Posts Tagged 'calcification'

Effects of nearshore processes on carbonate chemistry dynamics and ocean acidification

Time series from open ocean fixed stations have robustly documented secular changes in carbonate chemistry and long-term ocean acidification (OA) trends as a direct response to increases in atmospheric carbon dioxide (CO2). However, few high-frequency coastal carbon time series are available in reef systems, where most affected tropical marine organisms reside. Seasonal variations in carbonate chemistry at Cheeca Rocks (CR), Florida, and La Parguera (LP), Puerto Rico, are presented based on 8 and 10 years of continuous, high-quality measurements, respectively. This dissertation synthesizes autonomous and bottle observations to model carbonate chemistry and to understand how physical and biological processes affect seasonal carbonate chemistry at both locations. The autonomous carbonate chemistry and oxygen observations are used to examine a mass balance approach using a 1-D model to determine net rates of ecosystem calcification and production (NEC and NEP) from communities close (<5km) to the buoys. The results provide evidence to suggest that seasonal response between benthic metabolism and seawater chemistry at LP is attenuated relative to that at CR because their differences in benthic cover and how benthic metabolism modifies the water chemistry. Simple linear trends cannot explain the feedback between metabolism and reef water chemistry using long-term observations over natural variations. The effects of community production on partial pressure of CO2 (pCO2sw) make these interactions complex at short- and long-term scales. Careful consideration should be taken when inferring local biogeochemical processes, given that pCO2sw (and presumably pH) respond on much shorter time and local scales than dissolved inorganic carbon (DIC) and total alkalinity (TA). The observations highlight the need for more comprehensive observing systems that can reliably measure both the fast-response (pCO2sw, pH) and slow-response (DIC) carbon pools.

Continue reading ‘Effects of nearshore processes on carbonate chemistry dynamics and ocean acidification’

Crumbling reefs and cold-water coral habitat loss in a future ocean: evidence of “coralporosis” as an indicator of habitat integrity

Ocean acidification is a threat to the net growth of tropical and deep-sea coral reefs, due to gradual changes in the balance between reef growth and loss processes. Here we go beyond identification of coral dissolution induced by ocean acidification and identify a mechanism that will lead to a loss of habitat in cold-water coral reef habitats on an ecosystem-scale. To quantify this, we present in situ and year-long laboratory evidence detailing the type of habitat shift that can be expected (in situ evidence), the mechanisms underlying this (in situ and laboratory evidence), and the timescale within which the process begins (laboratory evidence). Through application of engineering principals, we detail how increased porosity in structurally critical sections of coral framework will lead to crumbling of load-bearing material, and a potential collapse and loss of complexity of the larger habitat. Importantly, in situ evidence highlights that cold-water corals can survive beneath the aragonite saturation horizon, but in a fundamentally different way to what is currently considered a biogenic cold-water coral reef, with a loss of the majority of reef habitat. The shift from a habitat with high 3-dimensional complexity provided by both live and dead coral framework, to a habitat restricted primarily to live coral colonies with lower 3-dimensional complexity represents the main threat to cold-water coral reefs of the future and the biodiversity they support. Ocean acidification can cause ecosystem-scale habitat loss for the majority of cold-water coral reefs.

Continue reading ‘Crumbling reefs and cold-water coral habitat loss in a future ocean: evidence of “coralporosis” as an indicator of habitat integrity’

Acclimatization drives differences in reef-building coral calcification rates

Coral reefs are susceptible to climate change, anthropogenic influence, and environmental stressors. However, corals in Kāneʻohe Bay, Hawaiʻi have repeatedly shown resilience and acclimatization to anthropogenically-induced rising temperatures and increased frequencies of bleaching events. Variations in coral and algae cover at two sites—just 600 m apart—at Malaukaʻa fringing reef suggest genetic or environmental differences in coral resilience between sites. A reciprocal transplant experiment was conducted to determine if calcification (linear extension and dry skeletal weight) for dominant reef-building species, Montipora capitata and Porites compressa, varied between the two sites and whether or not parent colony or environmental factors were responsible for the differences. Despite the two sites representing distinct environmental conditions with significant differences between temperature, salinity, and aragonite saturation, M. capitata growth rates remained the same between sites and treatments. However, dry skeletal weight increases in P. compressa were significantly different between sites, but not across treatments, with linear mixed effects model results suggesting heterogeneity driven by environmental differences between sites and the parent colonies. These results provide evidence of resilience and acclimatization for M. capitata and P. compressa. Variability of resilience may be driven by local adaptations at a small, reef-level scale for P. compressa in Kāneʻohe Bay.

