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SFS Annual Meeting

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Acidification frequently has negative impacts on aquatic macroinvertebrates, and drought-driven acidification events of increasing frequency and severity are expected due to climate change. These events may expose even well-adapted macroinvertebrate taxa to acidification regimes beyond their tolerance levels. In lowland Costa Rica, poorly-buffered tropical streams may exhibit extremely low pH levels (<4.5) during seasonal acidification events. We conducted laboratory mesocosm experiments at La Selva Biological Station to determine the thresholds of acidification effects on growth and survival of leptophlebiid mayflies (Traverella holzenthali) and paleomonid shrimp (Macrobrachium olfersi) from a poorly-buffered stream and larval chironomids (Chironomidae) from a poorly-buffered (pH 4.3-6.9) vs. a naturally well-buffered (pH 5.1-6.9) stream. Chironomids were unaffected by pH regimes above 3.5, indicating tolerance to pH levels in the poorly-buffered stream during natural seasonal acidification. Mayflies and shrimp showed decreased tolerance to the lowest pH levels (3.6-4.0) recorded after a previous extreme dry season, suggesting that increasingly severe extreme acidification events might negatively affect their survival. Our findings are not only relevant to lowland Neotropical streams, but also signal the need for further research in lotic ecosystems worldwide where drought-driven pH declines are probable in the future.

Carissa Ganong (Primary Presenter/Author), Missouri Western State University,;

Minor Hidalgo (Co-Presenter/Co-Author), Organization for Tropical Studies,;

Catherine Pringle (Co-Presenter/Co-Author), Odum School of Ecology, University of Georgia,;