Ocean acidification (OA) refers to the increase in acidity (decrease in pH) of the ocean's surface waters resulting from oceanic uptake of atmospheric carbon dioxide (CO₂). Mounting experimental ...evidence suggests that OA threatens numerous marine organisms, including reef-building corals. Coral recruitment is critical to the persistence and resilience of coral reefs and is regulated by several early life processes, including: larval availability (gamete production, fertilization, etc.), larval settlement, postsettlement growth, and survival. Environmental factors that disrupt these early life processes can result in compromised or failed recruitment and profoundly affect future population dynamics. To evaluate the effects of OA on the sexual recruitment of corals, we tested larval metabolism, larval settlement, and postsettlement growth of the common Caribbean coral Porites astreoides at three pCO₂ levels: ambient seawater (380 μatm) and two pCO₂ scenarios that are projected to occur by the middle (560 μatm) and end (800 μatm) of the century. Our results show that larval metabolism is depressed by 27% and 63% at 560 and 800 μatm, respectively, compared with controls. Settlement was reduced by 42-45% at 560 μatm and 55-60% at 800 μatm, relative to controls. Results indicate that OA primarily affects settlement via indirect pathways, whereby acidified seawater alters the substrate community composition, limiting the availability of settlement cues. Postsettlement growth decreased by 16% and 35% at 560 and 800 μatm, respectively, relative to controls. This study demonstrates that OA has the potential to negatively impact multiple early life history processes of P. astreoides and may contribute to substantial declines in sexual recruitment that are felt at the community and/or ecosystem scale.
Despite recent work to characterize gene expression changes associated with larval development in oysters, the mechanism by which the larval shell is first formed is still largely unknown. In ...Crassostrea gigas, this shell forms within the first 24 h post fertilization, and it has been demonstrated that changes in water chemistry can cause delays in shell formation, shell deformations and higher mortality rates. In this study, we use the delay in shell formation associated with exposure to CO
-acidified seawater to identify genes correlated with initial shell deposition.
By fitting linear models to gene expression data in ambient and low aragonite saturation treatments, we are able to isolate 37 annotated genes correlated with initial larval shell formation, which can be categorized into 1) ion transporters, 2) shell matrix proteins and 3) protease inhibitors. Clustering of the gene expression data into co-expression networks further supports the result of the linear models, and also implies an important role of dynein motor proteins as transporters of cellular components during the initial shell formation process.
Using an RNA-Seq approach with high temporal resolution allows us to identify a conceptual model for how oyster larval calcification is initiated. This work provides a foundation for further studies on how genetic variation in these identified genes could affect fitness of oyster populations subjected to future environmental changes, such as ocean acidification.
In 2007, the US west coast shellfish industry began to feel the effects of unprecedented levels of larval mortality in commercial hatcheries producing the Pacific oysterCrassostrea gigas. ...Subsequently, researchers at Whiskey Creek Shellfish Hatchery, working with academic and government scientists, showed a high correlation between aragonite saturation state (Ωarag) of inflowing seawater and survival of larval groups, clearly linking increased CO₂ to hatchery failures. This work led the Pacific Coast Shellfish Growers Association (PCSGA) to instrument shellfish hatcheries and coastal waters, establishing a monitoring network in collaboration with university researchers and the US Integrated Ocean Observing System. Analytical developments, such as the ability to monitor Ωaragin real time, have greatly improved the industry's understanding of carbonate chemistry and its variability and informed the development of commercial-scale water treatment systems. These treatment systems have generally proven effective, resulting in billions of additional oyster larvae supplied to Pacific Northwest oyster growers. However, significant challenges remain, and a multifaceted approach, including selective breeding of oyster stocks, expansion of hatchery capacity, continued monitoring of coastal water chemistry, and improved understanding of biological responses will all be essential to the survival of the US west coast shellfish industry.
