Posts Tagged 'performance'

A future 1.2 °C increase in ocean temperature alters the quality of mangrove habitats for marine plants and animals

Highlights
• Mangrove habitats are more resilient to climate change than other habitats.

• Climate change might have positive effects on mangrove-root species communities.

• Using mesocosms we show that an increase of 1.2 °C leads to community homogenisation.

• Warming also led to diversity loss and flattening of mangrove root epibiont communities.

• Juvenile fish altered their use of mangrove habitats under warming and acidification.

Abstract
Global climate stressors, like ocean warming and acidification, contribute to the erosion of structural complexity in marine foundation habitats by promoting the growth of low-relief turf, increasing grazing pressure on structurally complex marine vegetation, and by directly affecting the growth and survival of foundation species. Because mangrove roots are woody and their epibionts are used to ever-changing conditions in highly variable environments, mangrove habitats may be more resilient to global change stressors than other marine foundation species. Using a large-scale mesocosm experiment, we examined how ocean warming and acidification, under a reduced carbon emission scenario, affect the composition and structural complexity of mangrove epibiont communities and the use of mangrove habitat by juvenile fishes. We demonstrate that even a modest increase in seawater temperature of 1.2 °C leads to the homogenisation and flattening of mangrove root epibiont communities. Warming led to a 24% increase in the overall cover of algal epibionts on roots but the diversity of the epibiont species decreased by 33%. Epibiont structural complexity decreased owing to the shorter stature of weedy algal turfs which prospered under elevated temperature. Juvenile fishes showed alterations in mangrove habitat use with ocean warming and acidification, but these were independent of changes to the root epibiont community. We reveal that the quality of apparently resilient mangrove habitats and their perceived value as habitat for associated fauna are still vulnerable under a globally reduced carbon emission scenario.

Continue reading ‘A future 1.2 °C increase in ocean temperature alters the quality of mangrove habitats for marine plants and animals’

Paleobiological traits that determined Scleractinian coral survival and proliferation during the late Paleocene and early Eocene hyperthermals

Coral reefs are particularly sensitive to environmental disturbances, such as rapid shifts in temperature or carbonate saturation. Work on modern reefs has suggested that some corals will fare better than others in times of stress and that their life history traits might correlate with species survival. These same traits can be applied to fossil taxa to assess whether life history traits correspond with coral survival through past intervals of stress similar to future climate predictions. This study aims to identify whether ecological selection (based on physiology, behavior, habitat, etc.) plays a role in the long‐term survival of corals during the late Paleocene and early Eocene. The late Paleocene‐early Eocene interval is associated with multiple hyperthermal events that correspond to rises in atmospheric pCO2 and sea surface temperature, ocean acidification, and increases in weathering and turbidity. Coral reefs are rare during the late Paleocene and early Eocene, but despite the lack of reef habitat, corals do not experience an extinction at the generic level and there is little extinction at the species level. In fact, generic and species richness increases throughout the late Paleocene and early Eocene. We show that corals with certain traits (coloniality, carnivorous, or suspension feeding diet, hermaphroditic brooding reproduction, living in clastic settings) are more likely to survive climate change in the early Eocene. These findings have important implications for modern coral ecology and allow us to make more nuanced predictions about which taxa will have higher extinction risk in present‐day climate change.

Continue reading ‘Paleobiological traits that determined Scleractinian coral survival and proliferation during the late Paleocene and early Eocene hyperthermals’

An ecotoxicological study on physiological responses of Archaster typicus to salinity, thermal and ocean acidification stressors

Environmental biomarkers, also known as early warning signals, have increasingly
become a subject of interest in environmental studies. The common sea star, Archaster typicus, found in shallow sandy habitats associated with coral reefs in Singapore, was utilised to study the effects of varying treatment conditions of salinity, temperature and pH. Treatment conditions were derived from predicted future scenarios of thermal and ocean acidification conditions. Experiments were conducted to determine physiological responses of sea stars that were subjected to treatments over 24h (acute) and 120h (chronic) exposures. The biomarker responses examined included righting behaviour (time taken to right after being overturned), burrowing time and feeding responses (time
taken to close stomach/mouth plate) in experimental sea stars. To validate results of physiological biomarkers, two other biomarker responses were measured from coelomic fluid extracted from the experimental sea stars. These were the cellular lysosome integrity response (Neutral Red Retention time, NRRT) and the biochemical Ferric Reducing Antioxidant Power (FRAP) assay. In acute exposure experiments, results indicated that sea stars exhibited significant differences in physiological responses under various salinity, temperature and pH treatments. At chronic exposure regimes, lethal effects were more evident, with higher mortality rates observed in all salinity and temperature treatment regimes. Results from salinity treatments showed that physiological responses in sea stars were significantly impaired at treatments of 15‰ and 50‰ salinities. Significant results were observed in NRRT and burrowing behavioural assays in temperature treatments. Treatments with pH of 7.4 and 7.2 at the acute exposure duration resulted in a significant impairment of righting ability. The acute and chronic effects of salinity fluctuations, ocean warming and acidification on A
2 typicus were most consistently observed in the righting and burrowing behaviour assays. This indication of reduced fitness together with reduced cellular responses show a reduction in survival ability in the sea star under low salinity, high temperature and low pH conditions. Further studies could thus help us understand the effects of global warming on the physiology of organisms in various shallow water habitats.

