Posts Tagged 'mortality'

The effects of climate change on the heart rates & growth of sea slugs in the Gulf of Maine

In the next 80 years, sea surface temperatures are expected to increase by 1.5o to 2oC and ocean pH is expected to drop by 0.06 to 0.32 units, with exacerbated effects seen in coastal waters. Temperature increase has already forced organisms to shift their range polewards and ocean acidification has negatively affected calcifying organisms. Interactive effects, only more recently studied, vary depending on phylum and life cycle stage. This study examined both the upper thermal tolerance and interactive effect of temperature and acidification on the heart rate of five cold-water species of nudibranchs (Aeolidia papillosa, Cuthona gymnota, Dendronotus frondosus, Flabellina verrucosa, and Onchidoris bilamellata) and one species of sacoglossan (Placida dendritica) from the Gulf of Maine. Thermal tolerance was determined by recording heart rate for each organism starting at 4oC and increasing the temperature by increments of 4oC until the organism’s heartbeat slowed or ceased. For interactive effects, pH levels used were pH 8 (control) and pH 7 at temperatures: 4o, 8o (control), 12o, and 16oC. Upper thermal tolerance limits ranged from 16o to 20oC for the nudibranchs and 24oC for the sacoglossan. The combined effects of increasing temperature and lower pH were neutral, negatively additive, and antagonistic. Only F. verrucosa exhibited an interactive effect, with higher temperature and lower pH leading to decreased heart rate. Although no interactive effect was demonstrated in C. xgymnota, D. frondosus, and O. bilamellata, lower pH slowed heart rates across all temperatures. Subsequently, the relationship between temperature and growth rates was examined in D. frondosus and F. verrucosa. The nudibranchs were reared for eight weeks at 4o, 10o, or 16oC and growth was measured weekly. The ideal temperature for growth appeared to be 10oC, whereas 16oC was lethal. Additionally, an unsuccessful attempt was made to culture A. papillosa, but the number of embryos per egg capsule and larval growth rates were examined. Size of adult sea slug positively impacted the number of embryos per egg capsule, with embryos increasing in length by 50% over the first week and 10% over subsequent weeks. With an interactive effect only seen in one species and upper temperatures being lethal if held constant for a month, temperature appears to be the greatest threat to survival. What is happening to these sea slugs in the GOM is likely happening to other snails and marine invertebrates throughout the ocean. Knowing how organisms will react to the projected changes can help inform future policies and practices.

Continue reading ‘The effects of climate change on the heart rates & growth of sea slugs in the Gulf of Maine’

Combined effects of ocean acidification and temperature on larval and juvenile growth, development and swimming performance of European sea bass (Dicentrarchus labrax)

Ocean acidification and ocean warming (OAW) are simultaneously occurring and could pose ecological challenges to marine life, particularly early life stages of fish that, although they are internal calcifiers, may have poorly developed acid-base regulation. This study assessed the effect of projected OAW on key fitness traits (growth, development and swimming ability) in European sea bass (Dicentrarchus labrax) larvae and juveniles. Starting at 2 days post-hatch (dph), larvae were exposed to one of three levels of PCO2 (650, 1150, 1700 μatm; pH 8.0, 7.8, 7.6) at either a cold (15°C) or warm (20°C) temperature. Growth rate, development stage and critical swimming speed (Ucrit) were repeatedly measured as sea bass grew from 0.6 to ~10.0 (cold) or ~14.0 (warm) cm body length. Exposure to different levels of PCO2 had no significant effect on growth, development or Ucrit of larvae and juveniles. At the warmer temperature, larvae displayed faster growth and deeper bodies. Notochord flexion occurred at 0.8 and 1.2 cm and metamorphosis was completed at an age of ~45 and ~60 days post-hatch for sea bass in the warm and cold treatments, respectively. Swimming performance increased rapidly with larval development but better swimmers were observed in the cold treatment, reflecting a potential trade-off between fast grow and swimming ability. A comparison of the results of this and other studies on marine fish indicates that the effects of OAW on the growth, development and swimming ability of early life stages are species-specific and that generalizing the impacts of climate-driven warming or ocean acidification is not warranted.

