A taste for aliens: contribution of a novel prey item to native fishes\u2019 diet

Riikka Puntila-Dodd,Katariina Riipinen,Amy E Fowler,Olli Loisa

doi:10.1007/s10530-019-02021-w

Abstract

Non-indigenous species (NIS) can alter food web structure and function in many ways. While the predatory and competitive roles of NIS in aquatic environments are commonly studied, their role as a prey item for native predators is often overlooked. As the northern Baltic Sea lacks native crabs, the omnivorous estuarine Harris mud crab (Rhithropanopeus harrisii) is a novel invader to the system and provides an opportunity to observe how the species enters the prey field of predatory fish. In fall 2013, 1185 stomachs from 17 fish species were dissected and analyzed for the presence of R. harrisii. Fishermen had previously reported finding crabs mostly in the stomachs of perch (Perca fluviatilis), a frequent catch in recreational and commercial fisheries, but our study also found large numbers of crabs in four-horned sculpins (Myoxocephalus quadricornis) and small numbers in other species’ stomachs (Rutilus rutilus, Leuciscus ide, Gymnocephalus cernuus, and Blicca bjoerkna). In the study area occupied by R. harrisii, four-horned sculpins were the most frequent predator, with 83% having at least one crab in their stomach. In comparison, 7% of perch and roach had consumed R. harrisii. Most crabs eaten were 10–12 mm (carapace width), despite broader size range available (1–26 mm). Predation on R. harrisii in this system may be limited by the predators’ gape size (i.e., physical feeding restriction). These results highlight the need to understand the role of novel invasive species as prey items for native species, ultimately increase understanding of whether native predators can control NIS populations.

Highlights

Fishermen had previously reported finding crabs mostly in the stomachs of perch (Perca fluviatilis), a frequent catch in recreational and commercial fisheries, but our study found large numbers of crabs in four-horned sculpins (Myoxocephalus quadricornis) and small numbers in other species’ stomachs (Rutilus rutilus, Leuciscus ide, Gymnocephalus cernuus, and Blicca bjoerkna)
As the impacts of non-indigenous species (NIS) in aquatic environments have drawn increased attention in past years (Carlton and Geller 1993; Simberloff et al 2013), many studies have concentrated on the top-down predatory impacts of an invader on native prey or their competitive interactions with both native and other introduced species
Aiming to investigate which fish species and the proportions of species that consume novel R. harrisii in their invasive range in the Archipelago Sea in Finland, we investigated the stomachs of nearly 1200 fish, representing 17 species of commercial and noncommercial significance in the fall of 2013

Summary

Introduction

As the impacts of non-indigenous species (NIS) in aquatic environments have drawn increased attention in past years (Carlton and Geller 1993; Simberloff et al 2013), many studies have concentrated on the top-down predatory impacts of an invader on native prey or their competitive interactions with both native and other introduced species. Sometimes the increased resource leads to an increase in predator populations and results in increased predation on native species as well (Noonburg and Byers 2005). Prey naivety towards invasive predators has been widely studied and reported (e.g., Sih et al 2010), but far less attention has been given to the naivety of predators, similar naivety may occur especially towards novel prey (Ward et al 2010), which may result in low predation pressure on the novel species

Objectives

Methods

Results

Conclusion