Horizon scanning for alien predatory crabs: insights from South Africa

C Swart,Tb Robinson

doi:10.2989/1814232x.2019.1588782

Abstract

Due to the presence of few dominant predators on South African rocky shores, this coastline could be vulnerable to invasion by predatory crabs. This study applied horizon scanning to create an ordered watch list of alien crab species that could establish along this coastline under present-day and future temperature scenarios. This was done by: (i) identifying the species with both an invasion history and a possible pathway to South Africa; (ii) comparing the temperature ranges of the species’ native and introduced distributions to those of each of the four South African ecoregions; and (iii) ranking the species based on their potential ecological impacts. Of the 56 alien predatory crab species known worldwide, 28 species have pathways to South Africa. Incompatible temperature ranges excluded only two species from each ecoregion. Negative ecological impacts in their invaded ranges placed Japanese shore crab Hemigrapsus sanguineus, brush-clawed shore crab H. takanoi and Chinese mitten crab Eriocheir sinensis at the top of the watch list. This study highlights that many alien crab species have the potential to reach South Africa, with most likely to survive. This watch list should be used to support targeted monitoring and so facilitate early detection of these species, should they reach South Africa.

Highlights

The severe impacts associated with alien species and the difficulty of successfully managing marine invasions (Hopkins et al 2011) highlight the urgent need to prevent future incursions
From the list of 56 alien predatory crab species recorded globally (Swart et al 2018), we excluded those with a native range including South Africa (20 species), those already present in the region (2 species: Carcinus maenas and Homalaspis plana), and those occurring at depths greater than 60 m (1 species: snow crab Chionoecetes opilio)
In the slightly warmer Agulhas Ecoregion, 27 species have the potential to survive under present conditions, and future temperature rises may make this ecoregion accessible to M. oceanicus

Summary

Introduction

The severe impacts associated with alien species and the difficulty of successfully managing marine invasions (Hopkins et al 2011) highlight the urgent need to prevent future incursions. Within the context of invasive species, horizon scanning investigates the potential introduction, establishment, spread and impacts of alien species (Gallardo et al 2016), with an aim to support their early detection, and minimise their chances of successful establishment. This method has been implemented within the milieu of invasive species, with the most-recent work compiling watch lists of non-native species considered to pose the greatest risks to biodiversity (Roy et al 2014; Gallardo et al 2016).

Methods

Results

Conclusion