Posts Tagged 'mortality'



The weakest link: sensitivity to climate extremes across life stages of marine invertebrates

Predicting the effects of climate change on Earth’s biota becomes even more challenging when acknowledging that most species have life cycles consisting of multiple stages, each of which may respond differently to extreme environmental conditions. There is currently no clear consensus regarding which stages are most susceptible to increasing environmental stress, or ‘climate extremes’. We used a meta‐analytic approach to quantify variation in responses to environmental stress across multiple life stages of marine invertebrates. We identified 287 experiments in 29 papers which examined the lethal thresholds of multiple life stages (embryo, larva, juvenile, and adult) of both holoplanktonic and meroplanktonic marine invertebrates subjected to the same experimental conditions of warming, acidification, and hypoxia stress. Most studies considered short acute exposure to stressors. We calculated effect sizes (log response ratio) for each life stage (unpaired analysis) and the difference in effect sizes between stages of each species (paired analysis) included in each experiment. In the unpaired analysis, all significant responses were negative, indicating that warming, acidification and hypoxia tended to increase mortality. Furthermore, embryos, larvae, and juveniles were more negatively affected by warming than adults. The paired analysis revealed that, when subjected to the same experimental conditions, younger life stages were more negatively affected by warming than older life stages, specifically among pairings of adults vs. juveniles and larvae vs. embryos. Although responses to warming are well documented, few studies of the effects of acidification and hypoxia met the criteria for inclusion in our analyses. Our results suggest that while most life stages will be negatively affected by climate change, younger stages of marine invertebrates are more sensitive to extreme heating events.

Continue reading ‘The weakest link: sensitivity to climate extremes across life stages of marine invertebrates’

Individual and combined effects of low dissolved oxygen and low pH on survival of early stage larval blue crabs, Callinectes sapidus

A large number of coastal ecosystems globally are subjected to concurrent hypoxic and acidified conditions that will likely intensify and expand with continued climate change. In temperate regions, the spawning of many important organisms including the Atlantic blue crab Callinectes sapidus occurs during the summer months when the severity of coastal hypoxia and acidification is the greatest. While the blue crab earliest larval stage can be exposed to co-occurring hypoxia and acidification observed in many coastal ecosystems, the effects of these concurrent stressors on larval blue crab survival is unknown. This study investigated the individual and combined consequences of low dissolved oxygen (DO) and low pH on blue crab larvae survival through a series of short-term experiments. During 14-day experiments with moderately hypoxic conditions (117–127 μM O2 or 3.74–4.06 mg L-1) and acidified conditions (pH on total scale of 7.16–7.33), low DO and low pH individually and significantly reduced larval survival by 60% and 49%, respectively, with the combination of stressors reducing survival by 87% compared to the control treatment (210–269 μM O2 or 6.72–8.61 mg L-1, 7.91–7.94 DO and pH, respectively). During 4-day experiments with lower DO levels (68–83 μM O2 or 2.18–2.62 mg L-1) and comparable pH levels of 7.29–7.39, low DO individually reduced survival by >90% compared to the control (261–267 μM O2 or 8.35–8.54 mg L-1, 7.92–7.97 DO and pH, respectively), whereas low pH had no effect and there was no interaction between stressors. Over a 4-day period, the DO threshold at which 50% of the larval blue crab population died (LC50) was 121 μM O2 (3.86 mgL-1). In 14-day experiments, the DO and pH effects were additive, yielding survival rates lower than the individual treatments, and significantly correlated with DO and pH concentrations. Collectively, these findings indicate that blue crab sensitivity to both low DO and low pH are acute within the larval stage, depend on the intensity and duration of exposure, and leads to mortality, thereby potentially contributing to the interannual variability and possible regional declines of this fishery.

