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Approximately one-quarter of the CO 2 emitted to the atmosphere annually from human activities is absorbed by the ocean, resulting in a reduction of seawater pH and shifts in seawater carbonate chemistry. This multi-decadal process, termed "anthropogenic ocean acidification" (OA), has been shown to have detrimental impacts on marine ecosystems. Recent years have seen a globally coordinated effort to measure the changes in seawater chemistry caused by OA, with best practices now available for these measurements. In contrast to these substantial advances in observing physicochemical changes due to OA, quantifying their biological consequences remains challenging, especially from in situ observations under real-world conditions. Results from 2 decades of controlled laboratory experiments on OA have given insight into the likely processes and mechanisms by which elevated CO 2 levels affect biological process, but the manifestation of these process across a plethora of natural situations has yet to be fully explored. This challenge requires us to identify a set of fundamental biological and ecological indicators that are (i) relevant across all marine ecosystems, (ii) have a strongly demonstrated link to OA, and (iii) have implications for ocean health and the provision of ecosystem services with impacts on local marine management strategies and economies. This paper draws on the understanding of biological impacts provided by the wealth of previous experiments, as well as the findings of recent meta-analyses, to propose five broad classes of biological indicators that, when coupled with environmental observations including carbonate chemistry, would allow the rate and severity of biological change in response to OA to be observed and compared. These broad indicators are applicable to different ecological systems, and the methods for data analysis suggested here would allow researchers to combine biological response data across regional and global scales by correlating rates of biological change with the rate of change in carbonate chemistry parameters. Moreover, a method using laboratory observation to design an optimal observing strategy (frequency and duration) and observe meaningful biological rates of change highlights the factors that need to be considered when applying our proposed observation strategy. This innovative observing methodology allows inclusion of a wide diversity of marine ecosystems in regional and global assessments and has the potential to increase the contribution of OA observations from countries with developing OA science capacity. [ABSTRACT FROM AUTHOR]

Approximately one quarter of the CO2 emitted to the atmosphere annually from human activities is absorbed by the ocean, resulting in a reduction of seawater pH and shifts in seawater carbonate chemistry. This multi-decadal process, termed "anthropogenic ocean acidification" (OA) has been shown to have detrimental impacts on marine ecosystems. Recent years have seen a globally coordinated effort to measure the changes in seawater chemistry caused by OA, with best practices now available for these measurements. In contrast to these substantial advances in observing physico-chemical changes due to OA, quantifying their biological consequences remains challenging, especially from in-situ observations under real-world conditions. Results from two decades of controlled laboratory experiments on OA have given insight into the likely processes and mechanisms by which elevated CO2 levels affect biological process, but the manifestation of these process across a plethora of natural situations has yet to be explored fully. This challenge requires us to identify a set of fundamental biological and ecological indicators that are i) relevant across all marine ecosystems, ii) have a strongly demonstrated link to OA, and iii) have implications for ocean health and the provision of ecosystem services with impacts on local marine management strategies and economies. This paper draws on the understanding of biological impacts provided by the wealth of previous experiments, as well as the findings of recent meta-analyses, to propose five broad classes of biological indicators that, when coupled with environmental observations, including carbonate chemistry, would allow the rate and severity of biological change in response to OA to be observed and compared. These broad indicators are applicable to different ecological systems, and the methods for data analysis suggested here would allow researchers to combine biological response data across regional and global scales by correlating rates of biological change with the rate of change in carbonate chemistry parameters. Moreover, a method using laboratory observation to design an optimal observing strategy (frequency and duration) and observe meaningful biological rates of change highlights the factors that need to be considered when applying our proposed observation strategy. This innovative observing methodology allows inclusion of a wide diversity of marine ecosystems in regional and global assessments and has the potential to increase the contribution of OA observations from countries with developing OA science capacity. [ABSTRACT FROM AUTHOR]

