Posts Tagged 'calcification'

Development and application of foraminiferal carbonate system proxies to quantify ocean acidification in the California Current

The oceanic uptake of anthropogenic carbon has mitigated climate change, but has also resulted in a global average 0.1 decline in surface ocean pH over 20th century known as ocean acidification. The parallel reduction in carbonate ion concentration ([CO32-]) and the saturation state of seawater (Ω) has caused many major calcium carbonate-secreting organisms such as planktonic foraminifera to exhibit impaired calcification. We develop proxy calibrations and down core records that use calcification and geochemical characteristics of planktonic foraminifera as proxies for the marine carbonate system. This study focuses specifically on the surface ocean chemistry of the California Current Ecosystem (CCE), which has been identified as a region of rapidly progressing ocean acidification due to natural upwelling processes and the low buffering capacity of these waters. The calibration portion of this study uses marine sediments collected by the Santa Barbara Basin (SBB), California sediment-trapping program located in the central region of the CCE. We calibrate the relationships of Globigerina bulloides calcification intensity to [CO3 2-] and the B/Ca ratios of G. bulloides, Neogloboquadrina dutertrei and Neogloboquadrina incompta shells to Ω calcite using in situ measurements and model simulations of these independent variables. By applying these proxy methods to down core, our records from the SBB indicate a 20% reduction in foraminiferal calcification since ~1900, translating to a 35% decline in [CO 32-] in the CCE over this period. Our high-resolution calcification record also reveals a substantial interannual to decadal modulation of ocean acidification in the CCE related to the sign of Pacific Decadal Oscillation and El Niño Southern Oscillation. In the future we can expect these climatic modes to both enhance and moderate anthropogenic ocean acidification. Based on our historic record, we predict that if atmospheric CO2 reaches 540 ppm by the year 2100 as predicted by a conservative CO3 pathway, [CO32-] will experience a net reduction of 55%, resulting in at least a 30% reduction in calcification of planktonic foraminifera that will likely be mirrored by other adversely affected marine calcifiers.

Continue reading ‘Development and application of foraminiferal carbonate system proxies to quantify ocean acidification in the California Current’

Twenty years of marine carbon cycle observations at Devils Hole Bermuda provide insights into seasonal hypoxia, coral reef calcification, and ocean acidification

Open–ocean observations have revealed gradual changes in seawater carbon dioxide (CO2) chemistry resulting from uptake of atmospheric CO2 and ocean acidification (OA), but, with few long–term records (>5 years) of the coastal ocean that can reveal the pace and direction of environmental change. In this paper, observations collected from 1996 to 2016 at Harrington Sound, Bermuda, constitute one of the longest time–series of coastal ocean inorganic carbon chemistry. Uniquely, such changes can be placed into the context of contemporaneous offshore changes observed at the nearby Bermuda Atlantic Time-series Study (BATS) site. Onshore, surface dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2; >10% change per decade) have increased and OA indicators such as pH and calcium carbonate (CaCO3) saturation state (Ω) decreased from 1996 to 2016 at a rate of two to three times that observed offshore at BATS. Such changes, combined with reduction of total alkalinity over time, reveal a complex interplay of biogeochemical processes influencing Bermuda reef metabolism, including net ecosystem production (NEP = gross primary production–autotrophic and heterotrophic respiration) and net ecosystem calcification (NEC = gross calcification–gross CaCO3 dissolution). These long–term data show a seasonal shift between wintertime net heterotrophy and summertime net autotrophy for the entire Bermuda reef system. Over annual time-scales, the Bermuda reef system does not appear to be in trophic balance, but rather slightly net heterotrophic. In addition, the reef system is net accretive (i.e., gross calcification > gross CaCO3 dissolution), but there were occasional periods when the entire reef system appears to transiently shift to net dissolution. A previous 5–year study of the Bermuda reef suggested that net calcification and net heterotrophy have both increased. Over the past 20 years, rates of net calcification and net heterotrophy determined for the Bermuda reef system have increased by ~30%, most likely due to increased coral nutrition occurring in concert with increased offshore productivity in the surrounding subtropical North Atlantic Ocean. Importantly, this long–term study reveals that other environmental factors (such as coral feeding) can mitigate against the effects of ocean acidification on coral reef calcification, at least over the past couple of decades.

