Surprise in the Big Muddy
BY SARAH ETTINGER-DIETZEL, COLUMBIA FWCO
The hydraulics rowdily pulled the heavy benthic net back aboard the Silver Bullet stern trawl boat, a necessity of the Columbia Fish and Wildlife Conservation Office. The deck hands quickly hauled in the benthic net in hopes of collecting both larval and adult species of interest from the ever changing depths of the Missouri River. In most cases, benthic trawling yields a wide array of species for collection. This includes chubs, suckers, sturgeon and even shiners, but recently we were perplexed when finding a few very strange alien looking creatures.
Upon further study the small being was found to be a fairy shrimp, a type of branchiopod rarely found in the Missouri River system. The Columbia crew was able to get an up close look at these diminutive crustaceans while collecting samples for the Habitat Assessment Monitoring Program. Three specimens were collected in individual benthic trawls in the Missouri River, just outside of Columbia, Missouri.
Fairy shrimp are relatives of lobsters, crabs, shrimp and other small crustacean species, but are lacking a protective carapace. These little guys have evolved to live in habitats not normally known for containing predatory species, and often do not exceed 1.5 inches in length. Branchiopods are unusual due to their modified legs that serve as both a breathing apparatus and feeding mechanism for algae and plankton. Fairy shrimp are often found in vernal pools; temporary pools of water where they mature quickly at around 41 days and reproduce laying thick “cyst” eggs that can lay dormant in extreme conditions until the next rainy season. While fairy shrimp are special in evolutionary individuality and appearance they serve a large role in aquatic ecosystems as a much sought after food source due to their lack of protective cover.
The rare sightings of these little crustaceans leads to the question of just how they are able make it into the large Missouri River system? The simplest answer is flooding. Transitory wetlands and accompanying floodplains become inundated due to increased rainfall. These systems form temporary connections increasing macro invertebrates and other aquatic species; in this case fairy shrimp to be flushed into the larger riverine system.
The rainfall for 2015 has been at or above flood stage with little variation for quite some time. The increased depths have led to contingency sampling at much greater depths than what would be considered normal. With the influx of water from a multitude of tributaries and other groundwater sources, species not normally seen within the Missouri River have been maneuvered into this much larger body of water. While this can often lead to unwanted species entering the system, these small delicacies are much appreciated by fish species and unfortunately do not last long in the system before being consumed leaving little evidence of their presence.
The presence of fairy shrimp in the Big Muddy goes to show that when we haul in a net, we never know exactly what we are going to find.