Posts Tagged 'mortality'

Elevated pCO2 does not impair performance in autotomised individuals of the intertidal predatory starfish Asterias rubens (Linnaeus, 1758)

Highlights

• Ocean acidification research requires further understanding on the interactions with other stressors.

• We examined the combined effects of pCO2 and arm autotomisation on Asterias rubens.

• Neither stressor affected mortality, growth, arm regeneration, righting time or arm calcium content.

• Lipid content in the pyloric caeca increased in response to elevated pCO2.

• A. rubens appears unaffected by short-term exposure to pCO2 levels predicted for 2100.

Abstract

The impacts of ocean acidification remain less well-studied in starfish compared to other echinoderm groups. This study examined the combined effects of elevated pCO2 and arm regeneration on the performance of the intertidal predatory starfish Asterias rubens, as both are predicted to come at a cost to the individual. A two-way factorial experiment (~400 μatm vs ~1000 μatm; autotomised vs non-automised individuals) was used to examine growth rates, lipid content (pyloric caeca and gonads), and calcium content (body wall) in both intact and regenerating arms, as well as subsequent effects on rate of arm regeneration, righting time (behaviour) and mortality over 120 days. Autotomised individuals tended to show lower (not significant), survival and growth. Elevated pCO2 had no effect on mortality, body growth, arm regeneration, righting time or arm calcium content. Lipid content was higher in the pyloric caeca, but not in the gonads, in response to elevated pCO2 irrespective of autotomisation. The results of the study suggest that adult A. rubens remain unaffected by increased pCO2 and/or arm autotomy for 120 days, although longer term experiments are necessary as the results indicated that survival, growth and calcification may be impaired with longer-term exposure to elevated pCO2.

Continue reading ‘Elevated pCO2 does not impair performance in autotomised individuals of the intertidal predatory starfish Asterias rubens (Linnaeus, 1758)’

Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)

Minuca mordax is a model for studies on ocean acidification and sea-level rise because lives in mangroves and riverbanks with low pH. We investigated the physiology of the crabs exposed to differents pH (6.5 and 5.8) and salinity (25, 30, 35, 40 45S). There was not mortality or alterations in the hypo-osmoregulation, suggesting that the factors did not affect salt absorption/secretion. Reduced pH changed metabolism, ammonia excretion, and hepatosomatic index in relation to the animals kept in control pH. At elevated salinities, metabolism increased when animals were kept in control pH, but it decreased when they were exposed to acidified pH. energy substrate, varied between proteins to a mixture of proteins and lipids. Important physiological parameters, related to the catabolism of amino acids and to the energy demand are changed and the consequences might include alterations in growth and reproduction due to the energy channeling to limiting processes of homeostasis.

Continue reading ‘Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)’

Ecotoxicological responses of a reef calcifier exposed to copper, acidification and warming: a multiple biomarker approach

Highlights

• Copper increased bleaching, respiration and inhibited calcification-related enzymes.

• Thermal stress was the main driver of mortality.

• Relative tolerance to climate change scenario (ocean warming + acidification).

• Integrated biomarker response related more to co-exposures than isolated biomarkers.

• Integrated analysis showed higher stress under climate change + copper condition.

Abstract

Multiple global and local stressors threat coral reefs worldwide, and symbiont-bearing foraminifera are bioindicators of reef health. The aim of this study was to investigate single and combined effects of copper (Cu) and climate change related stressors (ocean acidification and warming) on a symbiont-bearing foraminifer by means of an integrated biomarker analysis. Using a mesocosm approach, Amphistegina gibbosa were exposed for 25 days to acidification, warming and/or Cu contamination on a full orthogonal design (two levels each factor). Cu was the main factor increasing bleaching and respiration rates. Warming was the main cause of mortality and reduced growth. Calcification related enzymes were inhibited in response to Cu exposure and, in general, the inhibition was stronger under climate change. Multiple biological endpoints responded to realistic exposure scenarios in different ways, but evidenced general stress posed by climate change combined with Cu. These biological responses drove the high values found for the ‘stress index’ IBR (Integrated Biomarker Response) – indicating general organismal health impairment under the multiple stressor scenario. Our results provide insights for coral reef management by detecting potential monitoring tools. The ecotoxicological responses indicated that Cu reduces the tolerance of foraminifera to climate change (acidification + warming). Once the endpoints analysed have a high ecological relevance, and that responses were evaluated on a classical reef bioindicator species, these results highlight the high risk of climate change and metal pollution co-exposure to coral reefs. Integrated responses allowed a better effects comprehension and are pointed as a promising tool to monitor pollution effects on a changing ocean.

