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1.
Rising atmospheric CO 2 and its equilibration with surface ocean seawater is lowering both the pH and carbonate saturation state (Ω) of the oceans.
Numerous calcifying organisms, including reef-building corals, may be severely impacted by declining aragonite and calcite
saturation, but the fate of coral reef ecosystems in response to ocean acidification remains largely unexplored. Naturally
low saturation (Ω ~ 0.5) low pH (6.70–7.30) groundwater has been discharging for millennia at localized submarine springs
(called “ojos”) at Puerto Morelos, México near the Mesoamerican Reef. This ecosystem provides insights into potential long
term responses of coral ecosystems to low saturation conditions. In-situ chemical and biological data indicate that both coral
species richness and coral colony size decline with increasing proximity to low-saturation, low-pH waters at the ojo centers.
Only three scleractinian coral species ( Porites astreoides, Porites divaricata, and Siderastrea radians) occur in undersaturated waters at all ojos examined. Because these three species are rarely major contributors to Caribbean
reef framework, these data may indicate that today’s more complex frame-building species may be replaced by smaller, possibly
patchy, colonies of only a few species along the Mesoamerican Barrier Reef. The growth of these scleractinian coral species
at undersaturated conditions illustrates that the response to ocean acidification is likely to vary across species and environments;
thus, our data emphasize the need to better understand the mechanisms of calcification to more accurately predict future impacts
of ocean acidification. 相似文献
2.
The effect of decreasing aragonite saturation state (Ω Arag) of seawater (elevated pCO 2) on calcification rates of Acropora muricata was studied using nubbins prepared from parent colonies located at two sites of La Saline reef (La Réunion Island, western
Indian Ocean): a back-reef site (BR) affected by nutrient-enriched groundwater discharge (mainly nitrate), and a reef flat
site (RF) with low terrigenous inputs. Protein and chlorophyll a content of the nubbins, as well as zooxanthellae abundance, were lower at RF than BR. Nubbins were incubated at ~27°C over
2 h under sunlight, in filtered seawater manipulated to get differing initial pCO 2 (1,440–340 μatm), Ω Arag (1.4–4.0), and dissolved inorganic carbon (DIC) concentrations (2,100–1,850 μmol kg −1). Increasing DIC concentrations at constant total alkalinity (A T) resulted in a decrease in Ω Arag and an increase in pCO 2. A T at the beginning of the incubations was kept at a natural level of 2,193 ± 6 μmol kg −1 (mean ± SD). Net photosynthesis (NP) and calcification were calculated from changes in pH and A T during the incubations. Calcification decrease in response to doubling pCO 2 relative to preindustrial level was 22% for RF nubbins. When normalized to surface area of the nubbins, (1) NP and calcification
were higher at BR than RF, (2) NP increased in high pCO 2 treatments at BR compared to low pCO 2 treatments, and (3) calcification was not related to Ω Arag at BR. When normalized to NP, calcification was linearly related to Ω Arag at both sites, and the slopes of the relationships were not significantly different. The increase in NP at BR in the high
pCO 2 treatments may have increased calcification and thus masked the negative effect of low Ω Arag on calcification. Removing the effect of NP variations at BR showed that calcification declined in a similar manner with
decreased Ω Arag (increased pCO 2) whatever the nutrient loading. 相似文献
3.
The decrease in the saturation state of seawater, Ω, following seawater acidification, is believed to be the main factor leading
to a decrease in the calcification of marine organisms. To provide a physiological explanation for this phenomenon, the effect
of seawater acidification was studied on the calcification and photosynthesis of the scleractinian tropical coral Stylophora pistillata. Coral nubbins were incubated for 8 days at three different pH (7.6, 8.0, and 8.2). To differentiate between the effects
of the various components of the carbonate chemistry (pH, CO 32−, HCO 3−, CO 2, Ω), tanks were also maintained under similar pH, but with 2-mM HCO 3− added to the seawater. The addition of 2-mM bicarbonate significantly increased the photosynthesis in S. pistillata, suggesting carbon-limited conditions. Conversely, photosynthesis was insensitive to changes in pH and pCO 2. Seawater acidification decreased coral calcification by ca. 0.1-mg CaCO 3 g −1 d −1 for a decrease of 0.1 pH units. This correlation suggested that seawater acidification affected coral calcification by decreasing
the availability of the CO 32− substrate for calcification. However, the decrease in coral calcification could also be attributed either to a decrease in
extra- or intracellular pH or to a change in the buffering capacity of the medium, impairing supply of CO 32− from HCO 3−. 相似文献
4.