Ocean acidification is projected to lower the Ωar of reefal waters by 0.3–0.4 units by the end of century, making it more difficult for calcifying organisms to secrete calcium carbonate while at the ...same time making the environment more favorable for abiotic and biotic dissolution of the reefal framework. There is great interest in being able to project the point in time when coral reefs will cross the tipping point between being net depositional to net erosional in terms of their carbonate budgets. Periodic in situ assessments of the balance between carbonate production and dissolution that spans seasonal time scales may prove useful in monitoring and formulating projections of the impact of ocean acidification on reefal carbonate production. This study represents the first broad‐scale geochemical survey of the rates of net community production (NCP) and net community calcification (NCC) across the Florida Reef Tract (FRT). Surveys were performed at approximately quarterly intervals in 2009–2010 across seven onshore‐offshore transects spanning the upper, middle, and lower Florida Keys. Averaged across the FRT, the rates of NCP and NCC were positive during the spring/summer at 62 ± 7 and 17 ± 2 mmol m−2 d−1, respectively, and negative during the fall/winter at −33 ± 6 and −7 ± 2 mmol m−2 d−1. The most significant finding of the study was that the northernmost reef is already net erosional (−1.1 ± 0.4 kg CaCO3 m−2 yr−1) and midreefs to the south were net depositional on an annual basis (0.4 ± 0.1 kg CaCO3 m−2 yr−1) but erosional during the fall and winter. Only the two southernmost reefs were net depositional year‐round. These results indicate that parts of the FRT have already crossed the tipping point for carbonate production and other parts are getting close.
Key Points
Seasonal reversal in the sign of NCP drives positive feedback on NCC in the summer and negative feedback in the winter
Seasonal net dissolution in waters supersaturated with respect to aragonite
Net loss of reefal substrate due to ocean acidification is already occurring
Ocean acidification (OA) refers to the ongoing decline in oceanic pH resulting from the uptake of atmospheric CO₂. Mounting experimental evidence suggests that OA will have negative consequences for ...a variety of marine organisms. Whereas the effect of OA on the calcification of adult reef corals is increasingly well documented, effects on early life history stages are largely unknown. Coral recruitment, which necessitates successful fertilization, larval settlement, and postsettlement growth and survivorship, is critical to the persistence and resilience of coral reefs. To determine whether OA threatens successful sexual recruitment of reef-building corals, we tested fertilization, settlement, and postsettlement growth of Acropora palmata at pCO₂ levels that represent average ambient conditions during coral spawning (∼400 μatm) and the range of pCO₂ increases that are expected to occur in this century ∼560 μatm (mid-CO₂) and ∼800 μatm (high-CO₂). Fertilization, settlement, and growth were all negatively impacted by increasing pCO₂, and impairment of fertilization was exacerbated at lower sperm concentrations. The cumulative impact of OA on fertilization and settlement success is an estimated 52% and 73% reduction in the number of larval settlers on the reef under pCO₂ conditions projected for the middle and the end of this century, respectively. Additional declines of 39% (mid-CO₂) and 50% (high-CO₂) were observed in postsettlement linear extension rates relative to controls. These results suggest that OA has the potential to impact multiple, sequential early life history stages, thereby severely compromising sexual recruitment and the ability of coral reefs to recover from disturbance.
We report results from an oyster hatchery on the Oregon coast, where intake waters experienced variable carbonate chemistry (aragonite saturation state < 0.8 to > 3.2; pH < 7.6 to > 8.2) in the early ...summer of 2009. Both larval production and midstage growth (∼ 120 to ∼ 150 μm) of the oyster Crassostrea gigas were significantly negatively correlated with the aragonite saturation state of waters in which larval oysters were spawned and reared for the first 48 h of life. The effects of the initial spawning conditions did not have a significant effect on early-stage growth (growth from D-hinge stage to ∼ 120 μm), suggesting a delayed effect of water chemistry on larval development.
The native Olympia oyster, Ostrea lurida, was once abundant in many US Pacific Northwest (PNW) estuaries, but was decimated by human activity in the late nineteenth early to twentieth centuries. ...Having been the subject of only few modern, detailed studies, a dearth of basic physiological information surrounded O. lurida and how it compared to the now dominant, non-native Pacific oyster, Crassostrea gigas. Utilizing laboratory and in situ studies in Yaquina Bay, OR, we explored the clearance rates of both species across a wide range of conditions. Pacific oysters not only had greater size-specific clearance rates than Olympia oysters, but also had a lower optimum temperature. Clearance rates for both species were reduced at lower salinity, at lower organic content, and at higher turbidity. Clearance rate models were constructed for each species using three approaches: (1) a single mechanistic model that incorporated feeding response functions of each species to the effects of temperature, salinity, turbidity, and seston organic content based on laboratory studies; (2) another additive model in which the number and type of response functions from laboratory studies were allowed to vary; and (3) a statistical model that utilized environmental data collected during in situ feeding trials. Clearance rate models that correlated feeding activity with in situ environmental data were found to often better predict oyster clearance rates (based on Adj R²) for both species in Yaquina Bay, OR, than mechanistic, additive models based on laboratory feeding response functions; however, in situ correlative models varied in accuracy by species and season. This work represents important first steps towards better understanding the physiological ecology of the native Olympia oyster and how it differs from introduced and now dominant Pacific oyster.
