No abstract

Antarctic fish of the suborder Notothenioidei have evolved several unique adaptations to deal with subzero temperatures. However, these adaptations may come with physiological trade-offs, such as an increased susceptibility to oxidative damage. As such, the expected environmental perturbations brought on by global climate change have the potential to significantly increase the level of oxidative stress and cellular damage in these endemic fish. Previous single stressor studies of the notothenioids have shown they possess the capacity to acclimate to increased temperatures, but the cellularlevel effects remain largely unknown. Additionally, there is little information on the ability of Antarctic fish to respond to ecologically relevant environmental changes where multiple variables change concomitantly. We have examined the potential synergistic effects that increased temperature and Ṗ CO2 have on the level of protein damage in Trematomus bernacchii, Pagothenia borchgrevinki and Trematomus newnesi, and combined these measurements with changes in total enzymatic activity of catalase (CAT) and superoxide dismutase (SOD) in order to gauge tissue-specific changes in antioxidant capacity. Our findings indicate that total SOD and CAT activity levels displayed only small changes across treatments and tissues. Short-term acclimation to decreased seawater pH and increased temperature resulted in significant increases in oxidative damage. Surprisingly, despite no significant change in antioxidant capacity, cellular damage returned to near-basal levels, and significantly decreased in T. bernacchii, after long-term acclimation. Overall, these data suggest that notothenioid fish currently maintain the antioxidant capacity necessary to offset predicted future ocean conditions, but it remains unclear whether this capacity comes with physiological trade-offs.

Bioluminescence of the marine worm Chaetopterus variopedatus was first investigated several decades ago mainly using tissue extract. Light production of the worm, however, originates from a secreted mucus only. Here, we report the optical and physicochemical properties of the luminous mucus. We show that the produced light occurs as a long glow in the blue range (455 nm), which is an unusual color for a shallow benthic invertebrate. We also show that the light originates from a photoprotein whose light production is independent of molecular oxygen yet somewhat related to the physicochemical (rheological) characteristics of the mucus itself. Indeed, the mucus seems to polymerize and become more viscous on exposure to H2O2, which in turn seems to inhibit the light production. Ferrous iron was not associated with any strong stimulatory effect. This is in contrast to past studies on worm tissues showing that the light production is strongly stimulated by H2O2 and ferrous iron. Overall, our results highlight the fact that working on the luminous mucus only (vs. worm tissues) provides the ability to study its chemical properties possibly involved in the fine control of light production-as well as its rheological properties-and identify the possible interactions between these two properties.

Organisms inhabiting the sub-zero waters surrounding Antarctica display remarkably narrow tolerances for environmental change. This study assessed three closely related fish exposed to simultaneous changes in oceanic conditions to ascertain the impact additive stress has on their capacity to acclimate and whether or not these fish employ similar metabolic responses.

No abstract

Ocean acidification is thought to benefit seagrasses because of increased carbon dioxide (CO2) availability for photosynthesis. However, in order to truly assess ecological responses, effects of ocean acidification need to be investigated in a variety of coastal environments. We tested the hypothesis that ocean acidification would benefit seagrasses in the northern Gulf of Mexico, where the seagrasses Halodule wrightii and Ruppia maritima coexist in a fluctuating environment. To evaluate if benefits of ocean acidification could alter seagrass bed composition, cores of H. wrightii and R. maritima were placed alone or in combination into aquaria and maintained in an outdoor mesocosm. Half of the aquaria were exposed to either ambient (mean pH of 8.1 ± 0.04 SD on total scale) or high CO2 (mean pH 7.7 ± 0.05 SD on total scale) conditions. After 54 days of experimental exposure, the δ 13 C values were significantly lower in seagrass tissue in the high CO2 condition. This integration of a different carbon source (either: preferential use of CO2, gas from cylinder, or both) indicates that plants were not solely relying on stored energy reserves for growth. Yet, after 41 to 54 days, seagrass morphology, biomass, photo-physiology, metabolism, and carbon and nitrogen content in the high CO2 condition did not differ from those at ambient. There was also no indication of differences in traits between the homo-or hetero-specific beds. Findings support two plausible conclusions: 1) these seagrasses rely heavily on bicarbonate use and growth will not be stimulated by near future acidification conditions or 2) the mesohaline environment limited the beneficial impacts of increased CO2 availability.

This study quantified physiological responses of skilletfish Gobiesox strumosus exposed to thermal and oxic stress. Fish acclimated at 12, 22 and 32 degrees C had low oxygen tolerance values (mean +/-s.d.) of 0.40 +/- 0.09, 0.40 +/- 0.08 and 0.35 +/- 0.03, and critical thermal maxima (mean +/-s.d.) of 33.2 +/- 0.5, 38.1 +/- 0.0 and 39.5 +/- 0.3 degrees C, respectively. Furthermore, G. strumosus were oxygen conformers at all acclimation temperatures, i.e. the fish allowed oxygen consumption rates to decrease with ambient oxygen concentration. High temperature tolerance, low oxygen tolerance and decreasing metabolic rates during hypoxic events allow the fish to survive harsh environmental conditions encountered in their natural environment.

Projected increases in ocean pCO 2 levels are anticipated to affect calcifying organisms more rapidly and to a greater extent than other marine organisms. The effects of ocean acidification (OA) have been documented in numerous species of corals in laboratory studies, largely tested using flow-through exposure systems. We developed a recirculating ocean acidification exposure system that allows precise pCO 2 control using a combination of off-gassing measures including aeration, water retention devices, venturi injectors, and CO 2 scrubbing. We evaluated the recirculating system performance in off-gassing effectiveness and maintenance of target pCO 2 levels over an 84-day experiment. The system was used to identify changes in calcification and tissue growth in response to elevated pCO 2 (1000 μatm) in three reef-building corals of the Caribbean: Pseudodiploria clivosa, Montastraea cavernosa, and Orbicella faveolata. All three species displayed an overall increase in net calcification over the 84-day exposure period regardless of pCO 2 level (control +0.28-1.12 g, elevated pCO 2 +0.18-1.16 g), and the system was effective at both off-gassing acidified water to ambient pCO 2 levels, and maintaining target elevated pCO 2 levels over the 3-month experiment.