Continue reading ‘Combined effects of ocean acidification and temperature on larval and juvenile growth, development and swimming performance of European sea bass (Dicentrarchus labrax)’

Restoring the flat oyster Ostrea angasi in the face of a changing climate

Across the globe, restoration efforts are stemming the loss of native oyster reefs and the ecosystem services they provide, but these efforts will need to consider climate change in order to be sustainable. South-eastern Australia is the focus of restoring the once abundant oyster Ostrea angasi. This region is also a climate change ‘hot spot’ where the ocean is warming rapidly, with the potential to be exacerbated by marine heatwaves and coastal acidification. In this study, the impact of near-future (~2050) elevated temperature and pCO2 on O. angasi was determined and considered in context with concerns for the long-term sustainability of oyster reef restoration efforts. Oysters were exposed to ambient and elevated pCO2 concentrations (mean ± SE: 408 ± 19.8 and 1070 ± 53.4 µatm) and ambient and elevated temperatures (22.78 ± 0.17 and 25.73 ± 0.21°C) for 10 wk in outdoor flow-through mesocosms. Shell growth, condition index, standard metabolic rate (SMR), extracellular pH and survival were measured. Elevated temperature caused high mortality (36%) and decreased the condition of oysters (33%). Elevated pCO2 increased SMR almost 4-fold and lowered the extracellular pH of O. angasi by a mean 0.29 pH units. In combination, elevated pCO2 and temperature ameliorated effects on SMR and survivorship of oysters. O. angasi appears to be living near the limits of its thermal tolerance. Restoration projects will need to account for the temperature sensitivity of this species and its changing habitat to ‘climate proof’ long-term restoration efforts.

Continue reading ‘Restoring the flat oyster Ostrea angasi in the face of a changing climate’

Impacts of ocean acidification on intertidal benthic foraminiferal growth and calcification

Foraminifera are expected to be particularly susceptible to future changes in ocean carbonate chemistry as a function of increased atmospheric CO2. Studies in an experimental recirculating seawater system were performed with a dominant benthic foraminiferal species collected from intertidal mudflats. We investigated the experimental impacts of ocean acidification on survival, growth/calcification, morphology and the biometric features of a calcareous species Elphidium williamsoni. Foraminifera were exposed for 6 weeks to four different pH treatments that replicated future scenarios of a high CO2 atmosphere resulting in lower seawater pH. Results revealed that declining seawater pH caused a decline in foraminiferal survival rate and growth/calcification (mainly through test weight reduction). Scanning electron microscopy image analysis of live specimens at the end of the experimental period show changes in foraminiferal morphology with clear signs of corrosion and cracking on the test surface, septal bridges, sutures and feeding structures of specimens exposed to the lowest pH conditions. These findings suggest that the morphological changes observed in shell feeding structures may serve to alter: (1) foraminiferal feeding efficiency and their long-term ecological competitiveness, (2) the energy transferred within the benthic food web with a subsequent shift in benthic community structures and (3) carbon cycling and total CaCO3 production, both highly significant processes in coastal waters. These experimental results open-up the possibility of modelling future impacts of ocean acidification on both calcification and dissolution in benthic foraminifera within mid-latitude intertidal environments, with potential implications for understanding the changing marine carbon cycle.

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Elevated temperature does not substantially modify the interactive effects between elevated CO2 and diel CO2 cycles on the survival, growth and behavior of a coral reef fish

Recent studies demonstrate that diel CO2 cycles, such as those prevalent in many shallow water habitats, can potentially modify the effects of ocean acidification conditions on marine organisms. However, whether the interaction between elevated CO2 and diel CO2 cycles is further modified by elevated temperature is unknown. To test this, we reared juvenile spiny damselfish, Acanthochromis polyacanthus, for 11 weeks in two stable (450 and 1000 μatm) and two diel- cycling elevated CO2 treatments (1000 ± 300 and 1000 ± 500 μatm) at both current-day (29°C) and projected future temperature (31°C). We measured the effects on survivorship, growth, behavioral lateralization, activity, boldness and escape performance (fast starts). A significant interaction between CO2 and temperature was only detected for survivorship. Survival was lower in the two cycling CO2 treatments at 31°C compared with 29°C but did not differ between temperatures in the two stable CO2 treatments. In other traits we observed independent effects of elevated CO2, and interactions between elevated CO2 and diel CO2 cycles, but these effects were not influenced by temperature. There was a trend toward decreased growth in fish reared under stable elevated CO2 that was counteracted by diel CO2 cycles, with fish reared under cycling CO2 being significantly larger than fish reared under stable elevated CO2. Diel CO2 cycles also mediated the negative effect of elevated CO2 on behavioral lateralization, as previously reported. Routine activity was reduced in the 1000 ± 500 μatm CO2 treatment compared to control fish. In contrast, neither boldness nor fast-starts were affected by any of the CO2 treatments. Elevated temperature had significant independent effects on growth, routine activity and fast start performance. Our results demonstrate that diel CO2 cycles can significantly modify the growth and behavioral responses of fish under elevated CO2 and that these effects are not altered by elevated temperature, at least in this species. Our findings add to a growing body of work that highlights the critical importance of incorporating natural CO2 variability in ocean acidification experiments to more accurately assess the effects of ocean climate change on marine ecosystems.

