Bimini Lagoon contains a wide variety of marine environments, most of which have readily recognizable counterparts in the larger epeiric seas of the geologic past.

Located on the northwest margin of the Great Bahama Bank, Bimini Lagoon is a shallow area with

End_Page 468------------------------------

depths exceeding 5 feet in very few places; the area is 8 square miles. It is divided into an inner and an outer lagoon. The outer lagoon opens to the Gulf Stream through a narrow, deep natural channel. The outer lagoon also opens onto the Great Bahama Bank proper across wide, shallow flats, exposed at low tide. Tidal range in the lagoon is 2-3 feet; large volumes of water enter and leave the lagoon with each tidal cycle. In the lagoon, bottom communities, sediments, and currents are closely interrelated. Distribution of the communities is controlled by current action, and by the degree of tidal exchange of water with the Gulf Stream; the nature of the sediment is determined by the organism community present.

Most of the tidal exchange into the lagoon takes place through the deep channel. Current velocities exceed 2 knots. Consequently the channel is floored by bare rock, sorted gravel, and coarse sand. The margin of the channel is marked by an abrupt rise and current velocities of about 1½ knots. The strong current over the channel margin promotes luxuriant growth of Thalassia, which acts as a sediment trap, and prevents erosion. The sediment is fine-grained and poorly sorted.

Away from the channel, the current velocity is less than 1 knot, Thalassia is sparse, and wave action affects the nature of the sediment. Many benthonic communities can be recognized.

The inner lagoon is an isolated hypersaline water mass. Current velocities are very low. Most of the bottom is covered by bare sand with a few species of algae, but the richest molluscan faunas occur here.

End_of_Article - Last_Page 469------------