Jcsgt:
What are the general differences, besides the hard corals, between Caribbean and Sea of Cortez diving?
Hi, Jcsgt,
I'm sure you've already checked the main Mexico forum, but...
In September, the water is significantly warmer than it is in April. You can get away with a skin, a shorty, or no exposure protection if you like.
There is a possibility of Pacific tropical storms/depressions/hurricanes. They rarely get up towards Cabo, but they can make the surf interesting (even in the Sea of Cortez side of the peninsula).
Visibility is typically much higher in the summer/fall than winter/spring.
Fewer "small colorful" fish (such as anthias or damsels) than in the Caribbean.
There are hard corals in Cabo San Lucas. I know a hard coral when I see one, and I saw favites-type corals. But they are not colorful, nor do they have interesting shapes. And in Cabo, they are not nearly big enough to make a reef. Cabo Pulmo, of course, lays claim to the "largest coral reef in some strange location" But lots of beautiful gorgonians in Cabo San Lucas, and orange cup coral (I used to know the latin name, but I forgot).
You may still see seahorses (I did!)
Check out my photo gallery for a selection of photos taken in May/June 2005 in Cabo & environs. If I remembered how to provide a direct link, I would, but my memory is going away on me...