Rising concentrations of atmospheric CO 2 are changing the carbonate chemistry of the oceans, a process known as ocean acidification (OA). Absorption of this CO 2 by the surface oceans is increasing the amount of total dissolved inorganic carbon (DIC) and bicarbonate ion (HCO 3
−) available for marine calcification yet is simultaneously lowering the seawater pH and carbonate ion concentration ([CO 3
2−]), and thus the saturation state of seawater with respect to aragonite (Ω ar). We investigated the relative importance of [HCO 3
−] versus [CO 3
2−] for early calcification by new recruits (primary polyps settled from zooxanthellate larvae) of two tropical coral species,
Favia fragum and Porites astreoides. The polyps were reared over a range of Ω ar values, which were manipulated by both acid-addition at constant pCO 2 (decreased total [HCO 3
−] and [CO 3
2−]) and by pCO 2 elevation at constant alkalinity (increased [HCO 3
−], decreased [CO 3
2−]). Calcification after 2 weeks was quantified by weighing the complete skeleton (corallite) accreted by each polyp over the
course of the experiment. Both species exhibited the same negative response to decreasing [CO 3
2−] whether Ω ar was lowered by acid-addition or by pCO 2 elevation—calcification did not follow total DIC or [HCO 3
−]. Nevertheless, the calcification response to decreasing [CO 3
2−] was nonlinear. A statistically significant decrease in calcification was only detected between Ω ar = <2.5 and Ω ar = 1.1–1.5, where calcification of new recruits was reduced by 22–37% per 1.0 decrease in Ω ar. Our results differ from many previous studies that report a linear coral calcification response to OA, and from those showing
that calcification increases with increasing [HCO 3
−]. Clearly, the coral calcification response to OA is variable and complex. A deeper understanding of the biomineralization
mechanisms and environmental conditions underlying these variable responses is needed to support informed predictions about
future OA impacts on corals and coral reefs. 相似文献
5.
Ocean acidification is thought to be a major threat to coral reefs: laboratory evidence and CO 2 seep research has shown adverse effects on many coral species, although a few are resilient. There are concerns that cold‐water corals are even more vulnerable as they live in areas where aragonite saturation (Ω ara) is lower than in the tropics and is falling rapidly due to CO 2 emissions. Here, we provide laboratory evidence that net (gross calcification minus dissolution) and gross calcification rates of three common cold‐water corals, Caryophyllia smithii, Dendrophyllia cornigera, and Desmophyllum dianthus, are not affected by pCO 2 levels expected for 2100 ( pCO 2 1058 μatm, Ω ara 1.29), and nor are the rates of skeletal dissolution in D. dianthus. We transplanted D. dianthus to 350 m depth (pH T 8.02; pCO 2 448 μatm, Ω ara 2.58) and to a 3 m depth CO 2 seep in oligotrophic waters (pH T 7.35; pCO 2 2879 μatm, Ω ara 0.76) and found that the transplants calcified at the same rates regardless of the pCO 2 confirming their resilience to acidification, but at significantly lower rates than corals that were fed in aquaria. Our combination of field and laboratory evidence suggests that ocean acidification will not disrupt cold‐water coral calcification although falling aragonite levels may affect other organismal physiological and/or reef community processes. 相似文献
6.
