Einfluß von salzgehalt und temperatur auf entwicklung,wachstum, fortpflanzung und energiebilanz von Artemia salina

The influence of salinity and temperature on various life processes of Artemia salina (L.) from the Great Salt Lake, Utah, USA, was investigated. Hatching rate, hatching success, energetics and metabolism of hatching, growth rate, maturation rate and reproductive rate were measured at all combinations of 4 temperature levels (10°, 15°, 20°, 30°C) and 4 salinity levels (5, 15, 32, 70‰S). Optimal temperature-salinity combinations differ for different life cycle stages and parameters. The hatching rate rises with increased temperature and sinks with increased salinity. Hatching success is optimal at 20°C and 32‰S. Larval growth is best at 30°C and 15‰S; however, the maximum growth is attained at 20°C and 32‰S. Maturation rate, onset of reproduction, interval between clutches as well as the total number of offspring are primarily influenced by temperature, whereas the clutch size is a function of salinity. As the temperature is lowered, the capacity to survive low salinities is decreased. At low temperature, reproduction is only possible at high salinity. The energy consumption of the hatching embryo is primarily determined by the salinity level of the medium and is directly proportional to it. Carbohydrate consumption is under all conditions greatest by weight, but measured by its caloric contribution the relative importance decreases with increased energy drain. Additional energy requirements, particularly during the later stages of hatching, are met by raising fat and protein metabolism, fat being the main energy reserve.     

Resistenzadaptation bei gehemmeter Proteinbiosynthese. Versuche mit Actinomycin D an dem Fisch Rhodeus amarus

Rhodeus amarus acclimated to 10° or 20°C die at 31.7° or 36.4°C, respectively (cessation of operculum movements). After raising the adaptation temperature (AT) from 10° to 20°C, adaptation is complete after 8 days. The toxicity of actinomycin D, injected intraperitoneally, is AT-dependent (e.g. at 5°C, LD_{50–7 days}=0.8 μg/g fish; at 25°C, LD_{50–7 days}=0.35 μg/g fish). In the following experiments 0.5 μg actinomycin/g fish were used. After actinomycin-injection, RNA-values in white dorsal muscle decreased about 50% within 12 h and the values of control individuals were finally attained after 16 days. Following an AT-change from 10° to 20°C, DNA-values in the white dorsal muscle increased about 10%, RNA-values about 30%, within 12 h. However, in fish injected intraperitoneally with actinomycin, no increase in DNA or RNA was noticed. Actinomycin injection per se causes increased heat resistance. This process lasts 10 days. If AT is raised now from 10° to 20°C, the new resistance level is reached later. The control fish gain resistance at a rate of about 1 C°/day during the first days after the temperature change. Actinomycin-treated individuals, however, exhibit an increase of 0.25 C°/day. Inhibition of resistance adaptation due to proteinbiosynthesis-inhibitors supports the view that protein synthesis is of importance for adjustments in heat resistance of intact animals.

     

Influence of algal concentration and temperature on the filtration rate of Mytilus edulis

The filtration rates of Mytilus edilis (=galloprovincialis; 40 mm) were determined in relation to food concentration and temperature, using pure suspensions of the unicellular alga Platymonas suecica in concentrations ranging from 3x10⁵ cells/l to 1.5x10⁸ cells/l. The rate of filtration (ml/h/mussel) generally decreased as cell concentrations increased, and dropped to low values when concentrations above 5x10⁷ cells/l were supplied. The amount of water swept clear varied continuously, and noticeable differences in the filtration activity of M. edulis were observed over short time intervals (5 min). Fluctuations of filtered volumes per unit time were greater with lower than with higher concentrations of algae. The influence of temperature on filtration activity was highest between 5°–15°C and 25°–30°C. A temperature increase from 15° to 25°C resulted in only a slight increase in filtration rate. At 5° and 30°C, filtration dropped to very low values, namely 350 and 100 ml/h, respectively. The temperature coefficients for the filtration rates of M. edulis were determined as: Q₁₀ (5° to 15°C)=4.96; Q₁₀ (10° to 20°C)=1.22. The amount of algae cells ingested per mussel per hour is directly related to food concentration. The maximum number of cells filtered/mussel/h in an algal suspension of 70x10⁶ cells/l was 21.5x10⁵ cells/h. Cell concentrations of up to 40x10⁶ cells/l were swept clear without producing pseudofaeces. The critical cell density for M. edulis was reached at algal concentrations of 70 to 80x10⁶ cells/l. Above these concentrations no normal filtration activity was observed.     

