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Crayfishes:

The largest stream arthropods, crayfish are distantly related to insects, arachnids, and their cousins. About 18 species of crayfish, all from the family Cambaridae inhabit the upper Coosa River system. This number of crayfish is considerably less than those for mussels, snails, or fishes. However, five crayfish species occur only in the upper Coosa River basin. This gives the crayfish the highest percentage (28%) of endemic species of any aquatic group in the drainage.

Crayfishes are well distinguished by their large pincers that help gather food, defend themselves, and mate. The animal’s body is wrapped in a hard protein-derived covering called an exoskeleton. The exoskeleton has two major components: the carapace that covers the head and thorax, and a flexible segmented abdomen. To accommodate growth, crayfish must regularly shed their entire exoskeleton, including legs and antennae, in a process called molting.

Most crayfishes inhabit streams where they find pockets under rocks or other objects for shelter. However, several species are burrowers and spend most, if not all, of their time underground in floodplains or other low-lying areas. Burrows, which have characteristic mud-ball ‘chimneys” at the entrance, are excavated to the water table and provide burrowing species with a safe haven during drought periods. Crayfish generally mate in late fall through early spring, and the males use a modified pair of appendages for sperm transfer to the females. After fertilization, the female attaches the eggs to the underside of her abdomen with a sticky substance and seeks shelter for protection from predators. Females are said to be “in berry” during this period as the egg mass is highly visible below the abdomen. After hatching, the young will continue to be carried on the underside of her abdomen for a period of time.

The largest threats to crayfishes are the loss of suitable floodplain habitats, destabilized river channels, and heavy sedimentation. Many crayfishes are habitat specialists and require specific areas within the stream channel for survival. Native crayfishes are especially sensitive to displacement by introduced species.

Fishes:

The upper Coosa River basin historically hosted 100 different fishes, and more than a dozen endemic species. In fact, for a river basin in a temperate climate, the Coosa River basin has the greatest number of endemic fish species in the world. Small fishes, such as minnows and darters, are among the most conspicuous fishes in streams, and they dominate species diversity. Minnows and darters represent over half the upper Coosa fishes and all endemic and federally listed species. Many darters are exceedingly colorful, sporting electric blues, emerald greens, fiery reds, and other dazzling hues. Male minnows and darters are often especially colorful during the spawning season when they vie for the attention of females.

Spawning typically occurs in the spring. Many species construct nests in the streambed, under rocks, in crevices, or on vegetation, which are fiercely guarded by one or both parents. Other species simply broadcast their fertilized eggs, offering no parental care. Numbers of eggs vary from a dozen or so for several smaller species to thousands for some of the larger fishes. The majority of fishes feed on aquatic insects but larger species feed on smaller fishes that share their habitat. Some have diets restricted to plant material, but most are opportunistic feeders ingesting seasonally-abundant food items.

Threats to native fish habitat include habitat destruction from dams, siltation, channel destabilization, and poor water quality. However, one of the most overlooked threats is the introduction of non-native species. Some 14 species of fishes have been introduced into the basin, most since 1960. Exotic fish often out-compete native species for food and space.

Mussels:

In the upper Coosa River basin, 43 species of freshwater mussels were found historically but now only 28 remain. Habitat conditions have become so poor that most species are limited to one or two localities in the basin. Of the 15 species extirpated (34%) from the basin, 5 are now extinct (12%).

Like all mollusks, mussels have a hard shell covering that protects the soft tissues of the animal within. The shell is actually two hard valves composed primarily of calcium carbonate with a thin surface protein veneer that gives the shell its color. Most mussels are yellowish, brownish, or greenish in color, and range in size from a quarter to a dinner plate. Adult mussels live in river bottoms where they lie partially or completely buried, anchored by a single muscular foot. Remaining relatively stationary, mussels may live from 10 to over 100 years. They are among the longest living animals on the planet. Breathing and feeding are conducted by means of two siphons where water is passed through one siphon, over two pairs of gills, then out the other siphon. Tiny food particles such as fine organic material, algae, tiny animals, and bacteria are captured on the gills during this process and ingested by the animal.

Mussels have a unique life history. Usually, the sexes are separate (males and females) and males shed sperm into the water column that is collected by females. Stored in modified portions of their gills, the eggs are fertilized and develop into specialized larvae termed glochidia. These tiny larvae are parasitic on fishes. The female mussel must place these tiny larvae onto a fish in order for the larva to develop into a juvenile mussel. However, the larvae are so small and attach for such a short time, they do not harm the fish host. Female mussels use all types of bizarre strategies to attract the fish host to its glochidia.

Mussels provide food for some birds, fishes, muskrats, raccoons, otters, and other animals. Recent studies have shown that high numbers of mussels can increase the richness of other species found in the river. Like fishes, mussels are limited by poor water quality and habitat problems and appear to have a much lower threshold to habitat disturbance than most fish. The loss of stable river bottoms, eutrophication, point-source discharges, hydroelectric dam operations, and continuing poor water quality has already eliminated the vast majority of suitable mussel habitat in the upper Coosa River basin.

Snails:

Another important group of mollusks inhabiting streams are freshwater snails. Distantly related to mussels, these animals are found in all types of aquatic habitats, but streams in the southeast support the highest diversity. In fact, the Coosa River basin contained the highest diversity of snails of any single river system in the world. Unfortunately, an incredible 30 species of snails were driven to extinction with the completion and operation of large hydroelectric dams. The loss of 37 species of freshwater mollusks (30 snails and 7 mussels) from the Coosa River basin is  considered the largest single extinction event in U.S. history. Of the 32 snail species historically found in the upper Coosa River basin, nearly a quarter are already extinct (5 species, 15%) or extirpated (3 species, 9%).

Like mussels, the soft tissues are protected by a hard shell into which the animal retreats when threatened. This shell grows in a coil around a central column giving most species a distinct spiral shape. The life histories of snails are highly varied but most have separate sexes and reproduce from winter to late spring. Females usually attach their fertilized eggs directly to rocks, submerged logs, and other firm objects. The eggs hatch in a few weeks and the hatchlings are much smaller than the head of a pin. Most species grow rapidly and are fully mature in one year. Many species live for three to five years. Snails feed by scraping algae and detritus from rocks, vegetation, and other firm surfaces with a radula. The radula is similar in structure to a tongue, but is covered with tiny teeth that are continually replaced as they are worn or lost.

Text Authored by:
Paul D. Johnson - TNARI, Cohutta, GA
Robert S. Butler - USFWS, Asheville, NC

Text Edited by:
Elizabeth Reitz - GA MNH / UGA, Athens, GA

Poster Concept and Design:
Paul D. Johnson - Concept, TNARI, Cohutta, GA
Jeffrey C. Worley - Design, Tennessee Aquarium, Chattanooga, TN