Critter Corner No. 29 – The Crayfish by George Sly

In previous Critter Corner episodes, I’ve referred to the fact that Goose Pond FWA is home to countless small, often unseen, but ecologically important animals. To that list, I now add the humble crayfish.

To the casual observer, crayfish (there are many species) may seem no more than a bottom-feeding scavenger, or a candidate for a nice plate of Cajun food. Yet this small crustacean plays a big role in the ecology of wetland communities such those at Goose Pond FWA.

First, as scavengers of dead plants and animals, they help recycle nutrients by breaking down organic matter into smaller nutrients that feed microorganisms in the bottom mud. Without the help of scavengers such as crayfish, the nutrient compounds in detritus would be locked up, unavailable for reuse. Recycling is the name of the game in nature.

As crayfish burrow in the bottom substrate, they create passageways that may provide hiding places for smaller aquatic insects or their larvae, amphibian larvae, perhaps even small fish. When marsh water levels decrease, crayfish burrows can hold water and provide habitats for themselves and other animals.

Crayfish often act as predators as well. By eating other macroinvertebrates, such as insects and their larvae, tadpoles, aquatic worms, or fish, they help to control the population of such species and thus help to maintain ecological balance within the wetland community.

Acting as herbivores, crayfish consume algae which helps in managing the populations of these tiny, plant-like organisms. Population explosions of algae, known as algal blooms, can be deadly to other aquatic organisms. When huge numbers of algal cells die off, the decay process consumes oxygen and can lead to suffocation of aquatic animals in the habitat.

Crayfish play an equally important role within aquatic ecosystems by serving as food for predatory animals such as bass, herons, and mammals such as mink and raccoons.

Structurally, crayfish are of great interest to biologists because their external appendages demonstrate an evolutionary phenomenon known as serial homology. The ancient ancestors of crayfish had a sequence of appendages, made of three basic parts, arranged in series from anterior to posterior along each side of their body. These have become the organs we now recognize as the antennae, multiple mouthparts, legs, and swimmerets of the crayfish. In other words, they offer a good example of how evolution, working through natural selection, can lead to the specialization of body parts to perform new, different, and more specialized functions.

So, as you can see, crayfish are much, much more than just casual tenants of the wetlands. They are fascinating in their own right anatomically, but of more practical importance is their vital role in the ecology of wetland ecosystems. Like many other small, easily unnoticed organisms, crayfish offer us an exceedingly important lesson. The existence of ecosystems, such as freshwater marshlands, depends very much upon the seldom noticed work of the smaller members of the community. Through their activities, these rarely acknowledged members of the wetland ecosystem maintain the very framework of nature’s complexly interconnected web of life-sustaining interactions.