No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Counteractive effects of increased temperature and pCO2 on the thickness and chemistry of the carapace of juvenile blue crab, Callinectes sapidus, from the Patuxent River, Chesapeake Bay
Abstract
Exoskeletons are central to the physiology and survival of marine invertebrates, but future increases in the temperature and pCO2 of the marine environment may alter the biomineralization processes involved in their formation. Thus, it is important to consider the impacts of a changing climate on the functionality of invertebrate exoskeletons. In this study, juvenile blue crab, Callinectes sapidus, from the Chesapeake Bay were exposed to increased temperature and pCO2 in a 2 × 2 factorial design for a period of two molts (approximately 30 days). Treatment levels were chosen to represent current (26 °C and 800 μatm CO2) and predicted future conditions in the year 2100 (32 °C and 8000 μatm CO2) in the Chesapeake Bay. Thickness was determined by light microscopy and carapace calcium (Ca) and magnesium (Mg) content were determined by Inductively Coupled Plasma – Atomic Emission Spectrometry. All Ca and Mg in the carapace were assumed to be present in the form of high‑magnesium calcite (HMC). Increased temperature decreased the thickness of juvenile blue crab carapaces by 8.5% and significantly reduced weight percent HMC by 2.0% (P < 0.05). Increased pCO2 significantly increased weight percent HMC by 2.0% but a significant increase in Mg content was also found. The observed counteractive effects of temperature and pCO2 on weight percent HMC underscore the importance of assessing such interactions in studies that quantify the impacts of multiple environmental stressors. Combined with new data regarding the influence of increased temperature and pCO2 on blue crab growth, the results of this study indicate tradeoffs between carapace thickness and chemistry with growth in juvenile blue crab exposed to future warming.
... Moreover, current and projected changes in precipitation patterns in Maryland and the Chesapeake Bay watershed are expected to add pressure to stormwater systems and increase agricultural runoff [29][30][31]. In turn, changes in the water quality and temperature in the bay pose considerable risks to the health of marine ecosystems, which are likely to have adverse economic and social impacts on coastal communities [32][33][34][35]. The economic underline of many climate impact data is not surprising, given that the Chesapeake Bay has long been an economically productive source of income; fish, shellfish, and oysters provided the State of Maryland with a $63 million in 2013 [14]. ...
... Although seasonal hypoxia is a natural feature of estuaries, indicators show that these "dead zones" are becoming more frequent in many parts of the world due to human impact on the ecosystem [16,74]. Moreover, changes in the water quality and chemistry, as well as higher water temperatures [33,75,76] and acidification [35], pose serious threats to aquatic life. These changes can affect aquatic life that is economically and ecologically important to the Chesapeake Bay; such as the blue crab [33,75] softshell clam [34,35], striped bass [77], algae [60,73], and marine grasses [77]. ...
... Moreover, changes in the water quality and chemistry, as well as higher water temperatures [33,75,76] and acidification [35], pose serious threats to aquatic life. These changes can affect aquatic life that is economically and ecologically important to the Chesapeake Bay; such as the blue crab [33,75] softshell clam [34,35], striped bass [77], algae [60,73], and marine grasses [77]. The Eco Health Report Card has been a consistent indicator of the Chesapeake Bay's water quality since 1986 [77]. ...
Climate change is increasingly threatening coastal communities around the world. This article reviews the literature on climate change impacts and adaptation in the Chesapeake Bay region (USA). We reviewed both climate impacts and adaptation literature (n = 283) published in the period 2007-2018 to answer the questions: (i) how are indicators of climate impacts measured and reported by different types of authors (e.g., scientists, government, and NGOs), document types (e.g., academic articles or reports), and geographic focus (e.g., State, region, county, or municipal level)? (ii) what are the current approaches for measuring the most pressing climate impacts in the Chesapeake Bay? We found that scientists produce the most amount of data but are increasingly shifting towards engaging with practitioners through reports and online resources. Most indicators focus on the Chesapeake Bay scale, but data is most needed at the local level where adaptive policies are implemented. Our analysis shows emerging approaches to monitoring climate hazards and areas where synergies between types of authors are likely to increase resilience in the 21st century. This review expands the understanding of the information network in the Chesapeake Bay and explores the institutional landscape of stakeholders involved in the production and consumption of environmental and social change data. The analysis and insights of this review may be extended to similar regions around the planet experiencing or anticipating similar climate hazards to the Chesapeake Bay.
... Most invertebrates with calcified structures experience reductions in mineral content (Chan and Connolly, 2013;Kroeker et al., 2013;Davis et al., 2021) under reduced pH/high pCO 2 exposure due to lowered carbonate ion concentration and carbonate mineral saturation state. In contrast, some crustacean species experience increases in calcification (McDonald et al., 2009;Long et al., 2013;Taylor et al., 2015;deVries et al., 2016;Glandon et al., 2018), which is potentially accomplished by drawing upon bicarbonate accumulated for acid-base regulation (Truchot, 1979;Pane and Barry, 2007;Spicer et al., 2007;Knapp et al., 2015;Whiteley et al., 2018). The degree of mineralization is strongly linked with material properties, whereby greater mineral content corresponds to greater stiffness and brittleness (Currey, 1984). ...
... For example, there was no change in either [Mg] or [Ca] at moderate (0.25 pH unit) decreases in pH for the early juvenile stage of the American lobster, H. americanus, after five weeks of exposure (Menu-Courey et al., 2018). Juvenile blue swimming crabs and hermit crabs exposed to reduced pH conditions incurred no changes in Ca content, but hermit crabs exhibited small increases in Mg (Glandon et al., 2018;Ragagnin et al., 2018). The above results were all found in animals that had molted during the experiment. ...
Spiny lobsters rely on multiple biomineralized exoskeletal predator defenses that may be sensitive to ocean acidification (OA). Compromised mechanical integrity of these defensive structures may tilt predator-prey outcomes, leading to increased mortality in the lobsters’ environment. Here, we tested the effects of OA-like conditions on the mechanical integrity of selected exoskeletal defenses of juvenile California spiny lobster, Panulirus interruptus . Young spiny lobsters reside in kelp forests with dynamic carbonate chemistry due to local metabolism and photosynthesis as well as seasonal upwelling, yielding daily and seasonal fluctuations in pH. Lobsters were exposed to a series of stable and diurnally fluctuating reduced pH conditions for three months (ambient pH/stable, 7.97; reduced pH/stable 7.67; reduced pH with low fluctuations, 7.67 ± 0.05; reduced pH with high fluctuations, 7.67 ± 0.10), after which we examined the intermolt composition (Ca and Mg content), ultrastructure (cuticle and layer thickness), and mechanical properties (hardness and stiffness) of selected exoskeletal predator defenses. Cuticle ultrastructure was consistently robust to pH conditions, while mineralization and mechanical properties were variable. Notably, the carapace was less mineralized under both reduced pH treatments with fluctuations, but with no effect on material properties, and the rostral horn had lower hardness in reduced/high fluctuating conditions without a corresponding difference in mineralization. Antennal flexural stiffness was lower in reduced, stable pH conditions compared to the reduced pH treatment with high fluctuations and not correlated with changes in cuticle structure or mineralization. These results demonstrate a complex relationship between mineralization and mechanical properties of the exoskeleton under changing ocean chemistry, and that fluctuating reduced pH conditions can induce responses not observed under the stable reduced pH conditions often used in OA research. Furthermore, this study shows that some juvenile California spiny lobster exoskeletal defenses are responsive to changes in ocean carbonate chemistry, even during the intermolt period, in ways that can potentially increase susceptibility to predation among this critical life stage.
... Although crustaceans were not initially believed to be particularly vulnerable to the effects of OA (Kroeker et al. 2010(Kroeker et al. , 2013Whittman and Pörtner 2013;Byrne and Fitzer 2019), recent studies have demonstrated that elevated pCO 2 levels can increase mortality of crustaceans (Miller et al. 2016;Giltz & Taylor 2017, reduce growth McLean et al. 2018), and alter energetics (Long et al. 2019) and behavior (Gravinese et al. 2019). In addition, OA can also alter the formation and maintenance of their mineralized exoskeleton (Taylor et al. 2015;Meseck et al. 2016;Glandon et al. 2018;Bednaršek et al. 2020;Dickinson et al. 2021), potentially limiting the defensive, predatory, and locomotive abilities of these organisms (Page et al. 2016;Coffey et al. 2017). Much of the OA research studying physiological and ecological responses of crustaceans to decreased pH has involved only short-term (~ 30 days) to medium-term (~ 6 month) exposure to OA; however, many crustaceans can live for a decade or longer, which makes long-term exposure experiments critically important (Whiteley 2011). ...
... It is important to note, however, that most decapods that are able to maintain acid-base homeostasis under ocean acidi cation conditions do so, at least in part, by buffering their hemolymph with bicarbonate via Cl − /HCO 3 − exchange at the gills (Pane and Barry 2007;Whiteley 2011, Appelhans et al. 2012. This response could make precipitation of calcium carbonate more likely, and could explain why many decapods show increased calci cation rates or content in response to ocean acidi cation (Ries et al. 2009;Long et al. 2013b;Glandon et al. 2018). Finally, ocean acidi cation can induce changes in the expression of genes involved in cuticle formation; red king crab adults and juveniles both exhibited an increase in the expression of such genes (Stillman et al. 2020). ...
Structural and mechanical properties of the decapod exoskeleton affect foraging, defense, and locomotion, making the ability of decapods to maintain their calcified exoskeleton a crucial physiological process. Ocean acidification (OA) poses a threat to marine biomes and their inhabitants, particularly calcifying organisms. Vulnerability of the snow crab, Chionecetes opilio, a commercially important, high-latitude species, to OA has not been explored. Although all oceans are experiencing acidification, abiotic factors in high-latitude areas increase the rate of acidification. We examined the effect of long-term (2-year) exposure to decreased seawater pH (7.8 and 7.5) on exoskeletal properties in post-terminal-molt female C. opilio. Since the effects of OA vary among body regions in decapods, exoskeletal properties (microhardness, thickness, and elemental composition) were measured in five body regions: the carapace, both claws, and both third-walking legs. Overall, the C. opilio exoskeleton was robust to OA in all body regions. Decreased pH had no effect on microhardness or thickness of the exoskeleton, despite a slight (~6%) reduction in calcium content in crabs held at pH 7.5. In contrast, exoskeletal properties varied dramatically among body regions regardless of pH. The exoskeleton of the claws was harder, thicker, and contained more calcium but less magnesium than that of other body regions. Exoskeleton of the legs was thinner than that of other body regions and contained significantly greater levels of magnesium (~2.5 times higher than the claws). Maintenance of exoskeletal properties after long-term OA exposure in C. opilio suggests that wild populations may tolerate future ocean pH conditions.
