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Biological invasions continue to grow at a rapid rate, fuelling the need for effective and feasible biomonitoring approaches. Citizen science is an increasingly popular way of undertaking long-term and/ or large-scale monitoring while simultaneously engaging people with science and scientific issues. In temperate regions, industrially created thermal pollution of freshwater systems provides suitable conditions for (sub)tropical neobiota to survive harsh winter months and establish populations. Here, we present a citizen science project designed to collect data on feral populations of guppies (Poecilia reticulata) and other ornamental fishes in Germany. So far, only one established population has been described for Germany, residing in the thermally altered Gillbach-Erft river system near Cologne. Yet, most thermal power plants use water as a cooling medium, thus increasing the probability that more thermally influenced freshwater systems (TIFs) exist across Germany. With our large-scale approach, we were able to identify two additional locations with non-native (sub)tropical fish currently established and compile more data on now extinct populations of P. reticulata. Further, we present evidence that-as in the case of the Gillbach/Erft-these phenomena are most likely very localized, as they are solely dependent on the presence of thermal refugia. However, we call for continuous monitoring of these TIFs, especially in the light of disease and parasite transmission to the native fauna. Zusammenfassung: Biologische Invasionen nichteinheimischer Arten nehmen weiterhin zu und verstärken damit die Notwendigkeit für effektive und praktikable Ansätze zur Überwachung und Aufzeichnung von Invasionsereignissen und -prozessen. Wissenschaftliche Bürgerbeteiligung, besser bekannt als ‚Citizen Science', bietet die Möglichkeit, langfristige und/oder groß angelegte Monitoringstudien durchzuführen und gleichzeitig Mitbürger in wissenschaftliche Themen und Problematiken einzubeziehen. In den gemäßigten Breiten führt das Einleiten von industriell erzeugtem warmem Abwasser in Flüsse und Bäche dazu, dass sich nichtheimische (sub)tropische Neobiota trotz der oftmals harschen Wintertemperaturen dauerhaft ansiedeln können. Hier präsentieren wir ein Citizen-Science-Projekt, das dazu entwickelt wurde, Daten über das Vorkommen von wilden Populationen von Guppys (Poecilia reticulata) und anderen Zierfischen in Deutschland zu sammeln. Bisher war nur eine Guppypopulation in Deutschland beschrieben, die sich im thermisch belasteten Gillbach-Erft-Flusssystem in der Nähe von Köln etabliert hat. Allerdings nutzen viele Kraftwerke Wasser als Kühlmedium und somit ist die Wahrscheinlichkeit hoch, dass mehr solcher thermisch belasteten Süßwassersysteme (TIFs) innerhalb Deutschlands existieren. Im Laufe des Projekts konnten wir zwei weitere Gebiete mit etablierten (sub)tropischen Fischen identifizieren und zusätzliche Daten über bereits ausgestorbene Populationen zusammentragen. Nach unserer Einschätzung sind solche Refugien-wie im Falle des Gillbachs-höchstwahrscheinlich nur lokal begrenzte Phänomene, da sie von der stetigen Warmwassereinleitung abhängen. Dennoch fordern wir eine kontinuierliche Überwachung solcher Systeme, vor allem angesichts der Tatsache, dass die Übertragung von Erkrankungen und Parasiten auf die einheimische Fauna bereits vereinzelt nachgewiesen worden konnte.
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Bull. Fish Biol. 17 (1/2)
Bulletin of Fish Biology Volume 17 Nos. 1/2 30.12.2017 13-27
Feral guppies in Germany – a critical evaluation of a citizen
science approach as biomonitoring tool
Verwilderte Guppys in Deutschland – eignet sich Citizen Science
zum Aufspüren invasiver Arten?
