Posts Tagged 'mortality'

Adult exposure to ocean acidification and warming remains beneficial for oyster larvae following starvation

Climate change is expected to warm and acidify oceans and alter the phenology of phytoplankton, creating a mismatch between larvae and their food. Transgenerational plasticity (TGP) may allow marine species to acclimate to climate change; however, it is expected that this may come with elevated energetic demands. This study used the oysters, Saccostrea glomerata and Crassostrea gigas, to test the effects of adult parental exposure to elevated pCO2 and temperature on larvae during starvation and recovery. It was anticipated that beneficial effects of TGP will be limited when larvae oyster are starved. Transgenerational responses and lipid reserves of larvae were measured for 2 weeks. Larvae of C. gigas and S. glomerata from parents exposed to elevated pCO2 had greater survival when exposed to elevated CO2, but this differed between species and temperature. For S. glomerata, survival of larvae was greatest when the conditions experienced by larvae matched the condition of their parents. For C. gigas, survival of larvae was greater when parents and larvae were exposed to elevated pCO2. Larvae of both species used lipids when starved. The total lipid content was dependent on parental exposure and temperature. Against expectations, the beneficial TGP responses of larvae remained, despite starvation.

Continue reading ‘Adult exposure to ocean acidification and warming remains beneficial for oyster larvae following starvation’

Viral-mediated microbe mortality modulated by ocean acidification and eutrophication: consequences for the carbon fluxes through the microbial food web

Anthropogenic carbon emissions are causing changes in seawater carbonate chemistry including a decline in the pH of the oceans. While its aftermath for calcifying microbes has been widely studied, the effect of ocean acidification (OA) on marine viruses and their microbial hosts is controversial, and even more in combination with another anthropogenic stressor, i.e., human-induced nutrient loads. In this study, two mesocosm acidification experiments with Mediterranean waters from different seasons revealed distinct effects of OA on viruses and viral-mediated prokaryotic mortality depending on the trophic state and the successional stage of the plankton community. In the winter bloom situation, low fluorescence viruses, the most abundant virus-like particle (VLP) subpopulation comprising mostly bacteriophages, were negatively affected by lowered pH with nutrient addition, while the bacterial host abundance was stimulated. High fluorescence viruses, containing cyanophages, were stimulated by OA regardless of the nutrient conditions, while cyanobacteria of the genus Synechococcus were negatively affected by OA. Moreover, the abundance of very high fluorescence viruses infecting small haptophytes tended to be lower under acidification while their putative hosts’ abundance was enhanced, suggesting a direct and negative effect of OA on viral–host interactions. In the oligotrophic summer situation, we found a stimulating effect of OA on total viral abundance and the viral populations, suggesting a cascading effect of the elevated pCO2 stimulating autotrophic and heterotrophic production. In winter, viral lysis accounted for 30 ± 16% of the loss of bacterial standing stock per day (VMMBSS) under increased pCO2 compared to 53 ± 35% in the control treatments, without effects of nutrient additions while in summer, OA had no significant effects on VMMBSS (35 ± 20% and 38 ± 5% per day in the OA and control treatments, respectively). We found that phage production and resulting organic carbon release rates significantly reduced under OA in the nutrient replete winter situation, but it was also observed that high nutrient loads lowered the negative effect of OA on viral lysis, suggesting an antagonistic interplay between these two major global ocean stressors in the Anthropocene. In summer, however, viral-mediated carbon release rates were lower and not affected by lowered pH. Eutrophication consistently stimulated viral production regardless of the season or initial conditions. Given the relevant role of viruses for marine carbon cycling and the biological carbon pump, these two anthropogenic stressors may modulate carbon fluxes through their effect on viruses at the base of the pelagic food web in a future global change scenario.