... Regarding acidification, blue crabs exhibit a variety of responses to lowered pH depending on life-stage [21,[52][53][54] with observed negative effects such as reductions in growth or survival mainly occurring in the larval stages [43]. Our study found significant reductions in zoeal Table. ...
... S1 and S2 Tables). The carapace of decapod crustaceans such as the blue crabs is comprised of amorphous calcium carbonate containing high amounts of magnesium packed within a chitin-protein matrix [53,55,56], and it may be that calcite undersaturation affects blue crab larvae calcification impacting survival. Molt-related mortality may also be the result of challenges in the regulation of acid-base balance, as suggested by Small et al. [57] explanation of increased mortality among juvenile European lobsters exposed to elevated pCO 2 . ...
A large number of coastal ecosystems globally are subjected to concurrent hypoxic and acidified conditions that will likely intensify and expand with continued climate change. In temperate regions, the spawning of many important organisms including the Atlantic blue crab Callinectes sapidus occurs during the summer months when the severity of coastal hypoxia and acidification is the greatest. While the blue crab earliest larval stage can be exposed to co-occurring hypoxia and acidification observed in many coastal ecosystems, the effects of these concurrent stressors on larval blue crab survival is unknown. This study investigated the individual and combined consequences of low dissolved oxygen (DO) and low pH on blue crab larvae survival through a series of short-term experiments. During 14-day experiments with moderately hypoxic conditions (117–127 μM O2 or 3.74–4.06 mg L-1) and acidified conditions (pH on total scale of 7.16–7.33), low DO and low pH individually and significantly reduced larval survival by 60% and 49%, respectively, with the combination of stressors reducing survival by 87% compared to the control treatment (210–269 μM O2 or 6.72–8.61 mg L-1, 7.91–7.94 DO and pH, respectively). During 4-day experiments with lower DO levels (68–83 μM O2 or 2.18–2.62 mg L-1) and comparable pH levels of 7.29–7.39, low DO individually reduced survival by >90% compared to the control (261–267 μM O2 or 8.35–8.54 mg L-1, 7.92–7.97 DO and pH, respectively), whereas low pH had no effect and there was no interaction between stressors. Over a 4-day period, the DO threshold at which 50% of the larval blue crab population died (LC50) was 121 μM O2 (3.86 mgL-1). In 14-day experiments, the DO and pH effects were additive, yielding survival rates lower than the individual treatments, and significantly correlated with DO and pH concentrations. Collectively, these findings indicate that blue crab sensitivity to both low DO and low pH are acute within the larval stage, depend on the intensity and duration of exposure, and leads to mortality, thereby potentially contributing to the interannual variability and possible regional declines of this fishery.
... a previous study, mineralized tissue from 7 body regions of the lobster Homarus americanus raised in ambient seawater were found to vary in Ca 2+ and Mg 2+ levels, but Ca:Mg ratios were consistent among body regions(Mergelsberg et al., 2019). Similarly, the Ca:Mg ratio was maintained under high experimental acidification (ambient: 800 µatm; OA: 8000 µatm) in the carapace of juvenile crabs, C. sapidus, collected from a comparable geographic and climatic region(Glandon et al., 2018), suggesting that stability of the Ca:Mg ratio is physiologically sustained even under acidified conditions. To determine how ocean acidification affects the Ca:Mg ratio in the crustacean exoskeleton, we applied a linear regression to model the Mg 2+ effect size as a product of the Ca 2+ effect size for Ca 2+ and Mg 2+ data acquired from the same experiment(Figure 3). ...
Crustaceans comprise an ecologically and morphologically diverse taxonomic group. They are typically considered resilient to many environmental perturbations found in marine and coastal environments, due to effective physiological regulation of ions and hemolymph pH, and a robust exoskeleton. Ocean acidification can affect the ability of marine calcifying organisms to build and maintain mineralized tissue and poses a threat for all marine calcifying taxa. Currently, there is no consensus on how ocean acidification will alter the ecologically relevant exoskeletal properties of crustaceans. Here, we present a systematic review and meta-analysis on the effects of ocean acidi-fication on the crustacean exoskeleton, assessing both exoskeletal ion content (cal-cium and magnesium) and functional properties (biomechanical resistance and cuticle thickness). Our results suggest that the effect of ocean acidification on crustacean exoskeletal properties varies based upon seawater pCO 2 and species identity, with significant levels of heterogeneity for all analyses. Calcium and magnesium content was significantly lower in animals held at pCO 2 levels of 1500-1999 µatm as compared with those under ambient pCO 2. At lower pCO 2 levels, however, statistically significant relationships between changes in calcium and magnesium content within the same experiment were observed as follows: a negative relationship between calcium and magnesium content at pCO 2 of 500-999 µatm and a positive relationship at 1000-1499 µatm. Exoskeleton biomechanics, such as resistance to deformation (microhardness) and shell strength, also significantly decreased under pCO 2 regimes of 500-999 µatm and 1500-1999 µatm, indicating functional exoskeletal change co-incident with decreases in calcification. Overall, these results suggest that the crustacean exoskeleton can be susceptible to ocean acidification at the biomechanical level, potentially predicated by changes in ion content, when exposed to high influxes of CO 2. Future studies need to accommodate the high variability of crustacean responses to ocean acidification, and ecologically relevant ranges of pCO 2 conditions, when designing experiments with conservation-level endpoints.
... Groups 1-3 are targeted towards water quality and ecosystems, with slight variations in the focus among groups, and overall make up the smallest fraction of the documents collected (Fig. 4). Group 2 contains scientific contributions [40][41][42][43][44] to understanding the sensitivity of water quality and aquatic ecosystems, as well as indicator-based report cards [45][46][47], while group 3 addresses nutrient impacts and management in terms of the science [48][49][50][51][52] and reporting of progress [53]. In contrast, group 1 predominantly consists of reports and fact sheets showing impact indicators for Chesapeake Bay ecosystems. ...
Adaptation planning and evaluation is challenging because adaptation is occurring on complex systems that are not completely understood. Though assessment is more straightforward for single projects, the larger question often asked is whether multiple adaptation actions, developed by different actors and for different purposes, are making a region more resilient. One way to comprehensively assess adaptation is through indicators—a promising decision support tool because they can be designed to efficiently and comprehensively summarize system behavior even if significant uncertainty exists. In practice, choosing indicators requires navigating a rich and often contradictory information landscape of peer-reviewed and non-peer reviewed documents and data products, largely produced for other purposes. In this paper, we review the available information applicable to resilience indicators for the Chesapeake Bay region of the USA. To provide consistency across such diverse projects and information sources, we develop a resilience framework through literature and stakeholder engagement that provides a consistent definition of objectives and frame for evaluation. Using systematic search methods, we identified 283 relevant documents, which were then qualitatively assessed for climate change and resilience themes. Predominant themes emerge around key regional impacts—sea level rise, water quality, flooding, and aquatic ecosystems—as well as magnitude of, exposure to, and impacts of climate hazards. Notably, relatively little information was found for designing indicators for coping and adaptive capacity and adaptation responses. This result highlights that even for well-known problems in the Chesapeake Bay region, much work remains in translating the existing information landscape into actionable indicators.
... Structure, elemental composition and mechanical properties of the decapod cuticle can vary among body regions (Boßelmann et al., 2007;Chen et al., 2008;Lian and Wang, 2011;Coffey et al., 2017;Steffel et al., 2019), among species (Boßelmann et al., 2007;Steffel et al., 2019;Rosen et al., 2020) and with environmental conditions (Taylor et al., 2015;Coffey et al., 2017;Glandon et al., 2018;Bednaršek et al., 2020). For example, in blue and red king crabs (Paralithodes platypus and Paralithodes camtschaticus, respectively), hardness of the claw is about twice that of the carapace, and calcium content is elevated in the claw in both species (Coffey et al., 2017). ...
Ocean acidification can affect the ability of calcifying organisms to build and maintain mineralized tissue. In decapod crustaceans, the exoskeleton is a multilayered structure composed of chitin, protein, and mineral, predominately magnesian calcite or amorphous calcium carbonate (ACC). We investigated the effects of acidification on the exoskeleton of mature (post-terminal-molt) female southern Tanner crabs, Chionoecetes bairdi . Crabs were exposed to one of three pH levels—8.1, 7.8, or 7.5—for two years. Reduced pH led to a suite of body-region-specific effects on the exoskeleton. Microhardness of the claw was 38% lower in crabs at pH 7.5 compared with those at pH 8.1, but carapace microhardness was unaffected by pH. In contrast, reduced pH altered elemental content in the carapace (reduced calcium, increased magnesium), but not the claw. Diminished structural integrity and thinning of the exoskeleton was observed at reduced pH in both body regions; internal erosion of the carapace was present in most crabs at pH 7.5, and the claws of these crabs showed substantial external erosion, with tooth-like denticles nearly or completely worn away. Using infrared spectroscopy, we observed a shift in the phase of calcium carbonate present in the carapace of pH-7.5 crabs: a mix of ACC and calcite was found in the carapace of crabs at pH 8.1, whereas the bulk of calcium carbonate had transformed to calcite in pH-7.5 crabs. With limited capacity for repair, the exoskeleton of long-lived crabs that undergo a terminal molt, such as C. bairdi , may be especially susceptible to ocean acidification.
... The Mg/Ca ratio in organisms growing under these stressors frequently increases in high temperature and reduces in low pH, equilibrating each other when the two conditions are applied together (e.g. Glandon et al., 2018). Because the increase in Mg proportions in calcifying organisms increases the mineral solubility, growing in such conditions might represent a problem for their survival (e.g. ...
