Impact of UV radiation on the red seaweedGelidium lingulatumand 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 agarophyteGelidium lingulatumto PAR or PAR+UV and monitored their photosynthetic performance usingin vivochlorophyll 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 degrees S) in comparison with other populations (33 degrees S and 42 degrees S). The lowest total amount of bacteria (22.2 +/- 2.5 x 10(3)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 ofAlteromonassp. increased but abundances ofMethylophagasp. andColwelliasp. decreased during UV exposure. Microbes associated withG. lingulatummay play an important ecological role in seaweed-microbial interactions. Future studies should explore the ecological function of microbial communities associated with seaweeds.

Automated summary

UV radiation affects seaweeds and their associated microorganisms, changing the composition of microbial communities on the thalli and reducing community diversity. The relative abundance of certain bacterial species increased while others decreased during UV exposure, highlighting the important ecological role of microbial communities in seaweed-microbial interactions. Future research should further explore the ecological functions of microbial communities associated with seaweeds.