McCorkle Daniel C.

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McCorkle

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Daniel C.

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Quantifying the effects of nutrient enrichment and freshwater mixing on coastal ocean acidification

(American Geophysical Union, 2019-11-07) Rheuban, Jennie E. ; Doney, Scott C. ; McCorkle, Daniel C. ; Jakuba, Rachel W.

The U.S. Northeast is vulnerable to ocean and coastal acidification because of low alkalinity freshwater discharge that naturally acidifies the region, and high anthropogenic nutrient loads that lead to eutrophication in many estuaries. This study describes a combined nutrient and carbonate chemistry monitoring program in five embayments of Buzzards Bay, Massachusetts to quantify the effects of nutrient loading and freshwater discharge on aragonite saturation state (Ω). Monitoring occurred monthly from June 2015 to September 2017 with higher frequency at two embayments (Quissett and West Falmouth Harbors) and across nitrogen loading and freshwater discharge gradients. The more eutrophic stations experienced seasonal aragonite undersaturation, and at one site, nearly every measurement collected was undersaturated. We present an analytical framework to decompose variability in aragonite Ω into components driven by temperature, salinity, freshwater endmember mixing, and biogeochemical processes. We observed strong correlations between apparent oxygen utilization and the portion of aragonite Ω variation that we attribute to biogeochemistry. The regression slopes were consistent with Redfield ratios of dissolved inorganic carbon and total alkalinity to dissolved oxygen. Total nitrogen and the contribution of biogeochemical processes to aragonite Ω were highly correlated, and this relationship was used to estimate the likely effects of nitrogen loading improvements on aragonite Ω. Under nitrogen loading reduction scenarios, aragonite Ω in the most eutrophic estuaries could be raised by nearly 0.6 units, potentially increasing several stations above the critical threshold of 1. This analysis provides a quantitative framework for incorporating ocean and coastal acidification impacts into regulatory and management discussions.
Corrigendum to "A culture-based calibration of benthic foraminiferal paleotemperature proxies: δ18O and Mg/Ca results" published in Biogeosciences, 7, 1335–1347, 2010

(Copernicus Publications on behalf of the European Geosciences Union, 2011-06-10) Filipsson, Helena L. ; Bernhard, Joan M. ; Lincoln, Sara ; McCorkle, Daniel C.
The impact of seawater saturation state and bicarbonate ion concentration on calcification by new recruits of two Atlantic corals

( 2010-11-05) de Putron, Samantha J. ; McCorkle, Daniel C. ; Cohen, Anne L. ; Dillon, A. B.

Rising concentrations of atmospheric CO2 are changing the carbonate chemistry of the oceans, a process known as ocean acidification (OA). Absorption of this CO2 by the surface oceans is increasing the amount of total dissolved inorganic carbon (DIC) and bicarbonate ion (HCO3 -) available for marine calcification, yet is simultaneously lowering the seawater pH and carbonate ion concentration ([CO3 2-]), and thus the saturation state of seawater with respect to aragonite (Ωar). We investigated the relative importance of [HCO3 -] versus [CO3 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 Ωar values, which were manipulated by both acid-addition at constant pCO2 (decreased total [HCO3 -] and [CO3 2-]) and by pCO2 elevation at constant alkalinity (increased [HCO3 -], decreased [CO3 2-]). Calcification after two 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 [CO3 2-] whether Ωar was lowered by acid-addition or by pCO2 elevation - calcification did not follow total DIC or [HCO3 -]. Nevertheless, the calcification response to decreasing [CO3 2-] was non-linear. A statistically significant decrease in calcification was only detected between Ωar = < 2.5 and Ωar = 1.1 – 1.5, where calcification of new recruits was reduced by 22 – 37 % per 1.0 decrease in Ωar. 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 [HCO3 -]. Clearly, the coral calcification response to OA is variable and complex. A deeper understanding of the biomineralization mechanisms and environmental conditions underlying these 3 variable responses is needed to support informed predictions about future OA impacts on corals and coral reefs.
Adverse effects of ocean acidification on early development of squid (Doryteuthis pealeii)

(Public Library of Science, 2013-05-31) Kaplan, Maxwell B. ; Mooney, T. Aran ; McCorkle, Daniel C. ; Cohen, Anne L.

