Posts Tagged 'mollusks'



Nano-TiO2 impairs digestive enzyme activities of marine mussels under ocean acidification

Highlights
• Effects of OA and nano-TiO2 on the digestive enzyme activity of mussels were studied.

• The Seven-day recovery was not sufficient for digestive enzymes to fully recover.

• Nano-TiO2 showed greater negative effects compared with low pH.

• Significant interactions between low pH and nano-TiO2 occurred.

Abstract
With the development of nanotechnology and increased nanomaterial application, TiO2 nanoparticles have been released into the aquatic environment, causing potential ecotoxicological effects on aquatic organisms. Ocean acidification caused by anthropogenic CO2 is one of the most common environmental stressors, occurring simultaneously with marine contaminants, e.g., nanoparticles. Marine bivalves can accumulate nanoparticles and their digestive functions may be affected. In this study, we investigated the potential influences of TiO2 nanoparticles on the digestive enzyme activities of marine mussels Mytilus coruscus under ocean acidification. Mussels were exposed to combined treatments with three concentrations of nano-TiO2 (0, 2.5, 10 mg/L) and two pH values (8.1, 7.3) for 14 days, and then recovered under ambient condition (pH 8.1 and no nanoparticle) for 7 days. Samples were taken on the 1st, 3rd, 7th, 14th, and 21st day, the digestive enzymes, including amylase, pepsin, trypsin, lipase, and lysozyme, were investigated. Our results showed that nano-TiO2 and low pH had negative effects on amylase, pepsin, trypsin, and lipase, while both of them led an increase in lysozyme activity. Nano-TiO2 showed greater effects on the digestive capacity of M. coruscus rather than low pH. Moreover, a recovery period of 7 days was not sufficient for these enzymes to fully recover.

Continue reading ‘Nano-TiO2 impairs digestive enzyme activities of marine mussels under ocean acidification’

Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean

The Scotia Sea (Southern Ocean) is a hotspot of biodiversity, however, it is one of the fastest warming regions in the world alongside one of the first to experience ocean acidification (OA). Thecosome (shelled) pteropods are planktonic gastropods which can dominate the Scotia Sea zooplankton community, form a key component of the polar pelagic food web and are important contributors to carbon and carbonate fluxes. Pteropods have been identified as sentinel species for OA, since their aragonitic shells are vulnerable to dissolution in waters undersaturated with respect to aragonite.

In this thesis I investigate the impact of a changing ocean on the physiology and life history of pteropods in the Scotia Sea. Firstly, I culture early stage pteropods within OA and warming conditions predicted to occur in 2100 (Chapter 2). I demonstrate that larval shell morphology and survival rates are detrimentally affected in these conditions. Secondly, I constrain the life cycle and population dynamics of pteropods collected over a year from a sediment trap deployed on a moored platform (Chapter 3). I show that Limacina helicina and Limacina retroversa both have distinct life history strategies, although, spawning of both species corresponds to phytoplankton blooms. Thirdly, I establish a baseline vertical and biogeographical distribution of pteropods using historical samples (Chapter 4). I elucidate the geographical range edges of L. retroversa and L. helicina, as well as vertical migration patterns in relation to predation threat. Finally, I examine in-situ pteropod shell condition in relation to carbonate chemistry using net and oceanographic samples collected during two recent cruises (Chapter 5). I demonstrate that larval shells are susceptible to dissolution on exposure to aragonite undersaturation, however, later life stages display some resilience, since shell dissolution is confined to breaches in the periostracum. Overall, I recommend that continued monitoring, combined with bioassays and mesocosm work, will be essential in identifying the continued threat to pteropods from rapid environmental changes.

