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

National Science Foundation 2009-2012

PI: Lisa A. Levin

Co-PI: Todd R. Martz

Graduate Student: Christina Frieder

Project Summary:

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. We will incorporate natural variability into a series of laboratory experiments to test how pH levels and variable pH affect the health of marine invertebrate larvae. We 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 we 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 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), and (b) varying pH about the mean on larval survivorship, growth, and calcification responses of multiple invertebrate 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. Ultimately these studies will help scientists design better experiments to study ocean acidification effects, identify field settings that may act as refugia from declining pH, and provide improved predictive powers concerning effects of ocean acidification on key living resources.

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Updated August 1, 2012
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