Physiological data and models of coral calcification indicate that corals utilize a combination of seawater bicarbonate and (mainly) respiratory CO 2 for calcification, not seawater carbonate. However, a number of investigators are attributing observed negative effects of experimental seawater acidification by CO 2 or hydrochloric acid additions to a reduction in seawater carbonate ion concentration and thus aragonite saturation state. Thus, there is a discrepancy between the physiological and geochemical views of coral biomineralization. Furthermore, not all calcifying organisms respond negatively to decreased pH or saturation state. Together, these discrepancies suggest that other physiological mechanisms, such as a direct effect of reduced pH on calcium or bicarbonate ion transport and/or variable ability to regulate internal pH, are responsible for the variability in reported experimental effects of acidification on calcification. To distinguish the effects of pH, carbonate concentration and bicarbonate concentration on coral calcification, incubations were performed with the coral Madracis auretenra (= Madracis mirabilis sensu Wells, 1973) in modified seawater chemistries. Carbonate parameters were manipulated to isolate the effects of each parameter more effectively than in previous studies, with a total of six different chemistries. Among treatment differences were highly significant. The corals responded strongly to variation in bicarbonate concentration, but not consistently to carbonate concentration, aragonite saturation state or pH. Corals calcified at normal or elevated rates under low pH (7.6–7.8) when the seawater bicarbonate concentrations were above 1800 μm . Conversely, corals incubated at normal pH had low calcification rates if the bicarbonate concentration was lowered. These results demonstrate that coral responses to ocean acidification are more diverse than currently thought, and question the reliability of using carbonate concentration or aragonite saturation state as the sole predictor of the effects of ocean acidification on coral calcification. 相似文献
7.
In response to the increases in pCO 2 projected in the 21st century, adult coral growth and calcification are expected to decrease significantly. However, no published
studies have investigated the effect of elevated pCO 2 on earlier life history stages of corals. Porites astreoides larvae were collected from reefs in Key Largo, Florida, USA, settled and reared in controlled saturation state seawater.
Three saturation states were obtained, using 1 M HCl additions, corresponding to present (380 ppm) and projected pCO 2 scenarios for the years 2065 (560 ppm) and 2100 (720 ppm). The effect of saturation state on settlement and post-settlement
growth was evaluated. Saturation state had no significant effect on percent settlement; however, skeletal extension rate was
positively correlated with saturation state, with ~50% and 78% reductions in growth at the mid and high pCO 2 treatments compared to controls, respectively. 相似文献
8.
Previous studies have demonstrated that coral and algal calcification is tightly regulated by the calcium carbonate saturation state of seawater. This parameter is likely to decrease in response to the increase of dissolved CO 2 resulting from the global increase of the partial pressure of atmospheric CO 2. We have investigated the response of a coral reef community dominated by scleractinian corals, but also including other calcifying organisms such as calcareous algae, crustaceans, gastropods and echinoderms, and kept in an open‐top mesocosm. Seawater pCO 2 was modified by manipulating the pCO 2 of air used to bubble the mesocosm. The aragonite saturation state ( Ωarag) of the seawater in the mesocosm varied between 1.3 and 5.4. Community calcification decreased as a function of increasing pCO 2 and decreasing Ωarag. This result is in agreement with previous data collected on scleractinian corals, coralline algae and in a reef mesocosm, even though some of these studies did not manipulate CO 2 directly. Our data suggest that the rate of calcification during the last glacial maximum might have been 114% of the preindustrial rate. Moreover, using the average emission scenario (IS92a) of the Intergovernmental Panel on Climate Change, we predict that the calcification rate of scleractinian‐dominated communities may decrease by 21% between the pre‐industrial period (year 1880) and the time at which pCO 2 will double (year 2065). 相似文献
9.
Zinc (Zn) is an essential element for corals. We investigated the effects of ocean acidification on zinc incorporation, photosynthesis,
and gross calcification in the scleractinian coral Stylophora pistillata. Colonies were maintained at normal pH T (8.1) and at two low-pH conditions (7.8 and 7.5) for 5 weeks. Corals were exposed to 65Zn dissolved in seawater to assess uptake rates. After 5 weeks, corals raised at pH T (8.1) exhibited higher 65Zn activity in the coral tissue and skeleton, compared with corals raised at a lower pH. Photosynthesis, photosynthetic efficiency,
and gross calcification, measured by 45Ca incorporation, were however unchanged even at the lowest pH. 相似文献
10.
