Green Crab (Carcinus maenas) Foraging Efficiency Reduced by Fast Flows

Elizabeth M Robinson,Delbert L Smee,Geoffrey C Trussell,Stuart Humphries

doi:10.1371/journal.pone.0021025

Elizabeth M Robinson, Delbert L Smee + Show 2 more

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https://doi.org/10.1371/journal.pone.0021025

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Abstract

Predators can strongly influence prey populations and the structure and function of ecosystems, but these effects can be modified by environmental stress. For example, fluid velocity and turbulence can alter the impact of predators by limiting their environmental range and altering their foraging ability. We investigated how hydrodynamics affected the foraging behavior of the green crab (Carcinus maenas), which is invading marine habitats throughout the world. High flow velocities are known to reduce green crab predation rates and our study sought to identify the mechanisms by which flow affects green crabs. We performed a series of experiments with green crabs to determine: 1) if their ability to find prey was altered by flow in the field, 2) how flow velocity influenced their foraging efficiency, and 3) how flow velocity affected their handling time of prey. In a field study, we caught significantly fewer crabs in baited traps at sites with fast versus slow flows even though crabs were more abundant in high flow areas. This finding suggests that higher velocity flows impair the ability of green crabs to locate prey. In laboratory flume assays, green crabs foraged less efficiently when flow velocity was increased. Moreover, green crabs required significantly more time to consume prey in high velocity flows. Our data indicate that flow can impose significant chemosensory and physical constraints on green crabs. Hence, hydrodynamics may strongly influence the role that green crabs and other predators play in rocky intertidal communities.

Highlights

Predators often have large effects on the structure and function of aquatic and terrestrial communities [1,2] by consuming prey [2,3] and by initiating trophic cascades that affect the abundance of resources within a food chain [4,5,6]
The total number of green crabs caught in high flow sites was significantly lower than those caught in low flow sites (t = 2.44, df = 36, p,0.05; Figure 2), even though green crab density is known to be greater in these faster flow sites
Flume Assays As free-stream velocity increased from 15 cm s21 to 19 cm s21, root mean square (RMS) increased from 1.79 cm s21 to 1.89 cm s21 and shear velocity increased from 2.79 cm s21 to 3.66 cm s21 (Table 2)

Summary

Introduction

Predators often have large effects on the structure and function of aquatic and terrestrial communities [1,2] by consuming prey [2,3] and by initiating trophic cascades that affect the abundance of resources within a food chain [4,5,6]. These effects are well appreciated, environmental forces can modify predator foraging activities and have large effects on predation rates and community dynamics. Mobile predators are often absent on wave-swept shores as hydrodynamic stress associated with waves prevents them from foraging effectively and poses risk of injury and death [7,8]. Substrate type and gas concentrations can reduce the foraging success of predators [15,16,17], providing a potential niche for stress-tolerant organisms [1,7,18]

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