Continue reading ‘Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean’

Cuttlefish early development and behavior under future high CO2 conditions

The oceanic uptake of carbon dioxide (CO2) is increasing and changing the seawater chemistry, a phenomenon known as ocean acidification (OA). Besides the expected physiological impairments, there is an increasing evidence of detrimental OA effects on the behavioral ecology of certain marine taxa, including cephalopods. Within this context, the main goal of this study was to investigate, for the first time, the OA effects (∼1000 μatm; ΔpH = 0.4) in the development and behavioral ecology (namely shelter-seeking, hunting and response to a visual alarm cue) of the common cuttlefish (Sepia officinalis) early life stages, throughout the entire embryogenesis until 20 days after hatching. There was no evidence that OA conditions compromised the cuttlefish embryogenesis – namely development time, hatching success, survival rate and biometric data (length, weight and Fulton’s condition index) of newly hatched cuttlefish were similar between the normocapnic and hypercapnic treatments. The present findings also suggest a certain behavioral resilience of the cuttlefish hatchlings toward near-future OA conditions. Shelter-seeking, hunting and response to a visual alarm cue did not show significant differences between treatments. Thus, we argue that cuttlefishes’ nekton-benthic (and active) lifestyle, their adaptability to highly dynamic coastal and estuarine zones, and the already harsh conditions (hypoxia and hypercapnia) inside their eggs provide a degree of phenotypic plasticity that may favor the odds of the recruits in a future acidified ocean. Nonetheless, the interacting effects of multiple stressors should be further addressed, to accurately predict the resilience of this ecologically and economically important species in the oceans of tomorrow.

Continue reading ‘Cuttlefish early development and behavior under future high CO2 conditions’

Effects of seasonal upwelling and runoff on water chemistry and growth and survival of native and commercial oysters

The effects of climate change, including ocean acidification and ocean heatwaves, on biological communities in estuaries are often uncertain. Part of the uncertainty is due to the complex suite of environmental factors in addition to acidification and warming that influence the growth of shells and skeletons of many estuarine organisms. The goal of this study was to document spatial and temporal variation in water column properties and to measure the in situ effects on larval and recently settled stages of ecologically important Olympia oysters (Ostrea lurida) and commercially important Pacific oysters (Crassostrea gigas) in a low‐inflow estuary with a Mediterranean climate in Northern California. Our results reveal that seasonal inputs of upwelled or riverine water create important and predictable gradients of carbonate system parameters, temperature, salinity, dissolved oxygen (DO), and other variables that influence oyster performance, and that the influence of these gradients is contingent upon the location in the estuary as well as seasonal timing. During upwelling events (dry season), temperature, carbonate chemistry, and DO had the greatest impact on oyster performance. During runoff events (wet season), gradients in salinity, nutrient concentrations, and total alkalinity driven by river discharge were comparatively more important. These results suggest that the spatial importance of carbonate chemistry and temperature are seasonally variable and are two of several other factors that determine oyster performance. We use these results to discuss future impacts on oysters given projected regional changes in the frequency and magnitude of upwelling and precipitation‐driven runoff events.

Continue reading ‘Effects of seasonal upwelling and runoff on water chemistry and growth and survival of native and commercial oysters’

Behavioral response of eastern oyster Crassostrea virginica larvae to a chemical settlement cue is not impaired by low pH

Ocean acidification poses a major threat to marine organisms, but little is known about how pH affects larval behavior. The transition from a pelagic larval stage to adult life in the benthos, known as settlement, is a critical period in invertebrate life-histories and is influenced by larval responses to multiple chemical and physical settlement cues. We investigated the effects of low pH on the swimming behavior during settlement of the important reef-forming eastern oyster Crassostrea virginica, by tracking larval behaviors in ambient (8.1) and low (7.4) pH conditions, in the presence and absence of a chemical settlement cue. We hypothesized that low pH would impede the ability of C. virginica larvae to interpret or respond to the cue. In a preliminary experiment, observations of swimming behavior in larvae of 3 different stages (pre-competent, competent-to-settle, and post-competent) in the presence of the settlement cue showed no significant effect of pH on downward velocity or proportion of larvae remaining on bottom. This result indicates the response to the cue was not impaired by low pH. There were, however, trends in the proportion of larvae remaining on the bottom or swimming in helices, both in the presence and absence of the cue, that suggested larvae in one or more stages may have become more active or exploratory in low pH. Results from a follow-up experiment confirmed the lack of a significant effect of pH on larval response to the cue, but did not demonstrate a consistent or significant effect of pH on larval activity or exploration.