Abstract Ocean acidification (OA) has potential to affect marine phytoplankton in ways that are partly understood, but there is less knowledge about how it may alter the coupling to secondary producers. We investigated the effects of OA on phytoplankton primary production, and its trophic transfer to zooplankton in a subtropical eutrophic water (Wuyuan Bay, China) under present day (400 μatm) and projected end-of-century (1000 μatm) p CO 2 levels. Net primary production was unaffected, although OA did lead to small decreases in growth rates. OA had no measurable effect on micro-/mesozooplankton grazing rates. Elevated p CO 2 had no effect on phytoplankton fatty acid (FA) concentrations during exponential phase, but saturated FAs increased relative to the control during declining phase. FA profiles of mesozooplankton were unaffected. Our findings show that short-term exposure of plankton communities in eutrophic subtropical waters to projected end-of-century OA conditions has little effect on primary productivity and trophic linkage to mesozooplankton. Highlights • Lower apparent growth was observed under elevated CO 2 of 1000 μatm. • Primary production and trophic transfer were unaffected by high CO 2. • Fatty acid profiles of phyto-/zooplankton were unaffected by ocean acidification. [ABSTRACT FROM AUTHOR]

Climate change pressures will influence marine planktonic systems globally, and it is conceivable that harmful algal blooms may increase in frequency and severity. These pressures will be manifest as alterations in temperature, stratification, light, ocean acidification, precipitation-induced nutrient inputs, and grazing, but absence of fundamental knowledge of the mechanisms driving harmful algal blooms frustrates most hope of forecasting their future prevalence. Summarized here is the consensus of a recent workshop held to address what currently is known and not known about the environmental conditions that favor initiation and maintenance of harmful algal blooms. There is expectation that harmful algal bloom (HAB) geographical domains should expand in some cases, as will seasonal windows of opportunity for harmful algal blooms at higher latitudes. Nonetheless there is only basic information to speculate upon which regions or habitats HAB species may be the most resilient or susceptible. Moreover, current research strategies are not well suited to inform these fundamental linkages. There is a critical absence of tenable hypotheses for how climate pressures mechanistically affect HAB species, and the lack of uniform experimental protocols limits the quantitative cross-investigation comparisons essential to advancement. A HAB “best practices” manual would help foster more uniform research strategies and protocols, and selection of a small target list of model HAB species or isolates for study would greatly promote the accumulation of knowledge. Despite the need to focus on keystone species, more studies need to address strain variability within species, their responses under multifactorial conditions, and the retrospective analyses of long-term plankton and cyst core data; research topics that are departures from the norm. Examples of some fundamental unknowns include how larger and more frequent extreme weather events may break down natural biogeographic barriers, how stratification may enhance or diminish HAB events, how trace nutrients (metals, vitamins) influence cell toxicity, and how grazing pressures may leverage, or mitigate HAB development. There is an absence of high quality time-series data in most regions currently experiencing HAB outbreaks, and little if any data from regions expected to develop HAB events in the future. A subset of observer sites is recommended to help develop stronger linkages among global, national, and regional climate change and HAB observation programs, providing fundamental datasets for investigating global changes in the prevalence of harmful algal blooms. Forecasting changes in HAB patterns over the next few decades will depend critically upon considering harmful algal blooms within the competitive context of plankton communities, and linking these insights to ecosystem, oceanographic and climate models. From a broader perspective, the nexus of HAB science and the social sciences of harmful algal blooms is inadequate and prevents quantitative assessment of impacts of future HAB changes on human well-being. These and other fundamental changes in HAB research will be necessary if HAB science is to obtain compelling evidence that climate change has caused alterations in HAB distributions, prevalence or character, and to develop the theoretical, experimental, and empirical evidence explaining the mechanisms underpinning these ecological shifts. [ABSTRACT FROM AUTHOR]