Continue reading ‘An ecotoxicological study on physiological responses of Archaster typicus to salinity, thermal and ocean acidification stressors’

Integrity of crustacean predator defenses under ocean acidification and warming conditions

Crustaceans are a diverse group of species, but all rely on an exoskeleton that is shed and formed anew throughout their lifetime. Exoskeletons perform a wide range of functions, sometimes acting as armor, a means to produce sound, a tool to crush hard prey, or even a window to facilitate transparency. The exoskeleton and its functions, however, are likely vulnerable to ocean acidification and ocean warming, which may alter its composition and the energy allocated towards its production. I investigated the effects of these future ocean conditions on two southern Californian crustaceans, the California spiny lobster Panulirus interruptus and the grass shrimp Hippolyte californiensis, which rely on their exoskeleton for different predator defenses. P. interruptus is an iconic feature of southern California’s kelp forest ecosystem but also a potential prey item for many of its large predators. Spiny lobsters use their antennae, mandibles, carapace, and horns to avoid predation. Each of these structures is specialized for a certain defense, displaying differences in composition, structure, and material properties that allow the antennae, for example, to remain flexible to avoid breaking when pushing predators away while imbuing hardness in crushing structures like the mandible (Chapter 1). Juvenile lobsters exposed to ocean acidification-like conditions largely maintained their predator defenses, displaying some differences in the composition across the exoskeleton but no strong effects to defense functionality, including the non-exoskeletal defenses of detecting chemical cues and the tail-flip escape response (Chapter 3). Additionally, larval P. interruptus, exposed to both ocean acidification and warming conditions, grew slightly smaller in reduced pH but maintained their transparency in both conditions (Chapter 2). In contrast, H. californiensis resides in eelgrass meadows where a primary defense strategy is cryptic colouration, accomplished via a transparent exoskeleton with underlying pigment. When exposed to both ocean acidification and ocean warming-like conditions, shrimp maintained their transparency and did not respond negatively to either condition (Chapter 4). Together, this work on both species demonstrates that a diversity of predator defenses in temperate crustaceans, included those afforded by the exoskeleton, appear to be relatively resilient to both future ocean acidification and ocean warming conditions.

Continue reading ‘Integrity of crustacean predator defenses under ocean acidification and warming conditions’

Marine mass mortality in a global change context: impacts on individuals, populations and communities

Human actions are pushing natural systems into states that have no historical precedent. In response, empirical and theoretical researchers are increasingly focused on developing ways to predict the responses of ecological systems to change. However, significant knowledge gaps remain, often leading to “ecological surprises” where observed impacts of global change do not align with existing theory or hypotheses. In this dissertation, I study the response to perturbations of a well-characterized system for ecological research, the Northeast Pacific rocky intertidal, to advance our understanding of and ability to predict the impacts of global change on individuals, populations and communities. In 2013 and 2014, sea star species along the west coast of North America were affected by an outbreak of Sea Star Wasting Syndrome (SSWS), resulting in an epidemic of mass mortality that spanned unprecedented geographic and temporal scales and resulted in the near extirpation of multiple sea star species from many locations along the coast. One of the species that was most strongly affected in the intertidal zone was Pisaster ochraceus, an iconic predatory sea star that has the ability to play a keystone role in its community through foraging on and ultimately controlling the lower boundary of mussel prey populations. The first two chapters of this dissertation take advantage of SSWS as a “natural” form of top predator removal to assess the consequences of this type of perturbation on ecosystem resilience. In Chapter 2, I tested the hypotheses that P. ochraceus loss would facilitate a population expansion of a smaller, mesopredator sea star, Leptasterias sp., and that this expansion would have negative effects on P. ochraceus population recovery. This result would follow expectations of competitive release and aligns with existing research on the competitive relationship between these species from the Northeast Pacific intertidal. I used field surveys to track Leptasterias populations just before the onset of and up to three years after SSWS. Contrary to expectation, I did not see an increase in the distribution or density of Leptasterias, and instead saw a decrease in individual size post-SSWS. Further, I found no evidence of competition between P. ochraceus recruits and Leptasterias for resources. Thus, although my hypotheses were grounded in theory and previous research, they were not supported by data. These results suggest that Leptasterias will not provide a bottleneck for P. ochraceus population recovery from SSWS, nor compensate for lowered P. ochraceus predation. The dynamics of P. ochraceus at the recruit (early benthic juvenile) life-history stage has long been considered a gap in our understanding of the species, as recruits have been historically rare in the intertidal and hard to study. Post-SSWS, however, many sites along the coast experienced unprecedented recruitment of P. ochraceus into intertidal ecosystems. In Chapter 3, I used a field experiment to test the hypothesis that this pulse of recruitment was facilitated by SSWS-related adult loss, the consequent decrease in predation by adult P. ochraceus, and increase in prey availability for recruits. Instead of finding evidence that adults dominate recruits in food competition and inhibit recruit success, I found that recruits have a negative effect on P. ochraceus adult densities. Further, treatments where recruits were excluded and only adults had access to prey communities showed the highest control of sessile invertebrate prey populations at the end of the year-long experiment. Thus, these results suggest that adult P. ochraceus will not hinder recruit recovery, but propose a mechanism whereby high recruit densities may increase vulnerability to SSWS-induced shifts in community structure. Outbreaks of mass mortality, particularly those as widespread as SSWS, are one of many ecological challenges driven by anthropogenic environmental changes such as warming and ocean acidification. However, predicting the vulnerability of species and populations to global change is an ongoing and significant challenge for researchers and managers. In Chapter 4 I assessed whether intraspecific physiological variability could help predict P. ochraceus recruit response to ocean acidification and warming. I found that individual metabolic rate interacted with ocean acidification and food availability to drive sea star growth, and that an interaction between metabolic rate and temperature also predicted sea star predation on Mytilus spp. mussels. Thus, these results have implications not only for P. ochraceus but also for its food web interactions. Incorporating these results into predictive frameworks may improve our ability to anticipate and scale up responses to global change across levels of ecological organization. In summary, my dissertation, although chock-full of surprises, presents several paths forward for improving predictive ability in the face of accelerating anthropogenic global changes. Further, we reinforce the notion that management strategies should be cautious and anticipate ecological surprises. Predicting the future is challenging even when predictions are well-informed, particularly in environmental contexts that have never been encountered before.

