The GBR is a very high energy environment, with very long wave fetches across the Pacific Ocean. For this reason, the exposed reef front can only be visited on about 9 days each year. High evaporation rates and restricted connections to the ocean may result in raised salinity, even hypersalinity. Influx of large volumes of river water into the lagoon may lower the salinity. Abnormally high or low salinity will have an effect on the sediment-forming organisms present in the lagoon.
Barrier reefs occur on a variety of scales.
On a smaller scale, patch reefs often occur in the lagoon behind a barrier reef. Pinnacle reefs may also occur on the fore-reef side. Atolls are areas of shallow water carbonate deposition in the open ocean. Most have a volcanic core. An essential feature is the central lagoon.