Ocean higher temperature and acidity levels affect its carbonate chemistry, and calcifying organisms that depend on the calcium carbonate saturation state (XCaCO 3) to build their skeleton may be vulnerable to these changes. Despite their important roles in the marine environment , little is known about the vulnerability of calcareous sponges under these stressors. We performed an acute short-term experiment (9 days) with thermal and pH stresses to explore their effects on the skeleton and microbiome of the calcareous sponge Sycettusa hastifera. We observed that sponge spicules showed no corrosion and no Mg/Ca ratio variation when exposed to stress conditions. However, the outer-most spicules were smaller in low pH treatment, although these effects were often diminished when higher temperatures were also applied. In general, the sponges synthesized normally shaped spicules under stress conditions, but the proportion of deformed spicules increased significantly in elevated temperature. In addition, we observed a stable host-microbiome association in which there is microbiome flexibility under thermal and pH stresses with a significantly increase in abundance of some associated bacteria. Our results suggest that S. hastifera has low vulnerability under the future ocean conditions here designed, since it showed indications of resistance that could help them adapt and survive.
... Previous research has suggested roles for environmental factors in regulating crab populations Miller 2010a, 2010b;Hurt et al. 1979). Recent research has examined the potential impacts of climate change on the dynamics of blue crab populations (Glandon et al. 2018(Glandon et al. , 2019. Trophodynamic relationships involving blue crab in the Bay have been well described (Maryland Sea Grant 2010). ...
Moving toward ecosystem-based fisheries management requires integration of biotic and abiotic factors into our understanding of population dynamics. Using blue crab (Callinectes sapidus) in the Chesapeake Bay as a model system, we applied Gaussian Graphical Models (GGMs) to understand the influence of climatic, water quality and biotic variables on estimates of key indices of blue crab recruitment for 1990‐2017. Variables included the North Atlantic Oscillation (NAO), Susquehanna River discharge, wind forcing, hypoxic volume, submerged aquatic vegetation and the catch-per-unit-effort of striped bass (Morone saxatilis). Direct effects of age‐1+ crabs and summer salinity on recruitment were significant. Phase of the NAO in summer and spring, summer and winter discharge, and hypoxic volume indirectly affected the recruitment. A simulation study shows that GGM model selection achieved nominal coverage and outperformed structural equation models (SEM) and Multivariate Adaptive Regression Splines (MARS). GGMs have the potential to improve ecosystem-based management of blue crabs in Chesapeake Bay. Specifically, the approach can be used to examine ecosystem impacts on blue crab productivity and to improve forecasts of blue crab recruitment.
... When the ambient pCO 2 was raised from 800 to 8,000 µatm, juvenile blue crabs showed no sensitivity to the duration of the intermolt period or to food consumption rate (Glandon and Miller, 2017). Additional studies using the same pCO 2 changes showed small but significant changes in the high-magnesium calcite weight in the carapace of juvenile blue crabs and an increase in magnesium content (Glandon et al., 2018). In adult blue crabs, performance was judged by quantifying fatigue behaviors using underwater treadmills and by quantifying mate-guarding behavior (Stover et al., 2013). ...
Coastal acidification in southeastern U.S. estuaries and coastal waters is influenced by biological activity, run-off from the land, and increasing carbon dioxide in the atmosphere. Acidification can negatively impact coastal resources such as shellfish, finfish, and coral reefs, and the communities that rely on them. Organismal responses for species located in the U.S. Southeast document large negative impacts of acidification, especially in larval stages. For example, the toxicity of pesticides increases under acidified conditions and the combination of acidification and low oxygen has profoundly negative influences on genes regulating oxygen consumption. In corals, the rate of calcification decreases with acidification and processes such as wound recovery, reproduction, and recruitment are negatively impacted. Minimizing the changes in global ocean chemistry will ultimately depend on the reduction of carbon dioxide emissions, but adaptation to these changes and mitigation of the local stressors that exacerbate global acidification can be addressed locally. The evolution of our knowledge of acidification, from basic understanding of the problem to the emergence of applied research and monitoring, has been facilitated by the development of regional Coastal Acidification Networks (CANs) across the United States. This synthesis is a product of the Southeast Coastal and Ocean Acidification Network (SOCAN). SOCAN was established to better understand acidification in the coastal waters of the U.S. Southeast and to foster communication among scientists, resource managers, businesses, and governments in the region. Here we review acidification issues in the U.S. Southeast, including the regional mechanisms of acidification and their potential impacts on biological resources and coastal communities. We recommend research and monitoring priorities and discuss the role SOCAN has in advancing acidification research and mitigation of and adaptation to these changes.
... Bars with different letters above them differ within each species. 2009); however, calcium content is not necessarily correlated with other measures of exoskeleton structure or function (Coffey et al., 2017;Glandon et al., 2018). In this study, neither red nor blue king crab increased their feeding rate under acidified conditions in either the short or long term despite a very high initial increase in respiration. ...
Effects of ocean acidification on the respiration and feeding of juvenile red and blue king crabs (Paralithodes camtschaticus and P. platypus). Ocean acidification is a decrease in pH resulting from dissolution of anthropogenic CO 2 in the oceans that has physiological effects on many marine organisms. Juvenile red and blue king crabs (Paralithodes camtschaticus and P. platypus) exhibit both increased mortality and decreased growth in acidified waters. In this study, we determined how ocean acidification affects oxygen consumption, feeding rates, and growth in both species. Juvenile crab were exposed to three pH levels: ambient (pH 8.1), pH 7.8, and pH 7.5 for 3 weeks. Oxygen consumption and feeding ration were determined immediately after exposure to treatment water and after 3 weeks' exposure. Growth was calculated as a change in wet mass. Both species exhibited initially increased oxygen consumption at pH 7.5, but not after 3 weeks. Feeding rations did not vary with pH or exposure time. Red king crabs that moulted grew more in ambient water than in pH 7.5. The initial increase in oxygen consumption at pH 7.5 suggests the crab increased metabolism and expended more energy in osmo-/iono-regulation. Without an increase in feeding ration, it is likely the crab reduced energy expenditure in other areas, explaining the reduced growth and increased mortality observed in this and other studies.
... The increase in energetic demands as a result of the predicted increase in the growing season combined with an increase in the vulnerability of crab prey in the more acidic water of the future may cause crab to target weaker prey items more heavily and could have ecosystem-wide effects. There is also evidence that the increased growth rates associated with increased temperature may come at a cost to blue crab carapace integrity [35]. In order to sustain increased growth rates when exposed to high temperature, the percent of high-magnesium calcite in the carapace declines, which has been associated with declines in carapace strength in other invertebrates [36][37][38]. ...
Quantifying the physiological impact of environmental stressors on living organisms is critical to predicting the response of any given species to future climate scenarios. Oxygen consumption rates (μmol/g/min) were measured to examine the physiological response of the juvenile blue crab Callinectes sapidus from the Chesapeake Bay (Patuxent River, Maryland) to elevated temperature and dissolved carbon dioxide in water (pCO2) reflective of projected future climate scenarios. Treatment levels were selected to represent current conditions in the Chesapeake Bay (26°C and 800 μatm) and conditions predicted to occur by the year 2100 (31°C and 8,000 μatm). Crabs were exposed in a factorial design to these conditions throughout two successive molts (approximately 30 days). At the end of the exposure, the oxygen consumption rates of individual crabs were determined over at least a 10-h period using a flow-through respiration chamber equipped with optical oxygen electrodes. No significant effect of temperature or pCO2 on oxygen consumption was observed, suggesting the absence of a respiratory impact of these two climate stressors on juvenile blue crabs. Oxygen consumption rates were also determined for crabs that experienced a rapid increase in temperature without prior acclimation. The oxygen consumption rate of crabs may have acclimated to increased temperature during the 30-day exposure period before respiratory measurement. This potential acclimation, combined with high individual variability, and a relatively small difference in temperature treatments are likely the cause for the lack of a statistically significant difference in mean oxygen consumption rates by temperature in the core experiment. The results of this study suggest that the blue crab may be quite resilient to future climate stressors and underscore the need for species-specific studies to quantify the effects of climate change on estuarine crustaceans.
... The increase in energetic demands as a result of the predicted increase in the growing season combined with an increase in the vulnerability of crab prey in the more acidic water of the future may cause crab to target weaker prey items more heavily and could have ecosystem-wide effects. There is also evidence that the increased growth rates associated with increased temperature may come at a cost to blue crab carapace integrity [35]. In order to sustain increased growth rates when exposed to high temperature, the percent of high-magnesium calcite in the carapace declines, which has been associated with declines in carapace strength in other invertebrates [36][37][38]. ...
Understanding how increases in water temperature may affect winter dormancy period duration and overwinter survival are important for the effective conservation and management of estuarine species in the face of a warming climate. In this study, we determined the length of the overwintering period and the probability of overwinter survival of blue crab (Callinectes sapidus), an ecologically and economically important estuarine crustacean. Overwintering period length and probability of overwinter survival were determined using projected water temperatures up to the year 2100, derived from a harmonic model that utilized air temperatures from multi-model ensemble of regional-scale climate projections. Our estimates of warming water temperatures by 2100 in Chesapeake Bay indicate that winters will be up to 50% shorter and overwinter survival will increase by at least 20% compared to current conditions. The warmer conditions will lead to faster and prolonged seasonal growth, which, when combined with lower winter mortality, will lead to increased population productivity. The level of expression of this increased productivity will depend on the response of other elements of the Chesapeake Bay food web, as well as possible changes to fishery management policies over the same time period.
... To supply enough oxygen, the beaker was stirred continuously with a 1095 cm plastic sheet attached to a motor (30 rpm). The beakers were placed in a water bath (50930910 cm) with a heater (SX003 N, GEX, Osaka, Japan) to adjust water temperature to 20±2°C to facilitate larval growth (Kornienko and Korn 2016;Glandon et al. 2018) under photoperiod (18 h light/6 h dark) conditions. The rearing seawater was changed once a day for each beaker; simultaneously, approximately 2 individuals per larva (0.2 indvid./ml) of newly hatched Artemia sp. ...
Ocean acidification (OA) is predicted to decrease the abundance of calcified organisms such as gastropods. Since hermit crabs utilize gastropod shell as mobile shelter, OA has indirect impacts on hermit crab population. To examine the impacts of OA on hermit crab communities, which use calcified shell as the mobile shelter, we conducted field surveys and laboratory experiments using volcanic CO2 seeps in Shikine Island, Japan. By comparing hermit crab community structures and shell availability among five intertidal rocky shores with different degrees of acidification, Paguroidea abundance and species richness were simplified in acidified areas. Rearing experiments comparing survival rates of two Paguroidea species, Pagurus filholi (de Man, 1887) and Clibanarius virescens (Krauss, 1843), at both adult and larval stages, between acidified and ambient aquaria revealed that acidified seawater reduced larval survival rate of C. virescens. Overall, the results indicated that the species-specific direct effect in elevated C. virescens larval mortality could simplify the Paguroidea species composition. In addition, such direct effect would also lead to reduction of Paguroidea abundance, along with indirect effects though a decrease in shell availability.
