Kelp (Laminaria digitata) uses iodide as a unique inorganic antioxidant to protect its surface and apoplastic space against reactive oxygen species such as ozone, hydrogen peroxide and superoxide, with implications for atmospheric and marine chemistry as well as regional climatic processes. If kelp is covered by seawater, this results in iodide leaching into surrounding sea water. In this study, the influence of the kelps Laminaria digitata, L. hyperborea, L. ochroleuca and Saccharina latissima on iodine speciation chemistry was explored at two sites in Oban (Argyll, Scotland) and Roscoff (Brittany, France) based on diver-operated in situ sampling. Seawater samples were subsequently analysed voltammetrically, accompanied by determination of extractable iodine concentrations in the tissues of the thalli surveyed by ICP-MS. The main result is that iodide concentrations in the vicinity of kelp thalli are strongly enhanced, especially at low tide, while iodate concentrations are decreased in comparison to open coastal water and open ocean concentrations.
We would like to thank Joanna Smart, Andrew Mogg, Hugh Brown and Elaine Azzopardi (Tritonia Scientific) and Wilfried Thomas (Roscoff) for diving support. We are also grateful to Kathryn Dawson (Tritonia Scientific) for drawing the maps in Fig. 1 and to Joanna Smart (University of Tasmania and Tritonia Scientific) for providing the photograph in Fig. 22. The authors are grateful for support from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 730984, for ASSEMBLE+ awards no. 410 (to CJC, for the
visit to Tritonia Scientific Ltd. and the Scottish Association for Marine Science) and no. 370 (to FCK, for the visit to the Station Biologique de Roscoff / CNRS-Sorbonne Universités).
from the UK Natural Environment Research Council (NERC) through grants NE/D521522/1, NE/F012705/1, and Oceans 2025 (WP4.5) programs to FCK; the National Science Foundation (CHE-1664657) to CJC and FCK; the MASTS pooling initiative (Marine Alliance for Science and Technology for Scotland, funded by the Scottish Funding Council and contributing institutions; grant reference HR09011) and a fellowship from the Hanse-Wissenschaftkolleg (HWK) to CJC are
also gratefully acknowledged.