Anthropogenic carbon dioxide (CO2) is being absorbed into the ocean, altering seawater chemistry, with potentially negative impacts on a wide range of marine organisms. The early life stages of invertebrates with internal and external aragonite structures may be particularly vulnerable to this ocean acidification. Impacts to cephalopods, which form aragonite cuttlebones and statoliths, are of concern because of the central role they play in many ocean ecosystems and because of their importance to global fisheries. Atlantic longfin squid (Doryteuthis pealeii), an ecologically and economically valuable taxon, were reared from eggs to hatchlings (paralarvae) under ambient and elevated CO2 concentrations in replicated experimental trials. Animals raised under elevated pCO2 demonstrated significant developmental changes including increased time to hatching and shorter mantle lengths, although differences were small. Aragonite statoliths, critical for balance and detecting movement, had significantly reduced surface area and were abnormally shaped with increased porosity and altered crystal structure in elevated pCO2-reared paralarvae. These developmental and physiological effects could alter squid paralarvae behavior and survival in the wild, directly and indirectly impacting marine food webs and commercial fisheries.
CTD data from coring cruise R/V Oceanus OC424-1 on the continental margin of the South Atlantic Bight and the Bahamas

( 2006-05) Bernhard, Joan M. ; McCorkle, Daniel C.

These CTD data were collected during a twelve-day cruise in May 2006 on the R/V Oceanus (OC-424-1; Woods Hole, MA – Charleston, SC). The principal goal of the cruise was to collect foraminiferal “livestock” for multiple-carbonate-chemistry culturing experiments. The main purpose of the CTD casts was to collect bottom water, which was used for shipboard sieving of the sediment samples. We also sampled bottom water for comparison with the shell chemistry of benthic foraminiferal field specimens. This included samples for oxygen, Dissolved Inorganic Carbon and Alkalinity to define bottom water carbonate chemistry and calcite saturation state, the d13C of DIC, and the d18O of water; the University of South Carolina group sampled for minor and trace elements, too. The CTD data archived here were not processed or subjected to any quality control evaluation.
Current velocity, wave velocity, and O2, H+, and momentum flux from the ECHOES system deployed at three sites in the Florida Keys in June 2018

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-08-20) Long, Matthew ; McCorkle, Daniel C.

An eddy covariance system, known as ECHOES, was deployed at three sites offshore of Key Largo, Florida during June 2018. The ECHOES systems logged the three-dimensional velocity, depth, O2 optode, pH sensor, and triaxial Inertial Measurement Unit. A separate frame at each site contained a photosynthetically active radiation (PAR) sensor and a Seabird SeapHOx, measuring salinity, temperature, depth, O2, and pH. This dataset contains current velocities, wave velocities, and O2, H+, and momentum flux. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/820984
Spectral analyses of high-frequency data during two hour-long periods from the ECHOES system deployed at three sites in the Florida Keys in June 2018

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-08-20) Long, Matthew ; McCorkle, Daniel C.

Spectral analyses (power spectra and cross power spectral density (CPSD)) of high-frequency data (turbulence; momentum, oxygen and hydrogen ion fluxes) from two hour-long periods during a high-energy wave period (Hr 38) and a low-energy wave period (Hr 116). For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/821294
pH, temperature, salinity, and oxygen data from SeapHOx sensors deployed at three sites in the Florida Keys in June 2018

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-08-20) Long, Matthew ; McCorkle, Daniel C.

