Update - it's late July, hot and humid weather in Florida, and the gaps in my floor have not closed up at all.
So back to my original question...
Is this a serious problem?? Will moisture penetrate and compromise the floor in any way more serious than if there were no gaps?
What is the remedy to this situation? The contractor said he could replace boards, but I don't see how he could do this without ripping out the entire floor since many of them are in the middle of the floor.
I'd appreciate any advice you experts out there have.
thanks !

Uhhh? Replacing a board with another board... You still have gaps, unless he is going to find a wider board

Do they really think your an idiot? Some unscrupulous flooring dealers and installers out there. Buyer Beware... AT ALL TIMES!

Heck, let the guy come color fill his gapped floor and be done with it. That or tell him to come rip it out.

Also, what could be done along with Perry's suggestion, is to recoat the floor after filling the gaps. This will coat the filler and help it from deteriorating too quickly. But be warned; this may void your warranty from the manufacterer. Use only the very best of finishes in this case. My favorite: Bona Traffic

well sk you consider yourself fortunate. In our area s.east i havent seen a floor that has moved any at all where the oil finish didn't break. It doesnt mattter if its shrunk or swollen oil based once cured tends to be brittle. waterborne will take a liitle movement oil wont. I see now you are in sunny cali, that can make a big diffrence.

reading these posts give me the feeling this is not a serviceable problem. This floor either shrank or was not installed properly... Southern California does not have excessive Relative Humidity swings like the rest of the country, so these gaps are likely to stay gapped. Gapping does nothing more than expose the edge to damage from furniture, dogs nails or anything moveing (slid) across the floor. It looks bad, especially in lighter colors.
No fixin this, in my opinion. The wood acclimated on the floor, not before it was installed....