Posts Tagged 'performance'

California mussels as bioindicators of ocean acidification

A critical need in California is to develop robust biological indicators that can be used to understand emerging impacts to marine systems arising from human-induced global change. Among the most worrisome environmental stressors are those associated with shifts in the carbonate system of seawater, including reductions in ocean pH and decreased availability of carbonate ions (together termed ‘ocean acidification’). In this study, we explored the utility of employing newly settled California mussels (Mytilus californianus) as a bio-indicator of effects of ocean acidification. Our approach involved a field assessment of the capacity to link patterns of mussel recruitment to climate-related oceanographic drivers, with the additional step of conducting measurements of mussel morphology and body condition to maximize the sensitivity of the bio-indicator. Our results indicate that larval shells retained in mussels that have settled on the shore are smaller in area when larval stages were likely to have been subjected to more acidic (lower-pH) seawater. Similarly, the body condition — a measure of general health — of newly settled juveniles subjected to lower-pH seawater was reduced in cases where those waters were also warm. These findings suggest a strong potential for newly settled California mussels to serve as informative bio-indicators of ocean acidification in California’s coastal waters. Future efforts should pursue additional validation and possible expansion of this methodology, as well as the feasibility of a sustained commitment to sampling newly settled individuals of this species at multiple locations throughout the State.

Continue reading ‘California mussels as bioindicators of ocean acidification’

Elevated pCO2 affects feeding behaviour and acute physiological response of the brown crab Cancer pagurus

Anthropogenic climate change exposes marine organisms to CO2 induced ocean acidification (OA). Marine animals may make physiological and behavioral adaptations to cope with OA. Elevated pCO2 may affect metabolism, feeding and energy partition of marine crabs, and thereby affect their predator-prey dynamics with mussels. Therefore, we examined the effects of simulated future elevated pCO2 on feeding behavior and energy metabolism of the brown crab Cancer pagurus. Following 54 days of pre-acclimation to control CO2 levels (360 μatm) at 11 °C, crabs were exposed to consecutively increased oceanic CO2 levels (two weeks for 1200 and 2300 μatm, respectively) and subsequently returned to control CO2 level (390 μatm) for two weeks in order to study their potential to acclimate elevated pCO2 and recovery performance. Standard metabolic rate (SMR), specific dynamic action (SDA) and feeding behaviour of the crabs were investigated during each experimental period. Compared to the initial control CO2 conditions, the SMRs of CO2 exposed crabs were not significantly increased, but increased significantly when the crabs were returned to normal CO2 levels. Conversely, SDA was significantly reduced under high CO2 and did not return to control levels during recovery. Under high CO2, crabs fed on smaller sized mussels than under control CO2; food consumption rates were reduced; foraging parameters such as searching time, time to break the prey, eating time and handling time were all significantly longer than under control CO2, and prey profitability was significantly lower than that under control conditions. Again, a two-week recovery period was not sufficient for feeding behavior to return to control values. PCA results revealed a positive relationship between feeding/SDA and pH, but negative relationships between the length of foraging periods and pH. In conclusion, elevated pCO2 caused crab metabolic rate to increase at the expense of SDA. Elevated pCO2 affected feeding performance negatively and prolonged foraging periods. These results are discussed in the context of how elevated pCO2 may impair the competitiveness of brown crabs in benthic communities.

Continue reading ‘Elevated pCO2 affects feeding behaviour and acute physiological response of the brown crab Cancer pagurus’

Hypercapnia-induced disruption of long-distance mate-detection and reduction of energy expenditure in a coastal keystone crustacean

• Long-distance mate tracking in males was disrupted by high CO2 exposure.
• High CO2-exposed males exhibited increased latency in response to female cues.
• Both males and females exhibited metabolic depression, likely as compensation.
• High CO2 potentially disrupts chemosensory-dependent behaviours in amphipods.

Ocean acidification (OA) has been shown to disrupt behavioural responses either by affecting metabolic processes, or by effectively impairing an organisms’ ability to gather and assess information and make decisions. Given the lack of information regarding the effects of high CO2 on olfactory-mediated mating behaviours in crustaceans, the possible chemosensory disruption in male mate-tracking in the keystone amphipod (Gammarus locusta) was assessed (after a two-generation acclimation to high CO2 conditions). In a series of behavioural trials, the response time, first direction of movement and the proportion of time spent in the presence of female scent cues were quantified. The possibility of high CO2-induced metabolic changes was assessed through routine metabolic rate (RMR) quantification. We found that hypercapnia was responsible for inducing a delay in response time latency and effectively disrupted accurate female cue-tracking. Moreover, RMR were significantly reduced under high CO2 in both genders. Such finding supports the hypothesis of hypercapnia-induced metabolic depression, which potentially underpins the increased latency in response time verified. Overall, the present study hints the potential disruption of chemosensory-dependent sexual behaviours, through some degree of chemosensory and metabolic disruption. These results emphasize the need for further behavioural tests regarding chemosensory communication in amphipods and energy metabolism, and suggest cascading consequences for the species’ reproductive success and overall fitness in a future less alkaline ocean.

