Bank erosion drastically reduces oyster reef filtration services in estuarine environments

Abstract

Oyster reefs near estuarine channels have experienced substantial mortality over the last decades, primarily due to bank erosion, potentially exacerbated by boat activity. Using aerial imagery, we measured bank erosion along the Intracoastal Waterway and its main tributaries in the Guana-Tolomato-Matanzas estuary, finding that erosion outweighs progradation. This notably threatens oyster reefs and their filtration capabilities. By modeling the impact of bank erosion on oyster habitats and filtration using hydrodynamic, water quality, and particle tracking models, we observed a 12% filtration reduction due to reef mortality. Erosion results in an exponential decrease in reef area and filtration services, due to the removal of channel-adjacent reefs, which play a critical role in water filtration. If current erosion rates continue, simulations suggest a potential 20% filtration reduction over 100 years, potentially worsening water quality. Our findings highlight the urgency to protect and restore reefs near banks to mitigate erosion and maintain filtration services.

Keywords: Bank erosion; Filtration services; Numerical modeling; Oyster reefs.

Figure 1

Study area and oyster reefs distribution. (a) The Guana-Tolomato-Matanzas estuary. The black line is the Delft3D model domain boundary. The colored squares are the boundary conditions of the model. The distribution of the oyster reefs with living (b) and dead (c) oyster populations along the model domain, according to the FWC Florida oyster beds database (Maps generated using ESRI ArcGIS, v.10.8.1, https://www.arcgis.com/index.html. Background: ESRI World Ocean base).

Figure 2

Bank erosion estimate. The lateral movement of banks in the ICW measured in the periods 2006–2015 and 2006–2023 from historical airborne images.

Figure 3

Filtration services vs. bank erosion, and reefs area. (a) $\mathit{FS}$ vs. bank erosion. (b) $\mathit{FS}$ vs. total oyster reefs area. Blue dots: Declining estuary-scale filtration due to oyster reef removal along distances from the bank (0 m to 1200 m), in 30 m intervals, to simulate bank erosion in the GTM estuary. Yellow dots: Current scenario with filtration only from reefs with live oyster populations. Red dots: Pre-mortality scenario with filtration from reefs with both live and dead oyster populations.

Figure 4

${\overline{\mathit{FS}}}_R^O$ vs. distance from the riverbank. The average value of Filtration Services per unit of oyster mass (${\overline{\mathit{FS}}}_R^O$) calculated for reefs located at various distances from the banks in the GTM estuary, in the scenario with filtration from reefs with live oyster populations.

Figure 5

Particle dynamics and residence time. (a) Number of particles entering the oyster reefs placed at increasing distances from the banks. (b) Average residence time calculated for reefs placed at increasing distances from the banks.