Temperature and salinity interactively impact early juvenile development: a bottleneck in barnacle ontogeny

When juvenile mortality or juvenile growth is impacted by temperature and salinity, these factors have a substantial effect on recruitment success and population dynamics in benthic ecosystems. Using freshly settled cyprids of Amphibalanus improvisus, we investigated the combined effects of temperature (12, 20 and 28 °C) and salinity (5, 15 and 30 psu) on early juvenile stage performance. Mortality as well as size (basal diameter, dry weight, and ash-free dry weight) was monitored for a period of 40 days. Mortality was high (42–63 %) during the first week following attachment, regardless of the temperature and salinity treatments. Subsequently, mortality and size were interactively influenced by temperature and salinity. Highest mortality and lowest size of juveniles occurred at lowest temperature (12 °C) and salinity (5 psu). Apparently, low temperature (12 °C) narrowed the barnacles’ salinity tolerance. Juvenile barnacles constructed more shell material compared to body mass at high temperature and high salinity, while a reverse situation was observed at low temperature and low salinity. Our results demonstrate that environmental changes can directly and/or indirectly alter patterns of survivorship and size. Warming and desalination as predicted for the Baltic Sea in the course of climate change may, however, act antagonistically and compensate each other’s isolated effect on barnacles.     

Age studies based on daily growth increments in statoliths and growth lamellae in cuttlebone of cultured Sepia officinalis

One hundred and six individuals of Sepia officinalis were cultured throughout its life cycle in two different temperature regimes: 13-15°C and 18-20°C. The number of increments in the statoliths and the number of lamellae in the cuttlebone were read at known ages in different individuals. The formation of growth increments in the statoliths was linearly related with individual age, but it was independent of temperature. By comparison between the slope of these linear relationships and the bisecting line, the hypothesis "1 increment=1 day" was validated in individuals as old as 240 days. In specimens older than 240 days, the number of increments was underestimated due to the poor resolution of the later growth increments. The maximum number of days in captivity (420) was about 80% of the life span estimated for this species in the area studied. Preliminary validation was also obtained from statoliths marked with tetracycline. Increments between tetracycline marks were not visible. The mean distance between marks in ten statoliths was 44 µm (Lj). Considering the same distance in statoliths of wild individuals, the mean number of increments counted was 37 (Lj). This result is very close to the 40 days passed between both tetracycline marks. A straight line significantly different for each culture temperature defined the relationship between number of the cuttlebone lamellae and age. The number of lamellae in the cuttlebone does not correspond to the real age. The time necessary for the formation of one lamella was 8DŽ.3 days at 13-15°C, whereas the deposition of one lamella lasted 3.1ǃ.06 days at 18-20°C. In conclusion, the periodicity for lamellar deposition can be defined only if the temperature where the animal lived is considered.     

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.     

Der einfluß einer Vorbehandlung mit konstanten und wechselnden Temperaturen auf die Hitzeresistenz von Gammarus salinus und Idotea balthica

The crustaceans Gammarus salinus Spooner and Idotea balthica Pallas live in brackish waters and are capable of tolerating a variety of temperature and salinity conditions. Thus far, the capacity for non-genetic adaptation of such euryplastic animals has only been tested at different levels of constant temperatures. If exposed to both constant (8°, 14° or 20°C) and fluctuating (daily fluctuation: 8°?20°C) temperatures, the tested individuals reveal significant differences in heat resistance which become apparent within 12 h. G. salinus and I. balthica exhibit reasonable (meaningful) heat resistance, i.e., a positive correlation between the degree of heat resistance and the level of adaptation temperature (AT). Following a shift in AT (8° → 20°C or 20° → 8°C) the degree of resistance changes rather fast. This leads, under fluctuating temperature conditions, to diurnal changes in the degree of heat resistance. I. balthica also shows an endogenous diurnal periodicity of its heat resistance. In G. salinus, long-term exposure (2 to 4 weeks) to fluctuating temperatures [duration of temperature change: 2 h (Δ/2 h)] produces, during the day, a mean resistance value which coincides with the value obtained for AT 14°C-controls. This fact results from temperature-independent adaptation speeds (same after decrease and increase of AT). However, fast temperature change (ΔT/1 h) during exposure to fluctuating temperatures leads to a significant augmentation of heat resistance, presumably due to additional stress; such fast temperature changes are less well tolerated than slow fluctuations (ΔT/2 h). In I. balthica, low ATs are less efficient in terms of heat resistance than high ATs (great difference between AT=14° and 20 °C; small difference between AT=8° and 14 °C). In males, lowering of AT from 20° to 8 °C results, within the first 12 h, to faster loss of heat resistance than is the case for gain in heat resistance after AT increase from 8° to 20 °C. However, after prolonged exposure to the new ATs, completion of readaptation is temperature-independent. Under conditions of fluctuating temperatures (ΔT/2 h) resistance increases beyond the mean value (AT=14 °C). Further increase in resistance can be obtained through fast temperature changes (ΔT/1 h). In G. salinus, which occupies habitats with more extensive temperature fluctuations, the responses studied are less pronounced than in I. balthica.     