Continue reading ‘Ecotoxicological responses of a reef calcifier exposed to copper, acidification and warming: a multiple biomarker approach’

Lipid biochemistry and physiology of Antarctic krill (Euphausia superba) in the present day and under future ocean acidification scenarios

Antarctic krill (Euphausia superba, hereafter ‘krill’) are lipid-rich euphausiids with an important role in the Southern Ocean, including as the primary prey of Antarctic megafauna (whales, seals, penguins), fish, squid and seabirds. They contain high levels of nutritious long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA), specifically eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). The sheer abundance of krill in the Southern Ocean means that the ecosystem is largely driven by energy derived from krill lipids. In addition to their ecological importance, a Scotia Sea krill fishery harvests krill, including for commercial use of their LC-PUFA. The existence of this year-round krill fishery provides a unique opportunity to collect krill samples for research over large spatial and temporal scales, which is unfeasible using scientific research vessels.

In this thesis, fishery caught krill samples were used to investigate the fatty acid content and composition of krill, during all seasons and over consecutive years (2013 – 2016). This research (presented in Chapter 2) aimed to fill knowledge gaps on the seasonal diet of krill (particularly in winter) in the Scotia Sea region, using fatty acids as dietary biomarkers. Krill were primarily herbivorous in summer (higher levels of 20:5n-3 and 22:6n-3, and low 18:1n-9c/18:1n-7c ratios) and became more omnivorous from autumn to spring (increasing ratios of 18:1n-9c/18:1n-7c and percentages of Σ 20:1 + 22:1 isomers). Seasonal proportions of herbivory and omnivory differed between years, and fatty acid composition differed between fishing locations. Selected samples were also used to investigate the composition of fatty acids in the structural (phospholipids) and storage lipids (triacylglycerols) of krill (Chapter 3). Triacylglycerol fatty acids (thought to better represent recent diet), reflected omnivorous feeding with highest percentages of flagellate biomarkers (18:4n-3) occurring in summer, diatom biomarkers (16:1n-7c) from autumn-spring, and greater carnivory (higher Σ 20:1 + 22:1 and 18:1n-9c/18:1n-7c ratios) in autumn. Phospholipid fatty acids were less variable and were higher in the essential membrane fatty acids 20:5n-3 and 22:6n-3. Percentages of the major krill sterol, cholesterol, were significantly higher in winter and spring compared with summer and autumn. Results presented in Chapters 2 and 3 highlighted the dynamic nature of krill lipids, and the flexible diet of krill, which likely contributes to their huge biomass and success as one of the most abundant organisms on Earth.

Because krill are so important in the Southern Ocean food web, any decreases in krill biomass could result in a major ecological regime shift. Very little is known about how climate change will affect krill. Increasing anthropogenic carbon dioxide (CO2) emissions are causing ocean acidification, as absorption of atmospheric CO2 in seawater alters ocean chemistry. Ocean acidification increases mortality and negatively affects physiological functioning in some marine invertebrates, and is predicted to occur most rapidly at high latitudes. Long-term laboratory studies are needed to understand how keystone species such as krill may respond to predicted future pCO2 levels. A long term experiment was conducted to test whether rising ocean pCO2 is likely to impact krill physiology and biochemistry (Chapters 4 and 5). Adult krill were exposed to near-future ocean acidification (1000 – 2000 μatm pCO2) for one year in the laboratory. Krill reared in near-future pCO2 conditions were able to survive, grow, store fat, mature, and maintain normal respiration rates. Haemolymph pH, lipid and fatty acid composition were also maintained at the same levels as krill in ambient pCO2 (400 μatm). Negative effects on physiology and lipid biochemistry were only observed in extreme pCO2 conditions (4000 μatm), which krill will not experience in the wild. These results place adult krill among the most resilient species in ocean acidification studies to date.

In summary, results in this thesis highlight the remarkable adaptability of krill in a changing environment, from short-term seasonal or annual scales, to longer-term decadal scales. Their flexible phenotype may aid their survival in an ocean that is rapidly changing with increasing anthropogenic CO2 emissions. The data obtained in this thesis can be used for fisheries management to guide fishing activities, and in fisheries models to predict how krill biomass may be affected by climate change. Krill lipid energy fuels the Southern Ocean ecosystem and to date, lipid data has not been included in Antarctic ecosystem models. The large scale of lipid data in this study makes it ideal for inclusion in such models, and it has important implications for the health of the wider Southern Ocean ecosystem.

