Posts Tagged 'survival'

Assessing the impacts of ocean acidification upon tropical tuna

Increasing concentrations of CO2 in the Earth’s atmosphere (IPCC 2007) are causing a gradual warming and acidification of the Earth’s oceans (e.g. Barnett et al. 2005; Caldeira and Wickett 2003; Feely et al. 2004). Both warming and acidification have the potential to affect the distribution and population dynamics of many marine organisms (IPCC 2007; Raven et al. 2005; Fabry et al. 2008). Significant advances in knowledge have been made over the last decade that have advanced understanding of how increasing ocean acidity will impact nearshore and coral reef ecosystems (Fabry et al. 2008). Our understanding about the effects of acidification on pelagic ecosystems, however, remains rudimentary. In the Pacific Ocean, improving our knowledge on the possible impacts on the pelagic environment is important, as the Pacific’s tuna populations are of one of the largest and most valuable fisheries in the world (Williams and Terawasi 2009). The income derived from tuna fisheries provides a significant contribution to the economies of many Pacific Island countries and territories (Gillett 2009). To ensure such economic benefits are maintainedthrough the sustainable management of this fishery requires an understanding of not only fishery impacts, but impacts of other factors upon population biomass and structure over time. While fishery scientists are now attempting to predict how ocean warming will affect Pacific tuna populations (Lehodey et al. 2010, 2013), no one has previously investigated how ocean acidification (OA) may affect these species and associated fisheries.

Continue reading ‘Assessing the impacts of ocean acidification upon tropical tuna’

Mangrove habitats provide refuge from climate change for reef-building corals

Risk analyses indicate that more than 90% of the world’s reefs will be threatened by climate change and local anthropogenic impacts by the year 2030 under “business as usual” climate scenarios. Increasing temperatures and solar radiation cause coral bleaching that has resulted in extensive coral mortality. Increasing carbon dioxide reduces seawater pH, slows coral growth, and may cause loss of reef structure. Management strategies include establishment of marine protected areas with environmental conditions that promote reef resiliency. However, few resilient reefs have been identified, and resiliency factors are poorly defined.

Here we characterize the first natural, non-reef, coral refuge from thermal stress and ocean acidification and identify resiliency factors for mangrove–coral habitats. We measured diurnal and seasonal variations in temperature, salinity, photosynthetically active radiation (PAR), and seawater chemistry; characterized substrate parameters; and examined water circulation patterns in mangrove communities where scleractinian corals are growing attached to and under mangrove prop roots in Hurricane Hole, St. John, US Virgin Islands. Additionally, we inventoried the coral species and quantified incidences of coral bleaching, mortality and recovery for two major reef-building corals, Colpophyllia natans and Diploria labyrinthiformis, growing in mangrove shaded and exposed (unshaded) areas.

At least 33 species of scleractinian corals were growing in association with mangroves. Corals were thriving in low-light (more than 70% attenuation of incident PAR) from mangrove shading and at higher temperatures than nearby reef tract corals. A higher percentage of C. natans colonies was living shaded by mangroves, and no shaded colonies bleached. Fewer D. labyrinthiformis colonies were shaded by mangroves, however more unshaded colonies bleached. A combination of substrate and habitat heterogeniety, proximity of different habitat types, hydrographic conditions, and biological influences on seawater chemistry generate chemical conditions that buffer against ocean acidification. This previously undocumented refuge for corals provides evidence for adaptation of coastal organisms and ecosystem transition due to recent climate change. Identifying and protecting other natural, non-reef coral refuges is critical for sustaining corals and other reef species into the future.

Continue reading ‘Mangrove habitats provide refuge from climate change for reef-building corals’

Effects of elevated CO2 in the early life stages of summer flounder, Paralichthys dentatus, and potential consequences of ocean acidification (update)