Continue reading ‘Twenty years of marine carbon cycle observations at Devils Hole Bermuda provide insights into seasonal hypoxia, coral reef calcification, and ocean acidification’

Response of Marginopora vertebralis (Foraminifera) from Laucala Bay, Fiji, to changing ocean pH

Increased CO2 emissions into the atmosphere lead to increased concentrations of dissolved CO2 in the ocean. A chemical reaction between the dissolved CO2 and seawater produces HCO3 −, CO3 2− and H+ ions. These H+ ions increase the acidity of seawater and decrease the pH. Increased acidity and decreased availability of CO3 2− ion affect calcite and aragonite production by marine calcifiers in the ocean. To assess potential responses of the larger benthic foraminifer Marginopora vertebralis to ocean acidification, we performed growth experiments at three pH levels [7.5, 7.8, 8.1 (ambient seawater)] for 11 weeks. Specimens were stained with the fluorescent compound Calcein ( ̴40 µmole/l) prior to treatment, allowing identification of calcite added during the treatment period. At pH 8.1, specimens increased their test weight by 8.4%, at pH 7.8 growth was 4.2%, and at pH 7.5, growth was only 3.2%. These differences represent a significant relationship between ocean pH and test growth (i.e., calcification). In addition, several specimens in the pH 8.1 treatment underwent asexual reproduction during the experiment, while no reproduction was observed in the pH 7.8 or 7.5 treatments. These results indicate that ocean acidification predicted to occur by the end of the 21st century will cause a decline in population densities of Marginopora vertebralis in their natural environment, as consequences of both reduced growth rates and rates of reproduction. And because the tests of these foraminifers are important components of carbonate sediments on coral cays and tropical beaches, a decline in their rates of sediment production will exacerbate the consequences of rising sea level.

Continue reading ‘Response of Marginopora vertebralis (Foraminifera) from Laucala Bay, Fiji, to changing ocean pH’

Conus Shell δ13C values as proxies for δ13CDIC in tropical waters

We use time-series δ18O and δ13C data from seawater and live-collected Conus shells from Panama’s Pacific coast to test the fidelity of the gastropod’s δ13C values as a proxy for the δ13C of marine dissolved inorganic carbon (DIC), and the potential of δ18O-δ13C correlations in shell profiles for resolving relative magnitudes of seasonal upwelling and freshening. Water samples were collected from March 2011 to August 2012 from Naos Island Marine Laboratory, and Conus specimens were collected from nearby Veracruz Beach in July 2013. In general, patterns corresponded with seasonal changes in rainfall and upwelling on the Pacific coast of Panama. During the long rainy season, the upwelling signal is absent and seawater salinity, δ18O, and δ13CDIC all decline. During the dry season, the upwelling signal increases and runoff declines increasing salinity, δ18O, and δ13CDIC values. Shell δ13C values strongly correlate with measured δ13CDIC values, but are lower than expected equilibrium for aragonite by approximately + 2‰ reflecting the incorporation of light metabolic C. The co-dependences of δ18O and δ13C provide reliable indicators of upwelling (negative correlation) and freshening (positive correlation) for nearshore environments, allowing for the study of historical climate change and upwelling based on beach-collected museum specimens.

