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Ocean acidification (OA) and hypoxic events are increasing worldwide problems, their interactive effects have not been well clarified, although their co-occurrence is prevalent. The East China Sea (the Yangtze River estuary area) suffers from not only coastal hypoxia but also pH fluctuation, representing an ideal study site to explore the combined effect of OA and hypoxia on marine bivalves. We experimentally evaluated the antioxidant response of the mussel Mytilus coruscus exposed to three pH levels (8.1, 7.7 and 7.3) at two dissolved oxygen (DO) levels (2.0mgL-1 and 6.0mgL-1) for 72h. Activities of superoxide dismutase, catalase, glutathione peroxidase, acid phosphatase, and alkaline phosphatase and levels of malondialdehyde were measured in gills and hemolymph. All enzymatic activities in hemolymph and gills followed a similar pattern throughout the experiment duration. Generally, low DO showed greater effects on enzyme activities than elevated CO2. Significant interactions between DO, pH and time were only observed at superoxide dismutase and catalase in both tissues. PCA revealed positive relationships between most enzyme activities in both gills and hemolymph with the exception of alkaline phosphatase activity and the level of malondialdehyde in the hemolymph. Overall, our results suggested that decreased pH and low DO induced similar antioxidant responses in the hard shelled mussel, and showed an additive effect on most enzyme activities. The evaluation of multiple environmental stressors, a more realistic scenario than single ones, is crucial to predict the effect of future global changes on coastal species and our results supply some insights on the potential combined effects of reduced pH and DO on marine bivalves.

Source: doi: 10.1016/j.envpol.2016.07.044 Increasing anthropogenic activities in the Arctic represent an enhanced threat for oil pollution in a marine environment that is already at risk from climate warming. In particular, this applies to species with free-living pelagic larvae that aggregate in surface waters and under the sea ice where hydrocarbons are likely to remain for extended periods of time due to low temperatures. We exposed the positively buoyant eggs of polar cod (Boreogadus saida), an arctic keystone species, to realistic concentrations of a crude oil water-soluble fraction (WSF), mimicking exposure of eggs aggregating under the ice to oil WSF leaking from brine channels following encapsulation in ice. Total hydrocarbon and polycyclic aromatic hydrocarbon levels were in the ng/L range, with most exposure concentrations below the limits of detection throughout the experiment for all treatments. The proportion of viable, free-swimming larvae decreased significantly with dose and showed increases in the incidence and severity of spine curvature, yolk sac alterations and a reduction in spine length. These effects are expected to compromise the motility, feeding capacity, and predator avoidance during critical early life stages for this important species. Our results imply that the viability and fitness of polar cod early life stages is significantly reduced when exposed to extremely low and environmentally realistic levels of aqueous hydrocarbons, which may have important implications for arctic food web dynamics and ecosystem functioning.

Marine brachyuran and anomuran crustaceans are completely absent from the extremely cold (− 1.8 °C) Antarctic continental shelf, but caridean shrimps are abundant. This has at least partly been attributed to low capacities for magnesium excretion in brachyuran and anomuran lithodid crabs ([Mg2+]HL = 20–50 mmol L− 1) compared to caridean shrimp species ([Mg2+]HL = 5–12 mmol L− 1). Magnesium has an anaesthetizing effect and reduces cold tolerance and activity of adult brachyuran crabs. We investigated whether the capacity for magnesium regulation is a factor that influences temperature-dependent activity of early ontogenetic stages of the Sub-Antarctic lithodid crab Paralomis granulosa. Ion composition (Na+, Mg2+, Ca2+, Cl−, SO42−) was measured in haemolymph withdrawn from larval stages, the first and second juvenile instars (crabs I and II) and adult males and females. Magnesium excretion improved during ontogeny, but haemolymph sulphate concentration was lowest in the zoeal stages. Neither haemolymph magnesium concentrations nor Ca2+:Mg2+ ratios paralleled activity levels of the life stages. Long-term (3 week) cold exposure of crab I to 1 °C caused a significant rise of haemolymph sulphate concentration and a decrease in magnesium and calcium concentrations compared to control temperature (9 °C). Spontaneous swimming activity of the zoeal stages was determined at 1, 4 and 9 °C in natural sea water (NSW, [Mg2+] = 51 mmol L− 1) and in sea water enriched with magnesium (NSW + Mg2+, [Mg2+] = 97 mmol L− 1). It declined significantly with temperature but only insignificantly with increased magnesium concentration. Spontaneous velocities were low, reflecting the demersal life style of the zoeae. Heart rate, scaphognathite beat rate and forced swimming activity (maxilliped beat rate, zoea I) or antennule beat rate (crab I) were investigated in response to acute temperature change (9, 6, 3, 1, − 1 °C) in NSW or NSW + Mg2+. High magnesium concentration reduced heart rates in both stages. The temperature–frequency curve of the maxilliped beat (maximum: 9.6 beats s− 1 at 6.6 °C in NSW) of zoea I was depressed and shifted towards warmer temperatures by 2 °C in NSW + Mg2+, but antennule beat rate of crab I was not affected. Magnesium may therefore influence cold tolerance of highly active larvae, but it remains questionable whether the slow-moving lithodid crabs with demersal larvae would benefit from an enhanced magnesium excretion in nature.

Population dynamics of the queen scallop, Aequipecten opercularis, was investigated in the western English Channel off Roscoff. Annual formation of natural growth rings on the shell surface was validated by stable isotope (y 18 O and y 13 C) analysis. A von Bertalanffy growth function (Ht = 58.9 mm . (1� e � 0.604 .(t + 0.235) )) was fitted to size-at-age data of 249 individuals. Annual somatic and gonad production amounted to 19.74 kJ m � 2 and 0.98 kJ m � 2 y � 1 , respectively. Total mortality rate Z was estimated to be 1.716 y � 1 . Net growth efficiencies (ranging from 45% in 1-y-old to 11% in 6-y-old individuals) were in the same range as in other short-lived scallops. Individual growth, however, was distinctly slower in this population than in other A. opercularis populations from similar latitudes, most likely due to a more stressful environment. D 2004 Elsevier B.V. All rights reserved.

Thermal tolerance of single larval stages has rarely been studied, eventhough the larva might be the actual physiological bottleneck of all life history stages setting distribution limits. Therefore, temperature tolerance of Zoea I was examined in two different population of the Chilean kelp crab Taliepus dentatus. We measured activity, oxygen consumption, cardiac performance and the CN composition of larval T. dentatus of two populations from central and southern Chile at various temperatures (1) to determine at which organisational level T. dentatus larvae get first affected by temperature, integrating variables from the organismal, tissue functional to the biochemical elemental level, and (2) to compare the thermal tolerance of larvae from varying environmental temperature regimes to look at functional differences between populations as a correlate of adaptation capacities of the Zoea. Our mechanistic analysis explicitly sheds light on how temperature affects the physiology of crab larvae. We found that the highest organisational level gets affected first, seen in activity decrements at unsuitably high or low temperatures, paralleled by decreases in oxygen consumption rates. Cardiac performance is more robust to temperature changes. Heart beat rate decreases only at very high and low temperature extremes and stroke volume is almost temperature independent. The comparison between the southern and central populations showed a limited but clear adaptation of larvae from the southern sampling site to the colder environmental temperature regime, visible at all organisational levels.