Posts Tagged 'performance'

Aerobic and behavioral flexibility allow estuarine gastropods to flourish in rapidly changing and extreme pH conditions

Despite efforts to understand marine organismal responses to ocean acidification (gradual change in pH/ pCO2pCO2 over decades), there is a lack of information about the capabilities of coastal organisms to endure rapid and extreme pH change (often full units within hours). We predicted that gastropods faced with estuarine acidification avoid extreme pH exposure through isolation and/or escape behavior, and energetically compensate for feeding and energy uptake limitations by facultative metabolic depression (FMD). To test this, we studied behavioral (organism activity) and aerobic (cardiac performance) responses to acidification in two closely related tropical intertidal species, the estuarine Indothais gradata (two populations) and the open-shore Reishia bitubercularis. Snails were exposed in the laboratory to either acutely declining or stable low pH conditions, using two acidification modes (HNO3-acidification and CO2-aeration). Under acutely declining pH, aerobic performance was regulated to unexpectedly low pH levels (4.5), effectively extending the field pH range for activity. This pH performance threshold marked the onset of behavioral isolation and FMD (as opposed to respiratory stress) and was lower in Indothais than Reishia snails during mineral acidification. Behavioral (in isolated gastropods) and environmental hypercapnic acidosis complicates interpretation of lowered metabolic performance. Stable reduced pH exposures resulted in different behavioral and physiological responses by the Indothais populations, including more prominent escape from water in the seaward population. Overall, these results suggest that aerobic and behavioral flexibility are crucial to organismal fitness in widely fluctuating pH circumstances. They further warn against overgeneralizing marine acidification consequences across physiological dispositions, taxonomic levels, and ecological systems.

Continue reading ‘Aerobic and behavioral flexibility allow estuarine gastropods to flourish in rapidly changing and extreme pH conditions’

Increased appendicularian zooplankton alter carbon cycling under warmer more acidified ocean conditions

Anthropogenic atmospheric loading of CO2 raises concerns about combined effects of increasing ocean temperature and acidification, on biological processes. In particular, the response of appendicularian zooplankton to climate change may have significant ecosystem implications as they can alter biogeochemical cycling compared to classical copepod dominated food webs. However, the response of appendicularians to multiple climate drivers and effect on carbon cycling are still not well understood. Here, we investigated how gelatinous zooplankton (appendicularians) affect carbon cycling of marine food webs under conditions predicted by future climate scenarios. Appendicularians performed well in warmer conditions and benefited from low pH levels, which in turn altered the direction of carbon flow. Increased appendicularians removed particles from the water column that might otherwise nourish copepods by increasing carbon transport to depth from continuous discarding of filtration houses and fecal pellets. This helps to remove CO2 from the atmosphere, and may also have fisheries implications.

Continue reading ‘Increased appendicularian zooplankton alter carbon cycling under warmer more acidified ocean conditions’

Moving ocean acidification research beyond a simple science: investigating ecological change and their stabilizers

The response of complex ecological communities to ocean acidification reflects interactions among species that propagate or dampen ecological change. Yet, most studies have been based on short-term experiments with limited numbers of interacting species. Both limitations tend to exaggerate measured effects and when combined with our predisposition for investigating change, we reduce insight into pathways of stability, acclimation and adaptation. Here, we review accepted and emerging insights into processes that drive ecological change (top-down and bottom-up) and the stabilizing processes by which ecological complexity may dampen change. With an emphasis on kelp forest examples, we show that boosted primary productivity from enriched CO2 creates competitive imbalances that drive habitat change, but we also recognise intensifying herbivory on these habitats dampens this change. Foraging herbivores thrive on CO2 enriched plants and over successive generations their populations expand. When we consider such population level responses, we open new questions regarding density-effects (e.g. competition, susceptibility to predation and disease), as well as the bottom-up benefits to predators. Nevertheless, research on predators has lagged behind because their wide-ranging behaviour typically imposes logistical difficulties for observational and experimental research. We know that ocean warming imposes elevated metabolic costs on their foraging whilst acidification hampers navigation of their larvae towards suitable habitat and impairs their hunting and avoidance of predators as adults. Connecting such top-down with bottom-up responses is fundamental for progress, and is also contingent on understanding the mechanisms that dampen change. These stabilizers have the potential to keep pace with abiotic change and thereby influence the drivers of acclimation and adaption. Certainly, we acknowledge that investigating change is often simpler and associated bold messages appeal to citation impact. Yet, if we are to anticipate the ability of complex ecological communities to persist in changing environments, then understanding the shifting balance between the propagation of resource enrichment and its consumption across trophic levels is central to this challenge.

