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Reef-Lections: Oyster Growth And Ecology Across Millennia, And The Modern Management Implications
Marquardt, Alexandria
Marquardt, Alexandria
Abstract
Coastal ecosystems are degraded worldwide and oyster reefs are among the most threatened coastal habitats. Oysters are a critical ecosystem engineers in temperate, boreal, and subtropical estuaries worldwide; however, oyster reefs are degraded globally. In the Chesapeake Bay, oyster populations are a fraction of their historic abundance, due to the combined pressures of disease epizootics, overfishing, and other anthropogenic impacts. Degradation and loss of oysters negatively impacts ecosystem functioning and coastal livelihoods. Restoration efforts for oysters are accelerating and focus on supplementing the shell base to provide habitat for reef formation. Broadly, the goal of this dissertation is to provide quantitative information on key oyster life history stages and oyster reef dynamics to inform and identify management strategies for eastern oysters in the Commonwealth of Virginia. Each chapter is a separate research question and is interdisciplinary, drawing upon larval biology, ecology, economics, paleobiology, and applied fisheries science approaches. Chapter 1 examines how oyster reproductive bet hedging impacts the early-post settlement period in wild oyster populations and if restoration timing could be optimized. Specifically, this chapter quantifies the impact of settlement date, temperature, and growing days on the mean size of oyster cohorts across a spawning season. Regardless of settlement date, oysters reach comparable sizes prior to the fall months, which suggests that current shell supplementation practices are adequate. Chapter 2 describes oyster allometric relationships across an estuarine gradient. This chapter describes the proportional carbonate contributions from each valve, examines length-weight relationships for both tissue and shell weight, and considers environmental drivers. Oysters have highly variable growth patterns, which enables them to rapidly produce shell even under physiologically stressful conditions. Chapter 3 uses preserved oyster shells to estimate the mean annual carbonate production and gross annual reef accretion rates for oyster populations during the early Holocene. Coastal environments during the early Holocene experienced rapid rates of relative sea level rise, which were nearly twice the rates of modern day sea level rise in the Chesapeake Bay. Early Holocene populations were more resilient when natural mortality was low and recruitment was high. Modern oysters are age truncated and in lower abundance, which limits their ability to create self-sustaining reefs. Chapter 4 integrates long term datasets to examine the impact of management strategies (rotational harvest areas, oyster sanctuaries, and shell replenishment practices) on public fishing grounds. Specifically, we evaluate how the reef structure, juvenile recruitment, market sized oyster abundance, and fisheries efficiency respond to management interventions. Our results demonstrate that harvest area rotation and sanctuaries, when coupled with shell replenishment, support oyster reef dynamics and enhance fisheries outcomes. Collectively, the findings from this dissertation fills knowledge gaps, provides recommendations, and supports sustainable oyster management in the Chesapeake Bay.
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2025-01-01
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Department
Virginia Institute of Marine Science
DOI
https://dx.doi.org/10.25773/v5-5q7m-6e17