Challenging the Cold: Crabs Reconquer the Antarctic

Abstract

Abstract. Recent records of lithodid crabs in deeper waters off the Antarctic continental slope raised the question of the return of crabs to Antarctic waters, following their extinction in the lower Miocene ϳ15 million years ago. Antarctic cooling may be responsible for the impoverishment of the marine high Antarctic decapod fauna, presently comprising only five benthic shrimp species. Effects of polar conditions on marine life, including lowered metabolic rates and short seasonal food availability, are discussed as main evolutionary driving forces shaping Antarctic diversity. In particular, planktotrophic larval stages should be vulnerable to the mismatch of prolonged development and short periods of food availability, selecting against complex life cycles. We hypothesize that larval lecithotrophy and cold tolerance, as recently observed in Subantarctic lithodids, represent, together with other adaptations in the adults, key features among the life-history adaptations of lithodids, potentially enabling them to conquer polar ecosystems. The return of benthic top predators to high Antarctic waters under conditions of climate change would considerably alter the benthic communities.

On the origin of Antarctic marine benthic community structure

“…One of the consequences of Antarctic cooling for Southern Ocean marine ecosystems was a dramatic change in their biodiversity, including the loss of major taxonomic groups such as pelagic and benthic top predators (e.g. sharks and crabs), and a reduction in the biodiversity of groups such as bivalve molluscs, teleost fishes and decapods [9,[21][22][23]. Although the long-term impacts of Antarctic cooling on Southern Ocean biodiversity and the consequences of biodiversity loss for Antarctic benthic community structure [17,21,24,25] are well known, our understanding of the effect of glacialinterglacial cycles on Milankovitch timescales on structuring Antarctic marine communities is still far from complete.…”

“…However, this work has addressed different evolutionary timescales when comparing the oceanographical and deep-sea gateways through which marine organisms can colonize the Southern Ocean [23,[26][27][28]. On short timescales, pelagic larvae, including taxa that went extinct during Antarctic cooling, might be at an advantage to successfully (re-)colonize Antarctica following glaciation by crossing the Antarctic Circumpolar Current, compared with species without pelagic lifehistory forms, which need to conquer Antarctica by migrating through the deep sea, which might take Box 1.…”

The future fate of the Antarctic marine biota?

“…The recently published record of the finding in 1986 of single male and female specimens of the North Atlantic spider crab Hyas araneus at the Antarctic Peninsula [7] highlights this potential. This collection record, however, prompts the question of how larvae or adults on ship hulls or in ballast water survive lethal subtropical temperatures [8,9] (Figure 1), and thus questions their origin [4]. The record might be the result of mislabelled collection material.…”

“…So far, there is no proof of any recently established populations of alien species in Antarctic waters. When considering the potential for non-native species to establish in Antarctic waters, it is important to distinguish between temperature adaptation on evolutionary timescales, which resulted in species such as lithodid king crabs being able to reconquer Antarctic benthic communities [3,4], and pelagic organisms occasionally being transported into Antarctic waters, but without being able to survive there [1][2][3]5]. For example, the successful speciation of limatulid bivalves across the Polar Front [6] is likely to have occurred only as a result of physiological preadaptations to the environmental conditions.…”

“…Mesoscale eddies are an important means of transport for the early pelagic life stages of benthic invertebrates across the Polar Front, as the recent record of early-stage pelagic anomuran and brachyuran crab larvae demonstrated [2]. However, for alien species to become established successfully, suitable ecological and habitat conditions, as well as the ability to tolerate the extreme temperatures, are also required; thus, for example, the pelagic larvae of the mole crab Emerita, as discussed in [1], would be unlikely to settle and establish successfully in Antarctica [2][3][4].…”