The Indian River Lagoon (IRL) stretches 251 kilometers along Florida’s east coast and is one of the most biodiverse estuaries in North America. Mosquito Lagoon, the northernmost portion of the IRL, is home to mangroves and intertidal oyster reefs that provide numerous ecosystem services. These two habitats are overlapping as climate change drives mangroves poleward. Scientists have documented mangrove expansion and the transition of oyster reef habitat to mangrove islands. Past studies have shown large, adult mangrove stands drive soil acidification. The goal of this study was to understand if stand-alone, or pioneer, Rhizophora mangle (red mangroves) and Avicennia germinans (black mangroves) acidify intertidal Crassostrea virginica (eastern oyster) reef sediment. We collected porewater (i.e., water within sediment) and measured pH with a portable pH meter. Porewater pH was sampled from 0 to 1 meter away from pioneer mangroves in 20 cm increments. Closest to the mangrove trunk, reef sediment pH was significantly more acidic (mean pH of 7.18 for R. mangle and 7.02 for A. germinans) compared to oyster reef-only control areas with a mean pH of 7.44 (p-value \u3c 0.001 for both mangrove species). By 1 meter away from the mangrove trunk, the pH for both mangrove species was no longer significantly different from the control areas (p-value = 1.0), indicating mangrove-driven acidification has a localized effect on oyster reef sediments. Acidification weakens oyster shells, and by understanding the extent of mangroves’ acidic effects on oyster reefs, resource managers can use this information to protect declining oyster reef habitat
