Every few years, following an exceptionally low tide, it is possible to see the sandy bottom of the reef exposed above the water line. The explanation for this unusual phenomenon is the low tide cycle: a phenomenon during which the height of the sea ‘rises’ and ‘falls in a fixed cycle. The first person who realized there is a connection between the cycle of tides and the moon was the Greek explorer Pytheas. The tide cycle occurs twice a day. The time between one tide and another is 12 hours and 24 minutes, due to a combination of the rotation of the Earth around itself, and the orbit of the Moon around the Earth.
On the shores of oceans in different parts of the world the difference between peak low tide and peak high tide can reach up to 8 meters. In the Mediterranean Sea and the Gulf of Eilat the difference is much less, due to the fact that these are seas are enclosed; in the Mediterranean it reaches half a meter, and in the Gulf of Eilat slightly more.
Corals that protrude from the sea during extremely low tide are damaged, and some of them even die (the bright white color of coral usually signifies that it has been damaged), but this is a natural process through which room is created so that young coral can settle. The degree of damage to coral and to creatures on coral reefs and in lagoons also depends on the wind: when there are strong winds in the Gulf of Eilat they cause waves, which preserve the moisture of the coral tissue, and fresh water flows into those same lagoons at the bottom of the reef. It must be remembered that there are hundreds of species of invertebrates that live in the lagoons amongst the corals and the fish.
On days of extreme low tides when there is no wind waves can be created by boats, thus minimizing the damage. Extreme low tides can be seen twice a year, at the end of the summer and at the end of the winter. Typically, due to the heat, the reef is damaged more during extreme low tides in the summer.
Corals are an endangered species; they grow between from 2 mm to 2 cm a year.
Aviv Levi – Scientific Director of the Underwater Observatory Park