Impact of ocean acidification on escape performance of the king scallop, Pecten maximus, from Norway

The ongoing process of ocean acidification already affects marine life, and according to the concept of oxygen and capacity limitation of thermal tolerance, these effects may be intensified at the borders of the thermal tolerance window. We studied the effects of elevated CO₂ concentrations on clapping performance and energy metabolism of the commercially important scallop Pecten maximus. Individuals were exposed for at least 30 days to 4 °C (winter) or to 10 °C (spring/summer) at either ambient (0.04 kPa, normocapnia) or predicted future PCO₂ levels (0.11 kPa, hypercapnia). Cold-exposed (4 °C) groups revealed thermal stress exacerbated by PCO₂ indicated by a high mortality overall and its increase from 55 % under normocapnia to 90 % under hypercapnia. We therefore excluded the 4 °C groups from further experimentation. Scallops at 10 °C showed impaired clapping performance following hypercapnic exposure. Force production was significantly reduced although the number of claps was unchanged between normocapnia- and hypercapnia-exposed scallops. The difference between maximal and resting metabolic rate (aerobic scope) of the hypercapnic scallops was significantly reduced compared with normocapnic animals, indicating a reduction in net aerobic scope. Our data confirm that ocean acidification narrows the thermal tolerance range of scallops resulting in elevated vulnerability to temperature extremes and impairs the animal’s performance capacity with potentially detrimental consequences for its fitness and survival in the ocean of tomorrow.     

The synergistic effects of increasing temperature and CO2 levels on activity capacity and acid–base balance in the spider crab, Hyas araneus

With global climate change, ocean warming and acidification occur concomitantly. In this study, we tested the hypothesis that increasing CO₂ levels affect the acid–base balance and reduce the activity capacity of the Arctic spider crab Hyas araneus, especially at the limits of thermal tolerance. Crabs were acclimated to projected oceanic CO₂ levels for 12 days (today: 380, towards the year 2100: 750 and 1,120 and beyond: 3,000 μatm) and at two temperatures (1 and 4 °C). Effects of these treatments on the righting response (RR) were determined (1) at acclimation temperatures followed by (2) righting when exposed to an additional acute (15 min) heat stress at 12 °C. Prior to (resting) and after the consecutive stresses of combined righting activity and heat exposure, acid–base status and lactate contents were measured in the haemolymph. Under resting conditions, CO₂ caused a decrease in haemolymph pH and an increase in oxygen partial pressure. Despite some buffering via an accumulation of bicarbonate, the extracellular acidosis remained uncompensated at 1 °C, a trend exacerbated when animals were acclimated to 4 °C. The additional combined exposure to activity and heat had only a slight effect on blood gas and acid–base status. Righting activity in all crabs incubated at 1 and 4 °C was unaffected by elevated CO₂ levels or acute heat stress but was significantly reduced when both stressors acted synergistically. This impact was much stronger in the group acclimated at 1 °C where some individuals acclimated to high CO₂ levels stopped responding. Lactate only accumulated in the haemolymph after combined righting and heat stress. In the group acclimated to 1 °C, lactate content was highest under normocapnia and lowest at the highest CO₂ level in line with the finding that RR was largely reduced. In crabs acclimated to 4 °C, the RR was less affected by CO₂ such that activity caused lactate to increase with rising CO₂ levels. In line with the concept of oxygen and capacity limited thermal tolerance, all animals exposed to temperature extremes displayed a reduction in scope for performance, a trend exacerbated by increasing CO₂ levels. Additionally, the differences seen between cold- and warm-acclimated H. araneus after heat stress indicate that a small shift to higher acclimation temperatures also alleviates the response to temperature extremes, indicating a shift in the thermal tolerance window which reduces susceptibility to additional CO₂ exposure.     

