Tides and waves can have a considerable impact on reef formation and the character of their development. Tides determine how long a reef may be exposed to air and can be responsible for strong currents that prevent coral growth. Waves, destructive as they can be, act like a lawnmower on grass, stimulating new growth in high energy environments.
Since tides are influenced by both the sun and moon, tidal ranges change with the seasons. Throughout the Barrier Reef, the range between high and low tide is greatest at the [G 10 / equinoxes]. In the northern reef the influence of the sun is greater. Summer tides at night, in January and February, and daytime winter tides, in June and July, are very low. The low summer tides cause greater widespread death of coral and other organisms than in winter because heavy rains occur at the same time. This reduces [G 26 / salinity] below tolerable levels, having a greater impact than the extended exposure to solar radiation of the winter tide.
In the southern Great Barrier Reef, the sun has less of an influence on tides, therefore, there is little difference between tides during the day. Also, since reefs are located much further offshore, the effects are not as drastic as on the northern reef.
Strong tidal currents affect reef growth patterns in [M002 / Torres Strait and the southern Pompey and Swain Reefs] complex. Phase differences in the [M001 / Arafura Sea] tidal system and the Coral Sea, on either side of Torres Strait, result in large tidal height differences. This leads to strong currents through the Strait that can reach as much as eight knots.
South of Bowen, large tide ranges result in colossal movements of water. Most passes through the Capricorn Channel. However, currents exceeding 10 knots have scoured narrow channels between individual reefs in the Pompey and Swain Reefs complex to depths as great as 295 feet. The currents are most likely responsible for keeping these channels free of coral growth.
