In recent decades, warmer winter air temperatures have enabled red (Rhizophora mangle) and black (Avicennia germinans) mangroves to expand into sub-tropical and temperate estuaries where eastern oyster (Crassostrea virginica) reefs occur and potentially reduce the reef substrate. Shoreline armoring may also be contributing to oyster reef loss. However, oysters can attach to these non-reef substrates and switch from a traditional 2-D to 3-D space for attachment and settlement. GIS digitization of aerial imagery from 1984 to 2021 in Mosquito Lagoon (ML), FL was used to examine changes in mangrove and oyster reef extents in relation to hard armoring coverage and climate change as days since a freeze event (≤ -4.0°C and ≤ -6.6°C). GIS analyses found significant increases in mangrove extents and decreases in oyster reef extents throughout ML. Days since a freeze event was positively correlated with mangrove presence and expansion on oyster reefs. Oyster abundances on non-reef substrates were monitored for live densities, shell heights, and reef canopy heights at 12 habitat types (red, black, and mixed mangrove islands, natural shorelines, mangrove stands on oyster reefs, riprap and seawall shorelines, and live oyster reefs). Live oyster densities and canopy heights were highest on seawalls and shell heights were largest on oyster reefs and black mangrove stands on oyster reefs. Together, these results suggest oyster attachment to mangrove roots and hard armoring may help counteract the loss the oyster reef substrate and encourage oyster recruitment and settlement.
Emily Suchonic
Dr. Linda Walters, Advisor
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