“Adjacent” the Daintree Rainforest is the Great Barrier Reef, a natural wonder experiencing mass bleaching events that are threatening it’s survival. I had one sales agent explain that bleaching is a natural event that is good for the ecosystem to which a marine biologist on my tour replied with speechlessness. I wanted to see them before they disappeared. When selecting from the dozens of available tour options, there are 3 criteria: group size, reef location, and food, which really all boils down to cost. I opted for more people, any location (not like I would be able to tell the difference), and the plainest food option plus the submersible, which ended up not being available due to high waves. The ride out to the reef was quite fast and bumpy across the water to the extent that even the crew found itself throwing up, but I found it to be a mental exercise and enjoyed observing others dwell on their imminent discomfort :). Confirming my point, after snorkeling/diving, everybody was too tired to worry about throwing up and there were no incidents! Once back to Cairns, I balked at the airport bus fare and made my own route via local bus and hitch hiking.
Mitigate sea sickness by distracting yourself so you take your mind off the queasy feeling. One way is to talk to your neighbors. Other people go out on the deck to watch the less turbulent horizon. I recommend using polarized sunglasses as you’re able to get a more complex view through the water and in the case of the reefs, they were more visible.