hydroid

Your zone is very close to mine 8b-9-ish. My naners always turn brown and die back in the winter, and depending on what kind will reflect the severity. Also seems that the more frost I get the worse it affects them. The stalk which fruits will eventually too. Like another poster says also you have a lot plants congested in the mat. I've also noticed that as my mats get older and thicker sometimes the outer ones will lean and sometimes fall. Hope this helps.
Bo