Ecological and potential socioeconomic impacts of two globally-invasive crayfish

Abstract

Quantifying the impacts of invasive species, relative to native analogues, is crucial for management and policy development. Two freshwater crayfish species of global concern, Cherax quadricarinatus and Procambarus clarkii, have established populations across Africa. Negative impacts on native biodiversity and socioeconomic impacts have been documented in other continents; however, there is a paucity of information on impacts from Africa and for C. quadricarinatus. To fill this literature gap, this study used laboratory experiments to determine potential ecological and socioeconomic impacts conferred by the crayfish species relative to a functionally similar native analogue, the river crab Potamonautes perlatus, on two static, but different resources. Consumption rates were derived for the three focal species consuming the macrophyte Potamogeton nodosus and dead Oreochromis mossambicus under different temperatures regimes (19 °C and 28 °C), representing summer and winter seasons in Southern Africa, with maximum feeding rate used to infer impact. Potamogeton represents ecologically-important nutrient cycling macrophytes, as well as crucial habitat for juvenile fish, whereas dead O. mossambicus was used as proxy for fish catches in artisanal gillnet fisheries often scavenged by crayfish. Consumption of both resources by all the decapods increased with temperature. However, the two invasive crayfish showed different impact trends where P. clarkii had a significantly higher consumption of macrophytes than the other two decapods regardless of temperature and the same trends seen, but for C. quadricarinatus scavenging on fish. Crayfish introductions clearly have potential for highly destructive ecological and socioeconomic impacts to invaded systems as compared to the native crabs. The disparity between resource use emphasises the necessity to use appropriate geographical and species-specific contexts to avoid erroneous conclusions from generalised risk assessments. Derived feeding rates can be used for rapid impact assessments and comparisons in other invasion cores.

Socioeconomic impacts of Australian redclaw crayfish Cherax quadricarinatus in Lake Kariba

“…The extent of impact on catch was directly related to the abundance of cray sh entangled in the net; this is expected given the relationship between per capita impact and numerical impact/abundance (Parker et al, 1999;Dickey et al, 2020). Similar to laboratory studies, the eyes, stomach and tail were frequently damaged which suggests opportunistic damage to accessible parts of the sh (Madzivanzira et al, 2022).…”

Socio-Economic and Environmental Challenges of Small-Scale Fisheries: Prognosis for Sustainable Fisheries Management in Lake Kariba, Zambia

“…By 2009, crayfish were widely distributed and had a fully established population throughout the lake. The introduction of the crayfish into Lake Kariba and on the African continent acts as a nuisance, destroying fish eggs, nests, and habitats for spawning fish [48,49]. Most fishermen have complained and reported anecdotally the manner in which crayfish affect their catches.…”

“…Crayfish can cause considerable damage to fishing gear, resulting in increased servicing costs [50]. The entanglement of crayfish in gillnets has often resulted in ghost fishing gear as the fishers opt to abandon their nets; the partial eating of fish trapped in static gillnets is a source of concern among fishers in Lake Kariba [48]. There has been no serious intervention or biosafety measures to control the spread and invasion of invasive fish species from the relevant authorities in Lake Kariba [46].…”

“…While the negative impact of the invasive Oreochromis niloticus has widely been documented in the literature [41,48,49], the positive aspect of this fish species as an efficient feed converter has made it acceptable as the most important fish species harvested in Lake Kariba, comprising 50% of the total catch [41]. O niloticus precipitated the development of the aquaculture sector and is now among the most popular sizes of table fish in Zambia [3].…”

Long-term trends in crayfish invasions across European rivers

“…Cherax quadricarinatus, Weiperth et al, 2020;Haubrock et al, 2021;Bláha et al, 2022). Non-indigenous crayfish species have substantial and often important consequences on local biodiversity (Lodge et al, 2000;Gherardi, 2007;Gherardi et al, 2011;Twardochleb et al, 2013;Madzivanzira et al, 2022), triggering bottom-up and top-down effects that alter ecosystem functioning by competing with species at multiple trophic levels, thus modifying the natural stability of ecosystems and interaction with native species (Angeler et al, 2001;Findlay et al, 2015;Ficetola et al, 2012;Nilsson et al, 2012;Hansen et al, 2013). North American crayfish are particularly problematic due to their propensity to locally exhibit a dominant influence in communities in their invaded ranges.…”