An eddy covariance system, known as ECHOES, was deployed at three sites offshore of Key Largo, Florida during June 2018. The ECHOES systems logged the three-dimensional velocity, depth, O2 optode, pH sensor, and triaxial Inertial Measurement Unit. A separate frame at each site contained a photosynthetically active radiation (PAR) sensor and a Seabird SeapHOx, measuring salinity, temperature, depth, O2, and pH. This dataset contains pH, temperature, salinity, and oxygen data recorded by the SeapHOx sensor. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/821091
Isotopic characterization of water masses in the Southeast Pacific Region: paleoceanographic implications

(American Geophysical Union, 2021-12-23) Reyes-Macaya, Dharma ; Hoogakker, Babette ; Martínez-Méndez, Gema ; Llanillo, Pedro J. ; Grasse, Patricia ; Mohtadi, Mahyar ; Mix, Alan C. ; Leng, Melanie J. ; Struck, Ulrich ; McCorkle, Daniel C. ; Troncoso, Macarena ; Gayo, Eugenia M. ; Lange, Carina B. ; Farias, Laura ; Carhuapoma, Wilson ; Graco, Michelle ; Cornejo-D’Ottone, Marcela ; De Pol-Holz, Ricardo ; Fernandez, Camila ; Narváez, Diego ; Vargas, Cristian A. ; García-Araya, Francisco ; Hebbeln, Dierk

In this study, we used stable isotopes of oxygen (δ18O), deuterium (δD), and dissolved inorganic carbon (δ13CDIC) in combination with temperature, salinity, oxygen, and nutrient concentrations to characterize the coastal (71°–78°W) and an oceanic (82°–98°W) water masses (SAAW—Subantarctic Surface Water; STW—Subtropical Water; ESSW—Equatorial Subsurface water; AAIW—Antarctic Intermediate Water; PDW—Pacific Deep Water) of the Southeast Pacific (SEP). The results show that δ18O and δD can be used to differentiate between SAAW-STW, SAAW-ESSW, and ESSW-AAIW. δ13CDIC signatures can be used to differentiate between STW-ESSW (oceanic section), SAAW-ESSW, ESSW-AAIW, and AAIW-PDW. Compared with the oceanic section, our new coastal section highlights differences in both the chemistry and geometry of water masses above 1,000 m. Previous paleoceanographic studies using marine sediments from the SEP continental margin used the present-day hydrological oceanic transect to compare against, as the coastal section was not sufficiently characterized. We suggest that our new results of the coastal section should be used for past characterizations of the SEP water masses that are usually based on continental margin sediment samples.
Impacts of multiple stressors on a benthic foraminiferal community: a long-term experiment assessing response to ocean acidification, hypoxia and warming

(Frontiers Media, 2021-04-22) Bernhard, Joan M. ; Wit, Johannes C. ; Starczak, Victoria R. ; Beaudoin, David J. ; Phalen, William G. ; McCorkle, Daniel C.

Ocean chemistry is changing as a result of human activities. Atmospheric carbon dioxide (CO2) concentrations are increasing, causing an increase in oceanic pCO2 that drives a decrease in oceanic pH, a process called ocean acidification (OA). Higher CO2 concentrations are also linked to rising global temperatures that can result in more stratified surface waters, reducing the exchange between surface and deep waters; this stronger stratification, along with nutrient pollution, contributes to an expansion of oxygen-depleted zones (so called hypoxia or deoxygenation). Determining the response of marine organisms to environmental changes is important for assessments of future ecosystem functioning. While many studies have assessed the impact of individual or paired stressors, fewer studies have assessed the combined impact of pCO2, O2, and temperature. A long-term experiment (∼10 months) with different treatments of these three stressors was conducted to determine their sole or combined impact on the abundance and survival of a benthic foraminiferal community collected from a continental-shelf site. Foraminifera are well suited to such study because of their small size, relatively rapid growth, varied mineralogies and physiologies. Inoculation materials were collected from a ∼77-m deep site south of Woods Hole, MA. Very fine sediments (<53 μm) were used as inoculum, to allow the entire community to respond. Thirty-eight morphologically identified taxa grew during the experiment. Multivariate statistical analysis indicates that hypoxia was the major driving factor distinguishing the yields, while warming was secondary. Species responses were not consistent, with different species being most abundant in different treatments. Some taxa grew in all of the triple-stressor samples. Results from the experiment suggest that foraminiferal species’ responses will vary considerably, with some being negatively impacted by predicted environmental changes, while other taxa will tolerate, and perhaps even benefit, from deoxygenation, warming and OA.
Community science for coastal acidification monitoring and research

