The detrital pathway, with decaying organic matter at its base, is an important part of this process. Most of the Bay's species app ear to be in good health, with some exceptions posing management concerns. Phytoplankton abundance has changed significantly through the years, apparently in response to increases in nutrients peaking in the late 1960s, followed by nutrient reductions du e to improved pollution control and the construction of reservoirs on the Trinity and San Jacinto Rivers. Today, plankton abundance is similar to levels seen prior to the major urban expansion on the bay's western shores.
Benthic communities have excelle nt value as indicators of environmental stress.
Over wide expanses of the bay, however, the benthi c community remains abundant and diverse, following a natural gradient of increasing diversity from the upper bay system seaward. Oyster reefs, if anything, have expanded in recent years. Some of the most productive reefs now occur on the shoulders of t he open-bay reach of the Houston Ship Channel, where current velocities and salinity structure favor reef development. However, two species, white shrimp and blue crab, appear to be suffering from commercial overfishing. The Texas Parks and Wildlife Department has responded by banning the harvesting of shrimp in areas where white shrimp are believed to spawn during two crucial summer months, and is considering new fishing limitations for blue crabs.