Ocean acidification impairs crab foraging behaviour

Anthropogenic elevation of atmospheric CO2 is driving global-scale ocean acidification, which consequently influences calcification rates of many marine invertebrates and potentially alters their susceptibility to predation. Ocean acidification may also impair an organism’s ability to process environmental and biological cues. These counteracting impacts make it challenging to predict how acidification will alter species interactions and community structure. To examine effects of acidification on consumptive and behavioural interactions between mud crabs (Panopeus herbstii) and oysters (Crassostrea virginica), oysters were reared with and without caged crabs for 71 days at three pCO2 levels. During subsequent predation trials, acidification reduced prey consumption, handling time and duration of unsuccessful predation attempt. These negative effects of ocean acidification on crab foraging behaviour more than offset any benefit to crabs resulting from a reduction in the net rate of oyster calcification. These findings reveal that efforts to evaluate how acidification will alter marine food webs should include quantifying impacts on both calcification rates and animal behaviour.

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Seminar: “Ocean acidification and coral reefs: facilitating a systems‐level understanding by working across scales and disciplines”, UC Davis, 19 August 2015

Date, time & location: 19 August 2015, 4 p.m., Bodega Marine Laboratory Lecture Hall, 2099 Westside Rd, Bodega Bay, CA 94923

Speaker: Rebecca Albright, Postdoctoral Research Scientist, Carnegie Institute for Science, Department of Global Ecology, Stanford

Host: T. Hill

More information.


Sponge erosion under acidification and warming scenarios: differential impacts on living and dead coral

Ocean acidification will disproportionately impact the growth of calcifying organisms in coral reef ecosystems. Simultaneously, sponge bioerosion rates have been shown to increase as seawater pH decreases. We conducted a 20-week experiment that included a 4-week acclimation period with a high number of replicate tanks and a fully orthogonal design with two levels of temperature (ambient and +1 °C), three levels of pH (8.1, 7.8 and 7.6) and two levels of boring sponge (Cliona varians, present and absent) to account for differences in sponge attachment and carbonate change for both living and dead coral substrate (Porites furcata). Net coral calcification, net dissolution/bioerosion, coral and sponge survival, sponge attachment, and sponge symbiont health were evaluated. Additionally, we used the empirical data from the experiment to develop a stochastic simulation of carbonate change for small coral clusters (i.e., simulated reefs). Our findings suggest differential impacts of temperature, pH and sponge presence for living and dead corals. Net coral calcification (mg CaCO3 cm−2 d−1) was significantly reduced in treatments with increased temperature (+1 °C) and when sponges were present; acidification had no significant effect on coral calcification. Net dissolution of dead coral was primarily driven by pH, regardless of sponge presence or seawater temperature. A reevaluation of the current paradigm of coral carbonate change under future acidification and warming scenarios should include ecologically relevant time scales, species interactions, and community organization to more accurately predict ecosystem-level response to future conditions.

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Response of Acropora digitifera to ocean acidification: constraints from δ11 B, Sr, Mg, and Ba compositions of aragonitic skeletons cultured under variable seawater pH

The response of Acropora digitifera to ocean acidification is determined using geochemical proxy measurements of the skeletal composition of A. digitifera cultured under a range of pH levels. We show that the chemical composition (δ11B, Sr/Ca, Mg/Ca, and Ba/Ca) of the coral skeletons can provide quantitative constraints on the effects of seawater pH on the pH in the calcification fluid (pHCF) and the mechanisms controlling the incorporation of trace elements into coral aragonite. With the decline of seawater pH, the skeletal δ11B value decreased, while the Sr/Ca ratio showed an increasing trend. The relationship between Mg/Ca and Ba/Ca versus seawater pH was not significant. Inter-colony variation of δ11B was insignificant, although inter-colony variation was observed for Ba/Ca. The decreasing trend of pHCF calculated from δ11B was from ~8.5, 8.4, and 8.3 for seawater pH of ~8.1, 7.8, and 7.4, respectively. Model calculations based on Sr/Ca and pHCF suggest that upregulation of pHCF occurs via exchange of H+ with Ca2+ with kinetic effects (Rayleigh fractionation), reducing Sr/Ca relative to inorganic deposition of aragonite from seawater. We show that it is possible to constrain the overall carbonate chemistry of the calcifying fluid with estimates of the carbonate saturation of the calcifying fluid (Ω CF) being derived from skeletal Sr/Ca and pHCF (from δ11B). These estimates suggest that the aragonite saturation state of the calcifying fluid Ω CF is elevated by a factor of 5–10 relative to ambient seawater under all treatment conditions.