To assess the role of methodological differences on measured trace-element concentrations in ice cores, we developed an experiment to test the effects of acidification strength and time on dust dissolution using snow samples collected in West Antarctica and Alaska. We leached Antarctic samples for 3 months at room temperature using nitric acid at concentrations of 0.1, 1.0 and 10.0% (v/v). At selected intervals (20 min, 24 hours, 5 days, 14 days, 28 days, 56 days, 91 days) we analyzed 23 trace elements using inductively coupled plasma mass spectrometry. Concentrations of lithogenic elements scaled with acid strength and increased by 100-1380% in 3 months. Incongruent elemental dissolution caused significant variability in calculated crustal enrichment factors through time (factor of 1.3 (Pb) to 8.0 (Cs)). Using snow samples collected in Alaska and acidified at 1% (v/v) for 383 days, we found that the increase in lithogenic element concentration with time depends strongly on initial concentration, and varies by element (e.g. Fe linear regression slope = 1.66; r = 0.98). Our results demonstrate that relative trace-element concentrations measured in ice cores depend on the acidification method used. [ABSTRACT FROM AUTHOR]

While solar ultraviolet radiation (UVR) is known to impact zooplankton, little has been documented on its impacts under elevated pCO 2. Here, we show that exposure to UVR decreased the feeding and survival rates of the copepod Acartia spinicauda , that artificial UV-B of 2.25 W·m−2 for 4 h resulted in a 52 % inhibition of its grazing rates and a 45 % reduction in survival rates compared to visible light alone. On the other hand, an increase in pCO 2 to 1000 μatm (pH drop of 0.4) immediately and significantly increased the UVR-induced inhibition of feeding. Subsequently, the combination of the high pCO 2 (1000 μatm) and UVR resulted in about 65 % lethal impact, with UV-A contributing 21 % and UV-B 44 % compared to the visible light alone and ambient pCO 2 conditions. While the copepod was shown to be able to sense and escape from UV-exposed areas, these findings suggest that UVR impacts on the copepod can be exacerbated with progressive ocean acidification or in high CO 2 waters, including upwelled regions. • Impact of UVR on the Physiological Activities of Copepod : • Exposure to UV-B radiation (2.25 W·m-2 for 4 hours) significantly inhibits the grazing rates (by 52 %) and reduces the survival rates (by 45 %) of the copepod Acartia spinicauda compared to visible light alone. • Synergistic Detrimental Effects of UVR and Elevated pCO 2 : • The combination of high pCO 2 and UVR results in approximately 65 % lethal impact on A. spinicauda , with UV-A contributing 21 % and UV-B contributing 44 % to the mortality compared to visible light alone and ambient pCO 2 conditions. • Photoprotective and Avoidance Behaviors : • A. spinicauda exhibits avoidance behavior by migrating to regions not exposed to UV radiation. [ABSTRACT FROM AUTHOR]

• HABs develop through the integration of physical, chemical, and temporal drivers. • We need a mechanistic understanding that reveals how climate affects these drivers. • Accelerating climate change in coastal regions signals the urgency for action. • New strategies, tools, and observatories for HABs will improve our forecast skill. • Focused research on subsets of HAB species would greatly accelerate advances. There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water column all influence the productivity, composition, and global range of phytoplankton assemblages, but large uncertainty remains about how integration of these climate drivers might shape future HABs. Presented here are the collective deliberations from a symposium on HABs and climate change where the research challenges to understanding potential linkages between HABs and climate were considered, along with new research directions to better define these linkages. In addition to the likely effects of physical (temperature, salinity, stratification, light, changing storm intensity), chemical (nutrients, ocean acidification), and biological (grazer) drivers on microalgae (senso lato), symposium participants explored more broadly the subjects of cyanobacterial HABs, benthic HABs, HAB effects on fisheries, HAB modelling challenges, and the contributions that molecular approaches can bring to HAB studies. There was consensus that alongside traditional research, HAB scientists must set new courses of research and practices to deliver the conceptual and quantitative advances required to forecast future HAB trends. These different practices encompass laboratory and field studies, long-term observational programs, retrospectives, as well as the study of socioeconomic drivers and linkages with aquaculture and fisheries. In anticipation of growing HAB problems, research on potential mitigation strategies should be a priority. It is recommended that a substantial portion of HAB research among laboratories be directed collectively at a small sub-set of HAB species and questions in order to fast-track advances in our understanding. Climate-driven changes in coastal oceanographic and ecological systems are becoming substantial, in some cases exacerbated by localized human activities. That, combined with the slow pace of decreasing global carbon emissions, signals the urgency for HAB scientists to accelerate efforts across disciplines to provide society with the necessary insights regarding future HAB trends. [ABSTRACT FROM AUTHOR]

