Posts Tagged 'morphology'

Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis

The rapidly intensifying process of ocean acidification (OA) due to anthropogenic CO2 is not only depleting carbonate ions necessary for calcification but also causing acidosis and disrupting internal pH homeostasis in several marine organisms. These negative consequences of OA on marine calcifiers, i.e. oyster species, have been very well documented in recent studies; however, the consequences of reduced or impaired calcification on the end-product, shells or skeletons, still remain one of the major research gaps. Shells produced by marine organisms under OA are expected to show signs of dissolution, disorganized microstructure and reduced mechanical properties. To bridge this knowledge gap and to test the above hypothesis, we investigated the effect of OA on juvenile shells of the commercially important oyster species, Magallana angulata, at ecologically and climatically relevant OA levels (using pH 8.1, 7.8, 7.5, 7.2). In lower pH conditions, a drop of shell hardness and stiffness was revealed by nanoindentation tests, while an evident porous internal microstructure was detected by scanning electron microscopy. Crystallographic orientation, on the other hand, showed no significant difference with decreasing pH using electron back-scattered diffraction (EBSD). These results indicate the porous internal microstructure may be the cause of the reduction in shell hardness and stiffness. The overall decrease of shell density observed from micro-computed tomography analysis indicates the porous internal microstructure may run through the shell, thus inevitably limiting the effectiveness of the shell’s defensive function. This study shows the potential deterioration of oyster shells induced by OA, especially in their early life stage. This knowledge is critical to estimate the survival and production of edible oysters in the future ocean.

Continue reading ‘Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis’

Climate change does not affect seafood quality of a common targeted fish

Climate change can affect marine and estuarine fish via alterations to their distributions, abundances, sizes, physiology and ecological interactions, threatening the provision of ecosystem goods and services. While we have an emerging understanding of such ecological impacts to fish, we know little about the potential influence of climate change on the provision of nutritional seafood to sustain human populations. In particular, the quantity, quality and/or taste of seafood may be altered by future environmental changes with implications for the economic viability of fisheries. In an orthogonal mesocosm experiment, we tested the influence of near‐future ocean warming and acidification on the growth, health and seafood quality of a recreationally and economically important fish, yellowfin bream (Acanthopagrus australis). The growth of yellowfin bream significantly increased under near‐future temperature conditions (but not acidification), with little change in health (blood glucose and haematocrit) or tissue biochemistry and nutritional properties (fatty acids, lipids, macro‐and micronutrients, moisture, ash, and total N). Yellowfin bream appear to be highly resilient to predicted near‐future ocean climate change, which might be facilitated by their broad spatio‐temporal distribution across habitats and broad diet. Moreover, an increase in growth, but little change in tissue quality, suggests that near‐future ocean conditions will benefit fisheries and fishers that target yellowfin bream. The data reiterate the inherent resilience of yellowfin bream as an evolutionary consequence of their euryhaline status in often environmentally challenging habitats, and imply their sustainable and viable fisheries into the future.We contend that widely‐distributed species that span large geographic areas and habitats can be “climate‐winners” by being resilient to negative direct impacts of near‐future oceanic and estuarine climate change.
Continue reading ‘Climate change does not affect seafood quality of a common targeted fish’

Adult Antarctic krill proves resilient in a simulated high CO2 ocean

Antarctic krill (Euphausia superba) have a keystone role in the Southern Ocean, as the primary prey of Antarctic predators. Decreases in krill abundance could result in a major ecological regime shift, but there is limited information on how climate change may 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. Here we show that, in the laboratory, adult krill are able to survive, grow, store fat, mature, and maintain respiration rates when exposed to near-future ocean acidification (1000–2000 μatm pCO2) for one year. Despite differences in seawater pCO2 incubation conditions, adult krill are able to actively maintain the acid-base balance of their body fluids in near-future pCO2, which enhances their resilience to ocean acidification.

Continue reading ‘Adult Antarctic krill proves resilient in a simulated high CO2 ocean’

Condition of pteropod shells near a volcanic CO2 vent region

Highlights

 • in situ shell dissolution and change in shell biomass were the predominant features observed in the live pteropods collected within and nearby CO2 vent regions.

• Low pteropod biomass shells (collected nearby the CO2 vents) were more fragile and therefore more prone to fracture than the more robust, high biomass shells (collected in the control stations).

• In the Gulf of Naples, intermittent shifts away from optimum Ωar values can significantly affect pteropod calcification despite waters remaining oversaturated.

Abstract

Natural gradients of pH in the ocean are useful analogues for studying the projected impacts of Ocean Acidification (OA) on marine ecosystems. Here we document the in situ impact of submarine CO2 volcanic emissions (CO2 vents) on live shelled-pteropods (planktonic gastropods) species Creseis conica in the Gulf of Naples (Tyrrhenian Sea, Mediterranean). Since the currents inside the Gulf will likely drive those pelagic calcifying organisms into and out of the CO2 vent zones, we assume that pteropods will be occasionally exposed to the vents during their life cycle. Shell degradation and biomass were investigated in the stations located within and nearby the CO2 vent emission in relation to the variability of sea water carbonate chemistry. A relative decrease in shell biomass (22%), increase in incidence of shell fractures (38%) and extent of dissolution were observed in Creseis conica collected in the Gulf of Naples compared to those from the Northern Tyrrhenian Sea (control stations). These results suggest that discontinuous but recurrent exposure to highly variable carbonate chemistry could consistently affect the characteristic of the pteropod shells.