Continue reading ‘Lipid biochemistry and physiology of Antarctic krill (Euphausia superba) in the present day and under future ocean acidification scenarios’

Independent effects of ocean warming versus acidification on the growth, survivorship and physiology of two Acropora corals

Climate change is the greatest threat to coral reef ecosystems. Importantly, gradual changes in seawater chemistry compounds upon increasing temperatures leading to declines in calcification and survivorship of reef-building corals. To assess relative versus synergistic effects of warming versus ocean acidification, Acropora muricata and Acropora hyacinthus were subjected to three temperature treatments (26 °C, 28.5 °C, 31 °C) crossed with three levels of pCO2 (410 μatm, 652 μatm, 934 μatm), representing current, mid and end-of-century scenarios for 12 weeks. Temperature increased gradually in the tanks from 26 °C to target temperatures over 5 weeks. Once stress was evident in the 31 °C (+ 2.5 °C above historical summer max) tanks, water temperature was decreased to normal summertime levels (29 °C) to assess recovery. pCO2 was gradually changed from control values (410 μatm) to target values over a 3 week period where they remained constant until the end of the experiment at 12 weeks. Temperature stress (31 °C) significantly impacted survivorship (90–95% decline), and over the long-term, there was a 50–90% decline in calcification across both coral species. Negative effects of mid and end-of-century pCO2 were largely independent of temperature and caused moderate reductions (36–74%) in calcification rates compared to temperature, over the long-term. Corals that survived temperature stress had higher lipid and protein content, showing that enhanced physiological condition provides an increased capacity to tolerate adverse temperatures. This study demonstrates that given the mortality rates in response to + 2.5 °C temperature stress, warming oceans (as opposed to ocean acidification) throughout the remainder of this century poses the greatest threat to reef-building corals.

Continue reading ‘Independent effects of ocean warming versus acidification on the growth, survivorship and physiology of two Acropora corals’

Complex and interactive effects of ocean acidification and warming on the life span of a marine trematode parasite

Highlights

• Functional and absolute life spans of cercariae were differentially affected by simulated ocean acidification and warming.

• High temperature negatively affected functional life span, suggesting warming may reduce the temporal transmission window.

• Warming and acidification reduced absolute life span, which may modify the role of cercariae as a food resource in future.

• The effect of acidification on cercarial life span was highly dependent on temperature.

Abstract

Human activities have caused an increase in atmospheric CO2 over the last 250 years, leading to unprecedented rates of change in seawater pH and temperature. These global scale processes are now commonly referred to as ocean acidification and warming (OAW), and have the potential to substantially alter the physiological performance of many marine organisms. It is vital that the effects of OAW on marine organisms are explored so that we can predict how marine communities may change in future. In particular, the effect of OAW on host-parasite dynamics is poorly understood, despite the ecological importance of these relationships. Here, we explore the response of one himasthlid trematode, Himasthla sp., an abundant and broadly distributed species of marine parasite, to combinations of elevated temperature and pCO2 that represent physiological extremes, pre-industrial conditions, and end of century predictions. Specifically, we quantified the life span of the free-living cercarial stage under elevated temperature and pCO2, focussing our research on functional life span (the time cercariae spend actively swimming) and absolute life span (the period before death). We found that the effects of temperature and pCO2 were complex and interactive. Overall, increased temperature negatively affected functional and absolute life span, e.g. across all pCO2 treatments the average time to 50% cessation of active swimming was approximately 8 h at 5°C, 6 h at 15°C, 4 h at 25°C, and 2 h at 40°C. The effect of pCO2, which significantly affected absolute life span, was highly variable across temperature treatments. These results strongly suggest that OAW may alter the transmission success of trematode cercariae, and potentially reduce the input of cercariae to marine zooplankton. Either outcome could substantially alter the community structure of coastal marine systems.

Continue reading ‘Complex and interactive effects of ocean acidification and warming on the life span of a marine trematode parasite’

Sensitivities to global change drivers may correlate positively or negatively in a foundational marine macroalga

Ecological impact of global change is generated by multiple synchronous or asynchronous drivers which interact with each other and with intraspecific variability of sensitivities. In three near-natural experiments, we explored response correlations of full-sibling germling families of the seaweed Fucus vesiculosus towards four global change drivers: elevated CO2 (ocean acidification, OA), ocean warming (OW), combined OA and warming (OAW), nutrient enrichment and hypoxic upwelling. Among families, performance responses to OA and OW as well as to OAW and nutrient enrichment correlated positively whereas performance responses to OAW and hypoxia anti-correlated. This indicates (i) that families robust to one of the three drivers (OA, OW, nutrients) will also not suffer from the two other shifts, and vice versa and (ii) families benefitting from OAW will more easily succumb to hypoxia. Our results may imply that selection under either OA, OW or eutrophication would enhance performance under the other two drivers but simultaneously render the population more susceptible to hypoxia. We conclude that intraspecific response correlations have a high potential to boost or hinder adaptation to multifactorial global change scenarios.

Continue reading ‘Sensitivities to global change drivers may correlate positively or negatively in a foundational marine macroalga’


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