Temperature and oxygen availability are key drivers of marine ecosystem metabolism

Matthew E. S. Bracken, Ecology & Evolutionary Biology, University of California Irvine, Irvine, CA, Luke P. Miller, Department of Biology, San Diego State University, San Diego, CA, Sarah E. Mastroni, Coastal Science and Policy Program, University of California Santa Cruz, Santa Cruz, CA, Stephany M. Lira, Ecology and Evolutionary Biology, University of California Irvine, Irvine, CA and Cascade J. B. Sorte, Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA

Background/Question/Methods
Given human modification of Earth’s ecosystems, it is essential to understand how these changes are influencing ecosystem functioning. An important set of ecosystem-level responses includes gross community production, community respiration, and net community production, collectively referred to as “ecosystem metabolism”. In freshwater and marine systems, these responses are often estimated in situ by measuring oxygen (O2) production in the light (net community production) and O2 consumption in the dark (community respiration). These estimates can then be combined to estimate gross community production. However, the method used to create “dark” conditions could result in substantially different estimates of respiration and production. We test this prediction using a series of environmental measurements under daytime dark/light and daytime vs. nighttime conditions conducted seasonally over a 1-year period in a set of tide pools in southeastern Alaska.

Results/Conclusions
We compared measurements made in experimentally darkened tide pools during the day with those made during the night and found that daytime community respiration rates were up to two orders of magnitude higher than those measured at night. These differences were associated with higher temperatures and O2 levels during the day and led to major differences in estimates of gross community production calculated using daytime versus nighttime measurements of community respiration. Our results highlight the need to measure respiration rates during both day and night to account for effects of temperature and O2 and to calculate integrated daily and annual rates of ecosystem metabolism. Additionally, given continuing and accelerating changes in both temperature and dissolved O2 levels (e.g., climate-mediated hypoxia and anoxia), our results elucidate important mechanisms for human alteration of ecosystem functioning.