Characterization of the exoskeleton of the Antarctic king crab Paralomis birsteini

Abstract

Ocean acidification is projected to inhibit the biogenic production of calcium carbonate skeletons in marine organisms. Antarctic waters represent a natural environment in which to examine the long‐term effects of carbonate undersaturation on calcification in marine predators. King crabs (Decapoda: Anomura: Lithodidae), which currently inhabit the undersaturated environment of the continental slope off Antarctica, are potential invasives on the Antarctic shelf as oceanic temperatures rise. Here, we describe the chemical, physical, and mechanical properties of the exoskeleton of the deep‐water Antarctic lithodid Paralomis birsteini and compare our measurements with two decapod species from shallow water at lower latitudes, Callinectes sapidus (Brachyura: Portunidae) and Cancer borealis (Brachyura: Cancridae). In Paralomis birsteini, crabs deposit proportionally more calcium carbonate in their predatory chelae than their protective carapaces, compared with the other two crab species. When exoskeleton thickness and microhardness were compared between the chelae and carapace, the magnitude of the difference between these body regions was significantly greater in P. birsteini than in the other species tested. Hence, there appeared to be a greater disparity in P. birsteini in overall investment in calcium carbonate structures among regions of the exoskeleton. The imperatives of prey consumption and predator avoidance may be influencing the deposition of calcium to different parts of the exoskeleton in lithodids living in an environment undersaturated with respect to calcium carbonate.

How to become a crab: Phenotypic constraints on a recurring body plan

“…[11,81] Although porcelain crabs and L. hirta (Figure 2J) have broad claws, these taxa are mainly filter feeders, occasionally using their claws to scrape algae. [82] While some king crabs (Figures 1, 2N) are indeed reported as shell-crushing predators with heavily calcified claws, [83,84] they appeared ∼35 million years after the end of the Mesozoic. [4] Overall, there is little relationship observed between gross claw morphology and function, and the timing or success of carcinization.…”

Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean

“…However, the energetic cost of calcification in cold waters may also lead to other compensatory responses. For example, the Antarctic king crab P. birsteini invest more resources in building robust, predatory chelae than in protective carapaces, suggesting a greater investment in predation than in defence as its predation pressure is limited in Antarctic waters (Steffel et al, 2019).…”

“…High (Miller et al, 2011;Margolin et al, 2014;Gori et al, 2016) Hydrozoa Low (Ries et al, 2009;Steffel et al, 2019) Rhodophyta Florideophyceae Corallinales HMC skeletons (8-18 wt% MgCO3)…”

“…In crustaceans, exoskeletons of several species have also been shown to contain Mg-calcite, although they generally have a very complex mineralogy (combination of calcite, Mg-calcite, calcium phosphate and chitin) compared to skeletons of other groups like bryozoans (Chave, 1954; Andersson and Mackenzie, 2011). King crabs (Lithodidae), inhabiting deep water habitats of the SO that are already undersaturated in aragonite (Steffel et al, 2019), produce calcareous, even robust, exoskeletons (e.g. Paralomis birsteini Macpherson, 1988).…”

How to Become a Crab: Phenotypic Constraints on a Recurring Body Plan

“…Although porcelain crabs and L. hirta ( Figure 2J) have broad claws, these taxa are mainly filter feeders, occasionally using their claws to scrape algae (Kropp 1981). While some king crabs (Figure 1, Figure 2N) are indeed reported as shell-crushing predators with heavily calcified claws (Steffel et al 2019), they appeared ~35 million years after the end of the Mesozoic (Bracken-Grissom et al 2013).…”