Effects of feeding and light intensity on the response of the coral Porites rus to ocean acidification

Recently, it has been suggested that there are conditions under which some coral species appear to be resistant to the effects of ocean acidification. To test if such resistance can be explained by environmental factors such as light and food availability, the present study investigated the effect of 3 feeding regimes crossed with 2 light levels on the response of the coral Porites rus to 2 levels of pCO₂ at 28 °C. After 1, 2, and 3 weeks of incubation under experimental conditions, none of the factors—including pCO₂—significantly affected area-normalized calcification and biomass-normalized calcification. Biomass also was unaffected during the first 2 weeks, but after 3 weeks, corals that were fed had more biomass per unit area than starved corals. These results suggest that P. rus is resistant to short-term exposure to high pCO₂, regardless of food availability and light intensity. P. rus might therefore represent a model system for exploring the genetic basis of tolerance to OA.     

Energy demand of larval and juvenile Cape horse mackerels, Trachurus capensis, and indications of hypoxia tolerance as benefit in a changing environment

Trachurus capensis is an important fisheries resource in the degraded Namibian upwelling ecosystem. Food supply and shoaling of hypoxic zones are hypothesised to influence the species’ recruitment success. This paper is the first to quantify energy requirements and hypoxia tolerance of larval and juvenile stages of a Trachurus species. We measured normoxic respiration rates of T. capensis with a size range from 0.001 to 20.8 g wet mass (WM) collected off Cape Town (33.9°S, 18.5°E, 12/2009) and in the northern Benguela (17–24°S, 11–15°E, 02/2011). Routine metabolic rate (RMR) and standard routine rate (SRR) (mg O₂ h^?1) followed the allometric functions RMR = 0.418 WM^0.774 and SRR = 0.275 WM^0.855, respectively. Larvae and juveniles had comparatively high metabolic rates, and the energy demand of juveniles at the upper end of the size range appeared too high to be fuelled by a copepod diet alone. T. capensis’ early life stages showed a high tolerance to hypoxic conditions. RMR in larvae did not change until 30 % O₂sat at 18 °C. In juveniles, critical oxygen saturation levels were low (P_C for SRR = 11.2 ± 1.7 % O₂sat and P_C for RMR = 13.2 ± 1.6 % O₂sat at 20 °C) and oxy-regulation effective (regulation index = 0.78 ± 0.09). A high hypoxia tolerance may facilitate the retention of larvae in near-shore waters providing favourable feeding conditions and allowing juveniles to exploit food resources in the oxygen minimum zone. These mechanisms seem to well adapt T. capensis to a habitat affected by spreading hypoxic zones and probably enhance its recruitment success.     

Interactive effects of UV radiation and enhanced temperature on photosynthesis, phlorotannin induction and antioxidant activities of two sub-Antarctic brown algae

Lessonia nigrescens and Durvillaea antarctica, two large sub-Antarctic brown algae from the southern Chilean coast, were exposed to solar UV radiation in an outdoor system during a summer day (for 11 h) as well as to artificial UV radiation under controlled laboratory conditions at two temperatures (15 and 20 °C) for 72 h. Chlorophyll a fluorescence–based photoinhibition of photosynthesis was measured during the outdoor exposure, while electron transport rates, lipid peroxidation, antioxidant activity and content of phlorotannins were determined at different time intervals during the laboratory exposure. Under natural solar irradiances in summer, both species displayed well-developed dynamic photoinhibition: F _v/F _m values decreased by 70 % at noon coinciding with the levels of PAR >1,500 μmol m^?2 s^?1 and UV-B radiation >1 W m^?2 and recovered substantially in the afternoon. In treatments including UV radiation, recovery in D. antarctica started already during the highest irradiances at noon. The results from laboratory exposures revealed that (a) elevated temperature of 20 °C exacerbated the detrimental effects of UV radiation on photochemical parameters (F _v/F _m and ETR); (b) peroxidative damage measured as MDA formation occurred rapidly and was strongly correlated with the decrease in F _v/F _m, especially at elevated temperature of 20 °C; (c) the antioxidant activity and increases in soluble phlorotannins were positively correlated mainly in response to UV radiation; (d) phlorotannins were rapidly induced but strongly impaired at 20 °C. In general, short-term (2–6 h) exposures to enhanced UV radiation and temperature were effective to activate the photochemical and biochemical defenses against oxidative stress, and they continued operative during 72 h, a time span clearly exceeding the tidal or diurnal period. Furthermore, when algae were exposed to dim light and control temperature of 15 °C for 6 h, F _v/F _m increased and lipid peroxidation decreased, indicating consistently that algae retained their ability for recovery. D. antarctica was the most sensitive species to elevated temperature for prolonged periods in the laboratory. Although no conclusive evidence for the effect of the buoyancy of fronds was found, the interspecific discrepancies in thermo-sensitivity in the UV responses found in this study are consistent with various ecological and biogeographical differences described for these species.     

