Broad morphological and reproductive variability of the endangered macroalga Lychnothamnus barbatus in the depth gradient

Authors:

• Michał Brzozowski,
• Mariusz Józef Pełechaty

Abstract

Factors that strongly affect morphological features and reproductive effort of charophytes (Charophyta, Characeae) are the depth of occurrence and light availability. Eutrophication of waters and global warming change the level and transparency of waters. As a response to light limitation, an elongation of the charophyte thallus and a decrease in the number of mature oogonia with increasing depth have been reported. The object of this study was the globally endangered charophyte Lychnothamnus barbatus, the only living representative of the genus and a sensitive bioindicator of low trophic conditions. We hypothesised that: (1) the morphological variability and (2) the number of mature oogonia decrease with increasing depth. The study was carried out in Lake Kuźnickie, a mesotrophic lake in Western Poland, hosting a stable and abundant population of L. barbatus. At shallow sites (0.5 – 4.0 m), L. barbatus revealed high variability in weight and branching of the thallus. The individuals were less elongated and produced less mature oogonia than those from deep sites (5.0 - 6.5 m). The latter were more homogeneous and characterised by significantly elongated thalli and high fertility. The first hypothesis was confirmed, while the second was falsified. We suggest that L. barbatus forms two phenotypes, one less variable and better adapted to deep waters and the other more variable and better adapted to shallow, more changeable environments. This rare macroalga may optimise resource allocation depending on environmental conditions and its phenotypic plasticity may be a key adaptation to global changes. © 2020 The Author(s)