Increasing anthropogenic carbon dioxide is altering marine carbonate chemistry through a process called ocean acidification. Many calcium carbonate forming organisms are sensitive to changes in ...marine carbonate chemistry, especially mollusk bivalve larvae at the initial shell building stage. Rapid calcification, limited energy reserves, and more exposed calcification surfaces, are traits at this stage that increase vulnerability to ocean acidification through our previously argued kinetic-energetic hypothesis. These developmental traits are common to broadcast spawning bivalve species that are the focus of most ocean acidification studies to date. Some oyster species brood their young, which results in slower development of the embryos through the initial shell formation stage. We examined the responses of the brooding Olympia oyster, Ostrea lurida, during their initial shell building stage. We extracted fertilized eggs from, O. lurida, prior to shell development, then exposed developing embryos to a wide range of marine carbonate chemistry conditions. Surprisingly, O. lurida showed no acute negative response to any ocean acidification treatments. Compared to the broadcast spawning Pacific oyster, Crassostrea gigas, calcification rate and standardized endogenous energy lipid consumption rate were nearly 10 and 50 times slower, respectively. Our results suggest that slow shell building may lessen the energetic burden of acidification at this stage and provides additional support for our kinetic-energetic hypothesis. Furthermore, these results may represent an example of exaptation; fitness conveyed by a coopted trait that evolved for another purpose, a concept largely lacking in the current perspective of adaptation and global climate change.
Global climate change threatens coral growth and reef ecosystem health via ocean warming and ocean acidification (OA). Whereas the negative impacts of these stressors are increasingly ...well-documented, studies identifying pathways to resilience are still poorly understood. Heterotrophy has been shown to help corals experiencing decreases in growth due to either thermal or OA stress; however, the mechanism by which it mitigates these decreases remains unclear. This study tested the ability of coral heterotrophy to mitigate reductions in growth due to climate change stress in the critically endangered Caribbean coral Acropora cervicornis via changes in feeding rate and lipid content. Corals were either fed or unfed and exposed to elevated temperature (30°C), enriched pCO2 (800 ppm), or both (30°C/800 ppm) as compared to a control (26°C/390 ppm) for 8 weeks. Feeding rate and lipid content both increased in corals experiencing OA vs. present-day conditions, and were significantly correlated. Fed corals were able to maintain ambient growth rates at both elevated temperature and elevated CO2, while unfed corals experienced significant decreases in growth with respect to fed conspecifics. Our results show for the first time that a threatened coral species can buffer OA-reduced calcification by increasing feeding rates and lipid content.
Host genetics influences the development of infectious diseases in many agricultural animal species. Identifying genes associated with disease development has the potential to make selective breeding ...for disease tolerance more likely to succeed through the selection of different genes in diverse signaling pathways. In this study, four families of Pacific oysters (Crassostrea gigas) were identified to be segregating for a quantitative trait locus (QTL) on chromosome 8. This QTL was previously found to be associated with basal antiviral gene expression and survival to ostreid herpesvirus 1 (OsHV-1) mortality events in Tomales Bay, California. Individuals from these four families were phenotyped and genotyped in an attempt to find candidate genes associated with the QTL on chromosome 8. Genome-wide allele frequencies of oysters from each family prior to being planting in Tomales Bay were compared with the allele frequencies of oysters from respective families that survived an OsHV-1 mortality event. Six significant unique QTL were identified in two families in these genome-wide allele frequency studies, all of which were located on chromosome 8. Three QTL were assigned to candidate genes (ABCA1, PIK3R1, and WBP2) that have been previously associated with antiviral innate immunity in vertebrates. The identification of vertebrate antiviral innate immunity genes as candidate genes involved in molluscan antiviral innate immunity reinforces the similarities between the innate immune systems of these two groups. Causal variant identification in these candidate genes will enable future functional studies of these genes in an effort to better understand their antiviral modes of action.
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