural carbohydrates) was measured. Both morphotypes regulated their water potential (Ψw) by reducing the osmotic potential (Ψπ) through osmolyte accumulation, but only high inter‐tidal plants were able to do this by adjusting the turgor pressure through cell wall hardening. This is a conservative mechanism for osmotic acclimation, which occurred only after long emersion periods (7 h). After a rapid increase in ion concentration under air exposure, the high inter‐tidal morphotype replaced them by more physiologically compatible solutes (proline and non‐structural carbohydrates) to maintain the osmotic adjustment. Altered ionic homeostasis was found in low inter‐tidal plants when exposed to such unnatural, long emersion periods. Osmotic unbalances were also observed during the submerged recovery phase. Descriptors of leaf pressure–volume (P–V) curves and Höfler diagrams were derived for seagrasses for the first time. They support the divergences in water relations observed between inter‐tidal and subtidal seagrasses according to their vertical distribution. More negative water and osmotic potentials and higher rigidity of cell walls (higher elastic modulus, ε) were found to be specific osmotic adaptations of seagrasses to the inter‐tidal.

Seasonal photoacclimation patterns in the intertidal macroalga <em>Cystoseira tamariscifolia</em> (Ochrophyta)

Cystoseira tamariscifolia thalli collected from rocky shores and rockpools in winter and summer in Southern Spain were incubated for 7 days in UV transparent cylindrical vessels under outdoor conditions. Photosynthetic activity estimated as in vivo chlorophyll α fluorescence of photosystem II, photosynthetic pigments, antioxidant activity (DPPH assay), phenolic compounds and total internal C and N contents were determined after short-term (3 d) and mid-term (7 d) periods. Maximum quantum yield of PSII (F v /F m ) was significantly higher in field-collected algae and after 7 d incubation in winter than in summer. In rocky shores and rockpools thalli, maximum electron transport rate (ETR max ) and photosynthetic efficiency (α ETR ) were much higher in summer than in winter. ETR of outdoor-grown thalli (in situ ETR) showed a daily pattern, with a decrease at noon in both winter and summer (3 rd and 7 th days). We found much higher antioxidant activity in thalli collected in summer than in winter. However, the concentration of internal UV screen substances (polyphenols) was higher in winter than in summer, whereas the release of phenolic compounds was lower. The highest capacity of acclimation in C. tamariscifolia found in summer and RS with emersion periods was explained by the highest dynamic photoinhibition, energy dissipation (non-photochemical quenching) and antioxidant activity (EC 50 ).

Stress modulation of cellular metabolic sensors: interaction of stress from temperature and rainfall on the intertidal limpet Cellana toreuma.

In the natural environment, organisms are exposed to large variations in physical conditions. Quantifying such physiological responses is, however, often performed in laboratory acclimation studies, in which usually only a single factor is varied. In contrast, field acclimatization may expose organisms to concurrent changes in several environmental variables. The interactions of these factors may have strong effects on organismal function. In particular, rare events that occur stochastically and have relatively short duration may have strong effects. The present experiments studied levels of expression of several genes associated with cellular stress and metabolic regulation in a field population of limpet Cellana toreuma that encountered a wide range of temperatures plus periodic rain events. Physiological responses to these variable conditions were quantified by measuring levels of mRNA of genes encoding heat-shock proteins (Hsps) and metabolic sensors (AMPKs and Sirtuin 1). Our results reveal high ratios of individuals in upregulation group of stress-related gene expression at high temperature and rainy days, indicating the occurrence of stress from both prevailing high summer temperatures and occasional rainfall during periods of emersion. At high temperature, stress due to exposure to rainfall may be more challenging than heat stress alone. The highly variable physiological performances of limpets in their natural habitats indicate the possible differences in capability for physiological regulation among individuals. Our results emphasize the importance of studies of field acclimatization in unravelling the effects of environmental change on organisms, notably in the context of multiple changes in abiotic factors that are accompanying global change.

Corallina and Ellisolandia (Corallinales, Rhodophyta) photophysiology over daylight tidal emersion: interactions with irradiance, temperature and carbonate chemistry.