To investigate annual variation in soil respiration ( R
S) and its components [autotrophic ( R
A) and heterotrophic ( R
H)] in relation to seasonal changes in soil temperature (ST) and soil water content (SWC) in an Abies holophylla stand (stand A) and a Quercus-dominated stand (stand Q), we set up trenched plots and measured R
S, ST and SWC for 2 years. The mean annual rate of R
S was 436 mg CO 2 m −2 h −1, ranging from 76 to 1,170 mg CO 2 m −2 h −1, in stand A and 376 mg CO 2 m −2 h −1, ranging from 82 to 1,133 mg CO 2 m −2 h −1, in stand Q. A significant relationship between R
S and its components and ST was observed over the 2 years in both stands, whereas a significant correlation between R
A and SWC was detected only in stand Q. On average over the 2 years, R
A accounted for approximately 34% (range 17–67%) and 31% (15–82%) of the variation in R
S in stands A and Q, respectively. Our results suggested that vegetation type did not significantly affect the annual mean
contributions of R
A or R
H, but did affect the pattern of seasonal change in the contribution of R
A to R
S. 相似文献
11.
Seven coral reef communities were defined on Shiraho fringing reef, Ishigaki Island, Japan. Net photosynthesis and calcification
rates were measured by in situ incubations at 10 sites that included six of the defined communities, and which occupied most
of the area on the reef flat and slope. Net photosynthesis on the reef flat was positive overall, but the reef flat acts as
a source for atmospheric CO 2, because the measured calcification/photosynthesis ratio of 2.5 is greater than the critical ratio of 1.67. Net photosynthesis
on the reef slope was negative. Almost all excess organic production from the reef flat is expected to be effused to the outer
reef and consumed by the communities there. Therefore, the total net organic production of the whole reef system is probably
almost zero and the whole reef system also acts as a source for atmospheric CO 2. Net calcification rates of the reef slope corals were much lower than those of the branching corals. The accumulation rate
of the former was approximately 0.5 m kyr −1 and of the latter was ~0.7–5 m kyr −1. Consequently, reef slope corals could not grow fast enough to keep up with or catch up to rising sea levels during the Holocene.
On the other hand, the branching corals grow fast enough to keep up with this rising sea level. Therefore, a transition between
early Holocene and present-day reef communities is expected. Branching coral communities would have dominated while reef growth
kept pace with sea level rise, and the reef was constructed with a branching coral framework. Then, the outside of this framework
was covered and built up by reef slope corals and present-day reefs were constructed. 相似文献
12.
Changes in the carbonate chemistry of coral reef waters are driven by carbon fluxes from two sources: concentrations of CO 2 in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air‐sea flux of CO 2 driven by benthic community processes can exceed that due to increases in atmospheric CO 2 (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae, and sand. Building on data from previous carbon flux studies along a reef‐flat transect in Moorea (French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon ( CT) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity ( AT) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Ω a). We use the model to test how changes in atmospheric CO 2 forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream–downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies. 相似文献
13.
The photosynthetic responses of the tropical tree species Acacia nigrescens Oliv. grown at different atmospheric CO 2 concentrations—from sub-ambient to super-ambient—have been studied. Light-saturated rates of net photosynthesis ( A
sat) in A. nigrescens, measured after 120 days exposure, increased significantly from sub-ambient (196 μL L −1) to current ambient (386 μL L −1) CO 2 growth conditions but did not increase any further as [CO 2] became super-ambient (597 μL L −1). Examination of photosynthetic CO 2 response curves, leaf nitrogen content, and leaf thickness showed that this acclimation was most likely caused by reduction
in Rubisco activity and a shift towards ribulose-1,5-bisphosphate regeneration-limited photosynthesis, but not a consequence
of changes in mesophyll conductance. Also, measurements of the maximum efficiency of PSII and the carotenoid to chlorophyll
ratio of leaves indicated that it was unlikely that the pattern of A
sat seen was a consequence of growth [CO 2] induced stress. Many of the photosynthetic responses examined were not linear with respect to the concentration of CO 2 but could be explained by current models of photosynthesis. 相似文献
14.
Acidification of ocean surface waters by anthropogenic carbon dioxide (CO 2) emissions is a currently developing scenario that warrants a broadening of research foci in the study of acid–base physiology.