How ocean acidification (OA) interacts with other stressors is understudied, particularly for predators and prey. We assessed long-term exposure to decreased pH and low salinity on (1) juvenile blue crab Callinectes sapidus claw pinch force, (2) juvenile hard clam Mercenaria mercenaria survival, growth, and shell structure, and (3) blue crab and hard clam interactions in filmed mesocosm trials. In 2018 and 2019, we held crabs and clams from the Chesapeake Bay, USA, in crossed pH (low: 7.0, high: 8.0) and salinity (low: 15, high: 30) treatments for 11 and 10 wk, respectively. Afterwards, we assessed crab claw pinch force and clam survival, growth, shell structure, and ridge rugosity. Claw pinch force increased with size in both years but weakened in low pH. Clam growth was negative, indicative of shell dissolution, in low pH in both years compared to the control. Growth was also negative in the 2019 high-pH/low-salinity treatment. Clam survival in both years was lowest in the low-pH/low-salinity treatment and highest in the high-pH/high-salinity treatment. Shell damage and ridge rugosity (indicative of deterioration) were intensified under low pH and negatively correlated with clam survival. Overall, clams were more severely affected by both stressors than crabs. In the filmed predator-prey interactions, pH did not substantially alter crab behavior, but crabs spent more time eating and burying in high-salinity treatments and more time moving in low-salinity treatments. Given the complex effects of pH and salinity on blue crabs and hard clams, projections about climate change on predator-prey interactions will be difficult and must consider multiple stressors.
Procambarus clarkii was harvested in different months (April, May, and June) and classified to different groups based on weight (small, 10–20 g; medium, 20–30 g; and large, 30–40 g). The head shells (HS) and tail shells (TS) were obtained and chemical proximate components, microstructure and texture of crayfish shell were investigated, and the principal component analysis (PCA) and correlation analysis among the indices was performed. The results indicated that the moisture content of crayfish shell was significantly decreased (P < 0.05), whereas the contents of chitin, ash, and calcium was increased with the passage of sampling time and the increase of sampling weight. Under the same crayfish weight and same sampling month, the hardness and lipid content of HS were higher than TS, while the protein content exhibited an opposite trend. The results of PCA and correlation analysis showed that the gradual harden crayfish shell from April to June exhibited an increased thickness, ordered protein, tighten intramolecular and intermolecular hydrogen bonds, which might possess a high mechanical properties of red swamp crayfish during transport. This work would be benefit for the replenishment of crayfish shell database and provided theoretical references for crayfish transportation standard.
Nowadays, due to increasing carbon dioxide released, water acidification poses a series of serious impacts on aquatic organisms. To evaluate the effects of water acidification on crustaceans, we focused on the Chinese mitten crab Eriocheir sinensis, which is a spawning migration and farmed species in China. Based on histological and oocyte transparent liquid observation, we found that the acidified environment significantly delayed the ovarian maturation of E. sinensis. Moreover, RNA-seq was applied to obtain gene expression profile from the crab's gills and ovaries in response to acidified environment. Compared with control groups, a total of 5471 differentially expressed genes (DEGs) were identified in acidified gills and 485 DEGs were identified in acidified ovaries. Enrichment analysis indicated that some pathways also responded to the acidified environment, such as PI3K-Akt signaling pathway, Chemokine signaling pathway, apoptosis and toll-like receptor signaling pathway. Subsequently, some DEGs involved in immune response (ALF, Cathepsin A, HSP70, HSP90, and catalase) and ovarian maturation (Cyclin B, Fem-1a, Fem-1b, and Fem-1c) were selected to further validate the influence of water acidification on gene expression by qRT-PCR. The results showed that the expression level of immune-related genes was significantly increased to response to the water acidification, while the ovarian maturation-related genes were significantly decreased. Overall, our data suggested that E. sinensis was sensitive to the reduced pH. This comparative transcriptome also provides valuable molecular information on the mechanisms of the crustaceans responding to acidified environment.
Skeletal carbonate mineralogy data from the literature was combined with new X-ray diffractometry data from New Zealand crabs, in order to elucidate mineralogical patterns related to body part, habitat, latitude, and phylogeny, with a view to understanding both the potential vulnerability and the preservation potential of crab shells. In general, crab carbonate is 100% Mg-calcite. In nine specimens from three New Zealand species (Austrohelice crassa, Charybdis japonica, and Hemigrapsus crenulatus) we found the first record of aragonite in brachyurid crab carbonate. Brachyurid crabs tested here generally produce Mg-calcite with mean of 6–7 wt% MgCO3, though families Epaltidae, Majidae, Menippidae and Oziidae produ\ce high-Mg calcite (8–9 wt% MgCO3), while Eiphiidae and Hymenosomatidae produce low-Mg calcite (3–4 wt% MgCO3). Anomurid crabs showed no aragonite in any specimen, but varied more in Mg content, with the family Porcellanidae producing the highest mean Mg content found (9.3 wt%MgCO3). In most cases the standard deviation and range of values within species is small (SD 0–1.5, range 1–3 wt% MgCO3. There is little evidence of partitioning of Mg in skeletal elements; Mg in the claw, for example, is not significantly different than that of the carapace, legs, or abdomen, whether considered across all species, or within individuals. Latitude (as a proxy for water temperature), too, does not appear to affect Mg in crabs, though it is possible that environment (rocky vs sandy shore) does. The strong tendency for crabs to produce mid-range Mg in calcite suggests that they may be striking a balance between mechanical strengthening of calcite while limiting solubility in sea water.
The estuaries and continental shelf system of the United States Mid-Atlantic are subject to ocean acidification driven by atmospheric CO2, and coastal acidification caused by nearshore and land-sea interactions that include biological, chemical, and physical processes. These processes include freshwater and nutrient input from rivers and groundwater; tidally-driven outwelling of nutrients, inorganic carbon, alkalinity; high productivity and respiration; and hypoxia. Hence, these complex dynamic systems exhibit substantial daily, seasonal, and interannual variability that is not well captured by current acidification research on Mid-Atlantic organisms and ecosystems. We present recommendations for research priorities that target better understanding of the ecological impacts of acidification in the U. S. Mid-Atlantic region. Suggested priorities are: 1) Determining the impact of multiple stressors on our resource species as well as the magnitude of acidification; 2) Filling information gaps on major taxa and regionally important species in different life stages to improve understanding of their response to variable temporal scales and sources of acidification; 3) Improving experimental approaches to incorporate realistic environmental variability and gradients, include interactions with other environmental stressors, increase transferability to other systems or organisms, and evaluate community and ecosystem response; 4) Determining the capacity of important species to acclimate or adapt to changing ocean conditions; 5) Considering multi-disciplinary, ecosystem-level research that examines acidification impacts on biodiversity and biotic interactions; and 6) Connecting potential acidification-induced ecological impacts to ecosystem services and the economy. These recommendations, while developed for the Mid-Atlantic, can be applicable to other regions will help align research towards knowledge of potential larger-scale ecological and economic impacts.
With the occurrence of global change, research aimed at estimating the performance of marine ectotherms in a warmer and acidified future has intensified. The concept of oxygen- and capacity-limited thermal tolerance, which is inspired by the Fry paradigm of a bell-shaped increase–optimum–decrease-type response of aerobic scope to increasing temperature, but also includes proposed negative and synergistic effects of elevated CO2 levels, has been suggested as a unifying framework. The objectives of this meta-analysis were to assess the following: (i) the generality of a bell-shaped relationship between absolute aerobic scope (AAS) and temperature; (ii) to what extent elevated CO2 affects resting oxygen uptake MO2rest and AAS; and (iii) whether there is an interaction between elevated temperature and CO2. The behavioural effects of CO2 are also briefly discussed. In 31 out of 73 data sets (both acutely exposed and acclimated), AAS increased and remained above 90% of the maximum, whereas a clear thermal o
Anthropogenic CO2 release is increasing the pCO2 in the atmosphere and oceans and causing a decrease in the pH of the oceans. This decrease in pH, known as ocean acidification, can have substantial negative effects on marine life. In this study, we use wild-brooded larvae and larvae from females held in treatment pH for two brooding cycles over 2 years to detect carryover effects from oogenesis and embryogenesis. Ovigerous females were held at three pHs: ∼8.1 (Ambient), 7.8, and 7.5. Exposure to acidified conditions at the larval stage alone had minimal effects on the larvae, possibly because larvae may be adapted to living in an environment with large pH swings. Exposure of Tanner crab larvae to low pH during the embryo phase had a more substantial effect on morphology, size, Ca/Mg content, and metabolic rate than exposure during the larval phase, and maternal exposure during the oogenesis phase increased the carryover effect. Although the larval phase itself is resilient to low pH, carryover effects are likely to have a negative effect on larvae in the wild. These results, combined with negative effects of high pCO2 at other life history stages, indicate that high pCO2 may have a negative effect on the Tanner crab populations and fisheries soon.
Ocean acidification, a decrease in ocean pH due to absorption of anthropogenic atmospheric CO2, has variable effects on different species. To examine the effects of long-term exposure on Tanner crab (Chionoecetes bairdi) embryonic development, hatching success, and calcification, ovigerous females were reared in one of three treatments: ambient
pH (∼8.1), pH 7.8, and pH 7.5 for 2 years. Embryos and larvae in year 1 were from oocytes developed in the field and appear
resilient to high pCO2. Embryos and larvae in year 2 were from oocytes developed under high pCO2 conditions. Oocyte development appears sensitive to high pCO2, effects carryover and altered embryonic development, and reduced hatching success with on average 71% fewer viable larvae
hatched in the pH 7.5 treatment than in the other treatments. Per cent calcium was reduced among females exposed to pH 7.5
waters, and their carapaces were noticeably more pliable than those in the other treatments. Softer carapaces may result in
reduced defences against predators, and a reduction in the ability to feed on prey with hard parts such as shells. The results
from this long-term study suggest that projected ocean pH levels within the next two centuries will likely have a pronounced
impact on Tanner crab populations unless the crab are able to acclimatize or adapt to changing conditions.
