Aloha! We (my fellow co-workers) do a good bit of kayak diving in the ocean over here and it is phe-nom-en-al!!! You, your dive buddy and the ocean - dolphins cruising right by to check you out, whales this time of year, etc. It is a pretty amazing experience and quite different from diving from a boat.
For starters, you really have to have good physical upper body strength a) to kayak to the dive site in sometimes fickle ocean conditions, b) to dive the site itself in a safe manner, c) to put your dive gear BACK into the kayak when you are done and then d) to make it safely back to your exit point safe and sound in sometimes fickle ocean conditions.
In addition, it is a much more "up close and personal" type of diving experience because you are so close to the water and its residents. As in a beautiful, majestic humpback whale cruising right by you or an endangered sea turtle popping its head up to say "hello." But you are also much more subject to the ocean as the kayak is a good bit smaller than a regular boat so an increase in wind, a subtle change in ocean conditions, etc. can have a huge and perhaps dangerous impact on your kayak dive.
Finally, you want to have a good emergency plan in place. A good friend of mine got injured while spearfishing/diving off his kayak. Thankfully, he had a buddy (although that was not always the case prior to this!) and his buddy assisted him into the kayak and paddled the both of them to shore against the current and wind. Had he been alone or had the dive buddy not been able to handle the two-person kayak single-handedly, the outcome might have been a bit different. A good plan is key to being successful, as well as people on shore who know your activities and estimated return time and who will be on the lookout for you at the appropriate time.
Hope all this info helps. I am not aware of any website on kayak diving specifically but will ask my dive buddies for more info you might find helpful. Best of luck to you and happy diving!
