Archive for the 'Science' Category

Ocean acidification affects calcareous tube growth in adult stage and reared offspring of serpulid polychaetes

The energetically costly transition from free-swimming larvae to benthic life stage and maintenance of a calcareous structure can make calcifying marine invertebrates vulnerable to ocean acidification. The first goal of this study was to evaluate the impacts of ocean acidification on calcified tube growth for two Serpulidae polychaete worms. Spirorbis sp. and Spirobranchus triqueter were collected at 11 m depth from the Northwest Mediterranean Sea and maintained for 30 and 90 d, at three mean pHT levels (total scale) of 8.1 (ambient), 7.7, and 7.4. Moderately decreased tube elongation rates were observed in both species at a pHT of 7.7 while severe reductions occurred at pHT 7.4. There was visual evidence of dissolution and tubes were more fragile at lower pH but, fragility was not attributed to changes in fracture toughness. Instead, it appeared to be due to the presence of larger alveoli covered in a thinner calcareous layer. The second objective of the study was to test for effects in offspring development of the species S. triqueter. Spawning was induced, and offspring were reared in the same pH conditions the parents experienced. Trochophore size was reduced at the lowest pH level but settlement success was similar across pH conditions. Post-settlement tube growth was most affected. At 38 d post-settlement, juvenile tubes at pHT of 7.7 and 7.4 were half the size of those at pHT 8.1. Results suggest future carbonate chemistry will negatively affect initiation and persistence of both biofouling and epiphytic polychaete tube worms.

Continue reading ‘Ocean acidification affects calcareous tube growth in adult stage and reared offspring of serpulid polychaetes’

Impact of climate change on the American lobster (Homarus americanus): Physiological responses to combined exposure of elevated temperature and pCO2

• Climate Change (2300 scenario) has a significant impact on the acid-base status in H. americanus.

• Climate Change causes retention of ammonia in hemolymph.

• Under Climate Change conditions hemolymph pCO2 does NOT exceed environmental pCO2.

• Climate Change causes increase in MO2 and ammonia excretion.

• Climate Change causes decrease in citrate synthase in tail muscle.

The physiological consequences of exposing marine organisms to predicted future ocean scenarios, i.e. simultaneous increase in temperature and pCO2, have only recently begun to be investigated. Adult American lobster (Homarus americanus) were exposed to either current (16 °C, 47 Pa pCO2, pH 8.10) or predicted year 2300 (20 °C, 948 Pa pCO2, pH 7.10) ocean parameters for 14–16 days prior to assessing physiological changes in their hemolymph parameters as well as whole animal ammonia excretion and resting metabolic rate. Acclimation of lobster simultaneously to elevated pCO2 and temperature induced a prolonged respiratory acidosis that was only partially compensated for via accumulation of extracellular HCO3– and ammonia. Furthermore, acclimated animals possessed significantly higher ammonia excretion and oxygen consumption rates suggesting that future ocean scenarios may increase basal energetic demands on H. americanus. Enzyme activity related to protein metabolism (glutamine dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) in hepatopancreas and muscle tissue were unaltered in future ocean scenario exposed animals; however, muscular citrate synthase activity was reduced suggesting that, while protein catabolism may be unchanged, the net energetic output of muscle may be compromised in future scenarios. Overall, H. americanus acclimated to ocean conditions predicted for the year 2300 appear to be incapable of fully compensating against climate change-related acid-base challenges and experience an increase in metabolic waste excretion and oxygen consumption. Combining our study with past literature on H. americanus suggests that the whole lifecycle from larvae to adult stages is at risk of severe growth, survival and reproductive consequences due to climate change.

Continue reading ‘Impact of climate change on the American lobster (Homarus americanus): Physiological responses to combined exposure of elevated temperature and pCO2’

Effects of ocean acidification on marine photosynthetic organisms under the concurrent influences of warming, UV radiation, and deoxygenation

The oceans take up over 1 million tons of anthropogenic CO2 per hour, increasing dissolved pCO2 and decreasing seawater pH in a process called ocean acidification (OA). At the same time greenhouse warming of the surface ocean results in enhanced stratification and shoaling of upper mixed layers, exposing photosynthetic organisms dwelling there to increased visible and UV radiation as well as to a decreased nutrient supply. In addition, ocean warming and anthropogenic eutrophication reduce the concentration of dissolved O2 in seawater, contributing to the spread of hypoxic zones. All of these global changes interact to affect marine primary producers. Such interactions have been documented, but to a much smaller extent compared to the responses to each single driver. The combined effects could be synergistic, neutral, or antagonistic depending on species or the physiological processes involved as well as experimental setups. For most calcifying algae, the combined impacts of acidification, solar UV, and/or elevated temperature clearly reduce their calcification; for diatoms, elevated CO2 and light levels interact to enhance their growth at low levels of sunlight but inhibit it at high levels. For most photosynthetic nitrogen fixers (diazotrophs), acidification associated with elevated CO2 may enhance their N2 fixation activity, but interactions with other environmental variables such as trace metal availability may neutralize or even reverse these effects. Macroalgae, on the other hand, either as juveniles or adults, appear to benefit from elevated CO2 with enhanced growth rates and tolerance to lowered pH. There has been little documentation of deoxygenation effects on primary producers, although theoretically elevated CO2 and decreased O2 concentrations could selectively enhance carboxylation over oxygenation catalyzed by ribulose-1,5-bisphosphate carboxylase/oxygenase and thereby benefit autotrophs. Overall, most ocean-based global change biology studies have used single and/or double stressors in laboratory tests. This overview examines the combined effects of OA with other features such as warming, solar UV radiation, and deoxygenation, focusing on primary producers.

