Macrophyte-induced variability in coastal ocean pH and consequences for invertebrate larvae

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Increased concentrations of atmospheric carbon dioxide are acidifying the marine environment at unprecedented rates. However, relative to the open ocean, predictions of ocean acidification for the coastal ocean are confounded by the greater inherent variability of carbonate chemistry which includes strong variability induced by macrophyte photosynthesis and respiration. This proposal addresses the interplay between anthropogenically driven pH changes and the inherently variable coastal ocean's carbonate chemistry, and will directly test the implications for a potentially sensitive life form, invertebrate larvae.The objectives of this study are to measure the impact of key coastal habitats on natural pH variance, and to evaluate the implications these pH regimes have for developing invertebrate larvae. The investigators will incorporate natural variability into a series of laboratory and in-situ transplant experiments to test how pH levels, variability regimes, and physiologically-relevant thresholds affect the health of marine invertebrate larvae. They will test the hypotheses that (1) Macrophytes induce variability in carbonate chemistry in a predictable spatial and temporal context corresponding to cycles of primary production and community respiration. (2) Planktonic invertebrate larval health is sensitive to decreased pH, but negative effects are ameliorated when incorporating variable pH. (3) Sensitivity of invertebrate larvae to decreases in pH is a function of developmental mode: calcifying larvae are more sensitive than non-calcifying larvae, and planktotrophic (feeding) larvae are more sensitive than lecithotrophic (non-feeding) larvae. To test these hypotheses the investigators will characterize temporal and spatial carbonate chemistry variability at kelp forests and seagrass beds in San Diego, California. With discrete water samples for the determination of total alkalinity and dissolved inorganic carbon, and continuous autonomous instruments which measure pH, salinity, and temperature, a statistical characterization of carbonate chemistry variability they will identify diurnal, seasonal and spatial trends as well as frequencies of maximum variation, rates of change, lowest potential pH (extreme statistics), and biologically-significant thresholds. Subsequently, prominent macrophyte-induced pH regimes will be mimicked in laboratory experiments and incorporated with ocean acidification predictions to test effects of (a) decreased pH (8.1 to 7.3), (b) varying pH about the mean, (c) changing variance about mean pH, and (c) pulsed exposure to extreme low pH, on larval survivorship, growth, and calcification responses of multiple species. A comparative assessment of the larval responses will provide scientists, managers, and policy-makers with predictions of larval types (and thus populations) most sensitive or tolerant to forecasted pH regimes. Complementary field experiments will expose laboratory-spawned larvae to known spatial and temporal pH gradients under ambient cycles of temperature, light, and food. Larvae will be outplanted at CO2 vents in Ischia, Italy, and in southern California kelp and seagrass beds. This study is the first to investigate the implications of pH declines on larval development under natural fluctuating regimes, and in the field. Together, these laboratory and field studies will offer a mechanistic understanding of the effects of natural variance of carbonate chemistry in the context of ocean acidification.The Project will build capacity for the next generation to address ecological problems associated with ocean acidification. It will incorporate interdisciplinary graduate student training, involve new faculty, and promote undergraduate student engagement via field and laboratory experiences for underrepresented minorities. Findings will be integrated into graduate courses in BO, benthic ecology, marine chemistry, and seminar courses. Strategic partnerships have been established with educational programs that target middle school girls in San Diego, the nation's science-interested public, and precollege students involved in science fairs. The PIs will blend basic science concepts concerning coastal habitats and acidification with enduring educational resources to enhance scientific understanding by students and the public.