The limited available evidence about effects on marine fishes of high CO2 and associated acidification of oceans suggests that effects will differ across species, be subtle, and may interact with other stressors. This report is on the responses of an array of early life history features of summer flounder (Paralichthys dentatus), an ecologically and economically important flatfish of the inshore and nearshore waters of the Mid-Atlantic Bight (USA), to experimental manipulation of CO2 levels. Relative survival of summer flounder embryos in local ambient conditions (775 μatm pCO2, 7.8 pH) was reduced to 48% when maintained at intermediate experimental conditions (1808 μatm pCO2, 7.5 pH), and to 16% when maintained at the most elevated CO2 treatment (4714 ppm pCO2, 7.1 pH). This pattern of reduced survival of embryos at high-CO2 levels at constant temperature was consistent among offspring of three females used as experimental subjects. No reduction in survival with CO2 was observed for larvae during the first four weeks of larval life (experiment ended at 28 d post-hatching (dph) when larvae were initiating metamorphosis). Estimates of sizes, shapes, and developmental status of larvae based on images of live larvae showed larvae were initially longer and faster growing when reared at intermediate- and high-CO2 levels. This pattern of longer larvae – but with less energy reserves at hatching – was expressed through the first half of the larval period (14 dph). Larvae from the highest-CO2 conditions initiated metamorphosis at earlier ages and smaller sizes than those from intermediate- and ambient-CO2 conditions. Tissue damage was evident in larvae as early as 7 dph from both elevated-CO2 levels. Damage included dilation of liver sinusoids and veins, focal hyperplasia on the epithelium, and separation of the trunk muscle bundles. Cranio-facial features changed with CO2 levels in an age-dependent manner. Skeletal elements of larvae from ambient-CO2 environments were comparable or smaller than those from elevated-CO2 environments when younger (7 and 14 dph) but were larger at developmental stage at older ages (21 to 28 dph), a result consistent with the accelerated size-development trajectory of larvae at higher-CO2 environments based on analysis of external features. The degree of alterations in the survival, growth, and development of early life stages of summer flounder due to elevated-CO2 levels suggests that this species will be increasingly challenged by future ocean acidification. Further experimental studies on marine fishes and comparative analyses among those studies are warranted in order to identify the species, life stages, ecologies, and responses likely to be most sensitive to increased levels of CO2 and acidity in future ocean waters. A strategy is proposed for achieving these goals.

Continue reading ‘Effects of elevated CO2 in the early life stages of summer flounder, Paralichthys dentatus, and potential consequences of ocean acidification (update)’

Experimental influence of pH on the early life-stages of sea urchins II: increasing parental exposure times gives rise to different responses

Many studies into the responses of early life-stages to ocean acidification utilise offspring obtained from parents reared under present-day conditions. Their offspring are directly introduced to altered-pH conditions. This study determined whether this approach is suitable by pre-exposing parent sea urchins (Psammechinus miliaris) to altered seawater pH (~1000 μatm) for several durations, spawning them and rearing their offspring to settlement. Parents acclimated when exposed to low seawater pH for extended periods (>42 d). Longer adult pre-exposures reduced larval survival and less competent offspring were removed from populations earlier than in controls. Control offspring were larger during earlier development stages (2–7 d), but smaller during later development stages (14 + d) than offspring reared under low pH conditions. Juvenile settlement levels were similar across all treatments. After 17 d, offspring sourced from parents pre-exposed to low pH for 42 and 70 d were larger than those pre-exposed for 28 d and ambient sourced offspring directly transferred to low pH. These different responses show that the use of ambient derived offspring utilised in many studies is likely not an ideal approach when assessing larval development responses via morphometric measurements and survivorship prior to settlement. This study also suggests that calcifying organisms have capacities to acclimate and possibly adapt towards conditions beyond natural rates of ocean acidification.
Continue reading ‘Experimental influence of pH on the early life-stages of sea urchins II: increasing parental exposure times gives rise to different responses’

Population trajectories for the Antarctic bivalve Laternula elliptica: identifying demographic bottlenecks in differing environmental futures

