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The St-Paul and Amsterdam (SPA) islands are surrounded by giant kelp of which the most abundant is Macrocystis pyrifera, a monospecific genus widely spread in both hemispheres. In SPA, the species is at the northern limit of its southern distribution. M. pyrifera is limited by the winter isotherm 3°C (lethality at 2°C) and the summer isotherm 18°C (lethality between 21 and 25°C). The average temperature of the sea water in SPA fluctuates between 12.5°C in winter and 19.5°C in summer. It is likely that the species may be threatened by the effects of climate change as observed in Tasmania. The problem would be related to the consequences of the El Niño Southern Oscillation (ENSO), notably a decrease in precipitation and an increase in sea surface temperatures as well as mortality due to storms. {"references": ["F\u00e9ral (J.-P.) 2023. Les composantes biologiques : flore et faune marines subtropicales de l'h\u00e9misph\u00e8re sud \u2013 Les ceintures de Phaeophyceae. In: G. Duhamel (coord.) Les \u00eeles Saint-Paul et Amsterdam (Oc\u00e9an Indien sud) : environnement marin et p\u00eacheries. Mus\u00e9um national d'histoire naturelle, Paris, pp. 44-50 (Patrimoines naturels : 84) \u27e8hal-03575185\u27e9, doi : 10.5281/zenodo.7768595"]}