Continue reading ‘Individual and combined effects of low dissolved oxygen and low pH on survival of early stage larval blue crabs, Callinectes sapidus’

Distinct bleaching resilience of photosynthetic plastid-bearing mollusks under thermal stress and high CO2 conditions

The impact of temperature on photo-symbiotic relationships has been highly studied in the tropical reef-forming corals but overlooked in less charismatic groups such as solar-powered sacoglossan sea slugs. These organisms display one of the most puzzling symbiotic features observed in the animal kingdom, i.e., their mollusk-plastid association, which enables them to retain photosynthetic active chloroplasts (i.e., kleptoplasts) retrieved from their algae feed sources. Here we analyze the impact of thermal stress (+4∘C) and high pCO2 conditions (ΔpH = 0.4) in survival, photophysiology (i.e., bleaching, photosynthetic efficiency, and metabolism) and stress defense mechanisms (i.e., heat shock and antioxidant response) of solar-powered sacoglossan sea slugs, from tropical (Elysia crispata) and temperate (E. viridis) environments. High temperature was the main factor affecting the survival of both species, while pH only affected the survival of the temperate model. The photobiology of E. viridis remained stable under the combined scenario, while photoinhibition was observed for E. crispata under high temperature and high pCO2. In fact, bleaching was observed within all tropical specimens exposed to warming (but not in the temperate ones), which constitutes the first report where the incidence of bleaching in tropical animals hosting photosynthetic symbionts, other than corals, occurs. Yet, the expulsion of kleptoplasts by the tropical sea slug, allied with metabolic depression, constituted a physiological response that did not imply signs of vulnerability (i.e., mortality) in the host itself. Although the temperate species revealed greater heat shock and antioxidant enzyme response to environmental stress, we argue that the tropical (stenotherm) sea slug species may display a greater scope for acclimatization than the temperate (eurytherm) sea slug. E. crispata may exhibit increased capacity for phenotypic plasticity by increasing fitness in a much narrower thermal niche (minimizing maintenance costs), which ultimately may allow to face severe environmental conditions more effectively than its temperate generalist counterpart (E. viridis).

Continue reading ‘Distinct bleaching resilience of photosynthetic plastid-bearing mollusks under thermal stress and high CO2 conditions’

Physiological responses of whitespotted bamboo shark (Chiloscyllium plagiosum) to high CO2 levels

Sharks have been roaming the planet for 400 million years and are vital elements for the health of our oceans. Due to occurring changes in the food-web and anthropogenic pressure from fishing and habitat degradation, sharks populations are now declining sharply. Ocean acidification, caused by continuous release of carbon dioxide (CO2) to the atmosphere, may represent an additional threat. Among other effects, it may cause physiological disturbances in the organisms and threaten marine ecosystems as we know them, especially the most vulnerable life stages. Hence, the present study focus on the effects that ocean acidification may have on the fitness, metabolism and swimming performance of juvenile whitespotted bamboo sharks (Chiloscyllium plagiosum). After hatching, sharks were placed in either control (pCO2 ~ 400 μatm, pH = 8.0) or high CO2 (pCO2 ~ 900 μatm, pH = 7.7) conditions, according to the pH levels expected by the end of the century. After an exposure of 45 days, several ecologically important traits were tested, namely their fitness [(i) Fulton condition], metabolic capacity [(i) routine metabolic rate (RMR), (ii) maximum metabolic rate (MMR), (iii) aerobic scope (AS)] and swimming performance [(i) maximum reached velocity, (ii) percentage of time swimming, (iii) number of bursts and (vi) pre and (vii) post-stress ventilation rates]. No changes were observed in their fitness, metabolism and the majority of the swimming performance end-points. Nevertheless, regarding the swimming performance, there was a decrease of the duration of swimming events and a decrease in the post-swimming ventilation rates. Over the past years, these cartilaginous fish have been coping with oscillations in the seawater chemistry and thus appear to be resilient to OA. However, this species’ conservation status is of concern, assessed as Near Threatened, and even the sub-lethal effects observed in this study may potentially reduce the organism’s overall fitness and ultimately impact population dynamics.