Continue reading ‘Behavioral response of eastern oyster Crassostrea virginica larvae to a chemical settlement cue is not impaired by low pH’

De novo transcriptome assembly and gene expression profile of thermally challenged green abalone (Haliotis fulgens: Gastropoda) under acute hypoxia and hypercapnia

Highlights

• Abalone gene expression under warming, hypoxia, and hypercapnia, individually and combined.

• The response reflects enhanced damage control at the expense of energy metabolism.

• Gene networks of gill and muscle conform with different levels of thermal sensitivity.

• Warming combined with hypercapnia and hypoxia enhanced mitochondrial capacity.

Abstract

Transcriptional regulation constitutes a rapid response of marine organisms facing stressful environmental conditions, such as the concomitant exposure to warming, ocean acidification and hypoxia under climate change. In previous studies, we investigated whole-organism physiological patterns and cellular metabolism in gill and muscle of the marine gastropod Haliotis fulgens in response to increasing temperature (18 °C to 32 °C at +3 °C per day) under hypoxia (50% air saturation), hypercapnia (1000 μatm pCO2) and both factors combined. Here, we report investigations of the molecular responses of H. fulgens to temperature and identify mechanisms concomitantly affected by hypoxia and hypercapnia. A de novo transcriptome assembly with subsequent quantitative PCR and correlation network analysis of genes involved in the molecular response were used to unravel the correlations between gene expression patterns under the different experimental conditions. The correlation networks identified a shift from the expression of genes involved in energy metabolism (down-regulated) to the up-regulation of Hsp70 during warming under all experimental conditions in gill and muscle, indicating a strong up-regulation of damage prevention and repair systems at sustained cellular energy production. However, a higher capacity for anaerobic succinate production was evicted in gill, matching with observations from our previous studies indicating succinate accumulation in gill but not in muscle. Additionally, warming under hypoxia and hypercapnia kept mRNA levels of citrate synthase in both tissues unchanged following a similar pattern as muscle enzyme capacity from a previous study, suggesting an emphasis on maintaining rather than down-regulating mitochondrial activity.

Continue reading ‘De novo transcriptome assembly and gene expression profile of thermally challenged green abalone (Haliotis fulgens: Gastropoda) under acute hypoxia and hypercapnia’

Biological modification of seawater chemistry by an ecosystem engineer, the California mussel, Mytilus californianus

Marine habitat‐forming species often play critical roles on rocky shores by ameliorating stressful conditions for associated organisms. Such ecosystem engineers provide structure and shelter, for example, by creating refuges from thermal and desiccation stresses at low tide. Less explored is the potential for habitat formers to alter interstitial seawater chemistry during their submergence. Here, we quantify the capacity for dense assemblages of the California mussel, Mytilus californianus, to change seawater chemistry (dissolved O2, pH, and total alkalinity) within the interiors of mussel beds at high tide via respiration and calcification. We established a living mussel bed within a laboratory flow tank and measured vertical pH and oxygen gradients within and above the mussel bed over a range of water velocities. We documented decreases of up to 0.1 pH and 25 μmol O2 kg−1 internal to the bed, along with declines of 100 μmol kg−1 in alkalinity, when external flows were  95% of the time. Reductions in pH and O2 inside mussel beds may negatively impact resident organisms and exacerbate parallel human‐induced perturbations to ocean chemistry while potentially selecting for improved tolerance to altered chemistry conditions.

Continue reading ‘Biological modification of seawater chemistry by an ecosystem engineer, the California mussel, Mytilus californianus’


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Ocean acidification in the IPCC AR5 WG II

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