This work describes efforts to improve methodologies and instrumentation for investigation of the marine CO2 system. In the first section of my thesis, a method was developed that provides simple, calibration-free measurements of seawater carbonate saturation states (Ωspec) based solely on the use of a laboratory spectrophotometer. Measurements of pH are made in paired optical cells, one with and one without added nitric acid. The amount of added nitric acid is determined through the direct proportionality between nitrate concentration and UV absorbance. After an initial calibration, the method is calibration-free and requires no volumetric or gravimetric analyses thereafter. Saturation state measurements can be obtained in twelve minutes and attain Global Ocean Acidification Observing Network accuracy goals over a wide range of conditions. This simple one-step measurement protocol is ideal for monitoring ocean acidification conditions in coastal areas, fish hatcheries and shellfish farms. The second section of my thesis outlines the development of a next-generation handheld photometer for field measurements of seawater pH. The hand-held instrument is simple to use, inexpensive, and has a pH measurement accuracy of ±0.01. Each photometer is calibrated by relating pH-indicator absorbance ratios (RB) obtained with the broadband photometer to indicator absorbance ratios (RN) obtained with a high quality, narrowband scanning spectrophotometer. The RB vs RN relationship for each photometer is entered into the instrument’s software, providing discrete, real-time pH observations from measurements of RB, salinity and temperature. Measurement accuracy is assessed through comparisons of photometer pH with pH observations obtained using standard measurement procedures and high-quality spectrophotometers. The targeted user-groups for these instruments include middle and high school students, citizen scientists, and resource managers

Cette étude a utilisé une approche interdisciplinaire pour évaluer les effets de l'acidification de l'océan sur des ptéropodes et les foraminifères Méditerranéennes. Une comparaison d'échantillons conservés et modernes de 2 espèces de ptéropodes a été réalisée pour étudier les effets du pH sur les propriétés de la coquille. Des populations de ptéropodes ont également été analysées à l'aide des données de séries temporelles. Pour permettre l'amélioration de futures expériences de perturbation, une revue collaborative des techniques de culture de ptéropodes a été produite. Enfin, le foraminifère O. universa a été cultivé dans des conditions de pH et de [CO32-] découplés pour évaluer les effets des changements dans la chimie du carbonate sur la composition en bore et le ?11B. Les coquilles des échantillons conservés de ptéropodes étaient plus épaisses que celles collectées en 2012 et les coquilles de C. inflexa recueillies en 1910 étaient nettement plus denses que celles de 2012, probablement en raison d'un effet de pH. Les abondances de ptéropodes ont montré une tendance croissante entre 1967-2003 et se sont révélées être influencées par les changements de température interannuelles, sans que des changements dans les propriétés des coquilles n'ai eu d'impacts négatifs. Lors de la dernière étude le pH était le seul paramètre du système de carbonate a affecter le ?11Bde la calcite de O. universa. Le B/Ca a diminué avec la diminution du [CO23-] à pH constant mais n'a pas montré de tendance cohérente avec une [CO23-] constant et un pH variable. Au lieu de cela, une étroite corrélation entre les B / Ca et [HCO3-] suggérant que le bore est contrôlé par la [HCO3-]. / This study used an interdisciplinary approach to assess the effects of ocean acidification on Mediterranean pteropods and foraminifers. A comparison of museum and modern samples of two pteropod species investigated the effects of pH on shell properties. Pteropod populations were analysed using time series data. To improve future perturbation experiments, a collaborative review of pteropod culture techniques was produced. Finally, the foraminifer O. universa was cultured under decoupled pH and [CO32-] to assess the effects of changes in the carbonate chemistry on boron incorporation and isotope fractionation. Museum pteropod samples were thicker than shells from 2012 and C. inflexa shells collected in 1910 were significantly denser than those from 2012, possibly due to a pH effect. Pteropod abundances displayed an increasing trend between 1967-2003 and are influenced by inter- annual temperature changes, with no sign of the observed changes in shell properties having had negative impacts. pH was the sole parameter of the carbonate system that affected the δ11B of O. universa calcite. The B/Ca ratio decreased with decreasing [CO32-] at constant pH but did not show consistent trends at constant [CO32-] and varying pH. Instead, a close correlation of B/Ca ratios and [HCO3-] was observed suggesting that boron is controlled by the [HCO3-].

