Prospects for the return of shell‐crushing crabs to Antarctica

Abstract

Rapidly rising sea temperatures off the western Antarctic Peninsula (WAP) are placing the Antarctic benthos at risk of increasing predation from durophagous (shell-breaking) brachyuran and anomuran crabs. Crabs are at present excluded from Antarctic-shelf environments by their limited capacity to down-regulate magnesium ions in their blood, a constraint that paralyses and kills them under cold conditions. Interspecific variation in the ability of Subantarctic crabs to flush out magnesium ions predicts which species should be capable of extending their ranges to shelf environments along the Antarctic Peninsula. In agreement with those predictions, the brachyuran Halicarcinus planatus was recently found in the shallow subtidal zone at Deception Island, an emergent volcanic cone located off the WAP. Geothermal activity at Deception Island provides a warm-water opportunity for persistence in a cold ocean, and heavy ship-traffic there could accelerate the delivery of non-native species. Large populations of anomuran king crabs (Lithodidae) have recently been discovered on the continental slope off the WAP, at ambient sea temperatures slightly warmer than the waters over the shelf. The lithodids are generalized, durophagous predators that could expand to shelf habitats as the overlying waters warm rapidly. Another brachyuran, the globally invasive, durophagous European green crab Carcinus maenas, also appears poised to expand to nearshore habitats in Antarctica. Successful expansion of predators and other benthic species to the Antarctic shelf would accelerate the global trend towards functional homogenization of the marine biota. Long-term monitoring programmes should be established immediately to assess the extent of the problem in Antarctica.

No barrier to emergence of bathyal king crabs on the Antarctic shelf

“…These bathymetric shifts have been driven by glacial dynamics in the Neogene and have not been impeded by the effects of temperature or hydrostatic pressure (27,57). Furthermore, movement of lithodids onto the outer Antarctic shelf-and shoreward as sea temperatures rise-would repeat their expansion onto the Patagonian shelf during deglaciation 10,000 y ago (20). Clearly the emergence of lithodids is physiologically and ecologically feasible.…”

“…Those impacts extend beyond autecological responses to include top-down and bottom-up effects on marine food webs (13)(14)(15)(16)(17). The endemic faunas of the Antarctic continental shelf are now at risk of invasion by durophagous (skeleton-breaking) predators (18), a functional group that (based on the limited paleontological and genetic data available) may not have been ecologically significant there for as long as tens of millions of years (19)(20)(21)(22).…”

“…In some respects, therefore, Antarctic-shelf communities are reminiscent of low-predation communities living in contemporary deep-sea habitats, as well as communities from shallow, Paleozoic environments (26)(27)(28)(29)(30). Now, as sea temperatures rise, the reintroduction of durophagous predators could radically alter the composition and trophic structure of the shelf-benthos in Antarctica (19,20,31).…”

Effects of sex and color phase on ion regulation in the invasive European green crab, Carcinus maenas

“…Invasions are often caused by transport of larvae trough ballast water of ships (Cohen et al 1995;Carlton and Cohen 2003;Hidalgo et al 2005;Pringle et al 2011). However, the invasion through the transport of adults is well documented (for example , Crawford 1999;Lau 1995;Cohen et al 2001, Aronson et al 2015. Adult C. maenas is recognized as a threat in seaweed packaging of other seafood species or through the solid ballast of ships.…”

The changing form of Antarctic biodiversity

“…Ocean acidification is already affecting calcified organisms 107 , and may influence krill via impacts on eggs 108 . Although records of marine invasive species are uncommon, introductions, such as of crabs, may pose considerable threats to local communities 88 . No agricultural production takes place in the Antarctic.…”