Population development of the invasive crab Hemigrapsus sanguineus (De Haan, 1853) and its potential native competitor Carcinus maenas (Linnaeus, 1758) at Helgoland (North Sea) between 2009 and 2014

Simon Jungblut,Reinhard Saborowski,Wilhelm Hagen,Karin Boos,Jan Beermann

doi:10.3391/ai.2017.12.1.09

Abstract

The Asian shore crab Hemigrapsus sanguineus (De Haan, 1853) has recently established populations in the North Sea and now occurs within the native ranges of the green crab Carcinus maenas (Linnaeus, 1758). To determine potential competitive effects and to assess the progress of the invasion, species-specific population characteristics (numerical abundances, biomasses, and size distributions) of the two species around the island of Helgoland (German Bight, southern North Sea) were compared for surveys conducted in 2009 and 2014. Sampling sites were chosen based on accessibility and differed in their topography and wave exposure, which allowed testing for the influence of these factors on the establishment success of H. sanguineus. The numerical abundance and biomass of H. sanguineus increased markedly and approached those of C. maenas in 2014. At a sheltered site, H. sanguineus even outnumbered C. maenas, whereas the converse was observed at a site exposed to strong winds and waves. Although such contrasting abundance patterns between the native and the introduced shore crab may be the result of direct interference, the dominance of H. sanguineus at the sheltered site may also be explained by enhanced larval settling rates caused by odors of conspecifics. The results suggest that the invasion of H. sanguineus has not yet reached its equilibrium, and population abundances in the North Sea are expected to further increase in the future.

Highlights

Non-indigenous species can affect ecosystem structure and functioning in many ways and sometimes drastically
The results suggest that the invasion of H. sanguineus has not yet reached its equilibrium, and population abundances in the North Sea are expected to further increase in the future
The results of the “first approach model” revealed that the numerical abundances of C. maenas and H. sanguineus varied between the two years for sampling sites around the island of Helgoland (LRTspecies*year*location: df = 3, χ2 = 35.475, p = 0.018)

Summary

Introduction

Non-indigenous species can affect ecosystem structure and functioning in many ways and sometimes drastically. Drastic alterations may affect human economic interest, ecosystem services, and even human health (Ruiz et al 2000; Simberloff et al 2013). Non-native species may compete with native residents for food or space (or both) and often largely displace resident species by spreading into all available habitats at high population densities (Bax et al 2003). While biotic interactions are crucial in determining invasion success, environmental characteristics such as temperature regime and wave exposure have repeatedly been shown to limit the spread of non-native species in their new habitats (Pörtner 2002; Hampton and Griffiths 2007; Russel et al 2008). Brachyuran crabs frequently invade estuarine and marine coastal ecosystems (Brockerhoff and McLay 2011). The European green crab Carcinus maenas (Linnaeus, 1758), for example, successfully invaded the Atlantic coast of North

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