It's probably more surprising that these areas aren't already subtropical. Climate change seems to reduce whatever factor caused the cooling there.
You should be! Per TFA: "60 miles north of its previously recorded range—by far the northernmost mangrove in the U.S"
IMHO each observation of a new out-of-range specimen will be unsurprising without remembering the poetic lessons of infinitesimals, ex. Ship of Theseus, if not the prosaics of infinitesimals themselves.
> It's probably more surprising that these areas aren't already subtropical.
Given my surprise at this comment, I think I may be missing the significance in the switch from unsurprising there's a new record for US mangrove latitude to surprising it wasn't already subtropical. Is a mangrove a sufficient condition for being subtropical? Is it a necessary condition? My understanding is Florida is firmly subtropical on all the tentpoles: hot summers, mild winters, and rarity of frosts (famously, enabling its orange farming).
> Climate change seems to reduce whatever factor caused the cooling there.
Occam's Razor would say this adds an unneeded factor of a previously-unknown-to-humanity outlier cooled state, to further an irrational argument that it isn't surprising.
I'm assuming the seeds would need to come in through the Gibraltar straight, which is not exactly wide... Also the Med is saltier than the Atlantic, not sure if that would be a problem for mangroves.
here's an article I found about dispersal of floating seeds. apparently there are some obstacles due to them sinking mumble mumble salinity:
https://insideclimatenews.org/news/19072022/mangrove-seeds-o...
Most mangrove propagules don’t travel far. They drop straight under their parent tree or get trapped in the tangled roots of the surrounding mangrove forest and take root a few feet or miles away. But long distance dispersal across oceans and seas is still important, said Van der Stocken. If mangroves need to expand their range because of unsuitable environmental conditions from climate change or weather events, as in Texas, being able to spread their genetic material long distances on ocean currents becomes important, he said.
Across the globe in the Atlantic and Eastern Pacific mangrove populations, including those along the Gulf of Mexico, reduced water density was less apparent in the study models. However, the model found these regions might develop saltier water than the Western Pacific. Even if propagules travel the same distance, increased salinity might affect their survival, which will have implications for the dispersal dynamics of mangroves in those regions.