One big tip - the pictures on your main pages are too big, both in dimensions and in filesize. Make thumbnails - smaller versions - for the page proper, instead of linking to the big ones and using HTML to make them display at the smaller size. If you really need the full size pics, use thumbnails as links to the full size ones. As it stands, they’re slow to load and unecessarily slow down the site’s loading time. If you’ve got any people on modems looking at your site, they’ll give up before getting anywhere.
Personal taste point - drop the animated gifs entirely. They don’t exactly give a professional air to the site.
The design overall is unbalanced. Too many graphics on the left side of the page. Balance things out, maybe some pics on the left, some on the right, text in the middle, something like that. In fact, in terms of information content, your site’s back to front. The average English speaker’s eyes flick over content from top-left to bottom-right, so the most important information should be at the top left. In fact, on that point, the column-based layout of all the information seems counterintuitive. See if you can rearrange things to conform more to the habits of viewers.
The link to the course info is unclear. It’s a PADI logo, but that seems more likely to link to the PADI site or something - label it “courses” or something. Make everything clear. If people can’t find what they’re looking for at a glance, they’re not likely to make the effort. Plus you’ve tripled up on linking to the courses - waste of space, bandwidth, and effort. Link it once and make it clear.
An animated dolphin as a link to “Photography”? Where’s the connection?
As an overall suggestion, I’d say slim down on the images, put the links to external sites - like the livingreef.org one - at the very bottom of the page, and put more content on the front page. Give a brief rundown on who you are, what services you provide, where you are, that sort of thing. Don’t make the viewer have to dig to find basic information. Provide links to other pages in the site - like you already do for the courses and photography - for people who want more information, but by providing a bit of information on the front page you minimize the amount of work people need to do to find out how much they want your services. People are lazy.