Juliane Lukas1,2 *, Gregor Kalinkat1, Michael Kempkes3, Udo Rose4, David Bierbach1
1Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Department of Biology
and Ecology of Fishes, Mueggelseedamm 310, D-12587 Berlin, Germany
2Humboldt University of Berlin, Faculty of Life Sciences, Invalidenstrasse 42, D-10115 Berlin, Germany
3Jenaer Weg 5, D-46397 Bocholt, Germany
4Erftverband, Am Erftverband 6, D-50126 Bergheim, Germany
*Corresponding author: contact@julianelukas.com
Summary: Biologic al invasions continue to grow at a rapid rate, fuelling the need for effective and feasible
biomonitoring approaches. Citizen science is an increasingly popular way of undertaking long-term and/
or large-scale monitoring while simultaneously engaging people with science and scienti c issues. In tem-
perate regions, industrially created thermal pollution of freshwater systems provides suitable conditions
for (sub)tropical neobiota to survive harsh winter months and establish populations. Here, we present a
citizen science project designed to collect data on feral populations of guppies (Poecilia reticulata) and other
ornamental shes in Germany. So far, only one established population has been described for Germany,
residing in the thermally altered Gillbach-Erft river system near Cologne. Yet, most thermal power plants
use water as a cooling medium, thus increasing the probability that more thermally in uenced freshwater
systems (TIFs) exist across Germany. With our large-scale approach, we were able to identify two additional
locations with non-native (sub)tropical sh currently established and compile more data on now extinct
populations of P. reticulata. Further, we present evidence that – as in the case of the Gillbach/Erft – these
phenomena are most likely very localized, as they are solely dependent on the presence of thermal refugia.
However, we call for continuous monitoring of these TIFs, especially in the light of disease and parasite
transmission to the native fauna.
Keywords: Thermally in uenced freshwaters, citizen science, invasive alien species, non-native species,
aquarium trade, thermal pollution, Poecilia reticulata
Zusammenfassung: Biologische Invasionen nichteinheimischer Arten nehmen weiterhin zu und verstär-
ken damit die Notwendigkeit für effektive und praktikable Ansätze zur Überwachung und Aufzeichnung
von Invasionsereignissen und -prozessen. Wissenschaftliche Bürgerbeteiligung, besser bekannt als ‚Citizen
Science’, bietet die Möglichkeit, langfristige und/oder groß angelegte Monitoringstudien durchzuführen und
gleichzeitig Mitbürger in wissenschaftliche Themen und Problematiken einzubeziehen. In den gemäßigten
Breiten führt das Einleiten von industriell erzeugtem warmem Abwasser in Flüsse und Bäche dazu, dass
sich nichtheimische (sub)tropische Neobiota trotz der oftmals harschen Wintertemperaturen dauerhaft
ansiedeln können. Hier präsentieren wir ein Citizen-Science-Projekt, das dazu entwickelt wurde, Daten
über das Vorkommen von wilden Populationen von Guppys (Poecilia reticulata) und anderen Zier schen in
Deutschland zu sammeln. Bisher war nur eine Guppypopulation in Deutschland beschrieben, die sich im
thermisch belasteten Gillbach-Erft-Flusssystem in der Nähe von Köln etabliert hat. Allerdings nutzen viele
Kraftwerke Wasser als Kühlmedium und somit ist die Wahrscheinlichkeit hoch, dass mehr solcher thermisch
belasteten Süßwassersysteme (TIFs) innerhalb Deutschlands existieren. Im Laufe des Projekts konnten wir
zwei weitere Gebiete mit etablierten (sub)tropischen Fischen identi zieren und zusätzliche Daten über bereits
ausgestorbene Populationen zusammentragen. Nach unserer Einschätzung sind solche Refugien – wie im
14
Falle des Gillbachs – höchstwahrscheinlich nur lokal begrenzte Phänomene, da sie von der stetigen Warm-
wassereinleitung abhängen. Dennoch fordern wir eine kontinuierliche Überwachung solcher Systeme, vor
allem angesichts der Tatsache, dass die Übertragung von Erkrankungen und Parasiten auf die einheimische
Fauna bereits vereinzelt nachgewiesen worden konnte.
Schlüsselwörter: Thermisch belastete Süßwassersysteme, wissenschaftliche Bürgerbeteiligung, invasive
fremde Arten, nichteinheimische Arten, Zier schhandel, thermische Belastung, Poecilia reticulata
rare organisms, such as newly-arrived neobiota
(e.g. ‘Check, Clean, Dry’, Invasive Tracers,
SeaLifeTracker, AquaInvaders; see appx. 1)
and disappearing native species (e.g. ‘The Lost
Ladybug Project’; see appx. 1).
The aquarium trade has been recognized as
an important source for species introductions
on a global scale (PADILLA & WILLIAMS 2004;
DUGGAN et al. 2006; GERTZEN et al. 2008; COPP
et al. 2010; STRECKER et al. 2011; MACEDA-VEIGA
et al. 2013; KALOUS et al. 2015; SEEBENS et al.
