What freshwater bug is 3-inch long and crawls downriver nearly 10 miles a year and eat everything on its path? Answer: invasive crayfish.
Two years ago, Laura Twardochleb from the Olden Lab published a comprehensive meta-analysis of the literature to summarize the extent of damage that non-native crayfish cause to freshwater ecosystems. She found that because of their omnivory and role as ecosystem engineers, non-native crayfish consistently lead to ecosystem-scale effects where they are introduced, regardless of species. Recently, the Olden Lab started to investigate the invasion of rusty crayfish (Orconectes rusticus) in the John Day River, a major tributary of the Columbia River in Oregon, to better grasp crayfish invasion dynamics. Discovered in 2005, this introduction is the first recorded occurrence of rusty crayfish west of the continental divide, and is likely a result of a release by a nearby school. From 2005 to 2010, rusty crayfish spread downstream at an average rate of 13.5 km/year (Sorenson, 2012). Given wide-ranging ecological effects in its non-native range and its rapid spread through Pacific salmon rearing habitat, there is considerable concern regarding O. rusticus in the region.
For my Master’s thesis, I am developing a model to estimate spread of rusty crayfish in the John Day River from the time of introduction until now based on its observed distribution in 2005 and 2010. I will then use this calibrated model to predict the future spread of rusty crayfish throughout the watershed until 2020. I will also use this model to test whether control measures such as trapping crayfish or the release of sterile males in the population could be effective in slowing its spread.
To validate my predictions, we conducted an extensive field survey for rusty crayfish in the John Day River in August 2016. We found that wherever rusty crayfish occurred, the native species of signal crayfish (Pacifastacus leniusculus) had been extirpated. We also found that rusty crayfish had dispersed more than 200km downstream since being introduced and is now spreading faster downstream than predicted by our initial model. This discrepancy between our predictions and observations could mean two things. First, rusty crayfish might respond to some environmental conditions more strongly as they spread downstream: for example, crayfish may display faster metabolism and rates of dispersal as they reach warmer waters downstream. Second, individuals at the “front lines” of the invasion may be dispersing faster than before. This second possibility is of particular interest as several studies have shown that rapid evolution can take place in invading populations, leading to accelerating invasion rates and increased impacts on the native communities. For instance, Cane toads (Rhinella marinus) at the leading edge of the invasion wave in Australia have been developing heritable morphological (longer hindlegs), physiological (more endurance), and behavioral traits (more often in movement) that allow them to spread faster, straighter, and for longer periods of time.
For crayfish as well, a handful of studies have reported changes in sex and age composition, behavior, morphology, and physiology between core and edge invading populations in rivers. Therefore, I also plan to investigate whether the population structure, morphology, or diet of rusty crayfish individuals at the leading edge of the invasion is different than that of those populations near the introduction site. I hope that this will allow us to better understand the drivers of the invasion patterns observed in crayfish invasions and give us an insight into the potential consequences for this valuable river ecosystem.
– Mathis Messager