(Taylor and Francis, 2021-07-26) Gassett, Parker Randall ; O’Brien-Clayton, Katie ; Bastidas, Carolina ; Rheuban, Jennie E. ; Hunt, Christopher W. ; Turner, Elizabeth ; Liebman, Matthew ; Silva, Emily ; Pimenta, Adam R. ; Grear, Jason S. ; Motyka, Jackie ; McCorkle, Daniel C. ; Stancioff, Esperanza ; Brady, Damian C. ; Strong, Aaron L.

Ocean and coastal acidification (OCA) present a unique set of sustainability challenges at the human-ecological interface. Extensive biogeochemical monitoring that can assess local acidification conditions, distinguish multiple drivers of changing carbonate chemistry, and ultimately inform local and regional response strategies is necessary for successful adaptation to OCA. However, the sampling frequency and cost-prohibitive scientific equipment needed to monitor OCA are barriers to implementing the widespread monitoring of dynamic coastal conditions. Here, we demonstrate through a case study that existing community-based water monitoring initiatives can help address these challenges and contribute to OCA science. We document how iterative, sequential outreach, workshop-based training, and coordinated monitoring activities through the Northeast Coastal Acidification Network (a) assessed the capacity of northeastern United States community science programs and (b) engaged community science programs productively with OCA monitoring efforts. Our results (along with the companion manuscript) indicate that community science programs are capable of collecting robust scientific information pertinent to OCA and are positioned to monitor in locations that would critically expand the coverage of current OCA research. Furthermore, engaging community stakeholders in OCA science and outreach enabled a platform for dialogue about OCA among other interrelated environmental concerns and fostered a series of co-benefits relating to public participation in resource and risk management. Activities in support of community science monitoring have an impact not only by increasing local understanding of OCA but also by promoting public education and community participation in potential adaptation measures.
An evaluation of staining techniques for marking daily growth in scleractinian corals

( 2012-12) Holcomb, Michael ; Cohen, Anne L. ; McCorkle, Daniel C.

In situ skeletal markers have been widely used to quantify skeletal growth rates of scleractinian corals on sub-annual time-scales. Nevertheless, an evaluation of different techniques, both in terms of their efficacy and potential impacts on the growth process itself, has not been undertaken. Here the effects of exposure to four different dyes (alizarin, alizarin complexone, calcein, oxytetracycline) and isotope spikes (Ba and Sr) on the growth rates of scleractinian corals are compared. Oxytetracycline increased coral growth. Alizarin, alizarin complexone, calcein, and Sr and Ba isotope spikes had no significant effect on coral growth, but polyp extension appeared reduced during exposure to alizarin and alizarin complexone. Calcein provided a more intense fluorescent mark than either alizarin or alizarin complexone. Isotope spikes were challenging to locate using isotope ratio analysis techniques. Thus, calcein appears best suited for marking short-term calcification increments in corals, while a combination of alizarin or alizarin complexone and calcein may be useful for dual labeling experiments as there is little overlap in their fluorescence spectra.
CTD data from coring cruise R/V Cape Hatteras CH1605 on the continental margin of the South Atlantic Bight and the Bahamas

( 2005-06) Bernhard, Joan M. ; McCorkle, Daniel C.

