Posts Tagged 'community'

Modelling coral calcification accounting for the impacts of coral bleaching and ocean acidification (update)

Coral reefs are diverse ecosystems that are threatened by rising CO2 levels through increases in sea surface temperature and ocean acidification. Here we present a new unified model that links changes in temperature and carbonate chemistry to coral health. Changes in coral health and population are explicitly modelled by linking rates of growth, recovery and calcification to rates of bleaching and temperature-stress-induced mortality. The model is underpinned by four key principles: the Arrhenius equation, thermal specialisation, correlated up- and down-regulation of traits that are consistent with resource allocation trade-offs, and adaption to local environments. These general relationships allow this model to be constructed from a range of experimental and observational data. The performance of the model is assessed against independent data to demonstrate how it can capture the observed response of corals to stress. We also provide new insights into the factors that determine calcification rates and provide a framework based on well-known biological principles to help understand the observed global distribution of calcification rates. Our results suggest that, despite the implicit complexity of the coral reef environment, a simple model based on temperature, carbonate chemistry and different species can give insights into how corals respond to changes in temperature and ocean acidification.

Continue reading ‘Modelling coral calcification accounting for the impacts of coral bleaching and ocean acidification (update)’

Shallow water marine sediment bacterial community shifts along a natural CO2 gradient in the Mediterranean Sea off Vulcano, Italy

The effects of increasing atmospheric CO2 on ocean ecosystems are a major environmental concern, as rapid shoaling of the carbonate saturation horizon is exposing vast areas of marine sediments to corrosive waters worldwide. Natural CO2 gradients off Vulcano, Italy, have revealed profound ecosystem changes along rocky shore habitats as carbonate saturation levels decrease, but no investigations have yet been made of the sedimentary habitat. Here, we sampled the upper 2 cm of volcanic sand in three zones, ambient (median pCO2 419 μatm, minimum Ωarag 3.77), moderately CO2-enriched (median pCO2 592 μatm, minimum Ωarag 2.96), and highly CO2-enriched (median pCO2 1611 μatm, minimum Ωarag 0.35). We tested the hypothesis that increasing levels of seawater pCO2 would cause significant shifts in sediment bacterial community composition, as shown recently in epilithic biofilms at the study site. In this study, 454 pyrosequencing of the V1 to V3 region of the 16S rRNA gene revealed a shift in community composition with increasing pCO2. The relative abundances of most of the dominant genera were unaffected by the pCO2 gradient, although there were significant differences for some 5 % of the genera present (viz. Georgenia, Lutibacter, Photobacterium, Acinetobacter, and Paenibacillus), and Shannon Diversity was greatest in sediments subject to long-term acidification (>100 years). Overall, this supports the view that globally increased ocean pCO2 will be associated with changes in sediment bacterial community composition but that most of these organisms are resilient. However, further work is required to assess whether these results apply to other types of coastal sediments and whether the changes in relative abundance of bacterial taxa that we observed can significantly alter the biogeochemical functions of marine sediments.
Continue reading ‘Shallow water marine sediment bacterial community shifts along a natural CO2 gradient in the Mediterranean Sea off Vulcano, Italy’

Effects of CO2 enrichment on cockle shell growth interpreted with a Dynamic Energy Budget model

The increase in human induced atmospheric CO2 level leads to an increase in ocean acidification (OA). Mitigation of this increase by storage of CO2 in abandoned marine oil and gas reservoirs is seen as an interesting cost effective solution. However, this involves a risk of CO2 loss causing localised reductions in seawater pH. In this paper we report on the effects of CO2 enhancement on the growth of the bivalve Cerastoderma edule in mesocosms. The experiments show significant reductions in shell length, shell weight and cockle flesh dry weight at increased CO2 level suggesting both direct (shell erosion) and indirect (metabolic) effects. Indirect effects were analysed and interpreted using a Dynamic Energy Budget model by describing changes in 3 metabolic processes: assimilation, maintenance, and growth. Based on cockle size data only we could not differentiate between these processes, however, by using variability of DEB parameter values in 11 bivalve species, we showed growth to be the least relevant process.
Continue reading ‘Effects of CO2 enrichment on cockle shell growth interpreted with a Dynamic Energy Budget model’

Population trajectories for the Antarctic bivalve Laternula elliptica: identifying demographic bottlenecks in differing environmental futures

The world’s oceans are changing, and dramatic shifts have been documented in the Southern Ocean. The consequences of these shifts to coastal benthic organisms are difficult to predict at present, as ocean warming may increase primary production and food resources for benthic consumers, whilst OA may have negative impacts that differentially affect various species and life stages. A model was developed to investigate how different scenarios of change may influence population size of the Antarctic bivalve Laternula elliptica. The model describes potential implications of both pH and temperature change on survivorship and reproductive output of a population of this bivalve species in McMurdo Sound, Ross Sea. Implications of increases and decreases in mortality rate across different life stages of the population (early, mid and late) were assessed. Additionally, effects on energetic resource partitioning and dictating reproductive potential (RP) were also investigated. Significant declines in RP, due to increased basal metabolic demand, were associated with even relatively small changes in temperature and pH, resulting in populations declining to 25 % of the starting equilibrium density within 60 years. As L. elliptica is a pivotal species to the functionality of the Antarctic coastal benthic ecosystem, wide spread repercussions are expected if populations are impacted as the model predicts. Although further model development is required to explore the ecosystem implications of the population decline described in this paper, this work allows a better understanding of the consequences of change as soon as data on the direction and magnitude of the changes affecting Antarctic seas become available.
Continue reading ‘Population trajectories for the Antarctic bivalve Laternula elliptica: identifying demographic bottlenecks in differing environmental futures’

