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. There are two main types of parasites found in fiddler crabs. One consists of worms and protozoans. The other category is bird parasites, the eggs of which the fiddlers consume when bird excretions mix with detritus. These parasites incubate as larvae inside the fiddlers, and reach maturity inside the bird when it consumes an affected fiddler.