Antarctic echinoids and climate change: a major impact on the brooding forms

Abstract

Ocean acidification (OA) and the accompanying changes to carbonate concentrations are predicted to have especially negative impacts in the Southern Ocean where, as a result of colder temperatures, there will be shallowing of both the aragonite (ASH) and calcite saturation horizons (CSH). Echinoids are a dominant group of the Antarctic macrofauna which, because of their high-Mg calcite skeleton, are particularly susceptible to changes in the ASH. Using published information on the bathymetric distributions of Antarctic echinoids, we show that the majority of heavily calcified echinoids have their lower bathymetric limit above a depth of ca. 3000 m, approximately the current depth of the CSH. Echinoids whose depth range extends below 3000 m generally have thin, weakly calcified tests and include species from the Order Holasteroida, and the Families Cidaridae and Schizasteridae. Examination of the reproductive mode of Antarctic echinoids shows that brooding, where calcification of the young occurs in the same CaCO 3 environment as the mother, is primarily found at a depth above 3000 m. The predicted shallowing of the ASH and CSH under OA conditions is likely to negatively impact growth and reproduction of heavily calcified brooders in the Family Cidaridae, which may result in changes to bathymetric ranges, local population extinction, and associated losses in macrofaunal biodiversity. As with other calcified deep sea invertebrates, echinoids may be particularly vulnerable to the impacts of increased CO 2 and OA in the Southern Ocean.

Risk and resilience: variations in magnesium in echinoid skeletal calcite

“…Even with the lower Mg content typical of cool-water echinoids, undersaturation in coastal waters could affect survival, calcification and especially reproductive success and settlement of larvae , Sewell & Hofmann 2011.…”

“…Parts of teeth that are higher in Mg may also be highly vulnerable. Very small skeletal elements that are not well protected from sea water (such as larval echinoids) would be the most vulnerable of all , Sewell & Hofmann 2011. Studies on the reduction in strength caused by exposure to acidified sea water thus far have concentrated on test thickness of adults, in terms of resistance to predators crushing whole skeletons (e.g.…”

The Skeleton of Postmetamorphic Echinoderms in a Changing World

“…It has frequently been argued that echinoderms would be particularly at risk from ocean acidification due to the high magnesium content of their skeleton, making the skeletal calcite more soluble, especially at high latitudes where OA will be more pronounced (e.g., Andersson et al, 2008;Sewell and Hofmann, 2011;McClintock et al, 2011). Evidence for this is currently poor.…”

Benthic marine calcifiers coexist with CaCO3‐undersaturated seawater worldwide

“…This could negatively impact marine communities [Sewell and Hofmann, 2011] and alter global biogeochemical cycles [Andersson, 2014] for which biogenic carbonate mineral production and dissolution are important processes [Milliman, 1974;Opdyke and Wilkinson, 1993]. Marine biomineralization is the process by which pelagic and benthic organisms actively control and build CaCO 3 structures such as shells, tests, spines, and ossicles [e.g., Lowenstam and Weiner, 1989].…”