Ocean acidification is a phenomenon associated with global change and anthropogenic CO2 emissions that is changing the chemistry of seawater. These changes result in elevated pCO2 and reduced pH in seawater and this is impacting marine organisms in various ways. Marine fishes are considered generally tolerant to conditions of ocean acidification; however, these assumptions are based on juvenile and adult fish tolerance and the larval stages have not been frequently assessed. Furthermore, it has been suggested that temperate species, particularly those with an estuarine association, may be tolerant to variable CO2 and pH. This study used an eco-physiological approach to understand how the early life stages of Argyrosomus japonicus, an estuarine dependent marine fisheries species found in warm-temperate regions, may be impacted by ocean acidification. The metabolic response of early stage larvae (hatching to early juvenile stage) was assessed under conditions of elevated pCO2 and reduced pH in a controlled laboratory setting. Small volume static respirometry was used to determine the oxygen consumption rate of larvae raised in three pCO2 treatments including a low (pCO2 = 327.50 ± 80.07 µatm at pH 8.15), moderate (pCO2 477.40 ± 59.46 µatm at pH 8.03) and high treatment (PCO2 910.20 ± 136.45 µatm at pH 7.78). These treatment levels were relevant to the present (low) and projected conditions of ocean acidification for the years 2050 (moderate) and 2100 (high). Prior to experimentation with ocean acidification treatments, baseline metabolic rates and diurnal variation in oxygen consumption rates in early stage A. japonicus was determined. Distinct ontogenetic structuring of metabolic rates was observed in early stage A. japonicus, with no cyclical fluctuations in metabolic rate occurring during the 24 hour photoperiodic cycle. Pre-flexion larvae showed no metabolic response to ocean acidification treatments; however post-flexion stage larvae showed metabolic depression of standard metabolic rate in the moderate (32.5%) and high (9.5%) pCO2 treatments (P = 0.02). Larvae raised in the high pCO2 treatment also showed high levels of mortality with no individuals surviving past the post-flexion stage. Larvae raised in the moderate pCO2 treatment were unaffected. This study concluded that ocean acidification conditions expected for the end of the century will have significant impacts on the metabolism of early stage A. japonicus, which may result in reduced growth, retardation of skeletal development and ultimately survival as a result of increased mortality. Furthermore, the timing of reduced metabolic scope will significantly impact the recruitment ability of A. japonicus larvae into estuarine habitats. This could ultimately impact the sustainability of A. japonicus populations. Most importantly, this study highlighted the need to consider the combined effect of ontogeny and life-history strategy when assessing the vulnerability of species to ocean acidification.

Ocean warming and acidification pose major threats to coral reef organisms. It is unknown how the early life history stages of Atlantic corals cope with the combined effects of these two global environmental stressors. Here, I investigate how these stressors influence the fertilization success, larval survivorship, and settlement of the threatened Atlantic coral, Orbicella faveolata. Gametes from O. faveolata were subjected to a factorial combination of present and future scenarios of oceanic temperatures (28.5° C and 30° C) and pH (8.2 and 8.0) predicted to occur by 2050. Results indicate that treatment type did not significantly affect fertilization success. Elevated temperature caused complete larval mortality and inhibited the settlement of O. faveolata. Interestingly, these negative effects of high temperature were partially mitigated when combined with ocean acidification. Overall, both the larval survivorship and settlement in the combined treatment was reduced to approximately half when compared to ambient treatment. Although ocean acidification may partially mitigate the negative effects of ocean warming during the larval stage, the overall reduced survival and settlement of larvae under future oceanic conditions, coupled to reduced calcification in adults, portends devastating effects on the health of this threatened species.

Cold-water corals act as critical foundation species in the deep sea by creating extensive three-dimensional habitat structures that support biodiversity hotspots. There is currently a paucity of data concerning the environmental requirements and physiology of cold-water corals, severely limiting our ability to predict how resilient they will be to future environmental change. Cold-water corals are expected to be particularly vulnerable to the effects of ocean acidification, the reduction in seawater pH and associated changes to the carbonate system caused by anthropogenic CO2 emissions. Here, the ecological niche and physiology of the cold-water coral Lophelia pertusa is explored to predict its sensitivity to ocean acidification. Species distribution models were generated in order to quantify L. pertusa’s niche in the Gulf of Mexico with regard to parameters including seafloor topography, the carbonate system, and the availability of hard substrate. A robust oceanographic assessment of the Gulf of Mexico was conducted in order to characterize the current environmental conditions at benthic sites, with a focus on establishing the baseline carbonate system in L. pertusa habitats. Finally, an experimental approach was used to test the physiological response of biogeographically separated L. pertusa populations from the Gulf of Mexico and the Norwegian coast to ocean acidification. Based on my findings, it appears that L. pertusa already persists near the edge of its viable niche space in some locations, and therefore may be highly vulnerable to environmental change. However, experimental results suggest that some populations may be surprisingly resilient to ocean acidification, yielding broad implications for the continued persistence of cold-water corals in future oceans. / Biology