Continue reading ‘Viral-mediated microbe mortality modulated by ocean acidification and eutrophication: consequences for the carbon fluxes through the microbial food web’

The effects on low pH on sea urchin larval survivorship and development

In recent decades, increasing atmospheric CO2 levels have contributed to the acidification of the world’s oceans. Seawater absorbs CO2 from the atmosphere, which, through a series of chemical reactions, causes an increase in free hydrogen ions and a subsequent decrease in carbonate ions. This adversely affects marine organisms, including sea urchins, since carbonate is critical for building calcium carbonate structures such as shells, without which organisms can die. Declines in urchin populations can have ecological and economic effects, as urchins play critical roles in maintaining ecological balance in marine habitats and are important commercially harvested invertebrates. Larval marine organisms are particularly vulnerable, and increased deformities and mortality are expected in more acidic environments. Therefore, we exposed green sea urchin (Lytechinus variegatus) larvae to different pH levels and examined the effects on development and mortality. Fertilized eggs were reared in seawater with environmentally realistic pH values ranging from pH 7.8 to pH 8.2 (normal seawater), and a larval sample from each treatment was collected every 24 hours for 7 – 10 days. Mortality was documented by counting dead larvae, and development was assessed by comparing morphology among the control and treatment groups. In general, both mortality and morphological abnormalities showed inverse correlations with pH, with the highest mortality rate and most severe abnormalities occurring in larvae exposed to the lowest pH seawater. Larval development was also somewhat delayed in urchin larvae exposed to low pH seawater. These results suggest that acidic seawater, at pH values currently found in the world’s oceans, can adversely affect sea urchin larval development, which can, in turn, have negative ecological and economic consequences.

Continue reading ‘The effects on low pH on sea urchin larval survivorship and development’

Ocean acidification induces changes in virus–host relationships in Mediterranean benthic ecosystems

Acidified marine systems represent “natural laboratories”, which provide opportunities to investigate the impacts of ocean acidification on different living components, including microbes. Here, we compared the benthic microbial response in four naturally acidified sites within the Southern Tyrrhenian Sea characterized by different acidification sources (i.e., CO2 emissions at Ischia, mixed gases at Panarea and Basiluzzo and acidified freshwater from karst rocks at Presidiana) and pH values. We investigated prokaryotic abundance, activity and biodiversity, viral abundance and prokaryotic infections, along with the biochemical composition of the sediment organic matter. We found that, despite differences in local environmental dynamics, viral life strategies change in acidified conditions from mainly lytic to temperate lifestyles (e.g., chronic infection), also resulting in a lowered impact on prokaryotic communities, which shift towards (chemo)autotrophic assemblages, with lower organic matter consumption. Taken together, these results suggest that ocean acidification exerts a deep control on microbial benthic assemblages, with important feedbacks on ecosystem functioning.

Continue reading ‘Ocean acidification induces changes in virus–host relationships in Mediterranean benthic ecosystems’

Ocean acidification but not elevated spring warming threatens a European Seas predator

Highlights

  • Treatments in marine climate research often ignore important, natural variation
  • Fish embryos were exposed to stable versus warming temperatures (T) and high pCO2
  • Development, hatching and metabolism of a predatory fish (garfish) were examined
  • Increased spring warming benefitted garfish but stable high T and pCO2 were lethal
  • Allospecific prey of garpike have adapted suggesting future, trophodynamic change

Abstract

Ocean acidification has the potential to negatively affect marine ecosystems by influencing the development and metabolism of key members of food webs. The garfish, Belone belone, is an ecologically important predator in European regional seas and it remains unknown how this species will be impacted by projected changes in climate. We artificially fertilized and reared garfish embryos until hatch at present (400 μatm) and future (1300 μatm) pCO2 levels within three temperature treatments, i.e. two daily warming regimes and one constant high temperature (17°C). For the two warming treatments, embryos were fertilized at 13°C and experienced 0.1 or 0.3°C/day warming. The 0.1°C/day treatment served as control: 13°C was the in situ temperature of parental fish in the Southwest Baltic Sea and 0.1°C/day is the average warming rate experienced by embryos of this population in nature. Survival was drastically reduced at both future pCO2 and at the constant high temperature while the highest survival in any treatment was observed at 0.3°C/day warming. The proportion of embryos with morphological deformities increased with elevated pCO2 but not temperature. Hatch characteristics and physiological measures such as heart rate and critical thermal ranges, however, were not affected by pCO2 but were influenced by temperature. Our results suggest that garfish in the Baltic Sea will benefit from projected increased rates of spring warming but not the concomitant increase in pCO2. Previous studies on the impacts of ocean acidification on resident fishes in the Baltic Sea indicate that this piscivorous fish is at higher risk compared to its prey which may have broader implications for the future trophodynamic structure and function of the coastal food web.

