The tidal regimes of three Indian Ocean atolls and some ecological implications

Coral atolls are areas of high biological productivity, supporting diverse and largely closed ecosystems. Cycling of nutrients within such systems and the input of additional nutrients from ocean waters are strongly influenced by wave and tidally induced water exchange. Tidal water exchange exerts a stabilizing effect on the physical and chemical characteristics of a lagoon. Tides affect the residence time of lagoon water, and the amount by which lagoon temperatures exceed ocean surface water temperatures, typically 2?C in cloud-free windless weather. Lagoon excess temperatures are independent of depth but vary inversely with the tidal range, with significant spring-neap modulations, but harmonic variations of lagoon temperatures at diurnal and semidiurnal periods are small except in very shallow lagoons. The effects on lagoon winds are also small, implying that measured winds are representative of open ocean conditions. The growth and zonation of corals and other organisms inhabiting shallow reef flats may be affected by the phase of the solar semidiurnal tide (S2), which determines the time of day at which extremely low tidal levels occur. Measurements at three Indian Ocean atolls are used to illustrate these effects.
Pugh D , Rayner R .
tidal flushing, tidal variations, tidal data, ecological distribution, zonation, Chagos Islands, Aldabra Atoll, Indian Ocean west