Mass Mortality Events of Invasive Freshwater Bivalves: Current Understanding and Potential Directions for Future Research

Abstract

Mass mortality events, the rapid, catastrophic die-off of organisms, have recently been recognized as important events in controlling population size, but are difficult to quantify given their infrequency. These events can lead to large inputs of animal carcasses into aquatic ecosystems, which can have ecosystem scale impacts. Invasive freshwater bivalves such as the Asian clam Corbicula fluminea, the zebra mussel Dreissena polymorpha, the golden mussel Limnoperna fortunei, and the Chinese pond mussel Sinanodonta woodiana can attain high densities and biomass and play important roles in aquatic ecosystems through filtration, bioturbation, and excretion. Invasive bivalve species can best be described as R-selected species and appear not to have the same tolerance to abiotic stressors as native species, causing them to be prone to mass mortality events in their invasive range. In contrast to their ecological effects while alive, the frequency and impacts of mass mortality events of invasive freshwater bivalves are not well-understood. Here we review the causes and impacts of mass mortality events, as well as identify important questions for future research. Extreme abiotic conditions, including both drought and flooding, as well as high and low temperatures were the primary drivers of mass mortality events. Short-term impacts of mass mortality events include large pulses of nitrogen and increased oxygen stress due to large amounts of soft tissue decomposition, while shells can impact habitat availability and nutrient cycling for decades. Impacts on biological communities (bacteria, fungi, and macroinvertebrates) are less studied but some examples exist concerning C. fluminea. Better documentation of mass mortality events, particularly their magnitude and frequency, is needed to fully understand the impacts invasive bivalve species have on ecosystems, especially as climate change may make mass mortality events more frequent and/or have a larger magnitude.

Steam and Flame Applications as Novel Methods of Population Control for Invasive Asian Clam (Corbicula fluminea) and Zebra Mussel (Dreissena polymorpha)

“…However, large and highly connected aquatic systems, such as major rivers, will likely better tolerate treatment effects than small isolated waterbodies. Further, due to a current paucity of empirical data, in situ assessments are required to determine the long-term impacts associated with both natural and human-instigated mass die-offs of bivalves on community structure and ecosystem functioning, such as the effect of large pulses of nitrogen and increased oxygen stress, and the accumulation of large numbers of empty bivalve shells (McDowell and Sousa 2019 ). Nevertheless, given the high levels of biological connectivity and relatively short invertebrate species recolonisation times associated with lotic systems (Yount and Niemi 1990 ; Caffrey et al 2010 ; Wittmann et al 2012a , b ; Coughlan et al 2017a ), rapid recovery may possibly ensue following thermal treatments, and this can be further aided with appropriate management strategies.…”

Influence of Environmental Stressors on the Microbiota of Zebra Mussels (Dreissena polymorpha)

“…Despite successful establishment in some systems, introduced bivalves, like ZMs, are susceptible to environmental extremes and climate variation -conditions many native species are able to endure [14,15]. For instance, over 99% of an invasive Asian clam (Corbicula fluminea) was extirpated from a river in Southern USA because of drought [16].…”

Fitness-related traits are maximized in recently introduced, slow-growing populations of a global invasive clam

“…extremely high or low temperatures, drought) could play an important role with infrequent, but catastrophic population declines (>99% in some cases; Ilarri et al, 2011;McDowell et al, 2017;Mouthon & Parghentanian, 2004). These events have been described (though not quantified) in several other systems as well (e. g. McDowell & Sousa, 2019;Vaughn et al, 2015). Despite that a given Corbicula population might approach or even grow beyond the carrying capacity of the ecosystem, evidence from previous studies (and those cited herein) suggests that population size significantly varies with time.…”

“…These events have been described (though not quantified) in several other systems as well (e.g. Vaughn et al 2015; McDowell and Sousa 2019). Despite a given Corbicula population might approach or even grow beyond the carrying capacity of the ecosystem, evidence from previous studies (and those cited herein) suggests that population size significantly varies with time.…”

“…To do so, we searched for peer-reviewed articles providing enough information to estimate time since population introduction as well as different population and individual processes and characteristics including population density, individual growth rate, minimum age at sexual maturity, and lifespan of global populations of this worldwide invader. Different studies suggest that Corbicula's population dynamics are chiefly regulated by environmental conditions (e. g. Crespo et al, 2015Crespo et al, , 2017Gama et al, 2017), whereby population declines are typically driven by periodic mass mortality due to extreme hydro-meteorological events (Ilarri et al, 2011;McDowell et al, 2017;McDowell & Sousa, 2019). This strongly suggests that invasive Corbicula populations would primarily follow a non-density regulated population increase and, hence, they might not level off at carrying capacity as happens with many other species (e.g.…”