Pteropods counter mechanical damage and dissolution through extensive shell repair

Victoria L Peck,Elizabeth M Harper,Rosie L Oakes,Geraint A Tarling,Clara Manno

doi:10.1038/s41467-017-02692-w

Abstract

The dissolution of the delicate shells of sea butterflies, or pteropods, has epitomised discussions regarding ecosystem vulnerability to ocean acidification over the last decade. However, a recent demonstration that the organic coating of the shell, the periostracum, is effective in inhibiting dissolution suggests that pteropod shells may not be as susceptible to ocean acidification as previously thought. Here we use micro-CT technology to show how, despite losing the entire thickness of the original shell in localised areas, specimens of polar species Limacina helicina maintain shell integrity by thickening the inner shell wall. One specimen collected within Fram Strait with a history of mechanical and dissolution damage generated four times the thickness of the original shell in repair material. The ability of pteropods to repair and maintain their shells, despite progressive loss, demonstrates a further resilience of these organisms to ocean acidification but at a likely metabolic cost.

Highlights

The dissolution of the delicate shells of sea butterflies, or pteropods, has epitomised discussions regarding ecosystem vulnerability to ocean acidification over the last decade
Polar oceans are predicted to be among the first to become undersaturated with respect to carbonate[3, 4] and calcifying organisms living in the polar regions, especially those which make their shell from aragonite, the more soluble form of calcium carbonate, have been the focus of studies investigating the likely impact of ocean acidification
Of the 28 stations where the British Antarctic Survey’s motion-compensated bongo net was deployed, L. helicina were recovered at four localities, associated with some of the coldest waters encountered during the cruise (Supplementary Table 1; Supplementary Figs. 1, 2). At one of these stations (Station 18; Fig. 1), within sea ice in Fram Strait, a third (13) of the recovered pteropods (n = 36) exhibited notable shell damage not observed at the other sites (Supplementary Fig. 3)

Summary

Introduction

The dissolution of the delicate shells of sea butterflies, or pteropods, has epitomised discussions regarding ecosystem vulnerability to ocean acidification over the last decade. A recent demonstration that the organic coating of the shell, the periostracum, is effective in inhibiting dissolution suggests that pteropod shells may not be as susceptible to ocean acidification as previously thought. While previous studies have indicated that internal thickening of the shell is likely to be common to pteropods[8, 14], the extent to which this process can protect these animals from the deleterious effects of exposure to undersaturated waters in the natural environment has not been observed. The ability of L. helicina to repair shell damage in naturally undersaturated conditions indicates that this species has more potential to counteract the deleterious effects ocean acidification may have on their shells than previously considered

Methods

Results

Conclusion