Yes of course. Seaweeds are not immune to diseases. See the link and PDF.

Best wishes

Suman Sarkar

https://link.springer.com/chapter/10.1007%2F978-94-009-1659-3_11

Thank you very much Sir for adding answer to my query. 

All living species can be infected by micro-organisms like ice-ice in seaweeds by bacterial infection.

Thank you Sir .

Documented in coralline algae as well.

http://science.sciencemag.org/content/267/5202/1356

Yes. For example, kelps (like Laminaria) can suffer from virus and even from parasitic endophytic macroalgae

Thank you Barrett Brooks & Loïc G. Carvalho for adding an answer to my query.

There are several diseases that infect seaweeds. I would like to recommend Dr. Ann Hurtado's researches, She is an expert in Seaweeds.