Thesis Defense Seminar - Neina Chapa

COASTAL AND MARINE SYSTEM SCIENCE PROGRAM
DEPARTMENT OF PHYSICAL AND ENVIRONMENTAL SCIENCES
TEXAS A&M UNIVERSITY-CORPUS CHRISTI

TITLE: Evaluating habitat provision by restored intertidal and subtidal oyster reefs in St. Charles Bay, Texas

GRADUATE COMMITTEE: Dr. Jennifer Pollack (Chair), Dr. Christopher Hollenbeck, Dr. Zachary Olsen, (TPWD)

ABSTRACT
Estuarine habitats, such as Crassostrea virginica oyster reefs, are critical to the resilience of coastal environments and provide many ecosystem services. To address declining oyster populations, oyster reef restoration has become a widespread management strategy to recover and restore lost ecosystem functions and biodiversity. While traditional restoration practices in Texas have focused on subtidal oyster reefs to ameliorate harvest impacts, there is growing interest in restoring intertidal reefs to maximize habitat benefits. This study evaluates the development of oyster populations and epifaunal communities on concurrently restored intertidal and subtidal oyster reefs in St. Charles Bay, TX, USA. In May 2022, 2.4 ha of oyster reef complex were restored in intertidal (0.5 m depth) and subtidal (1 m depth) areas using recycled oyster shells. Epifaunal and oyster dynamics were measured on the restored reefs and nearby natural reference reefs for 12 months (epifauna) and 18 months (oysters) following restoration. Results indicate distinct timelines for oyster population and epifaunal community development: restored subtidal reefs progressed faster, reaching peak oyster densities of 2203 ± 266 ind. m^-2 and similar epifaunal community composition to reference reefs within 6 months post- restoration. In contrast, intertidal reefs reached peak oyster densities of 390 ± 403 ind. m^-2 at 12 months post- restoration and epifaunal community composition never became similar to reference reefs. Spat recruitment to restored intertidal and restored subtidal reefs occurred immediately following restoration and oysters grew rapidly (0.95 - 0.97 mm d^-1)during the first 3 months. Submarket sized (25-75 mm) oysters were observed on both restored intertidal and restored subtidal reefs just 1 month after restoration, and market sized (≥ 76 mm) oysters occurred on the restored subtidal reefs within 6 months. Large quantities of drift algae were deposited on the restored intertidal reefs in August 2022 and persisted for 4 months, which may have affected oyster and faunal recruitment growth. On restored subtidal reefs, epifaunal densities, biomass, diversity, and community composition became similar to natural reference reefs within 6 months following restoration. On restored intertidal reefs, although epifauna diversity became similar to natural reefs within 12 months, epifaunal community composition remained distinct throughout the 18-month study period. The findings of this study offer important insights into key differences in restored intertidal and subtidal oyster reef development, making it possible to evaluate the ecological tradeoffs of restoration approaches and inform future restoration efforts.