1 | INTRODUCTION
Biological invasions are regarded as one of the largest threats to
native biodiversity (Mack et al., 2000), including in freshwater (Sala
et al., 2000, Caffrey et al., 2014). Alien species may display invasive
properties inducing serious ecological consequences through both direct
and indirect ecological interactions (Kumschick et al., 2015), as well
as major economic impacts (Dittel & Epifanio, 2009). Such alien
invasive species may spread rapidly and cause problems that escalate
from local to regional following establishment. Early targeted
eradication actions are often therefore the only effective management
method. This approach may be particularly effective when species are
required to move through environmental corridors, such as in freshwater
ecosystems (Hulme, 2009). However, options for cost-effective and
reliable measures are often limited since it may become virtually
impossible to eradicate invasive aquatic species in anything but small,
enclosed waterbodies (Holdich et al., 1999).
In aquatic ecosystems, one of the most widely used measures for
eradication of invasive species is rotenone. This is a piscicide which
is highly toxic to fish and to certain invertebrates but has low
toxicity to birds and mammals (Ling, 2003). Rotenone is a botanical
compound originating from plant species in the Leguminosae family and
have been used for centuries as a mean of capturing fish in areas where
these plants are naturally occurring (Brooks & Price, 1961, Meadows,
1973). It has also been used as a fish management tool for almost a
century (Finlayson et al., 2010), either with the purpose of quantifying
fish abundances, manipulating fish populations to maintain sport
fisheries or treatment of rearing ponds (McClay, 2000, 2005). It is one
of the few, or the only, cost-effective and widely accepted measure for
eradicating populations of invasive fish. In addition, rotenone has been
widely used for eradication of fish parasites through culling of host
populations.
Use of rotenone is controversial. This is largely due to its
indiscriminate impacts on the wider aquatic fauna. Short-term impacts on
non-target organisms, like benthic invertebrates is well documented
(e.g. Koksvik & Aagaard, 1984, Melaas et al., 2001, Dalu et al., 2015).
The observed effects often include reduction in the total abundance of
benthic invertebrates comparted to pre-treatment levels. However, there
are large variations ranging from little or no reduction (Cook & Moore,
1969, Dudgeon, 1990, Bellingan et al., 2019) to up to 95% reduction
(Hamilton et al., 2009). Part of the variation may be explained by
taxa-specific tolerance to rotenone. Ephemeroptera, Plecoptera and
Trichoptera, which are abundant in oxygen rich lotic habitats, are
generally reported to be rotenone sensitive (Mangum & Madrigal, 1999,
Arnekleiv et al., 2001, Eriksen et al., 2009), whereas Coleoptera,
Odonata and Gastropoda, which are often abundant in lentic habitats, are
considered rotenone tolerant (Chandler & Marking, 1982, Holocombe et
al., 1987, Arnekleiv et al.,1997, Kjærstad & Arnekleiv, 2011). There
are also species-specific differences in tolerance among closely related
taxa. For example, species of gill breathing Ephemeroptera are
particularly sensitive to rotenone (Arnekleiv et al. 2001). Recovery of
the total benthic invertebrate density can occur within a year (Kjærstad
& Arnekleiv, 2004, Pham et al., 2018). However, recovery of single taxa
may potentially take several years (Arnekleiv et al., 1997, Mangum &
Madrigal, 1999).
Long-term consequences of failing to act towards continuous spread of
invasive fish or parasites may be severe to the ecosystem and ecosystem
services. Short-term disturbances to the ecosystem are expected, and to
certain degree accepted, as appropriate collateral damage. However,
long-term consequences of rotenone treatment may be less accepted. It is
currently a lack of studies assessing long-term ecosystem effects caused
by rotenone treatments (Vinson et al., 2010). Therefore, this study
focused on the long-term consequences of an intensive rotenone treatment
on lotic and lentic benthic invertebrate communities. Specifically, we
tested for impact of rotenone treatment on the long-term abundance and
temporal turnover of key taxa by comparing time series from a rotenone
treated watercourse and a nearby control watercourse.