Because they are small, invertebrates are particularly susceptible to environmental contamination. Some invertebrates are more sensitive to environmental change than others. The collection of species living in an ecosystem is called an assemblage. Ecosystems with more species tend to be healthier, and the presence of certain, more sensitive species is a sign that the ecosystem is in good health.

Mayfly larvae are among the invertebrates found in the waters of Lake Erie. Photo by Jon Sullivan via Flickr CC BY-NC