Some facts concerning the occurrence of low-temperature magnesian calcites, and their chemistry, mineralogy and compositional controls in natural systms are discussed. This material provides a basis for understanding the experimental and theoretical work and its meaning in low-temperature, biogeochemical systems. The report considers unit cell parameters of synthetic inorganic and biogenic magnesian calcites. Differences between these calcite types are interpreted in terms of chemical and structural properties. The detailed discussion of the unit cell parameters forms the basis for magnesian calcite solubilities and solution behavior. Experimental data on solubilities are reviewed and interpreted in terms of thermodynamic equilibrium and stoichiometric saturation concepts. Finally, a fundamental thermodynamic approach to an understanding of the solubilties and solution behavior of magnesian calcites is presented. Refs.
Dissanayake, A., and Ishimatsu, A. 2011. Synergistic effects of elevated CO2 and temperature on the metabolic scope and activity in a shallow-water coastal decapod (Metapenaeus joyneri; Crustacea: Penaeidae). – ICES Journal of Marine Science, 68: 1147–1154.
The physical drivers of climate change (increased CO2; hypercapnia and temperature) are causing increasing warming of the earth's oceans, elevating oceanic CO2 concentrations, and acidity. Elucidating possible climate change impacts on marine biota is of paramount importance, because generally, invertebrates are more sensitive to hypercapnia than fish. This study addresses impacts of synergistic factors; hypercapnia and temperature on osmoregulation, acid–base balance, and resting and active metabolism (assessed as oxygen consumption rates) and behavioural performance in a model nektonic crustacean. Metapenaeus joyneri exposed to both hypercapnia (1 kPa) at two temperatures (15 and 20°C) demonstrated significant physiological effects, i.e. new regulatory set points (lower haemolymph osmolality and higher pH, i.e. alkalosis) and reduced metabolic scope (MS), compared with control individuals (normocapnia, 0.04 kPa). Behavioural effects included a significant 30% reduction in swimming ability and may be the result of reduced MS (i.e. difference between active and routine metabolism). Synergistic factors may cause organisms to shift energy utilization towards up-regulation of maintenance functions (i.e. osmoregulatory ability) resulting in a decrease in both aerobic scope and energy-demanding activities. Laboratory-derived evidence elucidating the impacts in key model groups is of paramount importance, if we are to improve our knowledge of physiological effects of synergistic climate change factors.
Adult infaunal clams Macoma balthica persist at low densities in sandy and muddy habitats in Chesapeake Bay, despite intense predation by Callinectes sapidus; another infaunal soft-shelled clam Mya arenaria only persists in sandy habitats. It was hypothesized that the persistence of M. balthica and M. arenaria in certain habitats was due to blue crabs exhibiting a type III (sigmoid) functional response whereby the risk of mortality is reduced at low clam densities. With the exception of M. balthica in mud, abundances of M. arenaria and M. balthica decreased as blue crab abundance increased during the summer. When blue crabs reached their peak abundances in July, M. balthica was predominant in mud whereas M. arenaria numbers dropped to zero in mud and persisted in sand at similar low densities to M. balthica in sand. In the laboratory, blue crabs exhibited density-dependent (type III) functional responses to M. balthica irrespective of sediment type and tank size, even though mortality rates of clams were significantly higher in sand than mud. Differences in habitat-specific burial depth probably accounted for the differential survival of M. balthica in sand and mud. Thus, M. balthica obtained a relative refuge from blue crab predatioin at low densities similar to those in the field near the end of the seasonal period of active predation. Experiments with blue crabs indicated a type III functional response to M. arenaria in sand and an inversely density-dependent type II response to M. arenaria in mud. -from Authors
Increased levels of atmospheric CO2 are anticipated to cause decreased seawater pH. Despite the fact that calcified marine invertebrates are particularly susceptible to acidification, bar- nacles have received little attention. We examined larval condition, cyprid size, cyprid attachment and metamorphosis, juvenile to adult growth, shell calcium carbonate content, and shell resistance to dislodgement and penetration in the barnacle Amphibalanus amphitrite reared from nauplii in either ambient pH 8.2 seawater or under CO2-driven acidification of seawater down to a pH of 7.4. There were no effects of reduced pH on larval condition, cyprid size, cyprid attachment and metamorpho- sis, juvenile to adult growth, or egg production. Nonetheless, barnacles exposed to pH 7.4 seawater displayed a trend of larger basal shell diameters during growth, suggestive of compensatory calcifi- cation. Furthermore, greater force was required to cause shell breakage of adults raised at pH 7.4, indicating that the lower, active growth regions of the wall shells had become more heavily calcified. Ash contents (predominately calcium carbonate) of basal shell plates confirmed that increased calci- fication had occurred in shells of individuals reared at pH 7.4. Despite enhanced calcification, pen- etrometry revealed that the central shell wall plates required significantly less force to penetrate than those of individuals raised at pH 8.2. Thus, dissolution rapidly weakens wall shells as they grow. The ramifications of our observations at the population level are important, as barnacles with weakened wall shells are more vulnerable to predators.
The integument of decapod crustaceans consists of an outer epicuticle, an exocuticle, an endocuticle and an inner membranous layer underlain by the hypodermis. The outer three layers of the cuticle are calcified. The mineral is in the form of calcite crystals and amorphous calcium carbonate. In the epicuticle, mineral is in the form of spherulitic calcite islands surrounded by the lipid-protein matrix. In the exo- and endocuticles the calcite crystal aggregates are interspersed with chitin-protein fibers which are organized in lamellae. In some species, the organization of the mineral mirrors that of the organic fibers, but such is not the case in certain cuticular regions in the xanthid crabs. Thus, control of crystal organization is a complex phenomenon unrelated to the gross morphology of the matrix.
Since the cuticle is periodically molted to allow for growth, this necessitates a bidirectional movement of calcium into the cuticle during postmolt and out during premolt resorption of the cuticle. In two species of crabs studied to date, these movements are accomplished by active transport effected by a Ca-ATPase and Na/Ca exchange mechanism.
The epi- and exocuticular layers of the new cuticle are elaborated during premolt but do not calcify until the old cuticle is shed. This phenomenon also occurs in vitro in cuticle devoid of living tissue and implies an alteration of the nucleating sites of the cuticle in the course of the molt.
Over the next century, elevated quantities of atmospheric CO2 are expected to penetrate into the oceans, causing a reduction in pH (-0.3/-0.4 pH unit in the surface ocean) and in the concentration of carbonate ions (so-called ocean acidification). Of growing concern are the impacts that this will have on marine and estuarine organisms and ecosystems. Marine shelled molluscs, that colonized a large latitudinal gradient and can be found from intertidal to deep-sea habitats, are economically and ecologically important species providing essential ecosystem services including habitat structure for benthic organisms, water purification and a food source for other organisms. The effects of ocean acidification on the growth and shell production by juvenile and adult molluscs are variable among species and even within the same species, precluding the drawing of a general picture. This is, however, not the case for pteropods, with all species tested so far, being negatively impacted by ocean acidification. The blood of shelled mollusks may exhibit lower pH with consequences for several physiological processes (e.g. respiration, excretion...) and, in some cases, increased mortality in the long term. While fertilization may remain unaffected by elevated pCO2, embryonic and larval development will be highly sensitive with important reductions in size and decreased survival of larvae, increases in the number of abnormal larvae and an increase in the developmental time. There are big gaps in the current understanding of the biological consequences of an acidifying ocean on shelled molluscs. For instance, the natural variability of pH and the interactions of changes in the carbonate chemistry with changes in other environmental stressors such as increased temperature and changing salinity, the effects of species interactions, as well as the capacity of the organisms to acclimate and/or adapt to changing environmental conditions are poorly described.
Ocean acidification, a decrease in the pH in marine waters associated with rising atmospheric CO2 levels, is a serious threat to marine ecosystems. In this paper, we determine the effects of long-term exposure to near-future levels of ocean acidification on the growth, condition, calcification, and survival of juvenile red king crabs, Paralithodes camtschaticus, and Tanner crabs, Chionoecetes bairdi. Juveniles were reared in individual containers for nearly 200 days in flowing control (pH 8.0), pH 7.8, and pH 7.5 seawater at ambient temperatures (range 4.4-11.9 °C). In both species, survival decreased with pH, with 100% mortality of red king crabs occurring after 95 days in pH 7.5 water. Though the morphology of neither species was affected by acidification, both species grew slower in acidified water. At the end of the experiment, calcium concentration was measured in each crab and the dry mass and condition index of each crab were determined. Ocean acidification did not affect the calcium content of red king crab but did decrease the condition index, while it had the opposite effect on Tanner crabs, decreasing calcium content but leaving the condition index unchanged. This suggests that red king crab may be able to maintain calcification rates, but at a high energetic cost. The decrease in survival and growth of each species is likely to have a serious negative effect on their populations in the absence of evolutionary adaptation or acclimatization over the coming decades.
Due to their aragonitic shell, thecosome pteropods
may be particularly vulnerable to ocean acidification driven
by anthropogenic CO2 emissions. This applies specifically to
species inhabiting Arctic surface waters that are projected to
become temporarily and locally undersaturated with respect
to aragonite as early as 2016. This study investigated the ef-
fects of rising partial pressure of CO2 (pCO2) and elevated
temperature on pre-winter juveniles of the polar pteropod
Limacina helicina. After a 29 day experiment in Septem-
ber/October 2009 at three different temperatures and under
pCO2 scenarios projected for this century, mortality, shell
degradation, shell diameter and shell increment were inves-
tigated. Temperature and pCO2 had a significant effect on
mortality, but temperature was the overriding factor. Shell
diameter, shell increment and shell degradation were signifi-
cantly impacted by pCO2 but not by temperature. Mortality ◦◦
was 46% higher at 8 C than at in situ temperature (3 C), and 14% higher at 1100 μatm than at 230 μatm. Shell diame- ter and increment were reduced by 10 and 12% at 1100 μatm and 230 μatm, respectively, and shell degradation was 41% higher at elevated compared to ambient pCO2. We conclude that pre-winter juveniles will be negatively affected by both rising temperature and pCO2 which may result in a possible decline in abundance of the overwintering population, the ba- sis for next year’s reproduction.