These CTD data were collected during a nine-day cruise in early June 2005 on the R/V Cape Hatteras (CH09-05; Beaufort, NC – Beaufort, NC). The principal goal of the cruise was to collect foraminiferal “livestock” for multiple-carbonate-chemistry culture experiments. The main purpose of the CTD casts was to collect bottom water, which was used for shipboard sieving of the sediment samples. We also sampled bottom water for comparison with the shell chemistry of benthic foraminiferal field specimens. This included samples for oxygen, Dissolved Inorganic Carbon and Alkalinity to define bottom water carbonate chemistry and calcite saturation state, the d13C of DIC, and the d18O of water; the University of South Carolina group sampled for minor and trace elements, too. We also collected two CTD-rosette profiles to provide samples to Ms. Angie Knapp at Princeton University, for use in isotopic studies of the marine N cycle. The CTD data archived here were not processed or subjected to any quality control evaluation.
Morphological and compositional changes in the skeletons of new coral recruits reared in acidified seawater : insights into the biomineralization response to ocean acidification

(American Geophysical Union, 2009-07-24) Cohen, Anne L. ; McCorkle, Daniel C. ; de Putron, Samantha J. ; Gaetani, Glenn A. ; Rose, Kathryn A.

We reared primary polyps (new recruits) of the common Atlantic golf ball coral Favia fragum for 8 days at 25°C in seawater with aragonite saturation states ranging from ambient (Ω = 3.71) to strongly undersaturated (Ω = 0.22). Aragonite was accreted by all corals, even those reared in strongly undersaturated seawater. However, significant delays, in both the initiation of calcification and subsequent growth of the primary corallite, occurred in corals reared in treatment tanks relative to those grown at ambient conditions. In addition, we observed progressive changes in the size, shape, orientation, and composition of the aragonite crystals used to build the skeleton. With increasing acidification, densely packed bundles of fine aragonite needles gave way to a disordered aggregate of highly faceted rhombs. The Sr/Ca ratios of the crystals, measured by SIMS ion microprobe, increased by 13%, and Mg/Ca ratios decreased by 45%. By comparing these variations in elemental ratios with results from Rayleigh fractionation calculations, we show that the observed changes in crystal morphology and composition are consistent with a >80% decrease in the amount of aragonite precipitated by the corals from each “batch” of calcifying fluid. This suggests that the saturation state of fluid within the isolated calcifying compartment, while maintained by the coral at levels well above that of the external seawater, decreased systematically and significantly as the saturation state of the external seawater decreased. The inability of the corals in acidified treatments to achieve the levels of calcifying fluid supersaturation that drive rapid crystal growth could reflect a limit in the amount of energy available for the proton pumping required for calcification. If so, then the future impact of ocean acidification on tropical coral ecosystems may depend on the ability of individuals or species to overcome this limitation and achieve the levels of calcifying fluid supersaturation required to ensure rapid growth.
Mineralization of ancient carbon in the subsurface of riparian forests

(American Geophysical Union, 2008-05-10) Gurwick, Noel P. ; McCorkle, Daniel C. ; Groffman, Peter M. ; Gold, Arthur J. ; Kellogg, D. Q. ; Seitz-Rundlett, Peter

Microbial activity in saturated, subsurface sediments in riparian forests may be supported by recent photosynthate or ancient (>500 ybp) soil organic carbon (SOC) in buried horizons. Metabolism of ancient SOC may be particularly important in riparian zones, considered denitrification hot spots, because denitrification in the riparian subsurface is often C-limited, because buried horizons intersect deep flow paths, and because low C mineralization rates can support ecosystem-relevant rates of denitrification. Buried horizons are common where alluvial processes (stream migration, overbank flow) have dominated riparian evolution. Our objectives were to determine: (1) the extent to which ancient SOC directly supports subsurface microbial activity; (2) whether different C sources support microbial activity in alluvial versus glaciofluvial riparian zones; and (3) how microbial use of ancient SOC varies with depth. In situ groundwater incubations and 14C dating of dissolved inorganic carbon revealed that ancient SOC mineralization was common, and that it constituted 31–100% of C mineralization 2.6 m deep at one site, at rates sufficient to influence landscape N budgets. Our data failed to reveal consistent spatial patterns of microbially available ancient C. Although mineralized C age increased with depth at one alluvial site, we observed ancient C metabolism 150 cm deep at a glaciofluvial site, suggesting that subsurface microbial activity in riparian zones does not vary systematically between alluvial and glaciofluvial hydrogeologic settings. These findings underscore the relevance of ancient C to contemporary ecosystem processes and the challenge of using mappable surface features to identify subsurface ecosystem characteristics or riparian zone N-sink strength.
A culture-based calibration of benthic foraminiferal paleotemperature proxies : δ18O and Mg/Ca results

