by Scott Brown
Michigan Lake Stewardship Associations
Author’s note: To view a well done report by WXYZ television regarding increasingly prolific invasive populations of red swamp crayfish appearing
in ponds located in the Detroit metropolitan area, click here
Extraordinarily abundant in the biologically diverse and highly productive marshes and swamps of the freshwater inundated Mississippi River delta region, red swamp crayfish have been serving as the miniature lobster-like “guests of honor” at south Louisiana “crawdad” boils for well over two centuries. The native distribution range of the red swamp crayfish stretches from the Gulf of Mexico coastal plain that extends from the Florida panhandle to northeast Mexico, and northward from the southern Mississippi River drainage area to Illinois and southwest Indiana (Nagy et al., 2015). Most abundant in the marshes and swamps of south central Louisiana (commonly referred to as bayous in southern Louisiana) (Hobbs, 1989, Taylor et al., 2007), the red swamp crayfish that have long since become a widely recognized symbol of Cajun-style cuisine have officially been introduced to the waters of Michigan. Michigan Department of Natural Resources (MDNR) aquatic biologists have confirmed the presence of the rapidly reproducing and often destructive invasive crayfish in Sunset Lake located near Vicksburg on the state’s west side, and in a retention pond located within the southeast Michigan City of Novi. Detections of the highly invasive red swamp crayfish in Michigan follows a July 2015 MDNR report that some anglers had illegally purchased the alien crayfish from food markets for use as a live bait, and of the detection of several dead specimens of the wayward crayfish in Ottawa County’s Lake Macatawa.
Frequently achieving extremely high density populations, crayfish are considered to be the largest and longest living of invertebrates that inhabit temperate freshwater environments (Gherardi and Acquistapace, 2007). Red swamp crayfish, scientific name Procambarus clarkii, are deep red in color and feature bright red raised spots that appear on their body and claws. Contributing to the ability of aquatic biologists and natural resource practitioners to positively identify “Louisiana mudbugs” in the field, red swamp crayfish are also endowed with a distinctive wedge-shaped black stripe on the top of their abdomen. Red swamp crayfish are voracious omnivores that readily and continuously feed upon fish eggs, aquatic plants, dead fish, and decaying organisms of all type. Ranging in overall length from two to five inches, red swamp crayfish are known to achieve body weights of just under two ounces in as little as three to five months from the time they hatch (Hentonnen and Huner, 1999).
Capable of flourishing in a wide range of freshwater habitats including swamps, marshes, wetlands, rivers, streams, ponds, lakes, and ditches hosting substrates consisting of soft sediments that are rich in organic debris (Huner and Barr, 1991), red swamp crayfish are capable of expeditiously altering or destroying the ecologically sensitive nearshore habitats that many native aquatic species depend upon for sustenance and survival (Gherardi, 2006). The red swamp crayfish is considered a highly effective ecosystem engineer due to their often noted ability to significantly modify surrounding physical habitat by building burrows in areas hosting fine sediments near the water’s edge. Consisting of a single opening and a tunnel that may extend fifteen to thirty five inches to the underlying water table, and that gradually expands into a larger “living” chamber (Correia and Ferreira, 1995; Huner and Barr, 1991), the self-constructed burrows of red swamp crayfish serve to protect the highly adept shellfish from intense mid-day sunlight, high air temperatures, and periods of extended drought (Ingle, 1997). The existence of physical habitat created by dense near-shore macrophyte growth, fallen logs, and/or other forms of woody structure may serve to increase the overall population density, and thus the foraging and burrowing activity of the notoriously disruptive freshwater crustacean (Correia and Ferreira, 1995).
The burrowing and foraging activities of the highly invasive Mississippi delta crayfish are also known to increase the likelihood and frequency of cyanobacteria blooms (Geiger et al., 2005; Yamamoto, 2010). The intensive burrowing activity of red swamp crayfish may have a negative impact on the water quality of the lakes, rivers, ponds, or reservoirs that they often colonize by causing the re-suspension of large volumes of fine particulate matter, therefore significantly reducing water clarity and the amount of sunlight that is available to support native submerged aquatic plants and a myriad of co-occurring native organisms that rely on aquatic plants for sustenance and survival (Rodríguez et al., 2005). Constructed in nearshore habitat areas hosting fine organic sediments, the abandoned burrows of the red swamp crayfish are known to cause the eventual collapse of river banks and other earthen structures (Barbaresi et al., 2004). In areas that are prone to significant water level fluctuations such as dams, levees, or irrigation systems, extensive networks of red swamp crayfish burrows are likely to damage the highly vulnerable structures through bank destabilization.
Due to their steadily increasing popularity as reasonably priced offerings on restaurant menus throughout Europe, red swamp crayfish have long since been the focus of aquaculture on the continent and currently represent approximately 90% of the total crayfish production in Europe (Perez et al., 1997; Ackefors, 1999). Since the 1950s red swamp crayfish have also been intentionally introduced to over twenty five countries around the world including several African nations where they have been the focus of commercial cultivation (Gherardi et al., 1999). In locations where the rapidly reproducing North American crustacean has been accidentally or intentionally introduced, red swamp crayfish have succeeded in creating sustainable breeding populations (Gherardi et al., 2007). Freshwater ecosystems that have been successfully colonized by the species are also known have experienced bio-diversity loss and severe habitat degradation (Gherardi, 2006). The rapidly expanding invasive range of the destructive crayfish in south-central Europe, for example, has contributed to decreasing rates of bio-diversity and habitat degradation in a steadily increasing number of freshwater systems that have undergone colonization (Gherardi, 2006).
The Michigan Department of Natural Resources asks that residents and visitors to the Sunset Lake area try to capture any red swamp crayfish they find and place them in a container in the freezer, then report the location of the find to the DNR at 269-685-6851, ext. 0, or by email to firstname.lastname@example.org. Sightings of red swamp crayfish in the Novi area or elsewhere in Michigan should be photographed and reported with the date and location of the find to email@example.com.
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