During times of extremely low tides, however, we have

 observed the tops of the Acropora reef protruding from the

 water, exposure of the Porites-Penicillus back-reef flats,

 and apparent cessation of water movement in the Lagoon.

 Both McNulty (1968) and Michel (1970) also observed simi-

 lar periodic loss of circulation. At such times, with calm

 weather, the southerly movement of Lagoon water is unopposed

 by the usual wind driven waves from the reefs, and hyper-

 saline or storm water may move south from the northwest

 Lagoon into the channels around Patricia and Bovoni Cays.

 This rather unique interaction of waves and tides and

 its effects on circulation and flushing of the Lagoon is

 crucial to the hydrography and ecology of the area. One

 of the most obvious of these effects is that increased

 circulation causes the water in Benner Bay and the Lagoon

 to become more homogenous, generally reflected by a reduc-

 tion of the usually higher salinities in northeast Benner

 Bay and northwest Lagoon to levels closer to those of the open

 sea to the south. This effect is less marked at deeper more

 exposed stations (2, 4, 11) which normally maintain salini-

 ties close to open sea values, and, as a consequence, the

 range of salinity throughout the area is compressed.

 On the other hand, during periods of poor circulation

evaporation increases salinity in the more remote areas and

distinct spatial heterogeneity develops.


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