Co-occurrence of the charophyte Lychnothamnus barbatus with higher trophy submerged macrophyte indicators

Lychnothamnus barbatus, one of the rarest and endangered charophytes world-wide, is a bioindicator of low water trophy. This study was carried out in a moderately fertile water body hosting a large population of L. barbatus (Lake Kuźnickie, Poland). In this lake, L. barbatus co-occurs in submerged vegetation with higher trophy indicators, aquatic angiosperms Ceratophyllum demersum and Myriophyllum spicatum and the common charophyte Nitellopsis obtusa. The study aim was to investigate the depth preferences of the above species and their proportions at sites they co-occur in the studied lake. Depth of occurrence and quantitative share of macrophytes were studied in a 1-m depth gradient along 12 transects in July 2016 and 2017. Physico-chemical water parameters evidenced meso-eutrophic status of the lake. Out of 23 taxa of aquatic macrophytes identified in Lake Kuźnickie high frequencies and abundances were recorded only for L. barbatus, N. obtusa, C. demersum and M. spicatum, thus being predominants in the lake's vegetation. L. barbatus co-occurred with higher trophy indicators not only in the same lake but also at the same sites. Ceratophyllum demersum, M. spicatum and N. obtusa were negatively correlated with depth. Lychnothamnus barbatus preferred deeper sites than other predominants, as evidenced by ANOVA. Whilst M. spicatum showed no statistically significant relationship with L. barbatus, C. demersum and N. obtusa were negatively correlated with this endangered charophyte. We postulate that due to shade tolerance and light use efficiency L. barbatus is a better competitor at deeper sites compared to angiosperms and N. obtusa.