Long-term responses of benthic invertebrates to rotenone treatment

Abstract

Biological invasions are regarded as one of the largest threats to native biodiversity. The eradication of non-native parasites by culling of hosts are a controversial conservation strategy, particularly when using indiscriminate methods involving whole ecosystem collateral damage. While short-term effects are abundantly documented, long-term surveys are needed to detect potential wider ecosystem effects. Here, we report a six-year study on effects of the piscicide rotenone on invertebrate communities from a Norwegian water course using a Before-After-Control-Impact design. Kick-net samples of benthic invertebrates were collected from three lentic sampling stations and two lotic stations two to four times per year in both a control and a treated watershed. In general, only relatively minor short-term effects immediately after the treatment on species turnover, measured as temporal beta-diversity, of benthic invertebrates were observed both in lentic and lotic locations. However, the lotic fauna was temporarily severely negatively affected following a period of rotenone exposure from an upstream lake. Species turnover co-varied markedly between control and treatment locations, indicating that natural environmental variation override effects of rotenone treatment. Likewise, the abundance of invertebrate taxa varied considerably both over time and between control and treatment locations. Our study indicates minor short-term (i.e. < one month) or long-term (i.e. four years) effects of rotenone treatment on benthic invertebrates, but severe effects on the lotic fauna eight months after treatment. However, long-term effects are likely to be taxa-specific and vary depending on habitat connectivity and thus potential for re-colonization and will differ among locations and among taxa.

The battle against the introduced pathogenic monogeneanGyrodactylus salarisin Norwegian Atlantic salmon rivers and fish farms

“…The chemical treatments in the rivers also kill much of the benthic fauna, including gill-breathing insect larvae (Kjaerstad & Arnekleiv, 2011). However, studies have shown that most of the invertebrate fauna reestablish within a year or so, and common species quicker than rare species (Kjaerstad et al, 2016;Kjaerstad et al, 2021). As only the anadromous part of the rivers is treated, the re-establishment of invertebrates is mostly due to drifting from the areas upstream of the salmon migration barrier (Kjaerstad et al, 2021).…”

Preventing and controlling nonnative species invasions to bend the curve of global freshwater biodiversity loss

“…Studies on benthic invertebrates in rotenone treated rivers suggest short term impacts, with increasing effects at higher water temperatures and rotenone concentrations, and longer exposure times. Although most invertebrate taxa recolonize within a year (Kjaerstad et al 2021), recolonization can take several years if the rotenone treatment comprised most of the basin (Mangum and Madrigal 1999).…”

Biological invasions in rivers and associated ecosystems: New insights, challenges, and methodological advancements

“…Three key aspects are evident from the studies presented within the special issue. First, long term studies (e.g., Bedmar et al, 2022; Guareschi et al, 2022; Kjærstad et al, 2022), are imperative within the field of invasion biology. Without such studies, understanding the temporal trajectories of invasion dynamics and factors influencing establishment may dictate that monitoring efforts are too short‐sighted to be effective (Christie et al, 2019).…”

“…As with most chemical control methods, application is extremely controversial, but long-term studies examining the ecological consequences are limited. Kjaerstad, Arnekleiv, Velle, and Finstad (2022) documented benthic macroinvertebrate's short (<1 month) and long term (4+ years) responses to rotenone treatment in a Norwegian watercourse. Although the effects were relatively minor (assessed via temporal beta-diversity), their findings stress the importance of exposure duration with severe effects occurring up to 8 months after treatment following a long-term low dose.…”