Sediment characteristics affect thallus and rhizoid growth of the charophyte Chara tomentosa L.

Shallow coastal bays and lagoons are important habitats supporting high biodiversity and many charophyte species. Charophyte habitats are particularly vulnerable to anthropogenic activity and restoring them has become a current management issue. To investigate the environmental requirements needed for charophyte site restorations, we tested how sediment characteristics affect the survival and growth of the key species Chara tomentosa. As C. tomentosa predominantly occurs in sheltered areas with organic muddy sediment, we hypothesised that sandier sediments would reduce its survival and growth. In aquaria, apical cuttings were planted in natural organic-rich sediment with three levels of sand addition (0, 40, and 80 vol%). Chara tomentosa survival was examined for 2.5 months, whereafter the growth of main thalli, developed side branches and rhizoids were analysed. Chara tomentosa survived and grew in all treatments, suggesting restoration through transplantation can be done by apical cuttings. The probability of rhizoid development and the length of side branch and rhizoid growth were the highest in the natural sediment with no added sand, indicating limited growth potential in sediments with elevated sand content. Soft, organic-rich sediment was identified as the most suitable substrate for C. tomentosa transplants, but practical considerations may constrain its use in restoration efforts.