Deep-water or cold-water corals are abundant and highly diverse, greatly increase habitat heterogeneity and species richness, thereby forming one of the most significant ecosystems in the deep sea. Despite this remote location, they are not removed from the different anthropogenic disturbances that commonly impact their shallow-water counterparts. The global decrease in seawater pH due to increases in atmospheric CO2 are changing the chemical properties of the seawater, decreasing the concentration of carbonate ions that are important elements for different physiological and ecological processes. Predictive models forecast a shoaling of the carbonate saturation in the water column due to OA, and suggest that cold-water corals are at high risk, since large areas of suitable habitat will experience suboptimal conditions by the end of the century. The main objective of this study was to explore the fate of the deep-water coral community in time of environmental change. To better understand the impact of climate change this study focused in two of the most important elements of deep-sea coral habitat, the reef forming coral Lophelia pertusa and the octocoral community, particularly the gorgonian Callogorgia delta. By means of controlled experiments, I examined the effects of long- and short-term exposures to seawater simulating future scenarios of ocean acidification on calcification and feeding efficiency. Finally In order to understand how the environment influences the community assembly, and ultimately how species cope with particular ecological filters, I integrated different aspects of biology such functional diversity and ecology into a more evolutionary context in the face of changing environment. My results suggest that I) deep-water corals responds negatively to future OA by lowering the calcification rates, II) not all individuals respond in the same way to OA with high intra-specific variability providing a potential for adaptation in the long-term III) there is a disruption in the balance between accretion and dissolution that in the long term can shift from net accretion to net dissolution, and IV) there is an evolutionary implication for certain morphological features in the coral community that can give an advantage under stresfull conditions. Nevertheless, the suboptimal conditions that deep-water corals will experience by the end of the century could potentially threaten their persistence, with potentially negative consequences for the future stability of this already fragile ecosystem. / Biology

Ocean acidification is the reduction in seawater pH due to the absorption of anthropogenic carbon dioxide by the oceans. Reductions in seawater pH can inhibit the precipitation of aragonite, a calcium carbonate mineral used by marine calcifiers such as corals. Lophelia pertusa is a cold-water coral that forms large reef structures which enhance local biodiversity on the seafloor, and is found commonly from 300-600 meters on hard substrata in the Gulf of Mexico. The present study sought to investigate the potential impacts of ocean acidification on L. pertusa in the Gulf of Mexico through combined field and laboratory analyses. A field component characterized the carbonate chemistry of L. pertusa habitats in the Gulf of Mexico, an important step in establishing a baseline from which future changes in seawater pH can be measured, in addition to collecting in situ data for the design and execution of perturbation experiments in the laboratory. A series of recirculating aquaria were designed and constructed for the present study, and support the maintenance and experimentation of live L. pertusa in the laboratory. Finally, experiments testing L. pertusa's mortality and growth responses to ocean acidification were conducted in the laboratory, which identified thresholds for calcification and a range of sensitivities to ocean acidification by individual genotype. The results of this study permit the monitoring of ongoing ocean acidification in the deep Gulf of Mexico, and show that ocean acidfication's impacts may not be consistent across individuals within populations of L. pertusa. / Biology

Recent concern over the effects of ocean acidification upon calcifying organisms in the modern ocean has highlighted the aragonitic shelled thecosomatous pteropods as being at a high risk. Laboratory studies have shown that increased pCO2, leading to decreased pH and low carbonate concentrations, has a negative impact on the ability of pteropods to calcify and maintain their shells. This study presents the micropalaeontological analysis of marine cores from the Caribbean Sea, Mediterranean Sea and Indian Ocean. Pteropods, heteropods and planktic foraminifera were picked from samples to provide palaeoenvironmental data for each core. Determination of pteropod calcification was made using the Limacina Dissolution Index (LDX) and the average shell size of Limacina inflata specimens. Pteropod calcification indices were compared to global ice volume and Vostok atmospheric CO2 concentrations to determine any associations between climate and calcification. Results show that changes in surface ocean carbonate concentrations throughout the Late Pleistocene did affect the calcification of thecosomatous pteropods. These effects can be detected in shells from marine sediments that are located well above the aragonite lysocline and have not undergone post-depositional dissolution. The results of this study confirm the findings of laboratory studies, showing a decrease in calcification during interglacial periods, when surface ocean carbonate concentrations were lower. During glacial periods, calcification was enhanced due to the increased availability of carbonate. This trend was found in all sediments studied, indicating that the response of pteropods to past climate change is of global significance. These results demonstrate that pteropods have been negatively affected by oceanic pH levels relatively higher and changing at a lesser rate than those predicted for the 21st Century. Results also establish the use of pteropods and heteropods in reconstructing surface ocean conditions. The LDX is a fast and appropriate way of determining variations in surface water carbonate saturation. Abundances of key species were also found to constrain palaeotemperatures better than planktic foraminifera, a use which could be further developed.

