Keywords

Crassostrea virginica, Rhizophora mangle, Avicennia germinans, climate change, expansion, oyster settlement

Abstract

Live eastern oyster (Crassostrea virginica) reefs have declined by 62.6% in Mosquito Lagoon (ML) along the eastern Florida coast since 1943. While this species creates reefs by successive generations of oysters recruiting to conspecific shells, C. virginica can also attach to non-reef substrates including mangrove roots and armoring (e.g., seawalls), which may help counteract reef habitat loss. In recent decades, warmer winters have enabled red (Rhizophora mangle) and black (Avicennia germinans) mangrove expansion in subtropical salt marshes and temperate estuaries where oyster reefs occur. Additionally, 11.8% of ML's shorelines have been armored as of 2018. These non-reef substrates add potential surface area and a 3-D substrate for oyster settlement. Aerial imagery from 1984 to 2021 was used to track extent (ha) changes in mangroves, oyster reefs, and hard armoring. Mangrove extent increased 859.2%, hard-armoring extent decreased 56.3%, and live oyster reef area decreased 55.3% (rate: -0.86 ha/yr). Additionally, 83 oyster reefs were 100% converted into mangrove islands, resulting in a 654.6% increase in the number of new conversions between 1984 and 2021. To determine if oyster abundances on non-reef substrates are comparable to live oyster reefs, oyster characteristics were compared between substrate types using field surveys to collect metrics (live densities, shell heights, canopy heights). Mean densities and canopy heights (± S.E.) were highest on concrete/metal seawalls (481.8 ± 113.0 oysters m2 and 678.4 ± 408.6 mm, respectively). Mean shell heights (± S.E.) were largest on oyster reefs (52.0 ± 2.2 mm) and within black mangrove pneumatophores on oyster reefs (41.3 ± 10.0 mm). Between 1984 and 2021, oyster reefs lost 291.0 oysters/ha versus non-reef habitats, which added an average (± S.E.) of 104.7 ± 78.2 oysters/ha. These findings suggest mangrove roots and armoring support oyster reef-level populations by providing 3-D attachment space and partially offset oyster losses on reefs.

Completion Date

2024

Semester

Spring

Committee Chair

Walters, Linda

Degree

Master of Science (M.S.)

College

College of Sciences

Department

Biology

Degree Program

Biology

Format

application/pdf

Language

English

Rights

In copyright

Release Date

May 2024

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Campus Location

Orlando (Main) Campus

Accessibility Status

Meets minimum standards for ETDs/HUTs

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