Multiple abiotic changes and species interactions mediate responses to climate change on rocky shores (PhD thesis)

Anthropogenic climate change poses a serious threat to biodiversity. Accurate predictions of the ecological consequences of future abiotic change will require a broad perspective that takes into account multiple climate variables, species-specific responses, and intra- and interspecific dynamics. I addressed these issues in the context of a marine rocky intertidal community to determine how abiotic and biotic factors can mediate the effects of climate change. I began with two studies on the organismal-level effects of multiple abiotic variables. In the first study, I found that acute exposure to low salinity reduced the survival of littorine snails facing thermal stress, but that ocean acidification (OA) had no such effect. In a second study, I showed that sustained exposure to increased temperature and OA had positive and additive effects on the growth and feeding of the purple ochre sea star. These findings demonstrate that studies of multiple climate variables will be important not only to identify additive and non-additive effects, but also to determine which climate variables will be detrimental for a given species. Next, I measured how species-specific responses to climate change can alter species interactions. By quantifying the effects of body size on the feeding behaviours of sea stars preying on mussels, I demonstrated that climate-driven changes in body size can have profound impacts on the strength of this interaction. Finally, I investigated how population-level responses to multiple abiotic variables can be affected by the presence of an interacting species. I built a predator-prey model that simulates the ecologically important interaction between the purple ochre sea star and its preferred prey, mussels. Using empirical estimates of sea star and mussel responses to increased temperature and OA, I simulated their interaction under various climate scenarios. I found that predation exacerbated the effects of climate change on mussel populations, and that climate change increased the strength of the sea star-mussel interaction. My work demonstrates that the effects of climate change will likely be mediated by a combination of biotic and abiotic factors, and that these factors should be considered when making predictions about the ecological consequences of climate change.
Continue reading ‘Multiple abiotic changes and species interactions mediate responses to climate change on rocky shores (PhD thesis)’

Photosynthetic activity buffers ocean acidification in seagrass meadows (update)

Macrophytes growing in shallow coastal zones characterised by intense metabolic activity have the capacity to modify pH within their canopy and beyond. We observed diel pH changes in shallow (5–12 m) seagrass (Posidonia oceanica) meadows spanning 0.06 pH units in September to 0.24 units in June. The carbonate system (pH, DIC, and aragonite saturation state (ΩAr)) and O2 within the meadows displayed strong diel variability driven by primary productivity, and changes in chemistry were related to structural parameters of the meadow, in particular, the leaf surface area available for photosynthesis (LAI). LAI was positively correlated to mean, max and range pHNBS and max and range ΩAr. In June, vertical mixing (as Turbulent Kinetic Energy) influenced max and min ΩAr, while in September there was no effect of hydrodynamics on the carbonate system within the canopy. Max and range ΩAr within the meadow showed a positive trend with the calcium carbonate load of the leaves, pointing to a possible link between structural parameters, ΩAr and carbonate deposition.

Calcifying organisms, e.g. epiphytes with carbonate skeletons, may benefit from the modification of the carbonate system by the meadow. There is, however, concern for the ability of seagrasses to provide modifications of similar importance in the future. The predicted decline of seagrass meadows may alter the scope for alteration of pH within a seagrass meadow and in the water column above the meadow, particularly if shoot density and biomass decline, on which LAI is based. Organisms associated with seagrass communities may therefore suffer from the loss of pH buffering capacity in degraded meadows.
Continue reading ‘Photosynthetic activity buffers ocean acidification in seagrass meadows (update)’

Modeling coral calcification accounting for the impacts of coral bleaching and ocean acidification

Coral reefs are diverse ecosystems threatened by rising CO2 levels that are driving the observed increases in sea surface temperature and ocean acidification. Here we present a new unified model that links changes in temperature and carbonate chemistry to coral health. Changes in coral health and population are able to explicitly modelled by linking the rates of growth, recovery and calcification to the rates of bleaching and temperature stress induced mortality. The model is underpinned by four key principles: the Arrhenius equation, thermal specialisation, resource allocation trade-offs, and adaption to local environments. These general relationships allow this model to be constructed from a range of experimental and observational data. The different characteristics of this model are also assessed against independent data to show that the model captures the observed response of corals. We also provide new insights into the factors that determine calcification rates and provide a framework based on well-known biological principles for understanding the observed global distribution of calcification rates. Our results suggest that, despite the implicit complexity of the coral reef environment, a simple model based on temperature, carbonate chemistry and different species can reproduce much of the observed response of corals to changes in temperature and ocean acidification.
Continue reading ‘Modeling coral calcification accounting for the impacts of coral bleaching and ocean acidification’


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Ocean acidification in the IPCC AR5 WG II

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