ABSTRACT
Provinces of the tropical western Atlantic Of the three ecological limiting factors discussed in Chapter 1, temperature is by far the most important in the establishment of provincial boundaries. The distributions and boundaries of the three tropical western Atlantic provinces are determined almost exclusively by the surface water currents of the western halves of the North Atlantic Gyre and South Atlantic Gyre systems: with the warm North Equatorial Current (North Atlantic Gyre) owing northward and dividing into the Antilles Current, Caribbean Current, and Gulf Loop Current, and later coalescing into the Gulf Stream (inuencing the Caribbean and Carolinian Provinces); and with the warm South Equatorial Current (South Atlantic Gyre) owing southward along northern South America and forming the Brazilian Current, which ows all along the Brazilian coast southward to Uruguay and northern Argentina (inuencing the Brazilian Province). The very warm Equatorial Countercurrent, owing between the North and South Equatorial Currents, carries long-lived planktotrophic larvae back and forth between West Africa and Brazil and has added a number of amphiatlantic species (taxa that are found on both sides of the Atlantic Ocean; discussed later in this chapter) to the western Atlantic fauna. Late Pleistocene and Holocene warm currents along the western sides of the two Atlantic gyres have created relatively stable oceanographic conditions that have allowed the evolution of the modern paratropical and eutropical provinces.
