Food Web Structures of Biotically Important Species


Since mercury (Hg) exposure in wild vertebrates is primarily through food consumption, and since methylmercury is highly bioaccumulative, food web analysis can be especially important to understanding exposure in wild fauna. Here, we summarize extensive and intensive studies of food habits and Hg exposure for four well-researched groups of vertebrates that have outsized effects on community structure and function in the Everglades—mosquitofish, Florida Bass, long legged wading birds, and Florida Panthers. Generally these studies show that a high degree of variation in tissue Hg is attributable to geographic location within south Florida, usually because of known differences in either prey consumed or Hg concentrations in prey. Prey identity may be strongly shaped by local community structure—for example bass in canals have access to a more diverse group of prey and larger prey than those foraging in marshes. Similarly, shifts in panther food habits and consequently Hg exposure have been strongly affected by changes in available prey, driven by hydrology or ungulate management practices. While trophic position can be important in predicting Hg exposure (panthers, mosquitofish), it is interesting that in some cases (bass) geographic location may have an even stronger effect. Each of these species or species-groups has shown value as an indicator of risk, with large variation seen in Hg concentrations over both time and space. The ability to attribute that variation to location, trophic, and contaminant exposure effects has been a major contribution of these long term studies.

Mercury and the Everglades. A Synthesis and Model for Complex Ecosystem Restoration: Volume II – Aquatic Mercury Cycling and Bioaccumulation in the Everglades