Due to their aragonitic shell, thecosome pteropods
may be particularly vulnerable to ocean acidification driven
by anthropogenic CO2 emissions. This applies specifically to
species inhabiting Arctic surface waters that are projected to
become temporarily and locally undersaturated with respect
to aragonite as early as 2016. This study investigated the ef-
fects of rising partial pressure of CO2 (pCO2) and elevated
temperature on pre-winter juveniles of the polar pteropod
Limacina helicina. After a 29 day experiment in Septem-
ber/October 2009 at three different temperatures and under
pCO2 scenarios projected for this century, mortality, shell
degradation, shell diameter and shell increment were inves-
tigated. Temperature and pCO2 had a significant effect on
mortality, but temperature was the overriding factor. Shell
diameter, shell increment and shell degradation were signifi-
cantly impacted by pCO2 but not by temperature. Mortality ◦◦
was 46% higher at 8 C than at in situ temperature (3 C), and 14% higher at 1100 μatm than at 230 μatm. Shell diame- ter and increment were reduced by 10 and 12% at 1100 μatm and 230 μatm, respectively, and shell degradation was 41% higher at elevated compared to ambient pCO2. We conclude that pre-winter juveniles will be negatively affected by both rising temperature and pCO2 which may result in a possible decline in abundance of the overwintering population, the ba- sis for next year’s reproduction.
Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean–carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.
Anthropogenic elevation of atmospheric carbon dioxide (pCO(2)) is making the oceans more acidic, thereby reducing their degree of saturation with respect to calcium carbonate (CaCO3). There is mounting concern over the impact that future CO2-induced reductions in the CaCO3 saturation state of seawater will have on marine organisms that construct their shells and skeletons from this mineral. Here, we present the results of 60 d laboratory experiments in which we investigated the effects of CO2-induced ocean acidification on calcification in 18 benthic marine organisms. Species were selected to span a broad taxonomic range (crustacea, cnidaria, echinoidea, rhodophyta, chlorophyta, gastropoda, bivalvia, annelida) and included organisms producing aragonite, low-Mg calcite, and high-Mg calcite forms of CaCO3. We show that 10 of the 18 species studied exhibited reduced rates of net calcification and, in some cases, net dissolution under elevated pCO(2). However, in seven species, net calcification increased under the intermediate and/or highest levels of pCO(2), and one species showed no response at all. These varied responses may reflect differences amongst organisms in their ability to regulate pH at the site of calcification, in the extent to which their outer shell layer is protected by an organic covering, in the solubility of their shell or skeletal mineral, and in the extent to which they utilize photosynthesis. Whatever the specific mechanism(s) involved, our results suggest that the impact of elevated atmospheric pCO(2) on marine calcification is more varied than previously thought.
The postmolt phase of the molt cycle of the blue crab was divided into soft (2–3 h), leathery (2–3 h), and paper shell (4–18 h) stages based on the rigidity of the lateral spine. The intermolt stages were determined by observing the growth of the endoskeleton, and the appearance of the membranous layer, at the edge of the paddle at low power magnification. The intermolt phase was divided into Stage C1 (exocuticle thicker than endocuticle), C2 (endocuticle thicker than exocuticle), and (membranous layer present). The onset of the premolt period was observed to occur before the white line condition. Stage was the dominant phase of the intermolt period and the duration of this stage was highly correlated with the length of the molt cycle. The average molt cycle duration was 38 days.
Carbonate-rich sediments at shoal to shelf depths (<200 m) represent a major CaCO3 reservoir that can rapidly react to the decreasing saturation state of seawater with respect to carbonate minerals, produced by the increasing partial pressure of atmospheric carbon dioxide (pCO2) and acidification of ocean waters. Aragonite is usually the most abundant carbonate mineral in these sediments. However, the second most abundant (typically ~24 wt%) carbonate mineral is high Mg-calcite (Mg-calcite) whose solubility can exceed that of aragonite making it the first responder to the decreasing saturation state of seawater. For the naturally occurring biogenic Mg-calcites, dissolution experiments have been used to predict their stoichiometric solubilities as a function of mol% MgCO3. The only valid relationship that one can provisionally use for the metastable stabilities for Mg-calcite based on composition is that for the synthetically produced phases where metastable equilibrium has been achieved from both
Ocean acidification resulting from human emissions of carbon dioxide has already lowered and will further lower surface ocean pH. The consequent decrease in calcium carbonate saturation potentially threatens calcareous marine organisms. Here, we demonstrate that the calcification rates of the edible mussel (Mytilus edulis) and Pacific oyster (Crassostrea gigas) decline linearly with increasing pCO2. Mussel and oyster calcification may decrease by 25 and 10%, respectively, by the end of the century, following the IPCC IS92a scenario (∼740 ppmv in 2100). Moreover, mussels dissolve at pCO2 values exceeding a threshold value of ∼1800 ppmv. As these two species are important ecosystem engineers in coastal ecosystems and represent a large part of worldwide aquaculture production, the predicted decrease of calcification in response to ocean acidification will probably have an impact on coastal biodiversity and ecosystem functioning as well as potentially lead to significant economic loss.
Many physiological responses in present-day coral reefs to climate change are interpreted as consistent with the imminent
disappearance of modern reefs globally because of annual mass bleaching events, carbonate dissolution, and insufficient time
for substantial evolutionary responses. Emerging evidence for variability in the coral calcification response to acidification,
geographical variation in bleaching susceptibility and recovery, responses to past climate change, and potential rates of
adaptation to rapid warming supports an alternative scenario in which reef degradation occurs with greater temporal and spatial
heterogeneity than current projections suggest. Reducing uncertainty in projecting coral reef futures requires improved understanding
of past responses to rapid climate change; physiological responses to interacting factors, such as temperature, acidification,
and nutrients; and the costs and constraints imposed by acclimation and adaptation.
This book provides students with the tools necessary to understand the processes that control the chemical species present in waters of both natural and engineered systems. After providing basic information about water itself and the chemical composition of water in environmental systems, the text coves the theory (thermodynamics, activity, and kinetics) and other background material necessary to solve chemical problems. The text emphasizes that both equilibrium and kinetic processes are important in aquatic systems. The content is focused not only on inorganic constituents, but also on the organic chemicals present in water. Quantitative equilibrium and kinetic problems related to acid-base chemistry, complexation, solubility, oxidation/reduction reactions, sorption, and the fate and reactions of organic chemicals are solved using mathematical, graphical, and computational tools. These concepts are extended to photochemistry, chlorine and disinfectants, geochemical controls on chemical composition, trace metals, nutrients, and natural organic matter. Numerous in-chapter examples are provided to show the application of theory and demonstrate how problems are solved using various techniques. Additional web material provides advanced content and context.
Ocean acidification (OA) adversely affects a broad range of marine calcifying organisms. Crustaceans, however, exhibit mixed responses to OA, with growth or survival negatively affected in some species, but unaffected or positively affected in others. In crustaceans, the mineralized cuticle resists mechanical loads, provides protection from the environment, and enables mobility, but little is known about how OA or interactions between OA and temperature affect its structure or function. Here, the effects of OA on the mechanics, structure, and composition of the cuticle in two Alaska king crab species was assessed. Juvenile blue king crabs (Paralithodes platypus) were exposed for a year to three pH levels, 8.1 (ambient), 7.8 and 7.5. Juvenile red king crabs (Paralithodes camtschaticus) were exposed for ~ 6 months to two pH levels, 8.0 and 7.8, at three temperatures: ambient, ambient + 2 °C, and ambient + 4 °C. Cuticle microhardness (a measure of resistance to permanent or plastic mechanical deformation), thickness, ultrastructure, and elemental composition were assessed in two body regions, the carapace and the crushing chela (claw). In both species tested, OA reduced endocuticle microhardness in the chela, but not in the carapace. There was no effect of pH or temperature on total procuticle thickness of the chela or carapace in either species. Reductions in microhardness were not driven by reduced calcium content of the shell. In fact, calcium content was significantly elevated in the carapace of blue king crabs and in the chela of red king crabs exposed to lower than ambient pH at ambient temperature, suggesting that calcium content alone is not a sufficient proxy for mechanical properties. Reduced chela microhardness, indicative of more compliant material, could compromise the utility of crushing chelae in feeding and defense.
Future climate scenarios predict increases in both ocean temperature and dissolved carbon dioxide (pCO2) over the next century. Calcifying invertebrates, which depend on specific conditions of temperature and carbonate chemistry for many processes, may be especially affected by these changes. In our study, juvenile blue crab, Callinectes sapidus, were exposed to one of four temperature/pCO2 treatments (ambient/low, ambient/high, high/low, and high/high) for two complete molts. Our study is the first to examine the effect of multiple climate stressors on blue crab and therefore basic responses, including the growth per molt (GPM), inter-molt period (IMP), and food consumption, were quantified. GPM was not affected by either increased temperature or pCO2. Although increased pCO2 did not significantly influence the duration of crab IMP, crabs in warm water had significantly shorter IMP (10.6 ± 3.1 days (± SD)) than crabs in ambient water (12.5 ± 2.8 days). Increased pCO2 did not significantly affect the amount of food crabs consumed, but crabs in warm water ate significantly more food than those in ambient water. These data suggest that the impact of warming outweighs the impact of acidification in juvenile blue crab. The effects of these changes on more complex physiological parameters such as metabolism and carapace chemistry remain to be examined. Additionally, quantifying the changes to the Chesapeake Bay food web that may occur due to the observed increase in crab growth and consumption is important to ensure sustainability of this resource in the face of future climatic changes.
Continued interest in carbonate minerals has fostered many new crystal structure studies, and today modern refinements have been undertaken for most of the common rhombohedral carbonates. The present view is primarily based on the more recent studies. The preferred technique for structural studies has been X-ray diffraction, although recently transmission electron microscopy and electron diffraction have been used. Refs.
Just after moulting the blue crab, Callinectes sapidus, is soft and defenceless, but in the following days, a hard calcareous shell is formed for support and protection. The carapace of intermoult (hard) crabs constitutes 27% of the wet weight and 53% of the dry weight, with 14% of the body water contained in a carapace fluid compartment. The pH of the shell fluid compartment is maintained at 0·3 to 0·5 pH units above that of the blood. The mineral portion of the carapace is primarily CaCO3, with minor components of Mg2+ and PO4−3 plus traces of other ions. The formation of a new shell after moulting is accomplished by apparent H+ excretion and Ca2+ uptake at remarkable rates, averaging 12·5 and reaching as high as 21 mequiv kg−1 h−1. Direct bicarbonate uptake from the sea water appears to be an important component of the apparent H+ efflux, since CO2 is deposited in CaCO3 at a rate greater than metabolic production, and the animals show a net CO2 uptake for several days.
