Abstract
Blue crabs (Callinectes sapidus) are highly mobile, ecologically-important mesopredators that support multimillion-dollar fisheries along the western Atlantic Ocean. Understanding how blue crabs respond to coastal landscape change is integral to conservation and management, but such insights have been limited to a narrow range of habitats and spatial scales. We examined how local-scale to landscape-scale habitat characteristics and bathymetric features (channels and oceanic inlets) affect the relative abundance (catch per unit effort, CPUE) of adult blue crabs across a > 33 km2 seagrass landscape in coastal Virginia, USA. We found that crab CPUE was 1.7 × higher in sparse (versus dense) seagrass, 2.4 × higher at sites farther from (versus nearer to) salt marshes, and unaffected by proximity to oyster reefs. The probability that a trapped crab was female was 5.1 × higher in sparse seagrass and 8 × higher near deep channels. The probability of a female crab being gravid was 2.8 × higher near seagrass meadow edges and 3.3 × higher near deep channels. Moreover, the likelihood of a gravid female having mature eggs was 16 × greater in sparse seagrass and 32 × greater near oceanic inlets. Overall, we discovered that adult blue crab CPUE is influenced by seagrass, salt marsh, and bathymetric features on scales from meters to kilometers, and that habitat associations depend on sex and reproductive stage. Hence, accelerating changes to coastal geomorphology and vegetation will likely alter the abundance and distribution of adult blue crabs, challenging marine spatial planning and ecosystem-based fisheries management.
Highlights
Ecological patterns and processes are linked to attributes of habitat structure and environmental heterogeneity across several spatial scales (Turner 1989; Wiens 1989; Levin 1992)
Our study demonstrates the value of considering multiple spatial perspectives in marine ecology by showing that seagrass meadows, salt marshes, and bathymetric features influence adult blue crab catch per unit effort (CPUE) across scales
Adult blue crab CPUE was negatively correlated with mean seagrass shoot density (Fig. 2a; Table 1, Table S1; χ2 = 4.9, P = 0.03), indicating that adult blue crabs were more abundant in sparser areas of seagrass than denser areas
Summary
Ecological patterns and processes are linked to attributes of habitat structure and environmental heterogeneity across several spatial scales (Turner 1989; Wiens 1989; Levin 1992). Understanding the drivers of ecological patterns such as population density can be difficult because their structuring processes often operate on different scales and can covary across space (Levin 1992). In marine and estuarine systems, free-swimming animals (nekton) are known to use multiple habitats across several. Seagrass meadows are model systems for understanding species-habitat relationships, as they create -quantifiable habitat structure that is heterogeneous over several spatial scales Knowledge of how habitat structure affects faunal abundance at several spatial scales is important to ecosystem-based fisheries management and spatial conservation planning (e.g., marine reserves and coastal restoration; Roberts et al 2003; Leslie 2005; Parsons et al 2014; Duarte et al 2020), and is especially urgent in the face of accelerating global degradation of coastal habitats (Lotze et al 2006; Waycott et al 2009; Halpern et al 2019).
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