Increasing our knowledge of the status and trends of estuarine populations is important, but challenging. Our knowledge about any given species seems directly proportionate to both the physical size of the species and its perceived economic importance. For most species little can be said about population status and trends, but still over 100 species in the MBNEP study area have been identified to be in decline or in need of protection. While some species are naturally rare, others become rare, at least in part, because of habitat loss and fragmentation, pollution, and overharvest. We must determine why certain species become rare and develop management strategies to minimize species loss.

A negative side effect of our diversity and wealth of habitat is that some exotic species - usually introduced through some human activity - become too at home in the Bay area. While most introduced species are fairly harmless with only minor impacts on the ecosystem, others go unchecked, having no natural predators to control their population growth, and outcompete native populations without contributing in all of the roles of the native species. Some exotic species are particularly detrimental to existing ecosystems and hydrology.