Shifts from saltmarsh to mangroves are well-documented at mangrove poleward boundaries. A regime shift from intertidal oyster (Crassostrea virginica) reefs to mangrove islands has recently been documented in transitional phases in Florida, USA. To understand the local drivers of an oyster/mangrove regime shift and potential tipping points leading to a permanent mangrove state, we tracked all mangrove propagules (n = 1681) across 15 intertidal oyster reefs with or without adult mangroves for 15 months in Mosquito Lagoon, FL. While no propagule bottleneck was observed, few (3.2%) mangrove propagules/seedlings survived on reefs with no prior encroachment, compared to 11.3% and 16.1% on reefs with established older (pre-1943) or newer (1943 to present) adult mangrove stands, respectively. In total, 90.6% of the arriving propagules were from the red mangrove Rhizophora mangle; 13.2% of these were alive at the end of this study. Survival was <1% for black (Avicenna germinans) and 0% for white (Laguncularia racemosa) mangroves. Factors that promoted red mangrove success included close proximity (≤0.3 m) to adult mangroves, especially black mangroves; partial, upright burial of propagules in sediment; and arrival on reefs after annual high-water season. Additionally, once reefs had 50% mangrove cover, the density of red mangrove seedlings increased from 0.04 to 0.46 individuals m⁻². Although climate change has alleviated the impact of extreme freezes on mangroves, local factors determine whether the regime shift will be complete and permanent; positive feedback loops associated with established mangroves suggest mangrove recruitment on intertidal oyster reefs will continue to increase.

Tropicalization, resulting from warmer minimum temperatures, has allowed mangroves to expand poleward and increase in abundance in historical ranges. Since 1984, mangrove abundance on intertidal oyster reefs in Mosquito Lagoon, Florida, USA, has increased by 198% due to tropicalization. Oysters provide abundant ecosystem services including engineering reef habitat and water filtration, but shells are prone to dissolution in acidic conditions. Mangroves are associated with soil acidification and therefore may alter the pH of oyster reef sediment. The goal of this research was to determine if mangroves acidify oyster reef porewater (i.e. water within the sediment) and determine if mangrove-correlated acidification caused oyster shell dissolution as indicated by shell mass loss. Porewater, up to 10 cm depth, was collected monthly for 2 yr, and the pH was compared between 4 habitats: mudflats, oyster-dominated reefs (oyster reefs), transitioning reefs (oyster reefs with mangroves), and mangrove-dominated sites (mangrove islands). Porewater was more acidic with mangroves present. Transitioning reefs had a mean pH of 7.13 compared to oyster-dominated reefs (mean pH: 7.52). To measure shell dissolution, bags containing 10 pre-weighed oyster shells were deployed and re-weighed after 6, 12, and 24 mo. After 24 mo, mangrove-dominated sites lost more shell mass (8% loss) compared to oyster-dominated sites (1% loss). Transitioning reefs had intermediate shell mass loss. Combined, these data suggest that mangrove expansion on intertidal oyster reefs can negatively impact oysters. With oyster reef habitats in global decline, understanding new sources of degradation, including mangrove-driven acidification, is crucial to supporting conservation and restoration efforts.

Introduction: Environmental outreach aims to create opportunities for students to engage with nature, but this can be challenging when ecosystems are difficult to access. In such cases, outreach programs often rely on hands-on games and classroom-based activities to foster learning and connection. These approaches, however, cannot replicate the experience of being in the habitat itself. Extended reality (XR) applications, including immersive 360° videos, can simulate realistic experiences with the potential to increase access to important ecosystems and promote deeper connection with nature. Methods: Our goal was to determine how an immersive 360° video experience impacted student learning and connectedness to nature compared to a traditional, hands-on classroom-based outreach lesson. Oyster reefs were used as a case study habitat. A 360° video experience was created and displayed through immersive virtual reality headsets. A hands-on lesson, incorporating live invertebrate animals commonly found on oyster reefs, was developed to mirror the 360° video content. Seventy-nine middle school students participated in a crossover study design. Results: The 360° video experience increased student learning, and the hands-on lesson improved both learning and connectedness to nature. However, the combination of the 360° video and hands-on lesson provided the most comprehensive outreach experience. Discussion: These findings offer relevant insights for educators, outreach practitioners, and environmental scientists seeking innovative ways to connect students with nature. While both outreach methods offer educational value, combining immersive virtual content with experiential hands-on opportunities provides the most effective and engaging way for students to explore important ecosystems within a classroom setting.