The exoskeleton of crustaceans is formed by the cuticle, a chitin-protein-based nano-composite with hierarchical organization over at least eight levels. On the molecular level, it consists of chitin associated with proteins forming fibres, which are organized in the form of twisted plywood. On the higher levels, the twisted plywood organization is modified and forms skeletal elements with elaborate functions. The load-bearing parts of crustacean cuticle are reinforced with both crystalline and amorphous biominerals. During evolution, all parts of the exoskeleton were optimized to fulfill different functions according to different ecophysiological strains faced by the animals. This is achieved by modifications in microstructure and chemical composition. In order to understand the relationship between structure, composition, mechanical properties and function we structurally characterized cuticle from the dorsal carapace of the edible crab Cancer pagurus using light and scanning electron microscopy (SEM). The local chemical composition was investigated using energy dispersive X-ray spectroscopy (EDX) and confocal m-Raman spectroscopy. Nanoindentation tests were performed to study the resulting local mechanical properties. The results show local differences in structure on several levels of the structural hierarchy in combination with a very heterogeneous mineralization. The distal exocuticle is mineralized with calcite, followed by a layer containing a magnesium, phosphate and carbonate rich phase and ACC in the proximal part. The endocuticle contains magnesian calcite and ACC in special regions below the exocuticle. Structure and mineral phase are reflected in the local stiffness and hardness of the respective cuticle regions. The heterogeneity of structural organization and mechanical properties suggests remarkable consequences for the mechanical behaviour of the bulk material.
Carbonic anhydrase (CA) activity in the epidermis of the blue crab Callinectes sapidus increases significantly during ecdysis, and remains elevated during the postmolt stages. Branchial enzyme activity increases prior to the molt in the posterior gills; in the anterior gills CA activity parallels that in the epidermis. Calcium deposition, as measured by the incorporation of 45Ca into the cuticle, begins in the late premolt stages and increases thereafter. Acetazolamide did not inhibit Ca uptake by the isolated epidermis over a 4-h period in our experiments. Thus, while CA appears to be important to the molt cycle in general, the role of CA in shell deposition is not clear.
Biogenic minerals often contain inorganic and organic impurities that are believed to harden and toughen the material. However, because of the complexity of these systems, it is difficult to deconvolute the effect of each of these impurities on the hardness of the material. We have created single-crystal samples with a range of magnesium concentrations and measured their hardness while controlling for orientation. We find that hardness increases linearly with magnesium content and that magnesium impurities could account for ~20% of the increased hardness in biogenic calcite from the mollusk Atrina rigida when compared with pure geologic calcite.
Structure and impact of the guild of epibenthic predators foraging on infaunal com-munities were measured in the Rhode River, a small mesohaline subestuary of Chesapeake Bay. Measures of long-term variation in guild structure (species composition, abundance, and size), patterns of prey uthzation (stomach contents), and predator exclusion experiments assessed the interaction of guild structure and function. Monthly otter trawls from 1981 to 1988 caught 38 species, which utilized the subestuary on a markedly seasonal cycle with peak abundances during summer months. Species composition was significantly consistent among years, with the blue crab Callinectes sapldus, a sciaenid fish Leiostomus xanthurus or, in one year, Micropogonias undulatus, and the sole Trinectes maculatus comprising the dominant members of the guild. However, abundances of all 4 dominant species fluctuated significantly among years and, except for M. undulatus, among stations. Seasonally con-sistent patterns of population size structure showed that: L. xanthurus was composed of only 1 year-class recruiting in May; M. undulatus had 1 year-class with recruitment in November; T. maculatus was composed of 3 year-classes with recruitment in October; and C. sapidus had a 2 year-class population with recruitment in late fall and spring. Despite marked juvenile growth over the season, ontogenetic changes in diets of the 4 species occur at sizes smaller than those comprising the populations. All predators consumed a diversity of infaunal prey early in the summer, but their diets varied significantly during the season as prey availability changed. L. xanthurus and T maculatus consumed mainly amphipods and polychaetes early in the season, and took increasing frequencies of clam s~phons later; while M. undulatus primarily consumed amphipods. C. sapidus consumed mainly whole clams, other blue crabs and fish, but shifted from amphipods early in the season to increased frequencies of clams late in the season. Dietary breadth and overlap within the guild reflected the generalized, overlapping diets of the 4 species, although dietary breadth varied with predator species and season. For all species stomach contents did not vary with sediment type. Natural densities of Macoma balthica, a major dietary component for C, sapidus, responded to annual fluctuations in crab abundance as well as to variation in clam recruitment. Experimental exclusion of predators from clams (M, balthica) placed in buckets in the subestuary significantly increased clam survival. Experimental exclusion of epibenthic predators at 5 stations in the subestuary resulted in significantly higher densities for 12 of 16 infaunal species as well as for total infaunal organisms and higher ratios of infaunal predators to prey. However, most infaunal species exhibited significant variation among stations, reflecting spatial variation in both predation intensity and prey abundances. Experimental exclusion of the epibenthic predators from plots of dyed sand showed that the guild caused major sedimentary disturbance to sediment depths of 10 cm, while low infaunal densities of subsurface deposit feeders caused comparatively little bioturbation. These experiments indicate that the guild's foraging activity not only has strong direct effects on infaunal community structure, but that the guild also has significant indirect effects on infaunal community organization and patch dynamics which are highly variable in space and time.
A method for rapid determination of high-precision Sr/Ca ratios in
scleractinian corals is presented. Using an inductively coupled plasma
atomic emission spectrophotometer, samples are corrected for instrument
drift using a reference solution, similar to the approach used for
analysis of stable isotopes using gas-source mass spectrometry. Further
correction for variation of the Sr/Ca ratio with Ca concentration is
accomplished using internal standards. The precision, once all
corrections have been made, is better than 0.1% (relative standard
deviation, 1σ) for samples of similar Ca concentration and better
than 0.2% for samples with variable Ca concentrations. This method
increases the sample throughput by approximately a factor of 20 relative
to thermal ionization mass spectrometry and significantly reduces
instrument and per sample costs. Comparison of Sr/Ca data for a coral
from the Galapagos Islands with an instrumental temperature record shows
excellent agreement and demonstrates the potential for application of
this technique to samples of modern and fossil scleractinian corals and
other marine carbonates, including foraminifera.
Anthropogenic environmental change is exposing animals to changes in a complex array of interacting stressors and is already having important effects on the distribution and abundance of species. However, despite extensive examination of the effects of stressors in isolation, knowledge of the effects of stressors in combination is limited. This lack of information makes predicting the responses of organisms to anthropogenic environmental change challenging. Here, we focus on the effects of temperature and hypoxia as interacting stressors in fishes. A review of the available evidence suggests that temperature and hypoxia act synergistically such that small shifts in one stressor could result in large effects on organismal performance when a fish is exposed to the 2 stressors in combination. Although these stressors pose substantial challenges for fish, there also is substantial intraspecific variation in tolerance to these stressors that could act as the raw material for the evolution of improved tolerance. However, the potential for adaptive change is, in part, dependent on the nature of the correlations among traits associated with tolerance. For example, negative genetic correlations (or trade-offs) between tolerances to temperature and hypoxia could limit the potential for adaptation to the combined stressors, while positive genetic correlations might be of benefit. The limited data currently available suggest that tolerances to hypoxia and to high-temperature may be positively correlated in some species of fish, suggesting the possibility for adaptive evolution in these traits in response to anthropogenic environmental change.
Calcium carbonate has been precipitated from aqueous solutions containing magnesium under conditions of high supersaturation. The precipitates were analysed over time using X-ray diffraction (XRD) and Infrared Spectroscopy (IR), and it was demonstrated that in all cases amorphous calcium carbonate (ACC) was the first phase formed. The magnesium content of the ACC was defined by the Mg:Ca ratio in the solution, and increased systematically with increasing Mg:Ca. In turn, ACC occluding higher magnesium concentrations was significantly more stable than low magnesium ACC. The crystalline phase produced on transformation of ACC depended on the Mg:Ca ratio, and ACC precipitated from solutions containing higher Mg concentrations crystallised to yield high-Mg calcites (occluding up to 47mol% Mg), together with CaCO3.H2O and/or CaCO3.6H2O. The magnesium content of the ACC phase also directly affected the final morphology of the precipitates, such that continuous sheets of CaCO3 were produced at the air/solution interface at solution ratios of 3:1 Mg:Ca and above. Previously, this effect has only been observed for ACC stabilised with organic additives. These results have relevance to the mechanism of formation of biological magnesian calcites, and suggest that the stabilisation of ACC by magnesium may provide organisms with a mechanism for controlling crystal morphologies.
The effects of the decline in ocean pH, known as ocean acidification, on marine species are not well understood. To test the effects on embryos and larvae of red king crab, Paralithodes camtschaticus, ovigerous crab and their larvae were held in CO(2)-acidified (pH 7.7) and control (ambient; pH 8.0) seawater during development. Morphometrics, hatch duration, fecundity, survival, mineral content, and condition were measured. Acidified embryos had 4% larger eyes and 5% smaller yolks, while mean hatch duration was 33% longer and female fecundity was unaffected. Acidified embryos also resulted in 4% longer larvae while acidified larvae had lower survival. Calcium content of both larvae and female carapaces after molting increased by 5% and 19%, respectively. Although ocean acidification may increase larval size and calcium content, the implications of this are unclear and decreased survival is likely to harm red king crab populations.
Since 1991, significant proportions of Amphistegina populations in the Florida Keys and elsewhere have exhibited stress symptoms that include loss of symbiont color ('bleaching'), anomalous shell breakage and reproductive damage. Previous studies of other taxa have reported elevated Mg/Ca ratios in tests from pollution-stressed foraminiferal populations. The purpose of this study was to test the hypothesis that anomalous shell breakage in stressed Amphistegina gibbosa is the result of loss of control of calcification, resulting in elevated concentrations of Mg that weaken the crystal structure of the test. Analysis of Mg and Ca concentrations in A. gibbosa tests, using an Inductively-Coupled Plasma Mass Spectrometer, revealed normal Mg/Ca (2-5 mol%) in all specimens analyzed, including normal specimens collected in 1982 (prior to the onset of the stress event), and both normal and broken specimens collected quarterly from afflicted populations in 1996. Analysis of specimens from the high Mg calcite taxon, Archaias angulatus, revealed Mg/Ca of 10-14 mol%. This study, which presents an ICP-MS procedure that can be used to assess Mg/Ca in individual foraminifera, does not support the hypothesis that shell breakage in stressed Amphistegina results from disruption of calcification at the ionic level.