Stable isotope profiles from subtropical marine gastropods of the family Fasciolariidae: growth histories and relationships to local environmental conditions

Oxygen and carbon stable isotope profiles were constructed for two species of large subtropical gastropods of the family Fasciolariidae—Triplofusus giganteus and Fasciolaria tulipa—from the Florida Keys and the Bahamas, to evaluate their life history and to assess their potential as paleoenvironmental proxies. Oxygen isotope profiles revealed T. giganteus and F. tulipa grew their shells for 6 and 3 years, respectively. Both mollusks show faster growth rates during the first half of their lifespan. Mean annual temperatures (MAT) derived from oxygen isotopes for T. giganteus were 26.5 °C and for F. tulipa were 26.7 °C, both matching instrumental MATs of 26.7 and 26.5 °C for the Florida Keys. Both shells, however, failed to record entire mean annual temperature ranges (MART). Fasciolaria tulipa yielded a calculated MART of 5.6 °C compared with a measured MART of 9.3 °C, and T. giganteus showed a calculated MART of 6.9 °C compared with a measured MART of 9.4 °C. Carbon isotopes of T. giganteus were ambiguous and reveal no significant relationships with trends in nutrient concentrations (N and P), dissolved oxygen, and dissolved organic carbon, although they did exhibit more negative values concomitant with landfall of Hurricane Irene and trended to increasing values with ontogeny that could reflect migration. Carbon isotopes in F. tulipa were lower during winters, possibly reflecting seasonal upwelling or seagrass-mediated carbon cycling.     

Preferences and tradeoffs in nectar temperature and nectar concentration in the Asian hive bee Apis cerana

Honey bee foragers need to asses and make trade-offs between a number of potentially conflicting floral attributes. Here, we investigate multi-attribute decision making in the eastern honey bee, Apis cerana, when foraging on food sources that varied in warmth and sucrose concentration. We show that foragers prefer warm (30 °C) sucrose solution over cool (10 °C) sucrose solution and concentrated (30 % w/w) sucrose solution over dilute (15 % w/w) sucrose solution. When we offered the preferred sucrose concentration (30 % w/w) at the less-preferred temperature (10 °C), and the less-preferred sucrose concentration (15 % w/w) at the preferred temperature (30 °C), foragers prioritized warmth by choosing the warmer, but lower concentration solution. When the temperature difference was less extreme, bees preferred more concentrated cooler syrup (30 % ww at 15 °C over 15 % 30 °C). However, the addition of a decoy item to the choice set had a significant effect on the bees' preferences. Our results highlight the critical importance of considering context effects when measuring the foraging preferences of animals.     

Foraging habitats and migration corridors utilized by a recovering subpopulation of adult female loggerhead sea turtles: implications for conservation

From 1998 to 2008, 68 adult female loggerhead sea turtles (Caretta caretta) were instrumented with platform transmitter terminals at nesting beaches in Georgia, North Carolina (NC) and South Carolina (SC) on the East Coast of the United States of America (30°48′N, 81°28′W to 33°51′N, 77°59′W). The majority of post-nesting loggerheads (N = 42, 62 %) migrated to foraging habitats in the Mid-Atlantic Bight during May–October, with a subsequent migration occurring during November–March to foraging habitats south of Cape Hatteras, NC. Nine (13 %) loggerheads initially foraged in the near-shore, coastal areas of the South Atlantic Bight, but moved to offshore habitats—closer to the Gulf Stream—during November–March, while fourteen (21 %) loggerheads remained in foraging areas along the mid-continental shelf off of the eastern coast of Florida and/or continued southward to Florida Bay and the Bahamas. The present study delineates important, post-nesting foraging habitats and migration corridors where loggerheads may interact with commercial fisheries—providing managers opportunities to develop and implement optimally effective conservation actions for the recovery of this threatened species.     