Continue reading ‘Acclimatization drives differences in reef-building coral calcification rates’

Ervilia castanea (Mollusca, Bivalvia) populations adversely affected at CO2 seeps in the North Atlantic

Highlights

  • The bivalve Ervilia castanea was studied at volcanic CO2 seeps and reference sites.
  • Abundance, size and net-calcification were inversely related to CO2 levels.
  • Large individuals were scarce or absent at high CO2 sites.
  • Recruitment of this bivalve was highest at the CO2 seeps.
  • Abundance and size of E. castanea were positively correlated with Chl-a in sediment.

Abstract

Sites with naturally high CO2 conditions provide unique opportunities to forecast the vulnerability of coastal ecosystems to ocean acidification, by studying the biological responses and potential adaptations to this increased environmental variability. In this study, we investigated the bivalve Ervilia castanea in coastal sandy sediments at reference sites and at volcanic CO2 seeps off the Azores, where the pH of bottom waters ranged from average oceanic levels of 8.2, along gradients, down to 6.81, in carbonated seawater at the seeps. The bivalve population structure changed markedly at the seeps. Large individuals became less abundant as seawater CO2 levels rose and were completely absent from the most acidified sites. In contrast, small bivalves were most abundant at the CO2 seeps. We propose that larvae can settle and initially live in high abundances under elevated CO2 levels, but that high rates of post-settlement dispersal and/or mortality occur. Ervilia castanea were susceptible to elevated CO2 levels and these effects were consistently associated with lower food supplies. This raises concerns about the effects of ocean acidification on the brood stock of this species and other bivalve molluscs with similar life history traits.

Continue reading ‘Ervilia castanea (Mollusca, Bivalvia) populations adversely affected at CO2 seeps in the North Atlantic’

Responses of coral gastrovascular cavity pH during light and dark incubations to reduced seawater pH suggest species-specific responses to the effects of ocean acidification on calcification

Coral polyps have a fluid-filled internal compartment, the gastrovascular cavity (GVC). Respiration and photosynthesis cause large daily excursions in GVC oxygen concentration (O2) and pH, but few studies have examined how this correlates with calcification rates. We hypothesized that GVC chemistry can mediate and ameliorate the effects of decreasing seawater pH (pHSW) on coral calcification. Microelectrodes were used to monitor O2 and pH within the GVC of Montastraea cavernosa and Duncanopsammia axifuga (pH only) in both the light and the dark, and three pHSW levels (8.2, 7.9, and 7.6). At pHSW 8.2, GVC O2 ranged from ca. 0 to over 400% saturation in the dark and light, respectively, with transitions from low to high (and vice versa) within minutes of turning the light on or off. For all three pHSW treatments and both species, pHGVC was always significantly above and below pHSW in the light and dark, respectively. For M. cavernosa in the light, pHGVC reached levels of pH 8.4–8.7 with no difference among pHSW treatments tested; in the dark, pHGVC dropped below pHSW and even below pH 7.0 in some trials at pHSW 7.6. For D. axifuga in both the light and the dark, pHGVC decreased linearly as pHSW decreased. Calcification rates were measured in the light concurrent with measurements of GVC O2 and pHGVC. For both species, calcification rates were similar at pHSW 8.2 and 7.9 but were significantly lower at pHSW 7.6. Thus, for both species, calcification was protected from seawater acidification by intrinsic coral physiology at pHSW 7.9 but not 7.6. Calcification was not correlated with pHGVC for M. cavernosa but was for D. axifuga. These results highlight the diverse responses of corals to changes in pHSW, their varying abilities to control pHGVC, and consequently their susceptibility to ocean acidification.

