Abstract

Recent scientific interest following the “discovery” of lithodid crabs around Antarctica has centred on a hypothesis that these crabs might be poised to invade the Antarctic shelf if the recent warming trend continues, potentially decimating its native fauna. This “invasion hypothesis” suggests that decapod crabs were driven out of Antarctica 40–15 million years ago and are only now returning as “warm” enough habitats become available. The hypothesis is based on a geographically and spatially poor fossil record of a different group of crabs (Brachyura), and examination of relatively few Recent lithodid samples from the Antarctic slope. In this paper, we examine the existing lithodid fossil record and present the distribution and biogeographic patterns derived from over 16,000 records of Recent Southern Hemisphere crabs and lobsters. Globally, the lithodid fossil record consists of only two known specimens, neither of which comes from the Antarctic. Recent records show that 22 species of crabs and lobsters have been reported from the Southern Ocean, with 12 species found south of 60°S. All are restricted to waters warmer than 0°C, with their Antarctic distribution limited to the areas of seafloor dominated by Circumpolar Deep Water (CDW). Currently, CDW extends further and shallower onto the West Antarctic shelf than the known distribution ranges of most lithodid species examined. Geological evidence suggests that West Antarctic shelf could have been available for colonisation during the last 9,000 years. Distribution patterns, species richness, and levels of endemism all suggest that, rather than becoming extinct and recently re-invading from outside Antarctica, the lithodid crabs have likely persisted, and even radiated, on or near to Antarctic slope. We conclude there is no evidence for a modern-day “crab invasion”. We recommend a repeated targeted lithodid sampling program along the West Antarctic shelf to fully test the validity of the “invasion hypothesis”.

Highlights

  • In recent years, the ‘crab invasion’ story has become a metaphor for climate change in the Antarctic marine realm, both in scientific literature and the media

  • Deep Sea Drilling Program (DSDP) drill holes have a long time range but no decapod fossil record (Fig. 2), most likely because exposure is restricted to the drill width, and because fossil decapods are rare in Neogene Antarctica fossil sites [48]

  • The relatively recent records of lithodid crabs living on the slopes of West Antarctica, the Ross Sea and in the overdeepend basins on the shelf, has led many to suggest that they are a new and expanding element of these marine communities

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Summary

Introduction

The ‘crab invasion’ story has become a metaphor for climate change in the Antarctic marine realm, both in scientific literature and the media. The underlying premise of the ‘invasion hypothesis’ is that crabs were driven out of Antarctica between 40 and 15 million years ago and are returning as ‘warm’ and favourable habitats become available once more. This hypothesis remains untested, and does not include evidence derived from repeated sampling showing a change or expansion in crab ranges. Increases in ocean surface temperatures have been detected to the west of the Antarctic Peninsula [4] Small increases, they are possibly significant as many believe that the Antarctic marine fauna is sensitive to changes in temperature [5,6,7,8]. Recent increases in air temperatures coupled with ever-increasing human activity have allowed the recorded introduction of many non-native species of terrestrial plants and animals in parts of Antarctica and the sub-Antarctic [9]

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