Microhabitat light regime drives a seasonal reversal of metal burdens in the photosymbiotic sea anemone Anemonia sulcata

Trace-metal accumulation in intertidal bioindicators can be strongly influenced by fine-scale ecological conditions, yet the role of microhabitat light regime in photosymbiotic species remains poorly understood. Here, we quantified Al, Fe, Zn, Cu, Cd and Pb in the sea anemone Anemonia sulcata from Tenerife and Gran Canaria using a fully crossed design that included island, microhabitat light regime (Light vs Dark), and season (Summer vs Winter). Metal profiles differed consistently between light regimes, but the strength and direction of this effect depended on season. In winter, individuals from Dark microhabitats showed higher concentrations for all analysed metals, whereas in summer the differences were weaker and restricted to a subset of elements. Multivariate and mixture-level analyses further showed that the Lighting × Season interaction explained the main structure of the dataset, while island contributed comparatively little to overall variation. These results indicate that microhabitat light regime is an important ecological modulator of metal burdens in A. sulcata, and that its effect changes seasonally. Accounting for both microhabitat and season may therefore improve the interpretation of biomonitoring data in intertidal photosymbiotic organisms.