Continue reading ‘Elevated temperature does not substantially modify the interactive effects between elevated CO2 and diel CO2 cycles on the survival, growth and behavior of a coral reef fish’

Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean

The Scotia Sea (Southern Ocean) is a hotspot of biodiversity, however, it is one of the fastest warming regions in the world alongside one of the first to experience ocean acidification (OA). Thecosome (shelled) pteropods are planktonic gastropods which can dominate the Scotia Sea zooplankton community, form a key component of the polar pelagic food web and are important contributors to carbon and carbonate fluxes. Pteropods have been identified as sentinel species for OA, since their aragonitic shells are vulnerable to dissolution in waters undersaturated with respect to aragonite.

In this thesis I investigate the impact of a changing ocean on the physiology and life history of pteropods in the Scotia Sea. Firstly, I culture early stage pteropods within OA and warming conditions predicted to occur in 2100 (Chapter 2). I demonstrate that larval shell morphology and survival rates are detrimentally affected in these conditions. Secondly, I constrain the life cycle and population dynamics of pteropods collected over a year from a sediment trap deployed on a moored platform (Chapter 3). I show that Limacina helicina and Limacina retroversa both have distinct life history strategies, although, spawning of both species corresponds to phytoplankton blooms. Thirdly, I establish a baseline vertical and biogeographical distribution of pteropods using historical samples (Chapter 4). I elucidate the geographical range edges of L. retroversa and L. helicina, as well as vertical migration patterns in relation to predation threat. Finally, I examine in-situ pteropod shell condition in relation to carbonate chemistry using net and oceanographic samples collected during two recent cruises (Chapter 5). I demonstrate that larval shells are susceptible to dissolution on exposure to aragonite undersaturation, however, later life stages display some resilience, since shell dissolution is confined to breaches in the periostracum. Overall, I recommend that continued monitoring, combined with bioassays and mesocosm work, will be essential in identifying the continued threat to pteropods from rapid environmental changes.

Continue reading ‘Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean’

Water acidification causes death of marine ornamental fish (Perciformes: Pomacentridae) during transport: contributing to the conservation of wild populations

Pomacentridae is a common family in the aquarium fish trade. Most species are harvested from nature. Here we evaluate the following water parameters in the pomacentrid sergeant major, Abudefduf saxatilis (Linnaeus, 1758), to assess their stress level during a 24, 48, and 72 hours transport: dissolved oxygen (DO), total ammonia, and pH. In addition, we evaluated the following physiological parameters: plasma osmolality, muscle water content, blood glucose, and the enzyme activities of the branchial carbonic anhydrase (CA), the hepatic glutathione S-transferase (GST), catalase (CAT), and superoxide dismutase (SOD). The mortality of fish measuring >6 cm total length was 22%, while no mortality was observed for fish measuring <6 cm. The pH of the water was significantly correlated with fish mortality, especially for the initial 24 hours of transport. Hypoxia after 24–48 hours also led to fish mortality, but build up ammonia was not a problem even after 72 hours. We suggest that a minimum water volume of 125 ml/g fish is necessary for safe and cost-effective transport of the sergeant major, preferably with <6 cm in total length.

Continue reading ‘Water acidification causes death of marine ornamental fish (Perciformes: Pomacentridae) during transport: contributing to the conservation of wild populations’


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Ocean acidification in the IPCC AR5 WG II

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