Description: In this research, three lines of investigation were pursued. (1) In vivo effects of temperature and H2O2 were evaluated in the limpet Nacella concinna. Production of reactive oxygen species was assessed with dihydrorhodamine 123 fluorescent probe, lysosome alterations with histological techniques, and antioxidant responses through superoxide dismutase and catalase assays. data suggest that Nacella spring migrations to intertidal levels, where rises in temperature occur, induce oxidative stress and antioxidant response. (2) In the scallop Adamussium colbecki, the sarcoplasmatic reticulum Ca2+ ATPase was characterized and heavy metal effects were assessed. An IC 50 of 0.9 µM was found for Hg2+ and of 3 µM for Cd 2+. (3) Effects of Cu2+, Cd2+, and Hg2+ (2.5 µM), and of temperature on Ca2+ homeostasis and cell viability were assessed in the Ciliate Euplotes focardii. Ca2+ homeostasis and cell viability were altered by Hg2+ at a temperature of 0°C and above, and by Cu2+ and Cd2+ at 20°C and 30°C, suggesting that rises in temperature cause an increased cell sensitivity to environmental contaminants.

Description: Antarctic marine ectotherms look back on several million years of adaptation to constant extreme cold temperatures. Most endemic species are cold stenothermal, with low and not thermally compensated metabolic rates, low scope for activity and narrow windows of thermal tolerance. Critical warming of the environment causes an exponential acceleration of mitochondrial oxygen demand in ectotherms and as many of them, especially small aquatic invertebrates, rely considerably (up to 50 %) on oxygen surface diffusion, the metabolic stress response to heat will increase surface oxygen flux to tissues. Elevated tissue oxygen flux under heat stress or during and after exhaustive exercise causes a necessity to buffer the tissue redox potential, because of an elevated probability of reactive oxygen species (ROS) formation. Basic ROS-buffering is achieved by the glutathione system and a significantly more oxidized glutathione redox ratio is found in marine ectotherms, when compared to higher organisms. The ratio of reduced to oxidized glutathione which is conserved at 10 : 1 in mammalian tissues comes down to 4 : 1 in fish and can be even more oxidized in marine bivalves, possibly in line with the decrement in oxygen consumption. Moreover, a pronounced necessity for oxygen redox buffering obviously characterizes polar animals, their tissues being equipped with double to 4-fold glutathione concentrations, compared to con-generic temperate water species.Mitochondria have been described as the major cellular ROS producers, especially under physiological stress. While we were able to detect a net production of ROS in mitochondria isolated from metabolically low tuned infaunal marine bivalves and worms, ROS release from mitochondria that we isolated from more active or higher evolved epibenthic animals, scallops and benthic fish, was null under all experimental conditions. It is conceivable that these mitochondria prevent ROS release into the cells, due to considerable antioxidant potential of the matrix. Higher mitochondrial volume densities and subsarcolemnal localization found in many polar species, may not only decrease diffusion distances of oxygen inside the cells but help to control the local dioxygen concentration and even mop up extra-mitochondrially produced ROS, rendering them innoxious and preventing initiation of lipid radical chain reactions.The question arises, whether especially in these more highly evolved epibenthic marine ectotherms, mitochondria may function as an extension of the basal antioxidant system (glutathione and antioxidant enzymes). A control of extra-mitochondrial ROS levels could be important to enable onset of stress signalling. In animals, many forms of stress converge into a state of functional hypoxia and ischemia. The physiological response is triggered as po2 dependent ROS formation by cytosolic NADPH-dependent oxidases ceases, enabling the stabilization of the hypoxia inducible transcription factor (HIF). We found first evidence that HIF may be involved in metabolic re-organisation during heat and cold stress in polar and North Sea fish. Higher oxygen flux under heat stress increases the probability of ROS formation and might hamper HIF stabilization. The enzymatic ROS quenching defence system of Antarctic ectotherms is optimised to function at low temperatures within the thermal envelope of the animals. Our hypothesis is that mitochondrial ROS quenching activity might substitute fading enzymatic antioxidant activity under heat stress and support HIF-induced metabolic re-organization (= hypoxic ventilatory slow down, HIF-related, erythropoesis & expression and activation of anaerobic enzymes and transporters).

