The Russians, Americans, French, British, Germans, and others all have active programs to disrupt undersea communications, and they have had them for a long, long time.
This is not rocket science. A group of undergrad and graduate engineering students has demonstrated the use of low-end side scanning sonar and Rube Goldberg AUV tech to detect and track underwater cables for up to 2 weeks and 350 miles autonomously. The cables themselves are scarcely bigger than your thumb in deep water, and quite fragile (easily cut or percussively disrupted). The current they carry (yes, the optical ones too) are detectable from dozens of meters with inexpensive sensors as well.
The undersea infrastructure has always been prone to periodic failure, let alone vulnerable to deliberate attack. There is little a determined naval forces can do to prevent these possibilities aside from attempt to provide redundancy, which is not a military function, or deterrence, which is arguably a function that can be effected with political or non-naval resources better than naval resources.
The bottom line: nothing new here, no greater vulnerability exists now than before the Navy was fighting the backchannel war to feed the mouthbreathers to get more funding.