I'm in California, and I have a 1990 model sailboat with a Volvo
two cylinder diesel engine. My question is ..... is there a difference
between "marine diesel fuel" that you buy in a marina, and the
typical diesel fuel for cars and trucks? Will car/truck diesel
fuel harm my marine engine?

The reason I ask is that I vaguely recall that changes in
deisel fuel formulation for over the road vehicles, made to
meet emissions regulations, might harm marine engines,
and accordingly that diesel fuel sold in marinas is different
than that sold for cars/trucks ???