 

Continue reading ‘Responses of coral gastrovascular cavity pH during light and dark incubations to reduced seawater pH suggest species-specific responses to the effects of ocean acidification on calcification’

Paracellular transport to the coral calcifying medium: effects of environmental parameters

Coral calcification relies on the transport of ions and molecules to the extracellular calcifying medium (ECM). Little is known about paracellular transport (via intercellular junctions) in corals and other marine calcifiers. Here, we investigated whether the permeability of the paracellular pathway varied in different environmental conditions in the coral Stylophora pistillata. Using the fluorescent dye calcein, we characterised the dynamics of calcein influx from seawater to the ECM and showed that increases in paracellular permeability (leakiness) induced by hyperosmotic treatment could be detected by changes in calcein influx rates. We then used the calcein-imaging approach to investigate the effects of two environmental stressors on paracellular permeability: seawater acidification and temperature change. Under conditions of seawater acidification (pH 7.2) known to depress pH in the ECM and the calcifying cells of S. pistillata, we observed a decrease in half-times of calcein influx, indicating increased paracellular permeability. By contrast, high temperature (31°C) had no effect, whereas low temperature (20°C) caused decreases in paracellular permeability. Overall, our study establishes an approach to conduct further in vivo investigation of paracellular transport and suggests that changes in paracellular permeability could form an uncharacterised aspect of the physiological response of S. pistillata to seawater acidification.

 

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Calcification and organic productivity at the world’s southernmost coral reef

Highlights

  • High-latitude coral reefs are hotspots of ocean change and vulnerable to bleaching.
  • Coral ecosystem calcification in winter was lower than most studied ecosystems.
  • The reef was net heterotrophic in the winter and net respiratory in the summer.
  • Detailed bathymetric observations reduce uncertainties in metabolic calculations.
  • Summer calcification was not driven by temperature or aragonite saturation state.

Abstract

Estimates of coral reef calcification and organic productivity provide valuable insight to community functionality and the response of an ecosystem to stress events. High-latitude coral reefs are expected to experience rapid changes in calcification rates and become refugia for tropical species following climate change and increasing bleaching events. Here, we estimate ecosystem-scale calcification and organic productivity at the world’s southernmost coral reef using seawater carbon chemistry observations (Lord Howe Island, Australia). We reduce uncertainties in metabolic calculations by producing a detailed bathymetric model and deploying two current meters to refine residence time and volume estimates. Bathymetry-modelled transect depths ranged from 74% shallower to 20% deeper than depths averaged from reef crest/flat current meters, indicating that higher-resolution depth observations help to reduce uncertainties in reef metabolic calculations. Rates of ecosystem calcification were 56.6 ± 14.8 mmol m−2 d−1 in the winter and 125.3 ± 39.4 mmol m−2 d−1 in the summer. These rates are lower than most other high-latitude reefs according to our compilation of high-latitude coral ecosystem metabolism estimates. Coral cover ranged from 14.7 ± 2.3% in winter to 19.8 ± 2.1% in the summer. A concurrent bleaching event and cyclone occurred during summer sampling (February – March 2019), resulting in 47% of corals bleached at the study site and 2% mortality due to cyclonal damage. Therefore, it is likely that the summertime Gnet rates underestimate baseline calcification. Our results enable future assessments of long-term change, but do not resolve the impact of bleaching at Lord Howe Island.

 

Continue reading ‘Calcification and organic productivity at the world’s southernmost coral reef’

Ocean acidification has impacted coral growth on the Great Barrier Reef

Ocean acidification (OA) reduces the concentration of seawater carbonate ions that stony corals need to produce their calcium carbonate skeletons, and is considered a significant threat to the functional integrity of coral reef ecosystems. However, detection and attribution of OA impact on corals in nature are confounded by concurrent environmental changes, including ocean warming. Here we use a numerical model to isolate the effects of OA and temperature, and show that OA alone has caused 13±3% decline in the skeletal density of massive Porites corals on the Great Barrier Reef since 1950. This OA‐induced thinning of coral skeletons, also evident in Porites from the South China Sea but not in the central equatorial Pacific, reflects enhanced acidification of reef water relative to the surrounding open ocean. Our finding reinforces concerns that even corals that might survive multiple heatwaves are structurally weakened and increasingly vulnerable to the compounding effects of climate change.

