Oyster reef restoration efforts increasingly consider not only oyster recruitment, but also the recovery of ecological functions and the prevention of deploying harmful plastics. This study investigated the efficacy of a biodegradable plastic-alternative, BESE-elements^®, in supporting oyster reef restoration in east-central Florida (USA) with consideration for how this material also influences biogeochemistry. Four experiments (two laboratory, two field-based) were conducted to evaluate the ability of BESE to serve as a microbial substrate, release nutrients, support oyster recruitment and the development of sediment biogeochemical properties on restored reefs, and degrade under field conditions. The results indicated BESE is as successful as traditional plastic in supporting initial reef development. In the lab, BESE accelerated short-term (10-day) sediment respiration rates 14-fold and released dissolved organic carbon, soluble reactive phosphorus, and nitrate to the surface water (71,156, 1980, and 87% increase, respectively) relative to without BESE, but these effects did not translate into measurable changes in reef sediment nutrient pools under field conditions. BESE lost 7–12% mass in the first year, resulting in a half-life of 4.4–6.7 years. Restoration practitioners should evaluate the biogeochemical properties of biodegradable materials prior to large-scale deployment and consider the fate of the restoration effort once the material degrades.

Oyster and shoreline restoration is occurring around the globe to recover lost ecosystem services. In the state of Florida, USA, dozens of estuarine habitat restoration projects are underway. These projects have traditionally relied on both natural and man-made materials, including plastics. As the impacts of plastics on marine ecosystems are better understood, practitioners are increasingly focused on plastic-free restoration. To better understand this transition, we surveyed Florida restoration practitioners in April 2021 to capture current non-plastic restoration project trends and their status. Our descriptive survey goals were to understand: (1) what non-plastic materials have been tested, (2) trade-offs between plastic and non-plastic materials (e.g., cost, sourcing, volunteer engagement), and (3) the performance of non-plastic materials. Responses indicated that a variety of non-plastic materials are currently being used, including rock, cement-infused jute structures, cement Reef Balls™ (Reef Ball Foundation, USA), BESE-elements^®, and metal gabions. Overall, these materials are more expensive and equally or more difficult to install than previously popular plastic-based materials. No “best” non-plastic material emerged from our survey in part because many novel materials have been deployed for under three years. Long-term performance under a variety of abiotic and biotic conditions is thus a future research priority.

Intertidal reefs of Crassostrea virginica (eastern oyster) provide ecologically valuable habitat in estuaries along the Atlantic coast of North America. In Mosquito Lagoon, a shallow-water estuary on the east coast of central Florida, USA, historical aerial imagery was used to document a 24% decline in the live C. virginica reef area between 1943 and 2009. Using 2021 imagery, every living and dead reef in the same region was manually digitized to identify changes during the intervening 12 years. Positive impacts of C. virginica reef restoration that took place between 2007 and 2021 were also digitized to quantify long-term restoration impact. Natural, live C. virginica reef coverage throughout the system was found to have decreased by 50.6% between 2009 and 2021 and, thus, 62.6% between 1943 and 2021. This was attributed to reef fragmentation, reef footprint loss, boating activity, and mangrove expansion. Of the 2542 live reefs identified using 2009 imagery, 219 reefs fragmented, 988 reefs no longer had an identifiable footprint, and 598 reefs contained visible mangroves with non-continuous canopies. Conservatively, 63.6% of directly restored reef area was classified as living reef in 2021, and 74.5% of restoration projects were more than 50% live reef. Dead reef area decreased by 57.9% throughout the system. Understanding changes in C. virginica reef acreage, reef numbers, and mangrove expansion is essential for resource management, restoration practices, and tracking climate change impacts on publicly protected estuaries.

Estuaries worldwide are grappling with deteriorating water quality and benthic conditions that coincide with the rising detection of pathogenic and potentially pathogenic microbes (PPM). Both indigenous PPM and those that enter estuaries through urban and agricultural runoff are funneled through suspension-feeding organisms and deposited onto the benthos, where they can be moved through food webs. This study explored PPM communities in the Indian River Lagoon system, a biodiverse but urbanized estuary in east central Florida (USA). PPM were surveyed in estuary water, at stormwater outfalls, and in biodeposits of a key suspension feeder, the eastern oyster Crassostrea virginica. A total of 52 microbial exact sequence variants, with per-sample relative abundances up to 61.4%, were identified as PPM. The biodeposits contained relatively more abundant and diverse PPM than the water samples. PPM community composition also differed between seasons and between biodeposits and water. The community differences were driven primarily by Vibrio and Pseudoalteromonas spp. This investigation provides evidence that, through biodeposition, oyster reefs in the IRL estuary are a reservoir for PPM, and it documents some taxa of concern that should be conclusively identified and investigated for their pathogenicity and potential to pervade food webs and fisheries.

Globally, little is known about the dispersal of microplastics (MP) and anthropogenic particles (AP) via atmospheric deposition (AD) into water bodies. Correlating AD to the large number of MP in estuaries is challenging but an important first step toward reducing this form of pollution. A previously published model of the surface waters of the Indian River Lagoon (IRL, east central coast of Florida, USA) estimated it contained 1.4 trillion microplastics. To determine if AD could produce this much plastic deposition, we deployed passive AD collectors throughout a 145 km² area at three site types with assistance from citizen scientists. We predicted that the rate of deposition of MP and AP would be greatest in residential areas, intermediate within a national park, and lowest on intertidal oyster reefs. Moreover, we predicted Florida’s wet season and individual rain events would increase deposition based on the published literature. Over 14 months, deposition averaged 1224 MP/m²/d; extrapolated, this yields 1.1 trillion MP for the lagoon-wide total deposition estimate (95% CI: 0.86–1.39 trillion MP). This value suggests that AD may represent an important pathway for MP to enter this estuary. More MP were deposited during rain events and in the wet season, with no differences among sites. Overall, our results provide important data for understanding AD of MP and AP in estuaries.

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.