Lotic ecosystems as important but tricky refugia for charophytes in warm climates – implications for biodiversity and conservation

Charophytes are an ecological and evolutionary important group of macroalgae characterizing the benthic vegetation of lakes and wetlands, where they exert crucial control over community and ecosystem dynamics. In spite of their widespread distribution, they are amongst the most endangered macrophytes in aquatic ecosystems, threatened by habitat loss and various forms of environmental alterations. The increasing ephemeral nature of many water bodies in Mediterranean and warmer climates further restricts the range of suitable habitats and acts as an environmental filter affecting biodiversity. In this context, lotic environments may represent suitable refugia, but their highly dynamical nature poses further challenges for the persistence of charophyte populations. With a view to investigate the ecological niche breadth of charophytes and the role of lotic refugia on their distribution and diversity, the present research investigated 23 populations belonging to the genera Chara, Nitella and Tolypella from southern Italy and northern Egypt. Results show that charophytes increasingly colonize lotic ecosystems in warmer climates, with morphological adaptations to mechanical stresses, but also that populations are likely to undergo local extinction events, dramatically shaping metapopulation dynamics. By shedding light on charophyte ecology, our findings contribute to understanding their dynamics and devising suitable conservation strategies.