Symbiont shuffling during thermal bleaching and recovery in the sea anemone Entacmaea quadricolor

The sea anemone Entacmaea quadricolor simultaneously harbours multiple symbiont types from the genus Symbiodinium, while providing essential habitat for anemonefish. This anemone lives close to its upper thermal threshold and experiences bleaching under elevated temperature and light stress. Here, we determine whether E. quadricolor experienced a shuffling in the abundance of two genetically distinct symbiont types (Symbiodinium C25 and C3.25) during bleaching and recovery. Anemones were exposed to control (22.9 °C) or elevated temperature (28.5 °C) for 42 days, whereas for the following 75 days, all anemones were exposed to 22.9 °C. By day 47, a more pronounced bleaching occurred via symbiont expulsion in the elevated temperature treatment than the control, and the proportion of C25 to C25 + C3.25 increased by 6.2 and 13.2 % in the control and bleached anemones, respectively. The increased relative abundance of C25 to C3.25 after exposure to thermal stress may indicate that C3.25 performs poorly when temperature is elevated. Although no significant recovery in symbiont density was detected, a revival of the C3.25 genotype was found at day 117, which may indicate that it is either more competitive or has qualities that are beneficial to the symbiosis when thermal stress is no longer apparent. This work demonstrates the potential for this anemone species to shuffle its symbiont types in response to environmental change and could provide resilience during times of stress.     

Elevated temperature elicits greater effects than decreased pH on the development, feeding and metabolism of northern shrimp (Pandalus borealis) larvae

Climate models predict that the average temperature in the North Sea could increase 3–5 °C and surface-waters pH could decrease 0.3–0.5 pH units by the end of this century. Consequently, we investigated the combined effect of decreased pH (control pH 8.1; decreased pH 7.6) and temperature (control 6.7 °C; elevated 9.5 °C) on the hatching timing and success, and the zoeal development, survival, feeding, respiration and growth (up to stage IV zoea) of the northern shrimp, Pandalus borealis. At elevated temperature, embryos hatched 3 days earlier, but experienced 2–4 % reduced survival. Larvae developed 9 days faster until stage IV zoea under elevated temperature and exhibited an increase in metabolic rates (ca 20 %) and an increase in feeding rates (ca 15–20 %). Decreased pH increased the development time, but only at the low temperature. We conclude that warming will likely exert a greater effect on shrimp larval development than ocean acidification manifesting itself as accelerated developmental rates with greater maintenance costs and decreased recruitment in terms of number and size.     

Facultative lecithotrophy during larval development of the burrowing shrimp Callianassa tyrrhena (Decapoda: Callianassidae)

Survival, developmental and consumption rate (Artemia nauplii ingested per day) as well as predation efficiency (ingested per available Artemia nauplii) were studied during the larval development of the shallow-water burrowing thalassinid Callianassa tyrrhena (Petagna, 1792), which exhibits an abbreviated type of development with only two zoeal stages and a megalopa. The larvae, hatched from berried females from S. Euboikos Bay (Aegean Sea, Greece), were reared at 10 temperature–food density combinations (19 and 24 °C; 0, 2, 4, 8 and 16 Artemia nauplii d⁻¹). Enhanced starvation resistance was evident: 92 and 58% of starved zoeas I molted to zoea II, while metamorphosis to megalopa was achieved by 76 and 42% of the hatched zoeas at 19 and 24 °C, respectively. The duration of both zoeal stages was affected by temperature, food density and their interaction. Nevertheless, starvation showed different effects at the two temperatures: compared to the fed shrimp, the starved zoeae exhibited accelerated development at 19 °C (8.4 d) but delayed metamorphosis at 24 °C (5.9 d). On the other hand, both zoeal stages were able to consume food at an increased rate as food density and temperature increased. Predation efficiency also increased with temperature, but never exceeded 0.6. Facultative lecithotrophy, more pronounced during the first zoeal stage of C.tyrrhena, can be regarded as an adaptation of a species whose larvae can respond physiologically to the different temperature–food density combinations encountered in the wide geographical range of their natural habitat. Received: 28 February 1998 / Accepted: 21 October 1998     