• Growth rates of an Alexandrium catenella decrease at future temperature levels. • Growth rates of co-occurring non-toxic dinoflagellate competitors increase. • The findings suggest fewer future toxic blooms in the southern Gulf of Maine. • But more toxic blooms may occur in the northeastern Gulf of Maine. Climate driven increases in ocean temperature and pCO 2 have the potential to alter the growth and prevalence of future Harmful Algal Blooms (HABs), but systematic studies on how climate drivers influence toxic algal species relative to non-toxic phytoplankton are lacking. In particular, little is known about how future climate scenarios will affect the growth of the toxic dinoflagellate Alexandrium catenella , which is responsible for the paralytic shellfish poisoning (PSP) events that threaten the health and economy of coastal communities in the Gulf of Maine and elsewhere. The growth responses of A. catenella and two other naturally co-occurring dinoflagellates in the Gulf of Maine— Scrippsiella sp., and Amphidinium carterae— were studied in mono and mixed species cultures. Experimental treatments tested the effects of elevated temperature (20 °C), lower pH (7.8), and the combination of elevated temperature and lower pH on growth rates relative to those in near-current conditions (15 °C; pH 8.1). Growth rates of A. catenella decreased under elevated temperature and lower pH conditions, a response that was largely attributable to the effect of temperature. In contrast, growth rates of Scrippsiella sp. and A. carterae increased under elevated temperature and lower pH conditions, with temperature also being the primary driver of the response. These trends did not change substantially when these species were grown in mixed cultures (A. catenella + Scrippsiella sp., and A. catenella + A. carterae), indicating that allelopathic or competitive interactions did not affect the experimental outcome under the conditions tested. These findings suggest that A. catenella blooms may become less prevalent in the southern regions of the Gulf of Maine, but potentially more prevalent in the northeastern regions of the Gulf of Maine with continued climate change. [ABSTRACT FROM AUTHOR]

Ocean Acidification (OA) effects on marine plankton are most often considered in terms of inorganic carbon chemistry, but decreasing pH may influence other aspects of cellular metabolism. Here we present the effects of OA on the fatty acid (FA) content and composition of an artificial phytoplankton community ( Phaeodactylum tricornutum , Thalassiosira weissflogii , and Emiliania huxleyi ) in a fully replicated, ∼4 m 3 mesocosm study in subtropical coastal waters (Wuyuan Bay, China, 24.52°N, 117.18°E) at present day (400 μatm) and elevated (1000 μatm) p CO 2 concentrations. Phytoplankton growth occurred in three phases during the 33-day experiment: an initial exponential growth leading to senescence and a subsequent decline phase. Phytoplankton sampled from these mesocosms were fed to mesozooplankton collected by net haul from Wuyuan Bay. Concentrations of saturated fatty acids (SFA) in both phytoplankton and mesozooplankton remained high under acidified and non-acidified conditions. However, polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA) increased significantly more under elevated p CO 2 during the late exponential phase (Day 13), indicating increased nutritional value for zooplankton and higher trophic levels. Indeed, uptake rates of the essential FA docosahexaenoic acid (C20:5n3, DHA) increased in mesozooplankton under acidified conditions. However, mesozooplankton grazing rates decreased overall with elevated p CO 2 . Our findings show that these selected phytoplankton species have a relatively high tolerance to acidification in terms of FA production, and local mesozooplankton in these subtropical coastal waters can maintain their FA composition under end of century ocean acidification conditions. [ABSTRACT FROM AUTHOR]