Seagrasses are important for coastal ecosystem function by stabilizing sediments, improving water quality, sequestering carbon and supporting nursery habitat for fisheries, yet they are increasingly threatened by intensifying marine heatwaves (MHWs). In Florida’s Indian River Lagoon (IRL), a shallow, highly managed estuary spanning subtropical to tropical regions, warming is amplified by local stressors, creating a natural laboratory for assessing resilience mechanism of seagrass. This thesis aims to integrate (1) marine heatwave modeling, (2) foundational genomic resource development, and (3) a controlled thermo-priming experiment to evaluate the effect of sub-lethal heat exposure prior to temperature extremes on shoal grass, Halodule wrightii. In Chapter 1, we will examine whether marine heatwaves are occurring and how these events may affect the diverse seagrass community of the estuary. Daily sea surface temperature data (2014-2024) from the St. Johns River Water Management District was analyzed using the heatwaveR framework to quantify the MHW frequency, duration and cumulative intensity (degree-days). Generalized additive mixed models (GAMs) will be used to test spatiotemporal trends and relationship to seagrass metrics such as percent cover. Preliminary analysis detected 159 MHWs across the IRL, with the strongest event occurring in the winter of 2020 (peak cumulative intensity 69 degree-days). Across years, seagrass showed a negative relationship with increasing mean cumulative intensity. GAM predictions indicated elevated thermal stress was associated with reduced seagrass cover, particularly during conditions with greater intensity. In Chapter 2, genomic resources will be developed for Halodule wrightii and Ruppia maritima, using Illumina RNA-seq data to generate a de novo reference transcriptome assembly to enable robust gene expression analysis. Chapter 3 will experimentally test the effect of thermo-priming by comparing morphological and transcriptomic responses of H. wrightii. Plants will be exposed to a sub-lethal priming phase (~34°C) followed by a simulated MHW triggering temperature (38°C), with growth, canopy height, health scores and differential gene expression assessed across time points. This research aims to link heat stress to diverse pathways of resilience, delivers new genomic resources for two ecologically dominant seagrasses in Florida, and provide actionable evidence to inform restoration strategies under increasingly frequent and intense climate extremes.
Carla Perscky
Dr. Linda Walters, Advisor & Dr. Robert Fitak, Co-Advisor