Ocean acidification represents a threat to marine species worldwide, and forecasting the ecological impacts of acidification is a high priority for science, management, and policy. As research on the topic expands at an exponential rate, a comprehensive understanding of the variability in organisms' responses and corresponding levels of certainty is necessary to forecast the ecological effects. Here, we perform the most comprehensive meta-analysis to date by synthesizing the results of 228 studies examining biological responses to ocean acidification. The results reveal decreased survival, calcification, growth, development and abundance in response to acidification when the broad range of marine organisms is pooled together. However, the magnitude of these responses varies among taxonomic groups, suggesting there is some predictable trait-based variation in sensitivity, despite the investigation of approximately 100 new species in recent research. The results also reveal an enhanced sensitivity of mollusk larvae, but suggest that an enhanced sensitivity of early life history stages is not universal across all taxonomic groups. In addition, the variability in species' responses is enhanced when they are exposed to acidification in multi-species assemblages, suggesting that it is important to consider indirect effects and exercise caution when forecasting abundance patterns from single-species laboratory experiments. Furthermore, the results suggest that other factors, such as nutritional status or source population, could cause substantial variation in organisms' responses. Last, the results highlight a trend towards enhanced sensitivity to acidification when taxa are concurrently exposed to elevated seawater temperature.

Ocean acidification is a pervasive stressor that could affect many marine organisms and cause profound ecological shifts. A variety of biological responses to ocean acidification have been measured across a range of taxa, but this information exists as case studies and has not been synthesized into meaningful comparisons amongst response variables and functional groups. We used meta-analytic techniques to explore the biological responses to ocean acidification, and found negative effects on survival, calcification, growth and reproduction. However, there was significant variation in the sensitivity of marine organisms. Calcifying organisms generally exhibited larger negative responses than noncalcifying organisms across numerous response variables, with the exception of crustaceans, which calcify but were not negatively affected. Calcification responses varied significantly amongst organisms using different mineral forms of calcium carbonate. Organisms using one of the more soluble forms of calcium carbonate (high-magnesium calcite) can be more resilient to ocean acidification than less soluble forms (calcite and aragonite). Additionally, there was variation in the sensitivities of different developmental stages, but this variation was dependent on the taxonomic group. Our analyses suggest that the biological effects of ocean acidification are generally large and negative, but the variation in sensitivity amongst organisms has important implications for ecosystem responses.

The global acidification of the earth's oceans is predicted to impact biodiversity via physiological effects impacting growth, survival, reproduction, and immunology, leading to changes in species abundances and global distributions. However, the degree to which these changes will play out critically depends on the evolutionary rate at which populations will respond to natural selection imposed by ocean acidification, which remains largely unquantified. Here we measure the potential for an evolutionary response to ocean acidification in larval development rate in two coastal invertebrates using a full-factorial breeding design. We show that the sea urchin species Strongylocentrotus franciscanus has vastly greater levels of phenotypic and genetic variation for larval size in future CO2 conditions compared to the mussel species Mytilus trossulus. Using these measures we demonstrate that S. franciscanus may have faster evolutionary responses within 50 years of the onset of predicted year-2100 CO2 conditions despite having lower population turnover rates. Our comparisons suggest that information on genetic variation, phenotypic variation, and key demographic parameters, may lend valuable insight into relative evolutionary potentials across a large number of species.

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High levels of intraspecific variability are often associated with HAB species, and this variability is likely an important factor in their competitive success. Heterosigma akashiwo (Hada) Hada ex Y. Hara et M. Chihara is an ichthyotoxic raphidophyte capable of forming dense surface-water blooms in temperate coastal regions throughout the world. We isolated four strains of H. akashiwo from fish-killing northern Puget Sound blooms in 2006 and 2007. By assessing numerous aspects of biochemistry, physiology, and toxicity, we were able to describe distinct ecotypes that may be related to isolation location, source population, or bloom timing. Contrasting elements among strains were cell size, maximum growth and photosynthesis rates, tolerance of low salinities, amino acid use, and toxicity to the ciliate grazer Strombidinopsis acuminatum (Fauré-Fremiet). In addition, the rDNA sequences and chloroplast genome of each isolate were examined, and while all rDNA sequences were identical, the chloroplast genome identified differences among the strains that tracked differences in ecotype. H. akashiwo strain 07A, which was isolated from an unusual spring bloom, had a significantly higher maximum potential photosynthesis rate (28.7 pg C · cell(-1)  · h(-1) ) and consistently exhibited the highest growth rates. Strains 06A and 06B were not genetically distinct from one another and were able to grow on the amino acids glutamine and alanine, while the other two strains could not. Strain 07B, which is genetically distinct from the other three strains, exhibited the only nontoxic effect. Thus, molecular tools may support identification, tracking, and prediction of strains and/or ecotypes using distinctive chloroplast gene signatures.