Temperature effects on the toxicity of four trace metals to adult spotted Babylonia snails (Babylonia areolata)

A study was conducted to determine the median lethal toxicity of four heavy metals on the marine gastropod Babylonia areolata. Median lethal toxicity tests were conducted to observe the sensitivity of this gastropod to metals and how variations in temperature might affect toxicity of test elements. Four heavy metals were used in the study. It was observed that the 96-hr LC₅₀ (in mg/L) for the different metals was found to be nickel (Ni) 33.53 (35.22–28.43), copper (Cu) 44.59 (46.43–41.53), cadmium (Cd) 21.53 (23.43–18.37), and zinc (Zn) 27.34 (28.81–24.24) at room temperature 24 °C. With temperature as a variable, median lethal concentration (LC₅₀) values were observed to increase from 22.41 mg/L at 10 °C to 27.34 mg/L at 28 °C and reduce to 18.43 mg/L at 30 °C and a further rise in toxicity was observed at 35 °C where LC₅₀ value was 12.7 mg/L as seen in the case of Zn. It was also observed that at 40 °C thermal and chemical toxicity overlapped as 100% mortality was observed in controls. This trend was noted in all metals for Babylonia areolata indicating that temperature played an important role in determining LC₅₀ values of toxicants.     

Effects of seawater temperature and pH on the boring rates of the sponge Cliona celata in scallop shells

Warmer, more acidic water resulting from greenhouse gas emissions could influence ecosystem processes like bioerosion of calcifying organisms. Based on summer-maxima values (temperature = 26 °C; pH = 8.1) at a collection site in New York (40°56″ N, 72°30″ W), explants of the boring sponge Cliona celata Grant, 1826 were grown for 133 days on scallop shells in seawater ranging from current values to one scenario predicted for the year 2100 (T = 31 °C; pH = 7.8). High water temperature had little effect on sponge growth, survival, or boring rates. Lower pH slightly reduced sponge survival, while greatly influencing shell boring. At pH = 7.8, sponges bored twice the number of papillar holes and removed two times more shell weight than at pH = 8.1. Greater erosion resulted in weaker scallop shells. This study suggests that lower seawater pH may increase boring rates of C. celata in shellfish, with potentially severe implications for wild and farmed shellfish populations.     

Lower thermal capacity limits of the common brown shrimp (Crangon crangon,L.)

Brown shrimp (Crangon crangon, L.) are subjected to a huge annual temperature range, and certain thermal conditions during winter have been identified to affect the brown shrimp population. Despite that, little is known about its thermal biology with regard to critically low temperatures. In the present study, we determined the critical thermal minima (CT_min) and the critical lethal minima (CL_min) of male and female brown shrimp of different body sizes in laboratory-based experiments. For the CT_min trials, shrimp were acclimated to 4.0, 9.0, and 14.0 °C and exposed to a cooling rate of ?0.2 °C min^?1. In the CL_min trials, brown shrimp were exposed to a cooling rate of ?1.0 °C day^?1 without prior thermal acclimation. Acclimation temperature significantly affected the temperature tolerance of brown shrimp (p < 0.001). CT_min among the experimental groups just varied slightly, and no clear effect of gender or body size was observed. In the CL_min trials, brown shrimp even tolerated the coldest temperature of ?1.7 °C that could be established in the experimental setup. However, we observed a negative relationship between temperature and reactivity within the range of 7.0 and 1.0 °C that was determined by means of the flicking response. This relationship suddenly broke between 1.0 and 0.0 °C where an abrupt drop in the reactivity of the shrimp became apparent. The results of this study revealed that brown shrimp hold a wider thermal range as originally reported and that it can cope with subzero temperatures. Implications of low-temperature tolerance are discussed in the context of the brown shrimp’s ecology as well as stock assessment.     

