I am having trouble identifing the major estuary types classed by salinity gradients?

Question

Why are they low in diversity but highly productive?
Most searches are over my head.

Thanks

Answer 1

These sites have your answers.

http://estuary.uconn.edu/EWP9.html

http://www.oceansatlas.org/servlet/CDSServlet?status=ND0xOTQxMiZjdG5faW5mb192aWV3X3NpemU9Y3RuX2luZm9fdmlld19mdWxsJjY9ZW4mMzM9KiYzNz1rb3M~