Continue reading ‘Marine mass mortality in a global change context: impacts on individuals, populations and communities’

Long-term acclimation to near-future ocean acidification has negligible effects on energetic attributes in a juvenile coral reef fish

Increased levels of dissolved carbon dioxide (CO2) drive ocean acidification and have been predicted to increase the energy use of marine fishes via physiological and behavioural mechanisms. This notion is based on a theoretical framework suggesting that detrimental effects on energy use are caused by plasma acid–base disruption in response to hypercapnic acidosis, potentially in combination with a malfunction of the gamma aminobutyric acid type A (GABAA) receptors in the brain. However, the existing empirical evidence testing these effects primarily stems from studies that exposed fish to elevated CO2 for a few days and measured a small number of traits. We investigated a range of energetic traits in juvenile spiny chromis damselfish (Acanthochromis polyacanthus) over 3 months of acclimation to projected end-of-century CO2 levels (~ 1000 µatm). Somatic growth and otolith size and shape were unaffected by the CO2 treatment across 3 months of development in comparison with control fish (~ 420 µatm). Swimming activity during behavioural assays was initially higher in the elevated CO2 group, but this effect dissipated within ~ 25 min following handling. The transient higher activity of fish under elevated CO2 was not associated with a detectable difference in the rate of oxygen uptake nor was it mediated by GABAA neurotransmitter interference because treatment with a GABAA antagonist (gabazine) did not abolish the CO2 treatment effect. These findings contrast with several short-term studies by suggesting that end-of-century levels of CO2 may have negligible direct effects on the energetics of at least some species of fish.

Continue reading ‘Long-term acclimation to near-future ocean acidification has negligible effects on energetic attributes in a juvenile coral reef fish’

The impact of climate change on intertidal species, camouflage and predation

To understand the impact of climate change on ecosystems we need to know not only how individual species will be affected, but also the relationships between them. Predator-prey relationships determine the structure and function of ecosystems worldwide, governing the abundance of populations, the distribution of different species within habitats and, ultimately, the composition of communities. Many predator-prey relationships are shifting as a result of environmental change, with climate change causing both mismatches in the abundance and distribution of species and changes in predator and prey behaviour. However, few studies have addressed how climate change might impact the interactions between species, particularly the development of anti-predator defences, which enable prey to limit their predation risk. One of the most widespread defences in nature is camouflage, with many species capable of changing colour to match their background to avoid being seen and eaten. The impact of climate change on this process is largely unknown, save for studies on species that exhibit seasonal changes in coloration. Using behavioural assays with predatory rock gobies (Gobius paganellus) and chameleon prawn prey (Hippolyte varians), I first demonstrate how background matching affects survival, shedding light on the fitness benefits of camouflage. Building on this fundamental understanding, this project explores how defensive coloration may be affected by anthropogenic climate change. Through a series of laboratory studies I test what impact ocean warming and ocean acidification have on the development of camouflage in intertidal crustaceans (chameleon prawns and common shore crabs, Carcinus maenas). Camouflage is modelled according to the visual systems of relevant predators, allowing us to understand what implications their coloration has for detectability, predation risk, and associated trophic links. Finally, this project investigates how camouflage can be applied to conservation and aquaculture. By rearing juvenile European lobster (Homarus gammarus) on different backgrounds, I show that they are capable of colour change for camouflage, as well as colour change throughout ontogeny. This capacity could be harnessed to help improve survival on release into the wild. As such, this thesis explores the fundamental science of camouflage, anthropogenic impacts on this process and its applications for conservation.

Continue reading ‘The impact of climate change on intertidal species, camouflage and predation’


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Ocean acidification in the IPCC AR5 WG II

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