The swimming kinematics of larval Atlantic cod, Gadus morhua L., are resilient to elevated seawater pCO2

Kinematics of swimming behavior of larval Atlantic cod, aged 12 and 27 days post-hatch (dph) and cultured under three pCO₂ conditions (control-370, medium-1800, and high-4200 μatm) from March to May 2010, were extracted from swim path recordings obtained using silhouette video photography. The swim paths were analyzed for swim duration, distance and speed, stop duration, and horizontal and vertical turn angles to determine whether elevated seawater pCO₂—at beyond near-future ocean acidification levels—affects the swimming kinematics of Atlantic cod larvae. There were no significant differences in most of the variables tested: the swimming kinematics of Atlantic cod larvae at 12 and 27 dph were highly resilient to extremely elevated pCO₂ levels. Nonetheless, cod larvae cultured at the highest pCO₂ concentration displayed vertical turn angles that were more restricted (median turn angle, 15°) than larvae in the control (19°) and medium (19°) treatments at 12 dph (but not at 27 dph). Significant reduction in the stop duration of cod larvae from the high treatment (median stop duration, 0.28 s) was also observed compared to the larvae from the control group (0.32 s) at 27 dph (but not at 12 dph). The functional and ecological significance of these subtle differences are unclear and, therefore, require further investigation in order to determine whether they are ecologically relevant or spurious.     

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.     

Latitudinal patterns of shell thickness and metabolism in the eastern oyster Crassostrea virginica along the east coast of North America

The goal of this study was to quantify growth and metabolic responses of oysters to increased temperatures like those that will occur due to global warming. Impact of temperature on eastern oyster (Crassostrea virginica) shell growth and metabolism was investigated by sampling 24 sites along the eastern North American seaboard ranging from New Brunswick, Canada, to Florida, USA, in March and August 2013. There was a positive correlation between oyster shell thickness and site temperature. At southern sites, shells were up to 65 % thicker than at the northernmost site, likely due to higher precipitation of CaCO₃ in warmer water. This was supported by laboratory experiments showing that thicker shells were produced in response to temperatures 2, 4, and 6 °C above ambient seawater temperatures (8–14 °C) in Connecticut, USA. Field experiments with oyster respiration were conducted during winter and summer at 13 sites to compare responses to thermal stress with latitude. Respiration rates were much higher during summer than winter, but the combination of summer and winter data fell along the same exponential curve with respect to temperature. At all sites, temperature-specific metabolic rates at elevated temperatures were lower than predicted, indicating significant seasonal acclimatization by C. virginica.     

Kinetics of the oxidation of endocrine disruptor nonylphenol by ferrate(VI)

The kinetics of the oxidation of endocrine disruptor nonylphenol (NP) by potassium ferrate(VI) (K₂FeO₄) in water as a function of pH 8.0–10.9 at 25°C is presented. The observed second-order rate constants, k _obs, decrease with an increase in pH 269–32 M^?1 s^?1. The speciation of Fe(VI) (HFeO ₄ ^? and FeO ₄ ^2? ) and NP (NP–OH and NP–O^?) species was used to explain the pH dependence of the k _obs values. At a dose of 10 mg L^?1 (50 μM) K₂FeO₄, the half-life for the removal of NP by Fe(VI), under water treatment conditions, is less than 1 min.     

Tolerance of juvenile barnacles (Amphibalanus improvisus) to warming and elevated pCO2

We investigated the impacts of warming and elevated pCO₂ on newly settled Amphibalanus improvisus from Kiel Fjord, an estuarine ecosystem characterized by significant natural pCO₂ variability. In two experiments, juvenile barnacles were maintained at two temperature and three pCO₂ levels (20/24 °C, 700–2,140 μatm) for 8 weeks in a batch culture and at four pCO₂ levels (20 °C, 620–2,870 μatm) for 12 weeks in a water flow-through system. Warming as well as elevated pCO₂ hardly affected growth or the condition index of barnacles, although some factor combinations led to temporal significances in enhanced or reduced growth with an increase in pCO₂. While warming increased the shell strength of A. improvisus individuals, elevated pCO₂ had only weak effects. We demonstrate a strong tolerance of juvenile A. improvisus to mean acidification levels of about 1,000 μatm pCO₂ as is already naturally experienced by the investigated barnacle population.     