Measurement of density and thickness of cuticle of an array of decapod crustaceans indicates that cuticle tends to be thick and dense in benthic organisms and thinner and less dense in nektobenthic decapods. Thin section analysis of the cuticle under crossed polarized light documents a broad range of area of biomineralization. Cuticle density is strongly correlated with area of calcification. One of the nektobenthic decapods in the study exhibited no calcification of the cuticle at all, and thus exhibited the lowest density. These data support the hypothesis that density and thickness of cuticle contribute to adaptation to benthic and nektobenthic lifestyles.
In an effort to use aspects of the cuticle as taxonomic characters in phylogenies of fossil and extant decapods, variation due to gender, growth, sample location on the carapace, and molt cycle must be understood so that taxonomically important characters can be identified. In this study, effects of sample location on the carapace and carapace size were examined. A series of male Callinectes sapidus Rathbun, 1896, specimens from 2-6 cm in length were collected on the Rhode River of the Chesapeake Bay, MD, USA. To study the effects of sample location and carapace size on parameters of the cuticle, the cuticle was examined in thin section and on the surface of the dorsal carapace. The distributional density of setal pits and nodes and node size were measured on the surface. In thin section, thickness of the cuticle and construction of the nodes and setal pits was examined. Thickness of the cuticle, node size, and setal pit density increased during growth of the crab. Node density decreased with growth. Construction of nodes and setal pits remained constant in all specimens and sample locations. Morphometric parameters of the cuticle were consistent with previously reported growth rates of the carapace in C. sapidus. Differences in the rate of change for the cuticle metrics studied occurred at carapace sizes that are attained upon reaching sexual maturity. Growth rates of cuticular features provide context for comparison with similar data in other species. In addition, the change in growth rates of these features, if recognized in fossil crab populations, may allow the determination of population age structures and size at maturity.
Male blue crabs (Callinectes sapidus Rathbun) were acclimated to salinities of 5 and 34 o/oo. Microsomal preparations of gills from these animals possessed Na+ + K+-dependent ATPase specific activities of 2.33 ± 0.11 and 1.29 ± 0.11 μmoles Pi min per mg protein respectively, implicating the Na+ + K+-dependent ATPase in the previously recognized ability of the blue crab to maintain high hemolymph sodium levels in low salinity environments. The specific ATPase activity of gill microsomes increased significantly within two and one-half hours after transfer of crabs from high to low salinity, prior to stabilization of hemolymph sodium levels. The ATPase isolated from crabs acclimated to the two different salinities were both highly sensitive to ouabain, and required either K+ or NH4+ as well as Na+. Sodium-dependent phosphorylation of both enzymes was blocked by K+ or NH4+. Polyacrylamide gel electrophoresis of the sodium dodecyl sulfate-solubilized ATPases revealed one band of radioactivity in each case, with an apparent molecular weight of 104,000. The ability of NH4+ to serve as an effective counterion supports the hypothesis that, in blue crabs acclimated to low salinity, Na+ uptake may be coupled to NH4+ excretion.
Increasing atmospheric pCO 2 reduces the saturation state of seawater with respect to the aragonite, high-Mg calcite (Mg/Ca N 0.04), and low-Mg calcite (Mg/Ca b 0.04) minerals from which marine calcifiers build their shells and skeletons. Notably, these polymorphs of CaCO 3 have different solubilities in seawater: aragonite is more soluble than pure calcite, and the solubility of calcite increases with its Mg-content. Although much recent progress has been made investigating the effects of CO 2 -induced ocean acidification on rates of biological calcification, considerable uncertainties remain regarding impacts on shell/skeletal polymorph mineralogy. To investigate this subject, eighteen species of marine calcifiers were reared for 60-days in seawater bubbled with air-CO 2 mixtures of 409 ± 6, 606 ± 7, 903 ± 12, and 2856 ± 54 ppm pCO 2 , yielding aragonite saturation states (Ω A) of 2.5 ± 0.4, 2.0 ± 0.4, 1.5 ± 0.3, and 0.7 ± 0.2. Calcite/aragonite ratios within bimineralic calcifiers increased with increasing pCO 2 , but were invariant within monomineralic calcifiers. Calcite Mg/Ca ratios (Mg/Ca C) also varied with atmospheric pCO 2 for two of the five high-Mg-calcite-producing organisms, but not for the low-Mg-calcite-producing organisms. These results suggest that shell/ skeletal mineralogy within some—but not all—marine calcifiers will change as atmospheric pCO 2 continues rising as a result of fossil fuel combustion and deforestation. Paleoceanographic reconstructions of seawater Mg/Ca, temperature, and salinity from the Mg/Ca C of well-preserved calcitic marine fossils may also be improved by accounting for the effects of paleo-atmospheric pCO 2 on skeletal Mg-fractionation.
The seeded precipitation (crystal growth) of aragonite and calcite from sea water, magnesium-depleted sea water, and magnesium-free sea water has been studied by means of the steady-state disequilibrium initial rate method. Dissolved magnesium at sea water levels appears to have no effect on the rate of crystal growth of aragonite, but a strong retarding effect on that of calcite. By contrast, at levels less than about 5 per cent of the sea water level, Mg has little or no effect on calcite growth. Extended crystal growth on pure calcite seeds in sea water of normal Mg content resulted in the crystallization of magnesium calcite overgrowths, containing 7–10 mole % MgCO3 in solid solution. This suggests that the rate inhibition by Mg is due to its incorporation within the calcite crystal structure during growth, which causes the resulting magnesian calcite to be considerably more soluble than pure calcite. The standard free energy of formation of 8.5 mole% Mg calcite calculated on this assumption is in good agreement with independent estimates of magnesian calcite stability.From the work of Katz (Geochim. Cosmochim. Acta37, 1563–1586, 1973), Plummer and Mackenzie (Amer. J. Sci. 273, 515–522, 1974), and the present paper, it can be predicted that the most stable calcite in Ca-Mg exchange equilibrium with sea water contains between 2 and 7 mole%MgCO3 in solid solution. Likewise, calcites containing more than 8.5 mole% MgCO3 are less stable, and those containing less than 8.5 mole% MgCO3 are more stable than aragonite plus Ca and Mg in sea water.
Magnesium/calcium, Sr/Ca, and Na/Ca atom ratios were determined in the calcite and aragonite regions of Mytilus edulis shells which were grown in semi-artificial ‘seawater’ solutions having varying Mg/Ca, Sr/Ca, and Na/Ca ratios. These ratios were measured by instrumental neutron activation, atomic absorption, and electron microprobe analytical techniques. Strontium/calcium ratios in both calcite and aragonite were linearly proportional to solution Sr/Ca ratios. Magnesium/calcium ratios in calcite increased exponentially when solution Mg/Ca ratios were raised above the normal seawater ratio; whereas in aragonite, Mg/Ca ratios increased linearly with increases in solution Mg/Ca ratios. Sodium/calcium and sulfur/calcium ratios in calcite covaried with Mg/Ga solution ratios. Conversely, in aragonite, Na/Ca ratios varied linearly with solution Na/Ca ratios.Magnesium is known to inhibit calcite precipitation at its normal seawater concentration. We infer from the results of the work reported here that Mytilus edulis controls the Mg activity of the outer extrapallial fluid, thus facilitating the precipitation of calcitic shell. Increases in sulfur content suggest that changes in shell organic matrix content occur as a result of environmental stress. Certain increases in Mg content may also be correlated to stress. Sodium/calcium variations, and their absolute amounts in calcite and aragonite, are best explained by assuming that a substantial amount of Na is adsorbed on the calcium carbonate crystal surface. Strontium/calcium ratios show more promise than either Mg/Ca or Na/Ca ratios as seawater paleochemistry indicators, because the Sr/Ca distribution coefficients for both aragonite and calcite are independent of seawater Ca and Sr concentrations.
This is an experimental study on the mechanical and structural gradients through the cuticle of Homarus americanus (American lobster). The exocuticle (outer layer) is characterized by a very fine woven structure of the fibrous chitin–protein matrix (‘twisted plywood’ structure) and by a high stiffness (8.5–9.5 GPa). The hardness increases within the exocuticle between the surface region (130 MPa) and the region close to the interface to the endocuticle (270 MPa). In the endocuticle, which is characterized by a much coarser twisted plywood structure, both the stiffness (3–4.5 GPa) and hardness (30–55 MPa) are much smaller than in the exocuticle. The transition in mechanical properties and structure between the exocuticle and endocuticle is abrupt. The differences underline the important role of the internal structure of the twisted plywood structure and of the interface between the two cuticle layers for the overall mechanical behavior of the exoskeleton. The excellent mechanical stability of the interface (irrespective of the change in the mechanical properties) is attributed to the fact that the structural change of the twisted plywood pattern across the interface consists only of a change of the stacking density of the chitin–protein layers. The observed gradients in stiffness and hardness through the cuticle thickness are interpreted in terms of honeycomb mechanics of the twisted plywood structure. The possible role of gradients in protein cross-linking and in the mineral content is also discussed.
The cuticle of arthropods (jointed-limb animals), and especially of insects is, by biological standards, a relatively simple composite. It is a single external layer of material forming the skeleton and many sense organs. The fibrous phase is crystalline chitin making nanofibrils of about 3 nm diameter, a few hundreds of nanometers long and a modulus probably in excess of 150 GPa. At least two surfaces of the nanofibril can have silk-like protein attached through specific H-bonds; the rest of the protein is globular. The protein matrix stiffens through dehydration controlled by the introduction of hydrophobic phenolics. Crustacea add up to 40% calcium salts. The stiffness of cuticle can range from tens of GPa to 1 kPa. It can be hardened by the addition of Zn or Mn. It can form springs and change its stiffness and plasticity under the control of the animal.
The exoskeletons of the American lobster Homarus americanus and of the edible crab Cancer pagurus were analysed with structural and chemical methods. The exoskeletons consist of crystalline magnesian calcite in the form of nanocrystals (domain size about 20 nm), amorphous calcium phosphate (ACP), and α-chitin. The composition varies among different parts of the skeleton and also between the two species. Differences are related to the mechanical requirements and biological escape behaviour of the animals. The finger and claw are strongly mineralized and very hard. The shell of the body (the carapace) is less mineralized and more elastic. The lobster, as a mobile, fast-swimming animal, typically escapes from a predator whereas the crab clings to the ground and burrows into the sand. Consequently, the shell of the lobster is less mineralized (and therefore lighter and less hard) than the shell of the crab.