Continue reading ‘Ocean acidification but not elevated spring warming threatens a European Seas predator’

Transgenerational plasticity responses of oysters to ocean acidification differ with habitat

Transgenerational plasticity (TGP) has been identified as a critical mechanism of acclimation which may buffer marine organisms against climate change, yet whether the TGP response of marine organisms is altered depending on their habitat is unknown. Many marine organisms are found in intertidal zones where they experience episodes of emersion daily as the tide rises and recedes. During episodes of emersion, the accumulation of metabolic carbon dioxide (CO2) leads to hypercapnia for many species. How this metabolic hypercapnia impacts the TGP response of marine organisms to climate change is unknown as all previous transgenerational studies have been done under subtidal conditions, where parents are constantly immersed. Herein, we assess the capacity of the ecologically and economically important oyster, Saccostrea glomerata to acclimate to elevated CO2 dependent on habitat, across its vertical distribution, from the subtidal to intertidal zone. Tidal habitat altered both the existing tolerance and transgenerational response of S. glomerata to elevated CO2. Overall, larvae from parents conditioned in an intertidal habitat had a greater existing tolerance to elevated CO2 than larvae from parents conditioned in a subtidal habitat but had a lower capacity for beneficial TGP following parental exposure to elevated CO2. Our results suggest that the transgenerational plasticity responses of marine species will not be uniform across their distribution and highlights the need to consider the habitat of a species when assessing TGP responses to climate change stressors.

Continue reading ‘Transgenerational plasticity responses of oysters to ocean acidification differ with habitat’

Transgenerational responses to seawater pH in the edible oyster, with implications for the mariculture of the species under future ocean acidification

Highlights

• Larval offspring of C. hongkongensis were resilient to OA exposure

• Phenotypic traits in out-planted juveniles improved with parental exposure

• Positive carry-over effect from exposed parents persisted and manifested in the estuary

• Linking multiple life stages is vital to assess OA-induced carry-over capacity

• OA exposure at early life stages revealed potential mariculture application and species fitness

Abstract

The majority of common edible oysters are projected to grow more slowly and have smaller impaired shells because of anthropogenic CO2-induced reductions in seawater carbonate ion concentration and pH, a process called ocean acidification (OA). Recent evidence has shown that OA has carryover effects, for example, larvae exposed to OA will also exhibit either positive or negative effects after metamorphosis. This study examined the hidden carryover effects of OA exposure during parental and larval stages on post-metamorphic traits of the commercially important oyster species Crassostrea hongkongensis. Adults of C. hongkongensis were exposed to control pH (pHNBS 8.0) and OA-induced low pH (pHNBS 7.4) conditions. Their larval offspring were then exposed to the same aquarium conditions before being out-planted as post-metamorphic juveniles at a mariculture site for 10 months. Initially, larval offspring were resilient to low pH with or without parental exposure. The larvae exposed to low pH had significantly faster development and higher percentage of settlement success compared to control groups. The out-planted juveniles with parental exposure had improved survival and growth compared to juveniles without parental exposure, regardless of the larval exposure history. This implies that transgenerational effects due to parental exposure not only persists but also have a greater influence than the within-generational effects of larval exposure. Our results shed light on the importance of linking the various life history stages when assessing the OA-induced carryover capacity of C. hongkongensis in the natural environment. Understanding these linked relationships helps us better predict the species rapid adaptation responses in the face of changing coastal conditions due to OA.

Continue reading ‘Transgenerational responses to seawater pH in the edible oyster, with implications for the mariculture of the species under future ocean acidification’

Will community calcification reflect reef accretion on future, degraded coral reefs?