Environmental change is a major threat to marine ecosystems worldwide. Understanding the key biological processes and environmental factors mediating spatial and temporal species' responses to habitat alterations underpins our ability to forecast impacts on marine ecosystems under any range of scenarios. This is especially important for calcifying species, many of which have both a high climate sensitivity and disproportionately strong ecological impacts in shaping marine communities. Although geographic patterns of calcifiers' sensitivity to environmental changes are defined by interacting multiple abiotic and biotic stressors, local adaptation, and acclimation, knowledge on species' responses to disturbance is derived largely from short- and medium-term laboratory and field experiments. Therefore, little is known about the biological mechanisms and key drivers in natural environments that shape regional differences and long-term variations in species vulnerability to global changes. In this thesis, I examined natural variations in shell characteristics, both morphology and biomineralisation, under heterogeneous environmental conditions i) across large geographical scales, spanning a 30° latitudinal range (3,334 km), and ii) over historical times, using museum collections (archival specimens from 1904 to 2016 at a single location), in mussels of the genus Mytilus. The aim was to observe whether plasticity in calcareous shell morphology, production, and composition mediates spatial and temporal patterns of resistance to climate change in these critical foundation species. For the morphological analyses, the combined use of new statistical methods and multiple study systems at various geographical scales allowed the uncoupling of the contribution of development, genetic status, and environmental factors to shell morphology. I found salinity had the strongest effect on the latitudinal patterns of Mytilus shape. Temperature and food supply, however, were the main predictor of mussel shape heterogeneity. My results suggest the potential of shell shape plasticity in Mytilus as a powerful indicator of rapid environmental changes. I found decreasing shell calcification towards high latitudes. Salinity was the best predictor of regional differences in shell deposition, and its mineral and organic composition. In polar, low-salinity environments, the production of calcite and organic shell layers was increased, while aragonite deposition was enhanced under temperate, higher-salinity regimes. Interacting strong effects of decreasing salinity and increasing food availability on compositional shell plasticity predict the deposition of a thicker external organic layer (periostracum) at high latitudes under forecasted future conditions. This response potential of Mytilus shell suggests an enhanced protection of temperate mussels from predators and a strong capacity for increased resistance of polar and subpolar individuals to dissolving water conditions. Analyses of museum specimens indicated increasing shell calcification during the last century. Deposition of individual shell layers was more closely related to temporal changes in the variability of key environmental drivers than to alterations of mean habitat conditions. Calcitic layer and periostracum showed marked responses to alterations of biotic conditions, suggesting the potential of mussels to trade-off between the deposition of calcareous and organic layers as a compensatory response to strategy-specific predation pressure. These changes in biomineralisation indicated a marked resistance to environmental change over the last century in a species predicted to be vulnerable, and how locally heterogeneous environments and predation levels can have a stronger effect on Mytilus responses than global environmental trends. My work illustrates that biological mechanisms and local conditions, driving plastic responses to the spatial and temporal structure of multiple abiotic and biotic stressors, can define geographic and temporal patterns of unforeseen species resistance to global environmental change.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Predicting the response of net community calcification (NCC) to ocean acidification OA and declining aragonite saturation state [Omega]a requires a thorough understanding of controls on NCC. The diurnal control of light and net community production (NCP) on NCC confounds the underlying control of [Omega]a on NCC and must be averaged out in order to predict the general response of NCC to OA. I did this by generating a general NCC-[Omega]a correlation based on data from 15 field and mesocosm studies around the globe. The general relationship agrees well with results from mesocosm experiments. This general relationship implies that NCC will transition from net calcification to net dissolution at a [Omega]a of 1.0 ± 0.6 and predicts that NCC will decline by 50% from 1880 to 2100, for a reef of any percent calcifier cover and short reef water residence time. NCC will also decline if percent calcifier cover declines, as evidenced by estimates of NCC in two Caribbean reefs having declined by an estimated 50-90% since 1880. The general NCC-([Omega]a relationship determined here, along with changes in percent calcifier cover, will be useful in predicting changes in NCC in response to OA and for refining models of reef water [Omega]a. / by Whitney Nicole Bernstein. / Ph.D.