Activation energy for skeletal aragonite deposited by the hermatypic coral Platygyra spp.

Average radial growth rates of the hemispherical aragonite colonies deposited by the Indo-Pacific scleractinian reef coral Platygyra spp. were determined by measuring the thickness of density variations in the skeleton that are revealed by X-radiography. Ninety-one specimens from 21 localities were examined, but only 54 of these exhibited well-defined growth-banding. The apparent temperature dependence of growth rate is linear over the range 23.9° to 29.3°C, averaging 5.4±0.94 mm/year at 24°C, 8.0±0.42 mm/year at 27°C, and 9.7 ±0.58 mm/year at 29°C (90% confidence limits). Expression of the influence of temperature on growth rate in terms of the Arrhenius equation yields an activation energy of 20,680 cal/mole, which is comparable to values for typical biological reactions, but is only half that reported for skeletogenesis in another reef coral, Pocillopora damicornis, on the basis of controlled incubation studies involving ⁴⁵Ca uptake.     

Modeling the effect of daily ration and feeding frequency on growth of redtail shrimp Penaeus penicillatus (Alock) at controlled temperatures

Obtaining optimal growth of redtail shrimp at an economic production cost is essential. An experiment was conducted to evaluate simultaneous effects of daily ration and feeding frequency on growth of redtail shrimp at controlled temperatures. Two series were operated contemporarily, one at 25°C and the other at 30°C. the three daily rations were 5, 15, and 25% of fresh body weight in association with three levels of daily feeding frequency: one, three, and five times. Each series lasted for 80 days. The growth rate and the combined effects were studied on day 40 and day 80 for each series.Response surface analyses showed that, at 25°C, two quadratic polynomial equations could describe the daily growth rates (G₁ and G₂) during growth periods 1 (day 1-day 40) and 2 (day 41-day 80). The optimal daily ration and feeding frequency in terms of maximum growth rate were found at 25°C to be 22.38% of fresh body weight with three feedings/day for growth period 1 and 22.68% of fresh body weight with three feedings/day for growth period 2.At 30°C, two dynamic models were derived for each growth period that included growth optimums of 21.94% and four feedings/day for the first growth period, and 21.27% and four feedings/day for the subsequent growth period.     

Catalytic hydrolysis of gaseous HCN over Cu–Ni/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst: parameters and conditions

To decompose efficiently hydrogen cyanide (HCN) in exhaust gas, g-Al₂O₃-supported bimetallicbased Cu–Ni catalyst was prepared by incipient-wetness impregnation method. The effects of the calcination temperature, H₂O/HCN volume ratio, reaction temperature, and the presence of CO or O₂ on the HCN removal efficiency on the Cu–Ni/g-Al₂O₃ catalyst were investigated. To examine further the efficiency of HCN hydrolysis, degradation products were analyzed. The results indicate that the HCN removal efficiency increases and then decreases with increasing calcination temperature and H₂O/HCN volume ratio. On catalyst calcined at 400°C, the efficiency reaches a maximum close to 99% at 480 min at a H₂O/HCN volume ratio of 150. The HCN removal efficiency increases with increasing reaction temperature within the range of 100°C–500°C and reaches a maximum at 500°C. This trend may be attributed to the endothermicity of HCN hydrolysis; increasing the temperature favors HCN hydrolysis. However, the removal efficiencies increases very few at 500°C compared with that at 400°C. To conserve energy in industrial operations, 400°C is deemed as the optimal reaction temperature. The presence of CO facilitates HCN hydrolysis andincreases NH₃ production. O₂ substantially increases the HCN removal efficiency and NO _x production but decreases NH₃ production.