Continue reading ‘Condition of pteropod shells near a volcanic CO2 vent region’

Responses to climate change of the sea urchin (Pseudechinus sp.) and sea star (Odontaster validus) through hybridisation, local adaptations and transgenerational plasticity

Climate change, through ocean warming and ocean acidification, can affect the life cycles and population dynamics of marine species, which react by developing acclimation mechanisms. Sea urchins (Pseudechinus sp.) may hybridise with sympatric species or induce local adaptations geographically and sea stars (Odontaster validus) may develop transgenerational plasticity (TGP) in response to climate change. I studied their stress responses and if they developed potential acclimation capacity against climate change.

Continue reading ‘Responses to climate change of the sea urchin (Pseudechinus sp.) and sea star (Odontaster validus) through hybridisation, local adaptations and transgenerational plasticity’

Ocean warming, but not acidification, accelerates seagrass decomposition under near-future climate scenarios

The majority of marine macrophyte production is not consumed by herbivores but instead is channeled into detrital pathways where it supports biodiversity and drives coastal productivity, nutrient cycling and blue carbon sequestration. While it is clear that detrital pathways will be affected by ocean climate change, the relative importance of changing temperature or pH, or their interactions, has not been assessed. We used outdoor mesocosm experiments to assess the relative importance of ocean warming, acidification and latitude of litter origin on the decomposition and biomechanical properties of seagrass Zostera muelleri. Seagrass, collected from 2 sites at each of 2 latitudes (29° and 35°S), was subjected to an orthogonal combination of current and predicted future ocean warming (+3°C) and acidification (-0.3 pH unit). Elevated temperatures resulted in a 15% greater loss of seagrass detrital mass. Mass loss of seagrass detritus was also greater in seagrass from higher than from lower latitudes. The stiffness (Young’s modulus) of decomposing seagrass was greater at 22°C than at 25°C. Elevated sea temperatures also weakened decomposing seagrass, but the magnitude of these effects was greater for Z. muelleri originating from higher than from lower latitudes. Overall, ocean warming is likely to have a much larger influence on seagrass decomposition than ocean acidification. As climate changes, however, if seagrass from higher latitudes takes on similar characteristics to seagrass currently growing at lower latitudes, there may be a negative feedback against the impacts of ocean warming on decomposition, moderating changes in associated primary and secondary productivity that supports coastal fisheries and ecosystem processes.

Continue reading ‘Ocean warming, but not acidification, accelerates seagrass decomposition under near-future climate scenarios’

Coral reef carbonate budgets and ecological drivers in the central Red Sea – a naturally high temperature and high total alkalinity environment

The structural framework provided by corals is crucial for reef ecosystem function and services, but high seawater temperatures can be detrimental to the calcification capacity of reef-building organisms. The Red Sea is very warm, but total alkalinity (TA) is naturally high and beneficial for reef accretion. To date, we know little about how such detrimental and beneficial abiotic factors affect each other and the balance between calcification and erosion on Red Sea coral reefs, i.e., overall reef growth, in this unique ocean basin. To provide estimates of present-day reef growth dynamics in the central Red Sea, we measured two metrics of reef growth, i.e., in situ net-accretion/-erosion rates (Gnet) determined by deployment of limestone blocks and ecosystem-scale carbonate budgets (Gbudget), along a cross-shelf gradient (25km, encompassing nearshore, midshore, and offshore reefs). Along this gradient, we assessed multiple abiotic (i.e., temperature, salinity, diurnal pH fluctuation, inorganic nutrients, and TA) and biotic (i.e., calcifier and epilithic bioeroder communities) variables. Both reef growth metrics revealed similar patterns from nearshore to offshore: net-erosive, neutral, and net-accretion states. The average cross-shelf Gbudget was 0.66kg CaCO3m−2yr−1, with the highest budget of 2.44kg CaCO3m−2yr−1 measured in the offshore reef. These data are comparable to the contemporary Gbudgets from the western Atlantic and Indian oceans, but lie well below optimal reef production (5–10kg CaCO3m−2yr−1) and below maxima recently recorded in remote high coral cover reef sites. However, the erosive forces observed in the Red Sea nearshore reef contributed less than observed elsewhere. A higher TA accompanied reef growth across the shelf gradient, whereas stronger diurnal pH fluctuations were associated with negative carbonate budgets. Noteworthy for this oligotrophic region was the positive effect of phosphate, which is a central micronutrient for reef building corals. While parrotfish contributed substantially to bioerosion, our dataset also highlights coralline algae as important local reef builders. Altogether, our study establishes a baseline for reef growth in the central Red Sea that should be useful in assessing trajectories of reef growth capacity under current and future ocean scenarios.

Continue reading ‘Coral reef carbonate budgets and ecological drivers in the central Red Sea – a naturally high temperature and high total alkalinity environment’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book