Impact of UV radiation on the red seaweed Gelidium lingulatum and its associated bacteria

UV radiation can affect the physiology of seaweeds and their associated microorganisms. In this study we exposed different Chilean populations of the agarophyte Gelidium lingulatum to PAR or PAR+UV and monitored their photosynthetic performance using in vivo chlorophyll fluorescence for 5 days to determine changes in abundance and composition of epibiotic bacteria. Before the experiment, the seaweeds had been acclimated for more than 1 year in outdoor tanks with flowing seawater. At the beginning of the experiment, maximum quantum yield (F_v/F_m) did not vary among different populations. During the recovery period, F_v/F_m increase was higher in thalli from La Pampilla (30°S) in comparison with other populations (33°S and 42°S). The lowest total amount of bacteria (22.2 ± 2.5 × 10³ cell mm^–2) on thalli was observed at the beginning of the experiment. At the end of the experiment, the density of bacteria was not significantly different among thalli from different populations, as well as among UV-exposed and non-exposed seaweeds. The bacterial community in seawater was different from that on the seaweed thalli as shown by MiSeq Illumina reads of 16S rRNA. UV exposure changed the composition of microbial communities on the thalli and led to a reduction in community diversity and evenness. Relative abundance of Alteromonas sp. increased but abundances of Methylophaga sp. and Colwellia sp. decreased during UV exposure. Microbes associated with G. lingulatum may play an important ecological role in seaweed-microbial interactions. Future studies should explore the ecological function of microbial communities associated with seaweeds.