First Advisor
Catherine de Rivera
Term of Graduation
January 2026
Date of Publication
6-1-2026
Document Type
Thesis
Language
English
Subjects
Carcinus maenas, eelgrass, green crab, non-consumptive effects, Pacific oyster, shellfish management
Physical Description
1 online resource ( pages)
Abstract
The establishment of the invasive green crab, Carcinus maenas, creates ecological and economic impacts in estuaries, particularly through predation on bivalves and alteration of species interactions. This thesis evaluates the direct predation, non-consumptive predator presence, and spatial management implications of C. maenas impacts on filtration rate of juvenile Pacific oysters, Magallana gigas, across laboratory, field, and GIS-based vulnerability mapping approaches. In laboratory conditions, clearance rates of M. gigas were measured over 72 hours across two temperatures (14°C and 18°C) and predator treatments including C. maenas, Pacific rock crab (Romaleon antennarium), both predators together, and a predator-free control. Predator effect was tested across three phases: an acclimation phase to temperature and chemical cues, a non-consumptive phase with crabs with banded chelae, and a consumptive phase with unrestrained crabs. M. gigas clearance rates were influenced by both predator presence and phase, with C. maenas treatments suppressing clearance the most, even without direct predation. Carcinus maenas consumed more M. gigas than both the native R. antennarium and mixed treatments, indicating stronger predation pressure on juvenile M. gigas spat. Unlike R. antennarium, which showed a positive foraging association with size, C. maenas consumed M. gigas across a broader size range, suggesting less size selectivity within our sample of juvenile M. gigas spat. Field experiments in Netarts Bay, Oregon, examined how habitat, prey size, vertical position, and predator assemblages influenced juvenile M. gigas survival. M. gigas were tethered in eelgrass (Zostera marina) and adjacent mudflat habitats across multiple sites and monitored for predation under natural conditions. Additional experiments tested the effects of M. gigas size and elevation above the substrate in areas with high C. maenas abundance. M. gigas survival was generally lower in mudflats, and predation patterns suggested greater vulnerability in areas with higher C. maenas abundance. Larger M. gigas and elevated M. gigas had higher survival, indicating that habitat structure and prey context mediate vulnerability to predation. To extend these experimental findings into an estuary-scale management context, a GIS-based Resource Vulnerability Index (RVI) was developed for Coos Bay, Netarts Bay, Tillamook Bay, and Yaquina Bay. The RVI integrated habitat and resources to identify areas where suitable C. maenas conditions and vulnerable estuarine resources overlap. Observed C. maenas CPUE did not show a simple linear correlation with RVI, indicating that trap catch and resource vulnerability inform management in different ways. Areas with both high RVI and observed C. maenas CPUE may represent high priority zones for trapping or monitoring, while high RVI areas with limited CPUE may indicate potential monitoring gaps. Together, these findings suggest that C. maenas affects M. gigas performance through both direct predation and non-consumptive effects on feeding, with outcomes shaped by temperature and habitat. By linking laboratory mechanisms, field predation patterns, and spatial vulnerability mapping, this thesis shows that C. maenas impacts are both biological and spatially structured. This work highlights the importance of considering both trophic and non-trophic impacts from invasive species in estuarine systems that can create ecosystem-level effects. It has implications for invasive species management, M. gigas aquaculture, shellfish restoration, and spatially targeted monitoring across Oregon estuaries.
Rights
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Recommended Citation
Mize, Isabel Helena, "Beyond Predation: Invasive Green Crab (Carcinus maenas) Alters Juvenile Pacific Oyster (Magallana gigas) Function and Survival Across Environmental Gradients" (2026). Dissertations and Theses. Paper 7126.