ORCID
- John I. Spicer: 0000-0002-6861-4039
- Katie N.G. Thiessen: 0009-0005-0990-8482
Document Type
Article
Abstract
Sea water provides a stable environment for marine animals. Most oceanic invertebrates have body fluids similar in ionic composition to sea water. However, Antarctic coastal ecosystems are increasingly exposed to freshening—a reduction in salinity driven by glacial melt, increased precipitation, and extreme weather events. Such changes can cause mortality in Antarctic invertebrates, which generally are intolerant to reduced salinity. This study investigated osmotic and ionic regulation of the Antarctic amphipod Paraceradocus miersi exposed to simulated freshening. When salinity was reduced (from S = 34.6 to 28.0) for 12–48 h, haemolymph osmolality and sodium concentration declined, while calcium remained stable; magnesium increased markedly, suggesting poor regulation. At S = 22.1, irreversible, catastrophic gill damage was clearly visible. We conclude that P. miersi is an osmoconformer capable of limited osmo- and variable iono-regulation, at least on the timescale investigated, and so is vulnerable to hyposaline damage, via compromised gill integrity Compared with Arctic amphipods, which possess stronger osmoregulatory capacity, P. miersi reflects adaptation to the historically stable Antarctic salinity regime. Haemolymph ion composition was broadly similar to sea water for Na + but differed markedly for K+ and Mg2+, with values more closely-aligned with Antarctic isopods. Freshening events in Ryder Bay have been rare but not absent; a 2017 event (S = 28.4) may have impaired osmotic and ion balance or even caused mortality in shallow-dwelling individuals. Continued ‘summer’ coastal freshening may therefore pose a significant physiological threat to this Antarctic amphipod and other marine invertebrates.
DOI Link
Publication Date
2026-08-20
Publication Title
Marine Environmental Research
Volume
222
ISSN
0141-1136
Acceptance Date
2026-08-19
Deposit Date
2026-09-01
Funding
JIS was supported by a NERC CASS award (no. 124), SAM and LP were supported by NERC core funding to the British Antarctic Survey’s “Biodiversity, Adaptation and Evolution” Team and KT was funded by a University of Plymouth Studentship.
Additional Links
https://doi.org/10.1016/j.marenvres.2026.108368, https://www.scopus.com/pages/publications/105047880663
Keywords
Hyposalinity, Ion regulation, Magnesium, Osmoconformer, Osmoregulation, Polar
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Spicer, J., Morley, S., Thiessen, K., & Peck, L. (2026) 'The giant Antarctic amphipod Paraceradocus miersi will not fare well if freshening continues in the Southern Ocean', Marine Environmental Research, 222. Available at: 10.1016/j.marenvres.2026.108368