Cattle egrets as a biosentinels of persistent organic pollutants exposure

We investigated selected chlorinated pollutants (β-HCH, γ-HCH, DDDs, DDEs, o,p′-DDT, p,p′-DDT, heptachlor, aldrin, dieldrin, and endrin) in the Lahore and the Sialkot districts of Pakistan, using eggs of cattle egret (Bubulcus ibis) collected during May and June 2007. The pollutant with highest level and frequency was ΣDDT, followed by β-HCH, γ-HCH, heptachlor, aldrin, dieldrin, and endrin in descending order. The concentration(s) were significantly higher in Sialkot heronry for all the pollutants (except p,p′-DDT) than in Lahore. The values for DDTs, β-HCH, γ-HCH, and heptachlor were significantly higher (p < 0.05) in the egg(s) than in sediment(s) and in the chicks’ diet, due to biomagnification. Among DDTs analogues, p,p′-DDD was the major contaminant with >60 % of total DDT burden, reflecting the widespread aged as well as recent use of DDT as well as anaerobic degradation (DDD/DDE > 1 in many cases) in the nearby paddy soils. In few samples, p,p′-DDT/(DDD + DDE) > 0.5 suggested the recent emission patterns from surrounding contaminated areas of demolished DDT units and obsolete pesticide stores. The higher levels of HCHs (i.e., β-HCH) in the samples collected from Sialkot indicate exposure from long-term agricultural use. Overall, concentrations of all studied POPs were less than the threshold levels known to affect reproduction. Nevertheless, total DDTs and/or HCHs burdens in some eggs contained concentrations of greater than what would educe adverse effects on birds. This is among few studies on OCPs exposure to avian species, which provide the evidence of Pakistan’s contribution toward the Global POPs emission.     

Effects of seawater pCO2 and temperature on shell growth, shell stability, condition and cellular stress of Western Baltic Sea Mytilus edulis (L.) and Arctica islandica (L.)

Acidification of the World’s oceans may directly impact reproduction, performance and shell formation of marine calcifying organisms. In addition, since shell production is costly and stress in general draws on an organism’s energy budget, shell growth and stability of bivalves should indirectly be affected by environmental stress. The aim of this study was to investigate whether a combination of warming and acidification leads to increased physiological stress (lipofuscin accumulation and mortality) and affects the performance [shell growth, shell breaking force, condition index (C_i)] of young Mytilus edulis and Arctica islandica from the Baltic Sea. We cultured the bivalves in a fully-crossed 2-factorial experimental setup (seawater (sw) pCO₂ levels “low”, “medium” and “high” for both species, temperature levels 7.5, 10, 16, 20 and 25 °C for M. edulis and 7.5, 10 and 16 °C for A. islandica) for 13 weeks in summer. Mytilus edulis and A. islandica appeared to tolerate wide ranges of sw temperature and pCO₂. Lipofuscin accumulation of M. edulis increased with temperature while the C_i decreased, but shell growth of the mussels only sharply decreased while its mortality increased between 20 and 25 °C. In A. islandica, lipofuscin accumulation increased with temperature, whereas the C_i, shell growth and shell breaking force decreased. The pCO₂ treatment had only marginal effects on the measured parameters of both bivalve species. Shell growth of both bivalve species was not impaired by under-saturation of the sea water with respect to aragonite and calcite. Furthermore, independently of water temperatures shell breaking force of both species and shell growth of A. islandica remained unaffected by the applied elevated sw pCO₂ for several months. Only at the highest temperature (25 °C), growth arrest of M. edulis was recorded at the high sw pCO₂ treatment and the C_i of M. edulis was slightly higher at the medium sw pCO₂ treatment than at the low and high sw pCO₂ treatments. The only effect of elevated sw pCO₂ on A. islandica was an increase in lipofuscin accumulation at the high sw pCO₂ treatment compared to the medium sw pCO₂ treatment. Our results show that, despite this robustness, growth of both M. edulis and A. islandica can be reduced if sw temperatures remain high for several weeks in summer. As large body size constitutes an escape from crab and sea star predation, this can make bivalves presumably more vulnerable to predation—with possible negative consequences on population growth. In M. edulis, but not in A. islandica, this effect is amplified by elevated sw pCO₂. We follow that combined effects of elevated sw pCO₂ and ocean warming might cause shifts in future Western Baltic Sea community structures and ecosystem services; however, only if predators or other interacting species do not suffer as strong from these stressors.     