Continue reading ‘Effects of ocean acidification on marine photosynthetic organisms under the concurrent influences of warming, UV radiation, and deoxygenation’

Physiological responses of a coccolithophore to multiple environmental drivers

• Coccolithophores were more stressful in the higher solar UV irradiance exposures.

• The cells increased their functional antennae sizes under the future ocean conditions.

• Coccolithophores photosynthesized more in the high CO2 and warming ocean.

• Synergistical or antagonistic interactions were observed among multiple drivers.

Ocean acidification is known to affect primary producers differentially in terms of species and environmental conditions, with controversial results obtained under different experimental setups. In this work we examined the physiological performances of the coccolithophore Gephyrocapsa oceanica that had been acclimated to 1000 μatm CO2 for ~400 generations, and then exposed to multiple drivers, light intensity, light fluctuating frequency, temperature and UV radiation. Here, we show that increasing light intensity resulted in higher non-photochemical quenching and the effective absorption cross-section of PSII. The effective photochemical efficiency (Fv′/Fm′) decreased with increased levels of light, which was counterbalanced by fluctuating light regimes. The greenhouse condition acts synergistically with decreasing fluctuating light frequency to increase the Fv′/Fm′ and photosynthetic carbon fixation rate. Our data suggest that the coccolithophorid would be more stressed with increased exposures to solar UV irradiances, though its photosynthetic carbon fixation could be enhanced under the greenhouse condition.

Continue reading ‘Physiological responses of a coccolithophore to multiple environmental drivers’

Characteristics of the carbonate system in a semiarid estuary that experiences summertime hypoxia

In oceanic environments, two sources of CO2 have been found to contribute to acidification of stratified water bodies, i.e., CO2 invasion due to anthropogenic atmospheric CO2 increase and respiration-produced CO2 from organic matter remineralization. Acidification caused by these CO2 sources has been observed frequently in numerous environments spanning from open continental shelves to enclosed estuaries. Here, we report observations on carbonate system dynamics in a relatively well-buffered lagoonal estuary, Corpus Christi Bay (CCB), in a semiarid subtropical region that is influenced by summertime hypoxia as well as strong evaporation and seagrass vegetation in the vicinity. While the relationship between dissolved oxygen (DO) and pH in the bottom waters of CCB was positive as in other coastal and estuarine environments prone to hypoxia, the slope was significantly less than in other systems. We attribute the high buffering capacity in CCB to the presence of abundant seagrass meadows adjacent to CCB and strong evaporation-produced density flow that delivers low CO2 waters to the bottom of CCB. Thus, despite the occurrence of hypoxia, neither bottom water carbonate saturation state with respect to aragonite (Ωarg) nor CO2 partial pressure (pCO2) reached critical levels, i.e., undersaturation (i.e., Ωarag1000 µatm), respectively.

Continue reading ‘Characteristics of the carbonate system in a semiarid estuary that experiences summertime hypoxia’

Spectrophotometric determination of pH and carbonate ion concentrations in seawater: choices, constraints and consequences

• Spectrophotometric pH and carbonate ion measurements in seawater.

• Different application platforms, such as shipboard, underway, in situ, etc.

• Quality improvement with indicator purification, sample pre-treatment, etc.

• Carbonate ion to be considered as the fifth parameter describing carbonate system.

Accurate and precise marine CO2 system measurements are important for marine carbon cycle research and investigations of ocean acidification. Seawater pH is important because it can be used to characterize a wide range of chemical and biogeochemical processes. Saturation states of calcium carbonate minerals, which are directly proportional to carbonate ion concentration ([CO32-]), influence biogenic calcification and rates of carbonate dissolution. Spectrophotometric pH and carbonate ion measurements can both benefit greatly from the high sensitivity, stability, consistency and processing speed made possible through automation. Spectrophotometric methods are well-suited for shipboard, underway and in situ deployments under harsh conditions. Spectrophotometric pH measurements typically have a reproducibility of 0.0004-0.001 for shipboard and laboratory measurements and 0.0014-0.004 for in situ measurements. Shipboard spectrophotometric measurements of [CO32-] are becoming common on research expeditions. This review highlights the development of methods and instrumentation for spectrophotometric pH and [CO32-] measurements, and discusses the pros and cons of current technology. A comprehensive summary of the analytical merits of different flow analysis instruments is given. Aspects of measurement protocols that bear on the quality of pH and [CO32-] measurements, such as indicator purification, sample pretreatment, etc., are also described. Based on three decades of experience with seawater analysis, this review includes method recommendations and perspectives directly applicable or potentially applicable to pH and [CO32-] analysis of seawater.

Continue reading ‘Spectrophotometric determination of pH and carbonate ion concentrations in seawater: choices, constraints and consequences’

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

OUP book