Continue reading ‘Response of Acropora digitifera to ocean acidification: constraints from δ11 B, Sr, Mg, and Ba compositions of aragonitic skeletons cultured under variable seawater pH’

Impacts of multiple environmental stressors on coral reef erosion and secondary accretion

Ocean acidification threatens to shift coral reefs from net accreting to net eroding. While corals build reefs through accretion of calcium carbonate (CaCO3) skeletons, net reef growth depends on bioerosion by grazers and borers and on secondary calcification by crustose coralline algae and other calcifying invertebrates. Primary calcification, secondary calcification, and erosion processes respond differently to climate change stressors; therefore, the combined accretion-erosion response is uncertain. Using a new micro-computed tomography (CT) method, we measured the simultaneous response of secondary accretion and bioerosion along an environmental gradient: bioerosion rates ranged from 0.02 to 0.91 kg m􀀀2 yr􀀀1 and secondary accretion rates ranged from 0.01 to 0.4 mm yr􀀀1 across a 32m transect. Co-located measures of secondary accretion and bioerosion had different environmental drivers: bioerosion rates were highly sensitive to ocean
30 acidity while secondary accretion rates were most sensitive to physical drivers. These results suggest that bioerosion plays a significant role in the shift from net accretion to net erosion on coral reefs.

Continue reading ‘Impacts of multiple environmental stressors on coral reef erosion and secondary accretion’

Patterns of coccolithophore pigment change under global acidification conditions based on in-situ observations at BATS site between July 1990–Dec 2008

Coccolith production is an important part of the biogenic carbon cycle as the largest source of calcium carbonate on earth, accounting for about 75% of the deposition of carbon on the sea floor. Recent studies based on laboratory experiment results indicated that increasing anthropogenic CO2 in the atmosphere triggered global ocean acidification leading to a decrease of calcite or aragonite saturation and calcium carbonate, and to decreasing efficiency of carbon export/pumping to deep layers. In the present study, we analyzed about 20 years of field observations of coccolithophore pigment, dissolved inorganic carbon (DIC), nutrients, and temperatures from the Bermuda Atlantic Time-series Study (BATS) site and satellite remote sensing to investigate the variable tendency of the coccolithophore pigment, and to evaluate the influence of ocean acidification on coccolithophore biomass. The results indicated that there was a generally increasing tendency of coccolithophore pigment, coupled with increasing bicarbonate concentrations or decreasing carbonate ion concentration. The change of coccolithophore pigment was also closely associated with pH, nutrients, mixed layer depth (MLD), and temperature. Correlation analyses between coccolithophores and abiotic parameter imply that coccoliths production or coccolithophore pigment has increased with increasing acidification in the recent 20 years.

Continue reading ‘Patterns of coccolithophore pigment change under global acidification conditions based on in-situ observations at BATS site between July 1990–Dec 2008′

Biochemical adaptation to ocean acidification

The change in oceanic carbonate chemistry due to increased atmospheric PCO2 has caused pH to decline in marine surface waters, a phenomenon known as ocean acidification (OA). The effects of OA on organisms have been shown to be widespread among diverse taxa from a wide range of habitats. The majority of studies of organismal response to OA are in short-term exposures to future levels of PCO2. From such studies, much information has been gathered on plastic responses organisms may make in the future that are beneficial or harmful to fitness. Relatively few studies have examined whether organisms can adapt to negative-fitness consequences of plastic responses to OA. We outline major approaches that have been used to study the adaptive potential for organisms to OA, which include comparative studies and experimental evolution. Organisms that inhabit a range of pH environments (e.g. pH gradients at volcanic CO2 seeps or in upwelling zones) have great potential for studies that identify adaptive shifts that have occurred through evolution. Comparative studies have advanced our understanding of adaptation to OA by linking whole-organism responses with cellular mechanisms. Such optimization of function provides a link between genetic variation and adaptive evolution in tuning optimal function of rate-limiting cellular processes in different pH conditions. For example, in experimental evolution studies of organisms with short generation times (e.g. phytoplankton), hundreds of generations of growth under future conditions has resulted in fixed differences in gene expression related to acid–base regulation. However, biochemical mechanisms for adaptive responses to OA have yet to be fully characterized, and are likely to be more complex than simply changes in gene expression or protein modification. Finally, we present a hypothesis regarding an unexplored area for biochemical adaptation to ocean acidification. In this hypothesis, proteins and membranes exposed to the external environment, such as epithelial tissues, may be susceptible to changes in external pH. Such biochemical systems could be adapted to a reduced pH environment by adjustment of weak bonds in an analogous fashion to biochemical adaptation to temperature. Whether such biochemical adaptation to OA exists remains to be discovered.

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Ocean acidification in the IPCC AR5 WG II

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