Synergistic effects of salinity,temperature and heavy metals on mortality and osmoregulation in marine and estuarine isopods (Crustacea)

The effects of cadmium (3CdSO₄·8H₂O), zinc (ZnSO₄·7H₂O) and lead [Pb (NO₃)₂] on mortality, and cadmium, zinc and mercury (HgCl₂) on osmoregulation, have been recorded for marine and estuarine species of isopods (Crustacea). The marine species studied were Idotea baltica, I. neglecta, I. emarginata and Eurydice pulchra, which were adapted to 100, 80, 60 and 40% sea water (SW) (100% SW э 34‰ S). The estuarine species used were Jaera albifrons sensu stricto and J. nordmanni, which were adapted to 100, 50, 10 and 1% SW. Both groups of isopods have low mortalities in 100% SW with 10 and 20 ppm of cadmium, zinc and lead, but a decrease in salinity caused an increase in the toxicities of these metals and reduced the LT₅₀ values (time, in hours, to 50% mortality). Mortalities at 10°C were generally higher than those recorded at 5°C. Cadmium had no significant effect on the osmoregulation of I. baltica and I. emarginata in 100 and 80% SW at 5°C, but this metal significantly lowered the blood osmotic concentration of I. neglecta in 80% SW. Zinc did not alter the haemolymph osmotic concentration of I. neglecta in 100 and 80% SW, but significantly lowered the blood osmotic concentration of I. baltica in 100% SW. Cadmium, zinc and mercury also significantly altered the osmoregulatory ability of J. albifrons in dilute saline.     

Escape performance of temperate king scallop,Pecten maximus under ocean warming and acidification

Among bivalves, scallops are exceptional due to their capacity to escape from predators by swimming which is provided by rapid and strong claps that are produced by the phasic muscle interspersed with tonic muscle contractions. Based on the concept of oxygen and capacity-limited thermal tolerance, the following hypothesis was tested: ocean warming and acidification (OWA) would induce disturbances in aerobic metabolic scope and extracellular acid-case status and impair swimming performance in temperate scallops. Following long-term incubation under near-future OWA scenarios [20 vs. 10 °C (control) and 0.112 kPa CO₂ (hypercapnia) vs. 0.040 kPa CO₂ (normocapnic control)], the clapping performance and metabolic rates (MR) were measured in resting (RMR) and fatigued (maximum MR) king scallops, Pecten maximus, from Roscoff, France. Exposure to OA, either alone or combined with warming, left MR and swimming parameters such as the total number of claps and clapping forces virtually unchanged. Only the duration of the escape response was affected by OA which caused earlier exhaustion in hyper- than in normocapnic scallops at 10 °C. While maximum MR was unaffected, warm exposure increased RMR in both normocapnic and hypercapnic P. maximus resulting in similar Q ₁₀ values of ~2.2. The increased costs of maintenance and the observation of strongly reduced haemolymph PO₂ levels indicate that at 20 °C scallops have reached the upper thermal pejus range with unbalanced capacities for aerobic energy metabolism. As a consequence, warming to 20 °C decreased mean phasic force during escape performance until fatigue. The observed prolonged recovery time in warm incubated scallops might be a consequence of elevated metabolic costs at reduced oxygen availability in the warmth.