(Copernicus Publications on behalf of the European Geosciences Union, 2010-04-29) Filipsson, Helena L. ; Bernhard, Joan M. ; Lincoln, Sara ; McCorkle, Daniel C.

Benthic foraminifera were cultured for five months at four temperatures (4, 7, 14 and 21 °C) to establish the temperature dependence of foraminiferal calcite δ18O and Mg/Ca. Two Bulimina species (B. aculeata and B. marginata) were most successful in terms of calcification, adding chambers at all four temperatures and reproducing at 7 and 14 °C. Foraminiferal δ18O values displayed ontogenetic variations, with lower values in younger individuals. The δ18O values of adult specimens decreased with increasing temperature in all but the 4 °C treatment, exhibiting a relationship consistent with previous δ18O paleotemperature calibration studies. Foraminiferal Mg/Ca values, determined by laser ablation inductively coupled plasma mass spectrometry, were broadly consistent with previous Mg/Ca calibration studies, but extremely high values in the 4 °C treatment and higher than predicted values at two of the other three temperatures make it challenging to interpret these results.
Ocean acidification not likely to affect the survival and fitness of two temperate benthic foraminiferal species : results from culture experiments

( 2014-10) McIntyre-Wressnig, Anna ; Bernhard, Joan M. ; Wit, Johannes C. ; McCorkle, Daniel C.

Specimens of Bolivina argentea and Bulimina marginata, two widely distributed temperate benthic foraminiferal species, were cultured at constant temperature and controlled pCO2 (ambient, 1000 ppmv, and 2000 ppmv) for six weeks to assess the effect of elevated atmospheric CO2 concentrations on survival and fitness using Adenosine Triphosphate (ATP) analyses and on shell microfabric using high-resolution SEM and image analysis. To characterize the carbonate chemistry of the incubation seawater, total alkalinity and dissolved inorganic carbon were measured approximately every two weeks. Survival and fitness were not directly affected by elevated pCO2 and the concomitant decrease in seawater pH and calcite saturation states (Ωc), even when seawater was undersaturated with respect to calcite. These results differ from some previous observations that ocean acidification can cause a variety of effects on benthic foraminifera, including test dissolution, decreased growth, and mottling (loss of symbiont color in symbiont-bearing species), suggesting that the benthic foraminiferal response to ocean acidification may be species specific. If so, this implies that ocean acidification may lead to ecological winners and losers even within the same taxonomic group.
Calcification by juvenile corals under heterotrophy and elevated CO2

( 2013-12) Drenkard, Elizabeth J. ; Cohen, Anne L. ; McCorkle, Daniel C. ; de Putron, Samantha J. ; Starczak, Victoria R. ; Zicht, A. E.