The photophysiology of three geniculate coralline algal species (Corallina officinalis, C. caespitosa and Ellisolandia elongata) was determined in intertidal rock pools in the south-west UK at Combe Martin (51°12′31N 4°2′19W) and Heybrook Bay (50°31′66N 4°11′41W), at the start, middle and end of summer (September 1 and 2) and winter (February 9 and 10) daylight tidal emersion periods, in relation to prevailing irradiance, temperature and carbonate chemistry conditions. Algal photophysiology was assessed from rapid light curves performed using pulse amplitude modulation fluorometry. Corallina and Ellisolandia experienced significant fluctuations in irradiance, temperature and carbonate chemistry over seasonal and tidal cycles. Rock pool carbonate chemistry was predictable (R 2 = 0.82, P < 0.0001) by photodose (summed irradiance) plus water temperature, but not significantly related to photophysiology. In contrast, Corallina and Ellisolandia relative maximum electron transfer rate showed a significant negative relationship (R 2 = 0.65, P < 0.0001) with irradiance plus water temperature. At a seasonal resolution, photoacclimation to maximize both light harvesting during winter months and photoprotection during summer months was observed for all species. Dynamic photoinhibition was apparent over both summer and winter tidal emersion, in relation to irradiance fluctuations. More effective photoinhibition was apparent during summer months, with greater sensitivity to irradiance and slower recovery in F v/F m, observed during winter. With sustained high irradiance over tidal emersion, the establishment of high pH/low inorganic carbon conditions may impact photochemistry. This study represents the first assessment of C. officinalis, C. caespitosa and E. elongata photophysiology underpinned by clear species concepts and highlights their ability to adapt to the dramatically fluctuating conditions experienced in intertidal rock pools.

Physiological and biochemical strategies for withstanding emersion in two galaxiid fishes

The galaxiid fishes of the Southern hemisphere display variable tolerance to aerial exposure. Brown mudfish (Neochanna apoda), for example, pseudoaestivate, inhabiting moist soil for months at a time, whereas inanga (Galaxias maculatus) emerse under unfavourable water conditions, but only for periods of a few hours. This study sought to identify the physiological and biochemical strategies that determine emersion tolerance in these species. Nitrogenous waste excretion was measured before and after an experimental emersion period (14days for mudfish, 6h for inanga). Both species showed significantly elevated ammonia “washout” upon return to water, but no increase in plasma or muscle ammonia. Post-emersion urea levels were elevated in plasma and muscle in both fish, however the extent of the accumulation did not indicate significant de novo urea production. This was supported by the lack of carbamoyl phosphate synthetase activity in tissues. Consequently, mudfish metabolism was examined to determine whether changes in parameters such as oxygen consumption, carbon dioxide excretion, and/or altered metabolic costs (represented by the key ionoregulatory enzyme Na+, K+-ATPase; NKA) could explain emersion tolerance. Oxygen consumption rates, already very low in immersed mudfish, were largely maintained over the course of emersion. Carbon dioxide excretion decreased during emersion, and a small, but significant, decrease in NKA was noted. These data suggest that the extended emersion capacity of mudfish may result from a generally low metabolic rate that is maintained throughout aerial exposure via cutaneous gas exchange, and which limits the production of potentially toxic nitrogenous waste.

Effect of varying conditions of exposure to an aggressive medium on the corrosion behavior of the 2050 Al–Cu–Li alloy

The corrosion behavior of aluminum alloy 2050 was studied as a function of varying conditions of exposure to an aqueous NaCl solution. Two metallurgical states were considered, i.e., an as-received alloy (NHT) and aged samples (HT). After continuous immersion tests, the NHT samples were susceptible to intergranular corrosion, whereas intragranular corrosion was observed for the HT samples. For the NHT samples, cyclic corrosion tests, with alternate immersion – emersion periods, induced subgrain boundary dissolution, and for the HT samples, grain and/or subgrain boundary sensibilization was induced. Hydrogen content measurements suggested a hydrogen enrichment of the alloy under cyclic corrosion tests.