Continue reading ‘Ocean acidification has impacted coral growth on the Great Barrier Reef’

Ocean acidification effects on calcification and dissolution in tropical reef macroalgae

Net calcification rates for coral reef and other calcifiers have been shown to decline as ocean acidification (OA) occurs. However, the role of calcium carbonate dissolution in lowering net calcification rates is unclear. The objective of this study was to distinguish OA effects on calcification and dissolution rates in dominant calcifying macroalgae of the Florida Reef Tract, including two rhodophytes (Neogoniolithon strictum, Jania adhaerens) and two chlorophytes (Halimeda scabra, Udotea luna). Two experiments were conducted: (1) to assess the difference in gross (45Ca uptake) versus net (total alkalinity anomaly) calcification rates in the light/dark and (2) to determine dark dissolution (45CaCO3), using pH levels predicted for the year 2100 and ambient pH. At low pH in the light, all species maintained gross calcification rates and most sustained net calcification rates relative to controls. Net calcification rates in the dark were ~84% lower than in the light. In contrast to the light, all species had lower net calcification rates in the dark at low pH with chlorophytes exhibiting net dissolution. These data are supported by the relationship (R2 = 0.82) between increasing total alkalinity and loss of 45Ca from pre-labelled 45CaCO3 thalli at low pH in the dark. Dark dissolution of 45CaCO3-labelled thalli was ~18% higher in chlorophytes than rhodophytes at ambient pH, and ~ twofold higher at low pH. Only Udotea, which exhibited dissolution in the light, also had lower daily calcification rates integrated over 24 h. Thus, if tropical macroalgae can maintain high calcification rates in the light, lower net calcification rates in the dark from dissolution may not compromise daily calcification rates. However, if organismal dissolution in the dark is additive to sedimentary carbonate losses, reef dissolution may be amplified under OA and contribute to erosion of the Florida Reef Tract and other reefs that exhibit net dissolution.

Continue reading ‘Ocean acidification effects on calcification and dissolution in tropical reef macroalgae’

Inorganic carbon utilization of tropical calcifying macroalgae and the impacts of intensive mariculture-derived coastal acidification on the physiological performance of the rhodolith Sporolithon sp.

Highlights

• Intensive mariculture activities contribute to coastal acidification.

• Inorganic carbon use of calcifying macroalgae is diverse and species-specific.

• Long term exposure to extreme low-pH lowers growth and calcification of Sporolithon sp.

Abstract

Fish farming in coastal areas has become an important source of food to support the world’s increasing population. However, intensive and unregulated mariculture activities have contributed to changing seawater carbonate chemistry through the production of high levels of respiratory CO2. This additional CO2, i.e. in addition to atmospheric inputs, intensifies the effects of global ocean acidification resulting in localized extreme low pH levels. Marine calcifying macroalgae are susceptible to such changes due to their CaCO3 skeleton. Their physiological response to CO2-driven acidification is dependent on their carbon physiology. In this study, we used the pH drift experiment to determine the capability of 9 calcifying macroalgae to use one or more inorganic carbon (Ci) species. From the 9 species, we selected the rhodolith Sporolithon sp. as a model organism to investigate the long-term effects of extreme low pH on the physiology and biochemistry of calcifying macroalgae. Samples were incubated under two pH treatments (pH 7.9 = ambient and pH 7.5 = extreme acidification) in a temperature-controlled (26 ± 0.02 °C) room provided with saturating light intensity (98.3 ± 2.50 μmol photons m-2 s-1). After the experimental treatment period (40 d), growth rate, calcification rate, nutrient uptake rate, organic content, skeletal CO3-2, pigments, and tissue C, N and P of Sporolithon samples were compared. The pH drift experiment revealed species-specific Ci use mechanisms, even between congenerics, among tropical calcifying macroalgae. Furthermore, long-term extreme low pH significantly reduced the growth rate, calcification rate and skeletal CO3-2 content by 79%, 66% and 18%, respectively. On the other hand, nutrient uptake rates, organic matter, pigments and tissue C, N and P were not affected by the low pH treatments. Our results suggest that the rhodolith Sporolithon sp. is susceptible to the negative effects of extreme low pH resulting from intensive mariculture-driven coastal acidification.

Continue reading ‘Inorganic carbon utilization of tropical calcifying macroalgae and the impacts of intensive mariculture-derived coastal acidification on the physiological performance of the rhodolith Sporolithon sp.’


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