Continue reading ‘Conus Shell δ13C values as proxies for δ13CDIC in tropical waters’

Plasticity and inter-population variability in physiological and life-history traits of the mussel Mytilus chilensis: A reciprocal transplant experiment

Geographically widespread species must cope with environmental differences between habitats. Information concerning geographic variations in response to climate variability is critical because many morphological, life-history and physiological traits show variation across space. Reciprocal transplant experiments have shown to be relevant to evaluate the role of phenotypic plasticity and potential local adaptation in ecophysiological responses when coping with environmental variability. In this study, we characterize through reciprocal transplant experiments the reaction norms of morphological, biochemical, physiological and life-history traits between two intertidal populations of the socioeconomically important mussel Mytilus chilensis, inhabiting contrasting local environments (estuarine vs coastal habitats). We found a gradient in phenotypic plasticity with plastic trait responses in metabolic, ingestion and clearance rates, and in HsP70 gene expression, and some traits with responses more canalized as growth and calcification rates. This emphasizes that responses not only vary across different local populations but also in different traits in M. chilensis, thus it is difficult to establish an overall trend of the responses at integrated organismal level. Moreover, the synergistic interaction of factors such as salinity and carbonate system parameters evaluated make it necessary to study the response at the population level with emphasis on benthic species important in aquaculture. Finally, field studies such as this one are useful for documenting the patterns of traits variation that occur in nature, identifying possible causes of such variation, and generating testable hypotheses for future controlled experiments.

Continue reading ‘Plasticity and inter-population variability in physiological and life-history traits of the mussel Mytilus chilensis: A reciprocal transplant experiment’

Variation in calcification rate of Acropora downingi relative to seasonal changes in environmental conditions in the northeastern Persian Gulf

There is a strong interest in understanding how coral calcification varies with changing environmental conditions, especially given the projected changes in temperature and aragonite saturation due to climate change. This study explores in situ variation in calcification rates of Acropora downingi in the northeastern Persian Gulf relative to seasonal changes in temperature, irradiance and aragonite saturation state (Ωarag). Calcification rates of A. downingi were highest in the spring and lowest in the winter, and intra-annual variation in calcification rate was significantly related to temperature (r2 = 0.30) and irradiance (r2 = 0.36), but not Ωarag (r2 = 0.02). Seasonal differences in temperature are obviously confounded by differences in other environmental conditions and vice versa. Therefore, we used published relationships from experimental studies to establish which environmental parameter(s) (temperature, irradiance, and/or Ωarag) placed greatest constraints on calcification rate (relative to the maximum spring rate) in each season. Variation in calcification rates was largely attributable to seasonal changes in irradiance and temperature (possibly ~57.4 and 39.7% respectively). Therefore, we predict that ocean warming may lead to increased rates of calcification during winter, but decelerate calcification during spring, fall and especially summer, resulting in net deceleration of calcification for A. downingi in the Persian Gulf.

Continue reading ‘Variation in calcification rate of Acropora downingi relative to seasonal changes in environmental conditions in the northeastern Persian Gulf’

Low pH conditions impair module capacity to regenerate in a calcified colonial invertebrate, the bryozoan Cryptosula pallasiana

Many aquatic animals grow into colonies of repeated, genetically identical, modules (zooids). Zooid interconnections enable colonies to behave as integrated functional units, while plastic responses to environmental changes may affect individual zooids. Plasticity includes the variable partitioning of resources to sexual reproduction, colony growth and maintenance. Maintenance often involves regeneration, which is also a routine part of the life history in some organisms, such as bryozoans. Here we investigate changes in regenerative capacity in the encrusting bryozoan Cryptosula pallasiana when cultured at different seawater pCO2 levels. The proportion of active zooids showing polypide regeneration was highest at current oceanic pH (8.1), but decreased progressively as pH declined below that value, reaching a six-fold reduction at pH 7.0. The zone of budding of new zooids at the colony periphery declined in size below pH 7.7. Under elevated pCO2 conditions, already experienced sporadically in coastal areas, skeletal corrosion was accompanied by the proportional reallocation of resources from polypide regeneration in old zooids to the budding of new zooids at the edge of the colony. Thus, future ocean acidification can affect colonial organisms by changing how they allocate resources, with potentially profound impacts on life-history patterns and ecological interactions.

Continue reading ‘Low pH conditions impair module capacity to regenerate in a calcified colonial invertebrate, the bryozoan Cryptosula pallasiana’

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Ocean acidification in the IPCC AR5 WG II

OUP book