Continue reading ‘Moving ocean acidification research beyond a simple science: investigating ecological change and their stabilizers’

Biological responses of sharks to ocean acidification

Sharks play a key role in the structure of marine food webs, but are facing major threats due to overfishing and habitat degradation. Although sharks are also assumed to be at relatively high risk from climate change due to a low intrinsic rate of population growth and slow rates of evolution, ocean acidification (OA) has not, until recently, been considered a direct threat. New studies have been evaluating the potential effects of end-of-century elevated CO2 levels on sharks and their relatives’ early development, physiology and behaviour. Here, we review those findings and use a meta-analysis approach to quantify the overall direction and magnitude of biological responses to OA in the species of sharks that have been investigated to date. While embryo survival and development time are mostly unaffected by elevated CO2, there are clear effects on body condition, growth, aerobic potential and behaviour (e.g. lateralization, hunting and prey detection). Furthermore, studies to date suggest that the effects of OA could be as substantial as those due to warming in some species. A major limitation is that all past studies have involved relatively sedentary, benthic sharks that are capable of buccal ventilation—no studies have investigated pelagic sharks that depend on ram ventilation. Future research should focus on species with different life strategies (e.g. pelagic, ram ventilators), climate zones (e.g. polar regions), habitats (e.g. open ocean), and distinct phases of ontogeny in order to fully predict how OA and climate change will impact higher-order predators and therefore marine ecosystem dynamics.

Continue reading ‘Biological responses of sharks to ocean acidification’

Ocean acidification increases larval swimming speed and has limited effects on spawning and settlement of a robust fouling bryozoan, Bugula neritina

Few studies to date have investigated the effects of ocean acidification on non-reef forming marine invertebrates with non-feeding larvae. Here, we exposed adults of the bryozoan Bugula neritina and their larvae to lowered pH. We monitored spawning, larval swimming, settlement, and post-settlement individual sizes at two pHs (7.9 vs. 7.6) and settlement dynamics alone over a broader pH range (8.0 down to 6.5). Our results show that spawning was not affected by adult exposure (48 h at pH 7.6), larvae swam 32% faster and the newly-settled individuals grew significantly larger (5%) at pH 7.6 than in the control. Although larvae required more time to settle when pH was lowered, reduced pH was not lethal, even down to pH 6.5. Overall, this fouling species appeared to be robust to acidification, and yet, indirect effects such as prolonging the pelagic larval duration could increase predation risk, and might negatively impact population dynamics.

Continue reading ‘Ocean acidification increases larval swimming speed and has limited effects on spawning and settlement of a robust fouling bryozoan, Bugula neritina’

Early life behaviour and sensory ecology of predatory fish under climate change and ocean acidification

