Given the growth in scuba diving activities and the importance of environmental education programs to alleviate the potential impacts on coral reef ecosystems, there is a need to better understand the diving community, its environmental knowledge, and subsequent behavioral actions. The purpose of this study was to explore the role or influence of specialization in scuba diving (as a moderator and mediator) on the relationship between marine-based environmental knowledge and behavior. Four hypotheses were formulated and empirically tested. Data from 370 scuba divers were collected (May--September 2002) in the St. Petersburg/Sarasota region of southwestern Florida. Marine-based environmental knowledge (11 items) and behaviors (16 items) were employed, along with recreation specialization (17 items) adapted from the literature. Specialization in scuba diving acted as a strong partial mediator but failed to be significant when tested as a moderator. Among scuba divers, marine-based knowledge did predict overall and specific proenvironmental behaviors; however, the level of specialization played a strong role in mediating the relationship. (Contains 4 tables and 2 figures.)