Keywords

Hydrodynamic, Seagrass, Threshold, Habitat

Abstract

Submerged aquatic vegetation shapes morphodynamic, hydrodynamic, and ecological attributes of shallow, coastal waters. Though seagrasses have been shown to exhibit threshold tolerances in response to varying light, salinity, and temperature, hydrodynamic thresholds have yet to be described. In this study, seagrass distribution data observed over 25 years were combined with modeled wave energy to quantify the hydrodynamic preferences of seagrass. The frequency distributions of wind-wave heights in the study area (Mosquito Lagoon, Indian River Lagoon, and Lake Worth Lagoon, Florida) were characterized using the Simulating WAves Nearshore (SWAN) numerical model. Seagrass distribution data, collected through direct observation and aerial imagery analysis backed by repeated ground truthing of fixed transects, were combined with the modeled hydrodynamic data to identify hydrodynamic preferences of seagrass. Analysis revealed that these preferences vary by water depth. Hydrodynamic thresholds at various depths were estimated using a logistic regression model. In shallow water (0.2 – 0.5 m), seagrass likelihood was maximized (>50%) where the 80th percentile significant wave height (H80) was greater than 5.9 cm (95% CI: 5.73-6.07 cm). When water depths were 0.5 – 1.0 m, the 50% probability threshold was observed at greater wave heights; when H80 exceeded 11.1 cm (95% CI: 11.33-11.73 cm). In shallow and moderate depths, seagrass likelihood increased with H80, indicating that seagrasses growing at those depths preferentially sought environments with greater wave energy. In deeper water (1.0 – 1.5 m), tolerance to greater wave heights was observed (50% probability threshold at H80 = 16.2 cm, 95% CI: 15.84-16.58 cm); however, the opposite preference was observed; seagrass likelihood increased as H80 decreased. Considering the findings across depth, a zone of seagrass hydrodynamic preference can be described where H80 is greater than 5.91 cm and less than 16.2 cm. Including hydrodynamic tolerance by depth in restoration planning will increase the success of seagrass planting efforts.

Completion Date

2025

Semester

Spring

Committee Chair

Kibler, Kelly

College

College of Graduate Studies

Department

Civil, Environmental, and Construction Engineering

Identifier

DP0029308

Document Type

Dissertation/Thesis

Campus Location

Orlando (Main) Campus

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