ABSTRACT The increasing demand for coastal and marine tourism and the negative impact of its exploitation call for strategies to promote sustainable forms of marine tourism. Citizen science (CS) as part of the marine tourism experience could support sustainable tourism by providing opportunities for people to learn about the natural environment and take actions that can influence conservation policy and encourage pro-environmental behaviours. The present study assessed marine tourists’ disposition towards marine conservation and their intention to participate in kelp CS in South Africa, using a modified version of the Theory of Planned Behaviour. A total of 250 people participated in a questionnaire survey from 10 August to 24 September 2021, in Simon’s Town, Cape Town. Although the tourists possessed moderate knowledge of kelp forests and a favourable disposition towards the environment, behavioural intention to participate in kelp monitoring/conservation as part of tourism was relatively low. Perceived behavioural control was the only factor influencing behavioural intention. These results offer insight into the drivers and barriers to participation in CS by tourists. There are opportunities for marine tourism businesses and organisations to package forms of CS-based tourism that can be educative and provide opportunities to actively participate in science for marine conservation.