Coastal ecosystems are highly variable environments where restricted water motion, terrestrial influences, and feedbacks between benthic productivity and calcification have the potential to strongly impact the local biogeochemistry. To understand how climate change stressors, such as rising CO2, will impact biodiversity and ecosystem functioning in dynamic coastal ecosystems, we investigated the degree to which local physical and biological processes drive coastal biogeochemistry. Using temperate tide pools as a study system, we compared biological (community composition and ecosystem metabolism) and physical (tide pool attributes, light, and temperature) drivers of pH variability and quantified the relationship between this variability ecosystem functioning (net community production and net ecosystem calcification). We investigated these biophysical feedbacks across four sites in California and Oregon, where we conducted daytime and nighttime sampling to assess community metabolism in 13-15 tide pools at each site. We used mixed effects models to (1) test the relative effect of physical and biological parameters on the pH means and ranges across tide pools and (2) test for feedbacks between community production, pH, and ecosystem calcification.
There was substantial spatiotemporal variability in pH both within and across tide pools, and biological parameters were consistently the dominant drivers of this variability. Overall, the range of pH values was greatest in pools that were both dominated by producers and also had a higher relative amount of production per unit calcification. Tide pool physical characteristics had negligible to no impacts on pH. Further, there was a significant relationship between net community production, pH, and net ecosystem calcification, indicating that biological feedbacks (in which species are both affected by and themselves affect pH conditions) are prominent in tide pool systems. Main conclusions from this study are that: (1) community metabolism both controls and responds to pH variability, complicating our ability to predict how ocean acidification will impact coastal ecosystems, and (2) the ability of organisms to control local biogeochemistry could potentially buffer or amplify the effect of global ocean acidification.