Continue reading ‘Physiological responses of whitespotted bamboo shark (Chiloscyllium plagiosum) to high CO2 levels’

Northern cod species face spawning habitat losses if global warming exceeds 1.5°C

Rapid climate change in the Northeast Atlantic and Arctic poses a threat to some of the world’s largest fish populations. Impacts of warming and acidification may become accessible through mechanism-based risk assessments and projections of future habitat suitability. We show that ocean acidification causes a narrowing of embryonic thermal ranges, which identifies the suitability of spawning habitats as a critical life-history bottleneck for two abundant cod species. Embryonic tolerance ranges linked to climate simulations reveal that ever-increasing CO2 emissions [Representative Concentration Pathway (RCP) 8.5] will deteriorate suitability of present spawning habitat for both Atlantic cod (Gadus morhua) and Polar cod (Boreogadus saida) by 2100. Moderate warming (RCP4.5) may avert dangerous climate impacts on Atlantic cod but still leaves few spawning areas for the more vulnerable Polar cod, which also loses the benefits of an ice-covered ocean. Emissions following RCP2.6, however, support largely unchanged habitat suitability for both species, suggesting that risks are minimized if warming is held “below 2°C, if not 1.5°C,” as pledged by the Paris Agreement.

Continue reading ‘Northern cod species face spawning habitat losses if global warming exceeds 1.5°C’

Performance and herbivory of the tropical topshell Trochus histrio under short-term temperature increase and high CO2

Highlights

• Tropical algae-herbivore interactions were studied under a climate change scenario.

• Survival of topshells did not vary but body fitness declined under high CO2.

• Elevated temperature resulted in better physical condition and stimulated herbivory.

• Dynamic index was temperature- and pCO2-interactively dependent.

• Dominance of bottom-up control (i.e. lower grazing pressure) under high CO2.

Abstract

Within tropical environments, short-term impacts of increased seawater temperature and pCO2 on algae-herbivore interactions remain poorly understood. We investigated the isolated and combined 7-day effects of increased temperature (+4 °C) and pCO2 (~1000 μatm) on the trophic interaction Ulva sp./Trochus histrio, by assessing: i) topshells’ survival and condition index; ii) grazer consumption rates, nutritional composition and interaction strength expressed as a dynamic index. No survival differences were observed whilst body condition varied significantly. Topshells under high pCO2 displayed poor performance, concomitant with lower consumption of macroalgae. Individuals exposed to increased temperature had better physical condition, thus stimulating herbivory, which in turn was negatively correlated with carbon and nitrogen contents. The dynamic index was temperature- and pCO2- interactively dependent, suggesting lower grazing pressure under single acidification. Despite some limitations inherent to a short-term exposure, this study provides new insights to accurately predict tropical species’ phenotypic responses in a changing ocean.

Continue reading ‘Performance and herbivory of the tropical topshell Trochus histrio under short-term temperature increase and high CO2’

Can larvae of a marine fish adapt to ocean acidification? Evaluating the evolutionary potential of California Grunion (Leuresthes tenuis)

Ocean acidification can reduce the growth and survival of marine species during their larval stages. However, if populations have the genetic capacity to adapt and increase their tolerance of low pH and high pCO2 levels, this may offset the harmful effects of ocean acidification. By combining controlled breeding experiments with laboratory manipulations of seawater chemistry, we evaluated genetic variation in tolerance of ocean acidification conditions for a nearshore marine fish, the California Grunion (Leuresthes tenuis). Our results indicated that acidification conditions increased overall mortality rates of grunion larvae, but did not have a significant effect on growth. Groups of larvae varied widely with respect to mortality and growth rates in both ambient and acidified conditions. We demonstrate that the potential to evolve in response to ocean acidification is best described by considering additive genetic variation in fitness‐related traits under both ambient and acidified conditions, and by evaluating the genetic correlation between traits expressed in these environments. We used a multivariate animal model to estimate additive genetic (co)variance in larval growth and mortality rates under both ambient and acidified conditions (low pH/high pCO2). Our results suggest appreciable genetic variation in larval mortality rates (h2Ambient = 0.120; h2Acidified = 0.183; rG = 0.460), but less genetic variation in growth (h2Ambient = 0.092; h2Acidified = 0.101; rG = 0.135). Maternal effects on larval mortality rates accounted for 26‐36% of the variation in phenotypes, but maternal effects accounted for only 8% of the variation in growth. Collectively, our estimates of genetic variation and covariation suggest that populations of California Grunion have the capacity to adapt relatively quickly to long‐term changes in ocean chemistry.

Continue reading ‘Can larvae of a marine fish adapt to ocean acidification? Evaluating the evolutionary potential of California Grunion (Leuresthes tenuis)’


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Ocean acidification in the IPCC AR5 WG II

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