Continue reading ‘Hypercapnia-induced disruption of long-distance mate-detection and reduction of energy expenditure in a coastal keystone crustacean’

Cherchez la femme – impact of ocean acidification on the egg jelly coat and attractants for sperm

The impact of ocean acidification on marine invertebrate eggs and its consequences for sperm chemotaxis are unknown. In the sea urchins Heliocidaris tuberculata and Heliocidaris erythrogramma, with small (93 µm) and large (393 µm) eggs, respectively, we documented the effect of decreased pH on the egg jelly coat, an extracellular matrix that increases target size for sperm and contains sperm-attracting molecules. In near-future conditions (pH 7.8, 7.6), the jelly coat of H. tuberculata decreased by 11% and 21%, reducing egg target size by 9% and 17%, respectively. In contrast, the egg jelly coat of H. erythrogramma was not affected. The reduction in the jelly coat has implications for sperm chemotaxis in H. tuberculata. In the presence of decreased pH and egg chemicals, the sperm of this species increased their velocity, motility and linearity, behaviour that was opposite to that seen for sperm exposed to egg chemicals in ambient conditions. Egg chemistry appears to cause a reduction in sperm velocity where attractants guide the sperm in the direction of the egg. Investigation of the effects of decreased pH on sperm isolated from the influence of egg chemistry does not provide an integrative assessment of the effects of ocean acidification on sperm function. Differences in the sensitivity of the jelly coat of the two species is likely associated with egg evolution in H. erythrogramma. We highlight important unappreciated impacts of ocean acidification on marine gamete functionality, and insights into potential winners and losers in a changing ocean, pointing to the advantage conveyed by the evolution of large eggs.

Continue reading ‘Cherchez la femme – impact of ocean acidification on the egg jelly coat and attractants for sperm’

A microcosm study on the impact of acidification on feeding, survival, nauplii production rate, post-embryonic development and nutritional composition of marine copepod

Ocean acidification is the ongoing decrease in the pH of the oceans, caused by their uptake of anthropogenic carbon dioxide from the atmosphere. Increased carbon dioxide (CO2) from the burning of fossil fuels and other human activities continues to affect our atmosphere, resulting in global warming and climate change. Less well known is that this carbon dioxide is altering the chemistry of the surface oceans and causing them to become more acidic. From scientists and marine resource managers to policy- and decision-makers, there is a growing concern that the process called ocean acidification could have significant consequences on marine organisms which may alter species composition, disrupt marine food webs and ecosystems and potentially damage fishing, tourism and other human activities connected to the seas.

Continue reading ‘A microcosm study on the impact of acidification on feeding, survival, nauplii production rate, post-embryonic development and nutritional composition of marine copepod’

Near-future CO2 levels impair the olfactory system of a marine fish

Survival of marine fishes that are exposed to elevated near-future CO2 levels is threatened by their altered responses to sensory cues. Here we demonstrate a physiological and molecular mechanism in the olfactory system that helps to explain altered behaviour under elevated CO2. We combine electrophysiology measurements and transcriptomics with behavioural experiments to investigate how elevated CO2 affects the olfactory system of European sea bass (Dicentrarchus labrax). When exposed to elevated CO2 (approximately 1,000 µatm), fish must be up to 42% closer to an odour source for detection, compared with current CO2 levels (around 400 µatm), decreasing their chances of detecting food or predators. Compromised olfaction correlated with the suppression of the transcription of genes involved in synaptic strength, cell excitability and wiring of the olfactory system in response to sustained exposure to elevated CO2 levels. Our findings complement the previously proposed impairment of γ-aminobutyric acid receptors, and indicate that both the olfactory system and central brain function are compromised by elevated CO2 levels.

Continue reading ‘Near-future CO2 levels impair the olfactory system of a marine fish’

The bloom-forming macroalgae, Ulva, outcompetes the seagrass, Zostera marina, under high CO2 conditions

This study reports on experiments performed with a Northwest Atlantic species of the macroalgae, Ulva, and the seagrass, Zostera marina, grown under ambient and elevated levels of pCO2, and subjected to competition with each other. When grown individually, elevated pCO2 significantly increased growth rates and productivity of Ulva and Zostera, respectively, beyond control treatments (by threefold and 27%, respectively). For both primary producers, significant declines in tissue δ13C signatures suggested that increased growth and productivity were associated with a shift from use of HCO3 toward CO2 use. When grown under higher pCO2, Zostera experienced significant increases in leaf and rhizome carbon content as well as significant increases in leaf carbon-to-nitrogen ratios, while sediments within which high CO2 Zostera were grown had a significantly higher organic carbon content. When grown in the presence of Ulva; however, above- and below-ground productivity and tissue nitrogen content of Zostera were significantly lower, revealing an antagonistic interaction between elevated CO2 and the presence of Ulva. The presence of Zostera had no significant effect on the growth of Ulva. Collectively, this study demonstrates that while Ulva and Zostera can each individually benefit from elevated pCO2 levels, the ability of Ulva to grow more rapidly and inhibit seagrass productivity under elevated pCO2, coupled with accumulation of organic C in sediments, may offset the potential benefits for Zostera within high CO2 environments.

Continue reading ‘The bloom-forming macroalgae, Ulva, outcompetes the seagrass, Zostera marina, under high CO2 conditions’

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Ocean acidification in the IPCC AR5 WG II

OUP book