If you're staying at the Montego Bay Resort, then you should consider yourself lucky that you are so close the best diving and snorkeling on the island. Then again, as a discriminating traveler, you should also feel your fair share of guilt that you are supporting a corporate resort instead of the impoverished communities that blanket Jamaica.
There are numerous dive and snorkel sites to be found here, many of which require a boat ride out into the coral to enjoy. Most prevalent are sponges, although there is an excellent range of tropical marine life to be seen wherever you'll be. Experienced divers will love Widowmaker's Cave, which has an entrance 85 feet under water and a chimney exit about 50 feet above it. For snorkelers, there is Doctor's Cave Beach, which is great for beach-side activities and better in the water for its drop off and the coral collections to be explored just offshore.
Note:Go to Pier One in Montego Bay for on site tour information and a further understanding of your responsibilities in helping to preserve this ecosystem; it has been featured on your map.