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Effect of body mass,temperature and food deprivation on oxygen consumption rate of common cuttlefish <Emphasis Type="Italic">Sepia officinalis</Emphasis>

Predictions of short and long term changes in Sepia officinalis metabolism are useful, since this species is both economically important for aquaculture and also is an ideal experimental laboratory organism. In this study standard and routine oxygen consumption rates of newly hatched and juvenile laboratory raised cuttlefish S. officinalis ranging between 0.04 and 18.48 g dry body mass (Dm), were measured over a range of temperatures (10, 15, 20 and 25°C). The mass exponent (b) ranged between 0.706 and 0.992 for standard oxygen consumption and between 0.694 and 0.990 for routine oxygen consumption. Oxygen consumption scaled allometrically (b = 0.7) with body mass for cuttlefish <2 g Dm and isometrically (b = 1) thereafter. No significant differences were apparent amongst the slopes of oxygen consumption and body mass at different temperatures for standard and routine oxygen consumption. However, the intercepts differed significantly amongst the regression lines, indicating a significant effect of temperature on the magnitude of oxygen consumption. The combined effect of temperature (T) and dry body mass (Dm) are best described by the following equations: cuttlefish <2 g, MO₂ = 0.116Dm^0.7111.086 ^T and >2 g, MO₂ = 0.076Dm^0.9831.091 ^T for standard oxygen consumption; cuttlefish <2 g, MO₂ = 0.538Dm^0.7291.057 ^T and >2 g, MO₂ = 0.225Dm^0.9621.081 ^T for routine oxygen consumption. Using these equations it was estimated that a cuttlefish of 1 g Dm held at 20°C, eating 5% Dm day⁻¹ and undergoing standard and routine metabolism consumes 21.3 and 35.4%, respectively of its total daily energy intake. Juvenile cuttlefish (3.32–5.08 g Dm) held at 15°C and deprived of food for 27 days maintained a stable standard oxygen consumption rate for the first 6 days following starvation. By the 18th day without food, oxygen consumption rate had declined by 53% and further declined to 65% below the standard oxygen consumption rate on the 27th day. Upon resumption of feeding, the respiration rate returned immediately to the initial level prior to food deprivation. The present study defines the basic energy requirements and general physiological state of young cuttlefish at temperatures of 10–25°C with and without food.     

Morphological and behavioral alterations induced by endocrine disrupters in amphibian tadpoles

Developmental toxicity effects of endocrine disrupter chemicals, acephate and cypermethrin were studied in Bufo melanostictus tadpoles. Thirty developing eggs of B. melanostictus were exposed to each concentration (0.01, 0.05, 0.1, 0.5, and 1?µg?L^?1) of acephate or cypermethrin in the laboratory (temperature: 23?±?1°C; photoperiod: 11.5–12.5?h). Eggs maintained in conditioned water alone served as controls. After hatching, larvae were fed on boiled spinach until the completion of metamorphosis. In control group, larvae that hatched on 3rd day were heavily pigmented, voracious feeders, and active swimmers; in these tadpoles, hind limb and forelimb-buds emerged on 16th and 24th day and metamorphosis was complete on 32nd day. Eggs exposed to acephate also hatched on 3rd day but larvae exhibited deformities such as, (i) tail distortions, (ii) laterally crooked trunk, (iii) decreased pigmentation, (iv) inactivity, (v) peeling of the skin, and (vi) delay in emergence of limbs and completion of metamorphosis. Cypermethrin-exposed eggs exhibited a delay (4–8 days) in hatching, there was no mortality, deformities in tail, trunk and head region, delay in the emergence of limbs, and completion of metamorphosis were evident. The demonstrated data indicate that these pesticides interfere with amphibian development when present in the aquatic system.     

Temperature-induced ontogenetic plasticity in sea bass (Dicentrarchus labrax)

We studied the ontogeny of Dicentrarchus labrax comparatively under constant rearing temperatures of 13, 15 and 20°C. At hatching, yolk-sac larval morphometry differed significantly between the temperatures and especially between the two extremes, while at the end of the yolk-sac larval stage, it mainly differed between the two lower temperature regimes and that of 20°C. Compared with the two lower temperature conditions, at 20°C D. labrax presented a significant ontogenetic acceleration which was morphologically expressed either as a significantly smaller total length (TL) at feeding onset, notochord flexion and fin differentiation, or as shifts of the allometric inflection points of 8 out of the 15 morphometric characters studied. Additionally, temperature significantly affected the allometry coefficients, with a decreasing growth intensity as the temperature difference decreased. The rate of TL growth increased under elevated temperature conditions throughout the entire ontogenetic period, except during the early larval period (feeding onset to metamorphosis onset), at which time D. labrax presented equal growth rates at 15°C and 20°C. The results are discussed with respect to the ontogeny of the functional morphology and the meanings of temperature-induced ontogenetic plasticity for the survival of fish larvae.     

