Work

Environmental history shapes ecophysiology and microbiota of Macrocystis pyrifera at contrasting glacier- and ocean-influenced sites in the Magellanic sub-Antarctic ecoregion

Year: 2026

Type: article

Abstract: Kelp forests are highly productive marine ecosystems that face increasing threats from global climate change, particularly in sub-Antarctic regions, where warming and glacial retreat are altering temperature, salinity, and light availability. In this study, we evaluated the responses of different frond types in Macrocystis pyrifera from two contrasting sites in the Magellanic sub-Antarctic ecoregion: one under glacial influence (Ultima Esperanza, UE) and the other under oceanic influence (Punta Carrera, PC). Ecophysiological responses were assessed under both natural conditions and controlled experiments manipulating temperature (6 and 10 °C) and irradiance (5 and 50 μmol photons m - ² s - ¹). In addition, we conducted an exploratory analysis of the associated epiphytic microbiota. The two sites differed markedly in underwater spectral composition and light attenuation, with UE showing lower light penetration. These site-level differences were accompanied by contrasting ecophysiological responses in natural populations: fronds from UE exhibited a higher optimum quantum yield of photosystem II ( F v /F m ) and distinct pigment profiles compared with fronds from PC. Experimental responses also varied among frond types: middle fronds were the most resistant in terms of survival and growth, apical fronds were the most sensitive but also showed the greatest pigment plasticity, and sporophylls were the most vulnerable overall. The composition of the epiphytic microbiota was structured primarily by site, with no significant effect of frond type once other factors were accounted for, indicating that local environmental conditions exerted a stronger influence than tissue identity. Overall, our results suggest that variation in M. pyrifera responses to local environmental conditions is expressed simultaneously through the ecophysiological condition of the host, functional differentiation within the thallus, and the structure of the associated microbiota, with site emerging as a common organizing axis. These findings provide a basis for anticipating the likely direction of response of M. pyrifera under environmental change and highlight the need to incorporate population-level environmental context and functional heterogeneity within the thallus into conservation strategies for kelp forests in sub-Antarctic ecosystems.

Source: Frontiers in Conservation Science

DOI: 10.3389/fcosc.2026.1873259