Description: Sedimentation is a major cause of mortality in scleractinian coral recruits.In this study, we compared the effects of muddy coastal sediments, withand without enrichment by "marine snow" on the survivorship of recruits ofthe hard coral Acropora willisae. Transparent exopolymer particles (TEP)were measured as characteristic components of marine snow using astaining method (Passow&Alldredge 1995). Four-week old recruits wereexposed to (i) muddy coastal sediments, (ii) TEP, (iii) TEP-enriched muddycoastal sediments, and (iv) unfiltered sea water, for 43 h in aerated flowchambers. Thirty-three percent (± 5 SE) of coral recruits died after 43-hexposure to TEP-enriched muddy coastal sediments (~14 mg cm-2sediments enriched with 3.8 ± 0.2 mg cm-2 gum xanthan equivalents [GX]TEP). In contrast, no or minimal mortality was observed in the other threetreatments. Mortality increased to 〉80% when the amount of deposited TEPwas almost tripled (10.9 ± 1.3 mg cm-2 GX) and sediment increased by50%. Thus, coral recruits survived short-term exposure to low levels of TEPand low levels of muddy sediments, but sediments enriched with TEP atconcentrations recorded at some of the inshore stations proved to bedetrimental. Concentrations of TEP were measured around and away fromreefs in inshore and shelf regions ???of the central Great Barrier Reef(latitude 16 ? 18° S) in summer, the season of coral spawning andrecruitment. Within 〈10 km off the coast, TEP concentrations were high(mean = 291 ± 49 SE mg GX L-1, range = 152 - 791 mg GX L-1).Concentrations declined with increasing distance from the coast, andaveraged 83 (± 26 SE) mg GX L-1 around oceanic reefs 〉40 km off thecoast. Our study suggests that both sediment composition and short-term(43 h) sediment deposition affect survivalof coral juveniles, which has implications for the capacity of inshore reefs to be recolonised by corals to recover from large-scale disturbance events.

Description: Mitochondria in active epibenthic ectotherms ? ROS consumers instead of producers?Abele#, D., Philipp#, E., Heise#, K., Keller#, M., Pörtner#, H.O., Nikinma*, M.#Dept. Marine Ecophysiol. Ecotoxicol., Alfred-Wegener Institute f. Polar-& Marine Res., Bremerhaven, Germany; *Dept. of Biology, University of Turku, FinlandMitochondria have been described as the major cellular ROS producers, especially under physiological stress. Whereas we were able to detect a net production of ROS in mitochondria isolated from metabolically low tuned infaunal marine bivalves and worms, ROS release from mitochondria, isolated from more active or higher evolved epibenthic animals, scallops and benthic fish, was null under all experimental conditions. Due to considerable antioxidant potential in the matrix, these mitochondria actually seem to prevent ROS release into the cell during routine activity. Higher mitochondrial volume densities and subsarcolemnal localization found in many active polar swimmers, may hence not only decrease diffusion distances of oxygen inside the cells, but help to control the local dioxygen concentration and even mop up extra-mitochondrially produced ROS in the cell periphery, preventing initiation of lipid radical chain reactions.A control of extra-mitochondrial ROS levels could be important to enable onset of stress signalling. In animals, many forms of stress converge into a state of functional hypoxia. We found first evidence that hypoxia inducible transcription factor HIF may be involved in metabolic re-organisation during heat and cold stress in polar and North Sea fish.

Description: Summary1. Daphnia was collected from five subarctic ponds which differed greatly in their DOC contents and, consequently, their underwater light (UV) climates. Irrespective of which Daphnia species was present the ponds with the lowest DOC concentrations contained Daphnia with the highest concentrations of eicosapentaenoic acid (EPA). In addition, EPA concentrations in these Daphnia generally decreased in concert with seasonally increasing DOC concentrations.2. Daphnia from three of the ponds was also tested for its tolerance to solar ultraviolet radiation (UVR) with respect to survival. D. pulex from the clear water pond showed, by far, the best UV-tolerance, followed by D. longispina from the moderately humic and D. longispina from the very humic pond.3. In addition, we measured sublethal parameters related to UV-damage such as the degree to which the gut of Daphnia appeared green (as a measure of their ability to digest algae), and whether their guts appeared damaged. We developed a simple, non-invasive scoring system to quantify the gut proportion in which digestive processes were presumably active. This method allowed repeated measurement of the same animals over the course of the experiment. We demonstrated, for the first time, that sublethal damage of the gut precedes mortality caused by exposure to UVR.4. In a parallel set of experiments we fed UV-exposed and non-exposed algae to UV-exposed and non-exposed daphnids. UVR pre-treatment of algae enhanced the negative effects of exposure to natural solar UV-irradiation in Daphnia.5. The UV-related effects we observed in Daphnia were generally not species-specific.