Even at a low concentration, these metals will reduce the crabs' growth. Reproduction can also be affected, and a smaller number of crabs means the fiddlers lose the protection provided by their herds. Chlorine-induced oxidants have detrimental effects on the survival and development of the fiddlers, and unfortunately, they are fairly common. Chlorine is used as a disinfectant in treatment plants, whose waste is often released into estuarine waters. These waters then flow into the marsh and the chemicals enter the detritus on which the fiddler feeds.
Pesticides are also acutely toxic to the crab larvae.
In addition to delayed development and abnormalities, they cause behavioral aberrations. Imagine the poor crab that was exposed to a toxic pesticide in its youth, and whose bright future was ruined because it lost its ability to filter detritus correctly, couldn't follow the complex mating ritual, or didn't run from predators. Pollutants do not have to be lethal to adversely affect marsh organisms such as the fiddler crab. Pollution can also have a synergistic, or combined, effect. Two little-known and understudied threats to the fiddlers are parasites and viruses.