The early life cycle of a fish species is presumed to be the most vulnerable to abiotic change. Their successful development and growth is key to sustaining and connecting existing populations and dispersal to new habitats. Larvae and juvenile fish have to progressively develop and fine tune their behavioural and sensory capabilities in order to successfully hunt and or forage for prey, avoid larger predators and find suitable habitat to reach maturity and reproduce. Their sensory capabilities typically involve multiple senses including, vision, olfaction and audition. Ocean warming and acidification alter the physiological performance and behaviour of many small bodied fish, however, the potential interactive effects of these stressors on large predatory fish has not been explored fully and may act synergistically or antagonistically. Predatory fish can have large effects on trophically-structured systems. The potential for altered predatory function through alterations in their metabolism as a result of temperature and behaviour from ocean acidification may not only affect their hunting ability but also the communities in which their prey live. In this thesis, I show that the combination of ocean warming with acidification can alter the metabolic function and hunting behaviour of a predatory shark leading to considerable reductions in growth rates. Laboratory experiments revealed faster embryonic development under elevated temperature, however elevated temperature and CO2 had detrimental impacts on sharks by increasing energetic demands. Subsequent mesocosm experiments showed reductions in growth rates under elevated CO2 either alone or in combination with elevated temperatures, where their metabolic efficiency was decreased and their ability to locate food through olfaction was reduced. Additionally, while elevated temperature increased the motivational drive to locate prey, elevated CO2 negated chemical and visual behavioural responses that enable effective hunting. I also found that ocean acidification alone altered the physicochemical sensing in a predatory teleost fish (Barramundi) such that cues for temperature and salinity were inhibited by reduced pH. This thesis reveals a more complex reality for predators where the combination of elevated temperature and CO2 reduces their ability to hunt effectively leading to smaller sharks, ultimately reduces their ability to exert strong top-down control over food webs. Furthermore, alterations to their perception and evaluation of environmental cues during the critical phase of dispersal have implications for ensuing recruitment and population replenishment. Alterations such as the ones brought about by ocean acidification and increased temperature far reaching consequences, not just for the individual predator population’s sustainability, but also the ecosystem food webs which they inhabit.

Continue reading ‘Early life behaviour and sensory ecology of predatory fish under climate change and ocean acidification’

Entering the Anthropocene: How ocean acidification and warmer temperatures affect the symbiotic sea anemone Exaiptasia pallida

Here I report the effects of long-term elevated CO2 combined with two subsequent elevated temperature intervals on the model symbiotic anemone Exaiptasia pallida. A central goal of this thesis was to investigate how altered CO2 and temperature affect the symbiotic relationship while this anemone hosted three different strains of endosymbiotic dinoflagellates (Symbiodinium minutum, Symbiodinium A4a, and Symbiodinium A4b). Exposure to elevated CO2 (930μatm) alone for 42 days led to no significant changes in either the anemone or the algae physiological response, with the exception of some separation between the photosynthesis to respiration ratio of S. A4a and S. A4b control and treatment animals. Exposure to both elevated CO2 (930μatm) and a moderate  elevation in temperature (29°C) for 49 days led to a significant increase in the net maximal photosynthesis (normalized to algal cell density) between the treatment and controls of all three  holobionts. Exposure to both elevated CO2 (930μatm) and an even higher temperature (33°C) for up to 20 days led to a significant decrease in photobiology and algal cell density, along with visible bleaching in the S. minutum holobiont. All three holobionts displayed a significant decrease in the photosynthesis to respiration ratio, thereby providing evidence for temperature having a greater impact on the phototrophic response of these anemones. However, anemones harboring the two A4 Symbiodinium did not show as large of a negative response in photosystem II  photochemistry when compared to anemones with S. minutum. The high temperature treatment also resulted in juvenile mortality in all three holobionts, with the greatest mortality seen in the S. minutum holobiont. The differential response to both elevated CO2 and elevated temperature between the three holobionts highlights the thermal sensitivity of the S. minutum symbiosis, and the thermal tolerance of the S. A4 holobionts. Thermal tolerance may enable these anemones to survive and thrive in future climate change conditions, while the effects of higher CO2 appear to be more neutral.

Continue reading ‘Entering the Anthropocene: How ocean acidification and warmer temperatures affect the symbiotic sea anemone Exaiptasia pallida’

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Ocean acidification in the IPCC AR5 WG II

OUP book