Ocean acidification (OA) threatens the existence of coral reefs by slowing the rate of calcium carbonate (CaCO3) production of framework-building corals thus reducing the amount of CaCO3 the reef can produce to counteract natural dissolution. Some evidence exists to suggest that elevated levels of dissolved inorganic nutrients can reduce the impact of OA on coral calcification. Here, we investigated the potential for enhanced energetic status of juvenile corals, achieved via heterotrophic feeding, to modulate the negative impact of OA on calcification. Larvae of the common Atlantic golf ball coral, Favia fragum, were collected and reared for 3 weeks under ambient (421 μatm) or significantly elevated (1,311 μatm) CO2 conditions. The metamorphosed, zooxanthellate spat were either fed brine shrimp (i.e., received nutrition from photosynthesis plus heterotrophy) or not fed (i.e., primarily autotrophic). Regardless of CO2 condition, the skeletons of fed corals exhibited accelerated development of septal cycles and were larger than those of unfed corals. At each CO2 level, fed corals accreted more CaCO3 than unfed corals, and fed corals reared under 1,311 μatm CO2 accreted as much CaCO3 as unfed corals reared under ambient CO2. However, feeding did not alter the sensitivity of calcification to increased CO2; Δcalcification/ΔΩ was comparable for fed and unfed corals. Our results suggest that calcification rates of nutritionally replete juvenile corals will decline as OA intensifies over the course of this century. Critically, however, such corals could maintain higher rates of skeletal growth and CaCO3 production under OA than those in nutritionally limited environments.
Long-term effects of nutrient and CO2 enrichment on the temperate coral Astrangia poculata (Ellis and Solander, 1786)

( 2010-01-15) Holcomb, Michael ; McCorkle, Daniel C. ; Cohen, Anne L.

Zooxanthellate colonies of the scleractinian coral Astrangia poculata were grown under combinations of ambient and elevated nutrients (5 μM NO3 -, 0.3 μM PO4 -3, and 2 nM Fe+2) and CO2 (~780 ppmv) treatments for a period of 6 months. Coral calcification rates, estimated from buoyant weights, were not significantly affected by moderately elevated nutrients at ambient CO2 and were negatively affected by elevated CO2 at ambient nutrient levels. However, calcification by corals reared under elevated nutrients combined with elevated CO2 was not significantly different from that of corals reared under ambient conditions, suggesting that CO2 enrichment can lead to nutrient limitation in zooxanthellate corals. A conceptual model is proposed to explain how nutrients and CO2 interact to control zooxanthellate coral calcification. Nutrient limited corals are unable to utilize an increase in dissolved inorganic carbon (DIC) as nutrients are already limiting growth, thus the effect of elevated CO2 on saturation state drives the calcification response. Under nutrient replete conditions, corals may have the ability to utilize more DIC, thus the calcification response to CO2 becomes the product of a negative effect on saturation state and a positive effect on gross carbon fixation, depending upon which dominates, the calcification response can be either positive or negative. This may help explain how the range of coral responses found in different studies of ocean acidification can be obtained.
Early exposure of bay scallops (Argopecten irradians) to high CO2 causes a decrease in larval shell growth

(Public Library of Science, 2013-04-15) White, Meredith M. ; McCorkle, Daniel C. ; Mullineaux, Lauren S. ; Cohen, Anne L.

Ocean acidification, characterized by elevated pCO2 and the associated decreases in seawater pH and calcium carbonate saturation state (Ω), has a variable impact on the growth and survival of marine invertebrates. Larval stages are thought to be particularly vulnerable to environmental stressors, and negative impacts of ocean acidification have been seen on fertilization as well as on embryonic, larval, and juvenile development and growth of bivalve molluscs. We investigated the effects of high CO2 exposure (resulting in pH = 7.39, Ωar = 0.74) on the larvae of the bay scallop Argopecten irradians from 12 h to 7 d old, including a switch from high CO2 to ambient CO2 conditions (pH = 7.93, Ωar = 2.26) after 3 d, to assess the possibility of persistent effects of early exposure. The survival of larvae in the high CO2 treatment was consistently lower than the survival of larvae in ambient conditions, and was already significantly lower at 1 d. Likewise, the shell length of larvae in the high CO2 treatment was significantly smaller than larvae in the ambient conditions throughout the experiment and by 7 d, was reduced by 11.5%. This study also demonstrates that the size effects of short-term exposure to high CO2 are still detectable after 7 d of larval development; the shells of larvae exposed to high CO2 for the first 3 d of development and subsequently exposed to ambient CO2 were not significantly different in size at 3 and 7 d than the shells of larvae exposed to high CO2 throughout the experiment.

McCorkle Daniel C.

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