The world’s oceans are changing, and dramatic shifts have been documented in the Southern Ocean. The consequences of these shifts to coastal benthic organisms are difficult to predict at present, as ocean warming may increase primary production and food resources for benthic consumers, whilst OA may have negative impacts that differentially affect various species and life stages. A model was developed to investigate how different scenarios of change may influence population size of the Antarctic bivalve Laternula elliptica. The model describes potential implications of both pH and temperature change on survivorship and reproductive output of a population of this bivalve species in McMurdo Sound, Ross Sea. Implications of increases and decreases in mortality rate across different life stages of the population (early, mid and late) were assessed. Additionally, effects on energetic resource partitioning and dictating reproductive potential (RP) were also investigated. Significant declines in RP, due to increased basal metabolic demand, were associated with even relatively small changes in temperature and pH, resulting in populations declining to 25 % of the starting equilibrium density within 60 years. As L. elliptica is a pivotal species to the functionality of the Antarctic coastal benthic ecosystem, wide spread repercussions are expected if populations are impacted as the model predicts. Although further model development is required to explore the ecosystem implications of the population decline described in this paper, this work allows a better understanding of the consequences of change as soon as data on the direction and magnitude of the changes affecting Antarctic seas become available.
Continue reading ‘Population trajectories for the Antarctic bivalve Laternula elliptica: identifying demographic bottlenecks in differing environmental futures’

Multiple abiotic changes and species interactions mediate responses to climate change on rocky shores (PhD thesis)

Anthropogenic climate change poses a serious threat to biodiversity. Accurate predictions of the ecological consequences of future abiotic change will require a broad perspective that takes into account multiple climate variables, species-specific responses, and intra- and interspecific dynamics. I addressed these issues in the context of a marine rocky intertidal community to determine how abiotic and biotic factors can mediate the effects of climate change. I began with two studies on the organismal-level effects of multiple abiotic variables. In the first study, I found that acute exposure to low salinity reduced the survival of littorine snails facing thermal stress, but that ocean acidification (OA) had no such effect. In a second study, I showed that sustained exposure to increased temperature and OA had positive and additive effects on the growth and feeding of the purple ochre sea star. These findings demonstrate that studies of multiple climate variables will be important not only to identify additive and non-additive effects, but also to determine which climate variables will be detrimental for a given species. Next, I measured how species-specific responses to climate change can alter species interactions. By quantifying the effects of body size on the feeding behaviours of sea stars preying on mussels, I demonstrated that climate-driven changes in body size can have profound impacts on the strength of this interaction. Finally, I investigated how population-level responses to multiple abiotic variables can be affected by the presence of an interacting species. I built a predator-prey model that simulates the ecologically important interaction between the purple ochre sea star and its preferred prey, mussels. Using empirical estimates of sea star and mussel responses to increased temperature and OA, I simulated their interaction under various climate scenarios. I found that predation exacerbated the effects of climate change on mussel populations, and that climate change increased the strength of the sea star-mussel interaction. My work demonstrates that the effects of climate change will likely be mediated by a combination of biotic and abiotic factors, and that these factors should be considered when making predictions about the ecological consequences of climate change.
Continue reading ‘Multiple abiotic changes and species interactions mediate responses to climate change on rocky shores (PhD thesis)’

Effect of carbon dioxide-induced water acidification on the physiological processes of the Baltic isopod Saduria entomon

Survival, behavior, hemolymph pH, osmolality, and chloride ion concentration as well the total metabolic rate (heat dissipation rate) of the isopod Saduria entomon from the brackish Baltic Sea were investigated after exposure to carbon dioxide-induced water acidification (pH, 7.5, 7.0, and 6.5; control pH, 8.2) keeping other parameters constant (temperature, 10°C; salinity, 7). The short-term (12 h per each pH treatment) exposure to carbon dioxide-induced water acidification did not cause significant changes (P < 0.05) in the resting metabolic rate or the scope of activity in S. entomon; however, high interindividual variability was observed. The 2-wk exposure to lowered pH values did not affect either the activity of the isopods or their survival rate significantly (P > 0.05), which was greater than 90% in all pH treatments. The hemolymph pH increased significantly (P < 0.05) with a decrease of water pH from a control pH of 8.2 down to a pH of 7.0. Hemolymph osmolality increased significantly (P < 0.05) at pH 7.5, but exposure to pH 7.0 did not cause further increase in this parameter. Reduction of water pH did not affect the hemolymph chloride ion concentration. Obtained results indicated that S. entomon is adapted to large fluctuations of carbon dioxide levels in the water primarily to compensate for acid—base disturbances without additional energetic costs.
Continue reading ‘Effect of carbon dioxide-induced water acidification on the physiological processes of the Baltic isopod Saduria entomon’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

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