1. Primary production in estuaries is generally low, but estuaries have high secondary production. Why? 2. Since salinity varies considerably within an estuary, give 3 ways estuarine organisms deal with changing salinity. 3. Biodiversity in an estuary varies considerably along its length. Biodiversity in the lower and upper segments of estuary is typically higher than biodiversity of the middle segment. Why does biodiversity change from segment to segment? .