Coral bleaching events continue to drive the degradation of coral reefs worldwide, causing a shift in the benthic community from coral to algae dominated ecosystems. Critically, this shift may decrease the capacity of degraded coral reef communities to maintain net positive accretion during warming-driven stress events (e.g., reef-wide coral bleaching). Here we measured rates of net ecosystem calcification (NEC) and net ecosystem production (NEP) on a degraded coral reef lagoon community (coral cover < 10 % and algae cover > 20 %) during a reef-wide bleaching event in February of 2020 at Heron Island on the Great Barrier Reef. We found that during this bleaching event, rates of community NEP and NEC across replicate transects remained positive and did not change in response to bleaching. Repeated benthic surveys over a period of 20 d indicated an increase in the percent area of bleached coral tissue, corroborated by relatively low Symbiodiniaceae densities (~0.6 × 106 cm−2) and dark-adapted photosynthetic yields in photosystem II of corals (~0.5) sampled along each transect over this period. Given that a clear decline in coral health was not reflected in the overall community NEC estimates, it is possible that elevated temperatures in the water column that compromise coral health enhanced the thermodynamic favourability for calcification in other, ahermatypic benthic calcifiers. These data suggest that positive NEC on degraded reefs may not equate to the net positive accretion of reef structure in a future, warmer ocean. Critically, our study highlights that if coral cover continues to decline as predicted, NEC may no longer be an appropriate proxy for reef growth as the proportion of the community NEC signal owed to ahermatypic calcification increases and coral dominance on the reef decreases.

Continue reading ‘Will community calcification reflect reef accretion on future, degraded coral reefs?’

Does acidification lead to impairments on oxidative status and survival of orange clownfish Amphiprion percula juveniles?

The nitrification process in recirculating aquaculture systems can reduce water pH. Fish can also be exposed to water acidification during transport, an important feature in the aquarium industry, as live fish can be kept in a closed environment for more than 24 h during overseas aerial transportation. Therefore, it is important to study the responses of fish to acidic environments. We investigated the impacts of acute exposure to decreasing pH levels in orange clownfish Amphiprion percula juveniles on their survival and oxidative stress status. Fish were exposed to pH 5, 6, 7, and 8 for 96 h. We observed a significant reduction in survival (85%) and protein damage as measured by P-SH (protein thiol) for fish maintained at pH 5. Despite no effects on survival or oxidative damage, fish exposed to pH 6 showed an increase in their antioxidant defense systems, demonstrating this pH level could not be suitable for them as well. Furthermore, there were no negative effects for fish kept at pH 7, compared to those maintained at pH 8 during this short-term evaluation.

Continue reading ‘Does acidification lead to impairments on oxidative status and survival of orange clownfish Amphiprion percula juveniles?’

Multiple-stressor effects of warming and acidification on the embryonic development of an estuarine fiddler crab

Highlights

  • Elevated temperature accelerated early and late embryonic development.
  • Reduced pH accelerated late embryonic development.
  • Elevated temperature reduced survivorship in later stages.
  • A negative synergetic effect between pH and temperature was evidenced in egg volume.
  • > 70% of embryos well-developed under elevated temperature and reduced pH.

Abstract

Predicted effects of anthropogenic climate change on estuarine and coastal organisms are complex, and early life history stages of calcified ectotherms are amongst the most sensitive groups. Despite the importance of understanding their vulnerability, we lack information on the effects of multiple stressors on the embryonic development of estuarine and burrowing organisms, mainly mangrove-associated species. Here, we determined the combined effects of elevated temperature and decreased pH on the embryonic development of the estuarine fiddler crab Leptuca thayeri. Initially, the microhabitat (burrow) of ovigerous (egg-bearing) females was measured for temperature, pH, and salinity, which provided control values in our laboratory experiment. Embryos at the early stage of development were subjected to cross-factored treatments of predicted temperature and pH and evaluated for development rate, survivorship, and volume until their later embryonic stage. Embryo development was faster at early and later stages of development, and survivorship was lower under elevated temperature. Embryos under reduced pH showed advanced embryonic stages at their late development stage. Higher egg volume was observed in a warmer and acidified environment, and lower volume in warmer and non-acidified conditions, indicating that embryo development is synergistically affected by warming and acidification. More than 70% of embryos developed until late stages under the multiple-stressors treatment, giving insights on the effects of a warm and acidified environment on burrowing estuarine organisms and their early stages of development.

Continue reading ‘Multiple-stressor effects of warming and acidification on the embryonic development of an estuarine fiddler crab’

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