Recent studies working with environmentally relevant CO 2 levels, indicate that some echinoderms and molluscs reduce metabolic rates, soft tissue growth and calcification during hypercapnic
exposure. In contrast to all prior invertebrate species studied so far, growth trials with the cuttlefish Sepia officinalis found no indication of reduced growth or calcification performance during long-term exposure to 0.6 kPa CO 2. It is hypothesized that the differing sensitivities to elevated seawater pCO 2 could be explained by taxa specific differences in acid–base regulatory capacity. In this study, we examined the acid–base
regulatory ability of S. officinalis in vivo, using a specially modified cannulation technique as well as 31P NMR spectroscopy. During acute exposure to 0.6 kPa CO 2, S. officinalis rapidly increased its blood [HCO 3
−] to 10.4 mM through active ion-transport processes, and partially compensated the hypercapnia induced respiratory acidosis.
A minor decrease in intracellular pH (pH i) and stable intracellular phosphagen levels indicated efficient pH i regulation. We conclude that S. officinalis is not only an efficient acid–base regulator, but is also able to do so without disturbing metabolic equilibria in characteristic
tissues or compromising aerobic capacities. The cuttlefish did not exhibit acute intolerance to hypercapnia that has been
hypothesized for more active cephalopod species (squid). Even though blood pH (pHe) remained 0.18 pH units below control values,
arterial O 2 saturation was not compromised in S. officinalis because of the comparatively lower pH sensitivity of oxygen binding to its blood pigment. This raises questions concerning
the potentially broad range of sensitivity to changes in acid–base status amongst invertebrates, as well as to the underlying
mechanistic origins. Further studies are needed to better characterize the connection between acid–base status and animal
fitness in various marine species. 相似文献
15.
Anthropogenic ocean acidification is likely to have negative effects on marine calcifying organisms, such as shelled pteropods, by promoting dissolution of aragonite shells. Study of shell dissolution requires an accurate and sensitive method for assessing shell damage. Shell dissolution was induced through incubations in CO 2‐enriched seawater for 4 and 14 days. We describe a procedure that allows the level of dissolution to be assessed and classified into three main types: Type I with partial dissolution of the prismatic layer; Type II with exposure of underlying crossed‐lamellar layer, and Type III, where crossed‐lamellar layer shows signs of dissolution. Levels of dissolution showed a good correspondence to the incubation conditions, with the most severe damage found in specimens held for 14 days in undersaturated condition (Ω ~ 0.8). This methodology enables the response of small pelagic calcifiers to acidified conditions to be detected at an early stage, thus making pteropods a valuable bioindicator of future ocean acidification. 相似文献
16.
All reef-building corals are symbiotic with dinoflagellates of the genus Symbiodinium, which influences many aspects of the host’s physiology including calcification. Coral calcification is a biologically controlled
process performed by the host that takes place several membranes away from the site of photosynthesis performed by the symbiont.
Although it is well established that light accelerates CaCO 3 deposition in reef-building corals (commonly referred to as light-enhanced calcification), the complete physiological mechanism
behind the process is not fully understood. To better comprehend the coral calcification process, a series of laboratory experiments
were conducted in the major Caribbean reef-building species Montastraea faveolata, to evaluate the effect of glycerol addition and/or the super-saturation of oxygen in the seawater. These manipulations were
performed in bleached and unbleached corals, to separate the effect of photosynthesis from calcification. The results suggest
that under normal physiological conditions, a 42% increase in seawater oxygen concentration promotes a twofold increase in
dark-calcification rates relative to controls. On the other hand, the results obtained using bleached corals suggest that
glycerol is required, as a metabolic fuel, in addition to an oxygenic environment in a symbiosis that has been disrupted.
Also, respiration rates in symbiotic corals that were pre-incubated in light conditions showed a kinetic limitation, whereas
corals that were pre-incubated in darkness were oxygen limited, clearly emphasizing the role of oxygen in this regard. These
findings indicate that calcification in symbiotic corals is not strictly a “light-enhanced” or “dark-repressed” process, but
rather, the products of photosynthesis have a critical role in calcification, which should be viewed as a “photosynthesis-driven”
process. The results presented here are discussed in the context of the current knowledge of the coral calcification process. 相似文献
17.
