Environmental Effects of the Cruise Tourism Boom: Sediment Resuspension from Cruise Ships and the Possible Effects of Increased Turbidity and Sediment Deposition on Corals (Bermuda)

In the wider caribbean, the cruise tourism boom is causing a transition from land-based (hotel) to ship-based (cruise ship) tourism. Associated with this boom has been an increase in the size of the cruise ships, with many now being Panamax/post-Panamax “mega” cruise ships. The social/environmental consequences of these changes are likely to be profound, but are also likely to be country-specific. In Bermuda, mega cruise ships can resuspend large amounts of sediment that drift onto nearby reefs. Data were compiled on cruise ship sizes and speeds entering and leaving two ports in Bermuda. In situ data were collected from multiple sites using a turbidity sensor, arrays of sediment traps, and water sample analysis. Turbidity levels in the plumes can reach 50 NTU (80 mg l^–1), but rapidly decrease to background levels (< 1 NTU) over ∼4–6 hrs. Particle size analysis revealed the plumes are composed of very fine sediments, with a median diam of < 5 μm (max < 200 μm). Sediment trap accumulation rates were found to be highest beside the shipping channels (up to ∼5 mg cm^–2 d^–1) and decrease to background rates (1–2 mg cm –2 d^–1) within a few hundred meters of the channels. These levels were significantly higher than the naturally very low levels within the lagoon. Based on existing literature, the intensity/duration/frequency of sediment exposure were considered unlikely to result in discernible physiological impacts on adult corals in the short term. However, long-term effects on juvenile coral survival and settlement success (i.e., at the population/community level) could not be discounted. Since sediment resuspension was found to be related to cruise ship speed, remedial action should involve reducing ships' speed to < 18.5–22 km hr^–1 (or 10–12 kts) when inside the lagoon.