Der einfluß von temperaturänderungen auf enzyme der fischmuskulatur. Versuche mit goldorfen Idus idus

Succinate respiration and various enzyme activities were measured in the white dorsal muscles of golden orfs (goldcoloured race of Idus idus L.) adapted to different temperatures. Some of the values obtained on enzyme activities measured on successive days revealed significant differences in fish adapted to the same temperature. These differences could not be attributed to variations between experimental groups, nor to disturbances caused by the removal of some fish (Figs. 2 and 3). In adaptation experiments, attention must be paid to diurnal fluctuations in enzyme activity; such fluctuations were especially apparent with isocitrate-dehydrogenase. Season can also influence the level of enzyme activity, possibly through changes in day-length. Succinate respiration of golden orfs adapted to 5°C is about 10% higher than in individuals adapted to 20°C (experimental temperature 25°C). Following reverse adaptation from 20° to 5°C (at the rate of 5C^o/h), the values approach, after fluctuations, those of 5°C individuals. After raising or lowering the adaptation temperature at the rate of 5 or 2 C^o/h), fluctuations in several enzymes appeared initially, as in the abrupt transfers reported by Lehmann (1970a); even if significant, these were, however, not always reproducible. Change in temperature causes a limited phase of increased functional lability.     

Factors affecting the accumulation and removal of mercury from tissues of the American oyster Crassostrea virginica

Adult oysters, Crassostrea virginica (Gmelin) were held in seawater containing 10 or 100 ppb mercury in the form of mercuric acetate for 45 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 91,600 and 12,100 ppb in the 100 and 10 ppb mercury groups, respectively. A slight decline in mercury residues in the 100 ppb group during the accumulation period was attributed to spawning. Clearance of mercury from tissues was studied in a constant temperature regime (25°C±2C^o) for 25 days and in a declining temperature regime (25° to 5°C) for 80 days by exposing treated adults to estuarine water with no mercury added. The biological half-life of mercuric acetate was 16.8 and 9.3 days in the 25°C temperature regime, and 35.4 and 19.9 days in the declining temperature regime, for the 10 and 100 ppb groups, respectively. Smaller oysters (0 to 7 g) consistently accumulated more mercury per gram wet weight than larger oysters (7 to 20 g) in populations exposed to 10 and 100 ppb mercury.     

Depth distribution and temperature preferences of wahoo (Acanthocybium solandri) off Baja California Sur, Mexico

The depth distribution and temperature preferences of wahoo (Acanthocybium solandri) were quantified in the eastern North Pacific using archival tags. One hundred and eight data-loggers were deployed on wahoo (105?C165-cm fork length) from 2005 to 2008 at three locations off of the coast of Baja California Sur, Mexico (Alijos Rocks, 25°00??N/115°45??W; Magdalena Bay Ridge, 25°55??N/113°21??W; Hurricane Bank, 16°51??N/117°29??W). Twenty-five tagged individuals (23%) were recaptured within close proximity (<20?km) of their release sites. Collectively, depth and temperature data from 499?days revealed a predominant distribution within the upper mixed layer, with an average (±SD) depth of 18?±?4?m during the day and 17?±?6?m at night. Wahoo spent 99.2% of the daytime and 97.9% of night above the thermocline, and the greatest depth achieved by any fish was 253?m. Mean dive duration (3.8?±?2.9 vs. 2.3?±?0.8?min) and the vertical rate of movement (3.8?±?1.3 vs. 3.0?±?0.5?m?min^?1) were greater at night when compared to day. Ambient temperatures obtained from tag records ranged from 11.1 to 27.9°C, with an average of 25.0?±?1.1°C. These data identify the importance of the warm, upper mixed layer for the wahoo. High recapture rates proximal to the deployment sites suggest seasonal site fidelity and reveal the economic importance of this resource to both commercial and recreational fisheries of the region.     

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.