One-third of the world’s coral reefs have disappeared over the last 30 years, and a further third is under threat today from
various stress factors. The main global stress factors on coral reefs have been identified as changes in sea surface temperature
(SST) and changes in surface seawater aragonite saturation (Ω arag). Here, we use a climate model of intermediate complexity, which includes an ocean general circulation model and a fully
coupled carbon cycle, in conjunction with present-day observations of inter-annual SST variability to investigate three IPCC
representative concentration pathways (RCP 3PD, RCP 4.5, and RCP 8.5), and their impact on the environmental stressors of
coral reefs related to open ocean SST and open ocean Ω arag over the next 400 years. Our simulations show that for the RCP 4.5 and 8.5 scenarios, the threshold of 3.3 for zonal and
annual mean Ω arag would be crossed in the first half of this century. By year 2030, 66–85% of the reef locations considered in this study would
experience severe bleaching events at least once every 10 years. Regardless of the concentration pathway, virtually every
reef considered in this study (>97%) would experience severe thermal stress by year 2050. In all our simulations, changes
in surface seawater aragonite saturation lead changes in temperatures. 相似文献
18.
Reviews suggest that that the biogeochemical threshold for sustained coral reef growth will be reached during this century due to ocean acidification caused by increased uptake of atmospheric CO 2. Projections of ocean acidification, however, are based on air‐sea fluxes in the open ocean, and not for shallow‐water systems such as coral reefs. Like the open ocean, reef waters are subject to the chemical forcing of increasing atmospheric pCO 2. However, for reefs with long water residence times, we illustrate that benthic carbon fluxes can drive spatial variation in pH, pCO 2 and aragonite saturation state (Ω a) that can mask the effects of ocean acidification in some downstream habitats. We use a carbon flux model for photosynthesis, respiration, calcification and dissolution coupled with Lagrangian transport to examine how key groups of calcifiers (zooxanthellate corals) and primary producers (macroalgae) on coral reefs contribute to changes in the seawater carbonate system as a function of water residence time. Analyses based on flume data showed that the carbon fluxes of corals and macroalgae drive Ω ain opposing directions. Areas dominated by corals elevate pCO 2 and reduce Ω a, thereby compounding ocean acidification effects in downstream habitats, whereas algal beds draw CO 2 down and elevate Ω a, potentially offsetting ocean acidification impacts at the local scale. Simulations for two CO 2 scenarios (600 and 900 ppm CO 2) suggested that a potential shift from coral to algal abundance under ocean acidification can lead to improved conditions for calcification in downstream habitats, depending on reef size, water residence time and circulation patterns. Although the carbon fluxes of benthic reef communities cannot significantly counter changes in carbon chemistry at the scale of oceans, they provide a significant mechanism of buffering ocean acidification impacts at the scale of habitat to reef. 相似文献
19.
This study tested the interactive effects of increased seawater temperature and CO2 partial pressure (pCO2) on the photochemistry, bleaching, and early growth of the reef coral Pocillopora damicornis. New recruits were maintained at ambient or high temperature (29 or 30.8 °C) and pCO2 (~ 500 and ~ 1100 μatm) in a full-factorial experiment for 3 weeks. Neither a sharp decline in photochemical efficiency (Fv/Fm) nor evident bleaching was observed at high temperature and/or high pCO2. Furthermore, elevated temperature greatly promoted lateral growth and calcification, while polyp budding exhibited temperature-dependent responses to pCO2. High pCO2 depressed calcification by 28% at ambient temperature, but did not impact calcification at 30.8 °C. Interestingly, elevated temperature in concert with high pCO2 significantly retarded the budding process. These results suggest that increased temperature can mitigate the adverse effects of acidification on the calcification of juvenile P. damicornis, but at a substantial cost to asexual budding.
相似文献
20.
Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Ω ar). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Ω ar∼0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Ω ar levels slightly above 1 and lower at Ω ar levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Ω ar derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Ω ar levels close to 1, with net shell growth ceasing at an Ω ar of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean. 相似文献
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