Well I'm a layman here, but there's the whole debate if viruses are even alive. I'm sure this generalisation is very wrong, but most viruses are fatty capsules of genetic material at the end of the day. They don't really need a host to survive - just to proliferate.

Ah no doubt. It's just one of those believable claims that somehow just needs more, y'know? Nothing personal, I assure you.

It's completely believable which is one of those alarms that makes me want a citation.

Edit: I'll do the homework.

1 - "A teaspoon of seawater typically contains about fifty million viruses." - https://en.wikipedia.org/wiki/Marine_viruses - Suttle, C. (2005). "Viruses in the sea". Nature

2 - "10 million viruses in a drop of seawater" - https://www.futurity.org/millions-of-marine-viruses-ebb-and-flow/

So it's the low-end estimate and probably accurate enough for trivia and Internet gossip.