Anthropogenic carbon dioxide (CO 2 ) emissions and the resultant acidification of surface ocean waters are predicted to have far-reaching consequences for biological processes in the marine environment. For example, because changes in pH and pCO 2 can alter sperm performance, ocean acidification may be accompanied by reductions in the success of fertilization in marine broadcast spawners. Several studies have attempted to determine the effects of elevated pCO 2 on marine invertebrate fertilization success, albeit with differing results. These conflicts may stem from the use of inappropriate sperm-egg contact times and, in several cases, the lack of measurements over a range of sperm concentrations extending from sperm-limited conditions to polyspermy scenarios. In our study, we used biologically realistic sperm-egg contact times and a full range of sperm concentrations to assess the effect of elevated pCO 2 on fertilization in the broadcast spawning sea urchin, Strongylocentrotus franciscanus. Fertilization experiments were carried out in seawater bubbled with CO 2 to 400 (control), 800, and 1800 ppm. Using a fertilization kinetics model, we estimate that elevated pCO 2 levels both increased sperm limitation and reduced the efficiency of fast blocks to polyspermy. Thus, elevated pCO 2 decreased the range of sperm concentrations over which high fertilization success was likely. Given the inherent difficulties in achieving high fertilization success in broadcast spawners, raised pCO 2 levels are likely to exacerbate low fertilization success in low-density populations or in areas with high water turbulence.

6Predicting how populations will respond to ocean change across generations is critical to 7 effective conservation of marine species. One emerging factor is the influence of parental 8 exposures on offspring phenotype, known as intergenerational carryover effects. Parental 9 exposure may deliver beneficial or detrimental characteristics to offspring that can influence 10 larval recruitment patterns, thus shaping how populations and community structure respond to 11 ocean change. Impacts of adult exposure to elevated winter temperature and pCO2 on 12 reproduction and offspring viability were examined in the Olympia oyster (Ostrea lurida) using 13 three populations of adult, hatchery-reared O. lurida, plus an additional cohort spawned from one 14 of the populations. Oysters were sequentially exposed to elevated temperature (+4°C, at 10°C), 15 followed by elevated pCO2 (+2204 µatm, at 3045 µatm) during winter months. Male gametes 16 were more developed after elevated temperature exposure and less developed after high pCO2 17 exposure, but there was no impact on female gametes or sex ratios. Oysters previously exposed 18 to elevated winter temperature released larvae earlier, regardless of pCO2 exposure. Those 19 exposed to elevated winter temperature as a sole treatment released more larvae on a daily basis, 20 but when also exposed to high pCO2 there was no effect. These combined results indicate that 21 elevated winter temperature accelerates O. lurida spermatogenesis, resulting in earlier larval 22 release and increased production, with elevated pCO2 exposure negating effects of elevated 23 temperature. Altered recruitment patterns may therefore follow warmer winters due to 24 precocious spawning, but these effects may be masked by coincidental high pCO2. Offspring 25 were reared in common conditions for one year, then deployed for three months in four estuarine 26 bays with distinct environmental conditions. Offspring of parents exposed to elevated pCO2 had 27 Spencer et al. preprint September 2019 3 higher survival rates in two of the four bays. This carryover effect demonstrates that parental 28 conditions can have substantial ecologically relevant impacts that should be considered when 29 predicting impacts of environmental change. Furthermore, Olympia oysters may be more 30 resilient in certain environments when progenitors are pre-conditioned in stressful conditions. 31Combined with other recent studies, our work suggests that the Olympia may be more equipped 32 than other oysters for the challenge of a changing ocean. 33