How do you know that it is meaning to "many crabs" instead of "big crabs"?
It's not very probable that an adjective will end with -o. I believe it will only be for masculine/neuter Genitive, but it will be -ego anyway, so it will be easily recognizable.
'dużo' is a numeral or an adverb (Polish and English wiktionaries disagree).
Yes but would sound better if you say "on the beach there are lots of crabs"
the sentence 'there IS a lot of crabs on the beach' is grammatically correct in English. Why is it replaced by one that is not (There ARE a lot of crabs)?
If you google "There are a lot of", the results seem to prove that "there is" is acceptable, but "there are" is really the correct one.
But clearly that's a very confusing matter, even for natives, it seems.
As a native I would say "there are" when referring to quantities of more than one and "there is" when referring to a single item or anything that is not countable.
"There ARE a lot of fish in the sea" "There IS a lot of litter on the beach" "There IS a stone on the beach" "There ARE many stones on the beach"
Yeh, because grammar books don't give 'there are a lot of' as correct, at least not the ones I read. Because you can't put a plural verb with a singular form (and 'a lot' is a singular).
The Polish word for beach is very similar to the Spanish word playa. A bit more in its pronunciation but it's really interesting. At least for me.
In French, it's 'plage' - pronounced the same as the Polish without the final 'a'.