2016; ZIERITZ et al. 2016; LUKAS et al. 2017).
A study investigating main pathways of intro-
ductions of freshwater non-natives in Europe
showed that the release of pets was only second
to aquaculture in terms of biological introduc-
tions caused (NUNES et al. 2015). Most released
aquarium species have (sub)tropical origins and
thus are unable to survive winter temperatures in
temperate regions, such as Germany. However,
as these thermal constraints start to diminish
with climate change, the likelihood for non-
natives to persist, establish and eventually spread
increases (RIXON et al. 2005). In fact, some
freshwaters already experience increases in water
temperatures that are consistent with climate
change projections due to thermal pollution
(e.g. Rivers Mississippi, Rhine and Weser; RAP-
TIS et al. 2016). In the case of the River Rhine,
richness and abundance of non-native species
has increased continuously since the early 20th
century (LEUVEN et al. 2009; PANOV et al. 2009).
Nevertheless, water temperatures in the Rhine
can drop to below 4 °C in winter (e.g. January
2017 near Düsseldorf-Flehe; LANUV 2017) and
thus most non-natives of (sub)tropical origin do
not survive. Some often overlooked areas, where
non-native species might survive the harsh win-
ter months, are thermally in uenced freshwater
systems (TIFs, also termed thermally altered
1. Introduction
Invasive species are drivers of global environ-
mental change (SALA et al. 2000; CLAVERO &
GARCIA-BERTHOU 2005; SCHRÖTER et al. 2005;
SHVIDENKO et al. 2005; BUTCHART et al. 2010),
which in its course is likely to drive even more
new invasions (WALTHER et al. 2002; PARMESAN
& YOHE 2003; RIXON et al. 2005; HICKLING et
al. 2006; BRITTON et al. 2010). When managing
non-native species, one of the top issues identi-
ed is a general lack of awareness and education
(CAFFREY et al. 2014; PIRIA et al. 2017). In fact,
some non-native species remain undetected
or are detected only after their successful es-
tablishment (e.g. GELLER et al. 1997; LOHRER
2001). Control measures are most effective
when intervening at an early stage of invasion,
thus a timely detection and rapid response are
pivotal to the success of most management
actions (BAX et al. 2001; CAMBRAY 2003; COPP et
al. 2005a, b; VERBRUGGE et al. 2014). Monitoring
efforts increase the chance of early detection
(MYERS et al. 2000; BAX et al. 2001; LODGE et al.
2006) and the collection of spatial and temporal
information of species’ ranges – native and non-
native alike – are integral to this feat (RICCIARDI
et al. 2000). Yet, the intensity of biomonitoring
approaches is often limited by the availability of
funding and staff. Volunteer-based monitoring
may be the only practical way to achieve the
reach relevant to species’ range shifts. Over the
past decade, this type of citizen science (see
ROY et al. 2012 for de nition) has contributed
greatly to the wealth of information available
on spatial variation in colonization/extinction
events (e.g. ROCHA-CAMARERO & DE TRUCIOS
2002; STOHLGREN et al. 2006; ERAUD et al. 2007;
DELANEY et al. 2008; CROWL et al. 2008). In that,
citizen science has proven effective in nding
15
Bull. Fish Biol. 17 (1/2)
aquatic systems (TAAS)). These systems are
either heated by natural geothermal sources (e.g.
SPECZIÁR 2004; PETUTSCHNIG et al. 2008; PIAZZINI
et al. 2010; MILENKOVIC et al. 2013; O’GORMAN
et al. 2012, 2014; SAS-KOVACZ et al. 2015) or due
to anthropogenic activities (LANGFORD 1990; SI-
MARD et al. 2012; KLOTZ et al. 2013; COHEN et al.
2014; HUSSNER 2014; JOURDAN et al. 2014; EMDE
et al. 2016; MULHOLLEM et al. 2016; LUKAS et al.
2017). Despite Germany’s Renewable Energy
Sources Act (“Energiewende”), thermal power
stations fuelled by black and brown coal or nu-
clear energy are still abundant. Water is the stan-
dard cooling medium in thermal power plants,
which take it in from nearby rivers and streams
and in a once-through system return it to the
natural environment at a higher temperature.
Maximum discharge temperatures are assigned
with the operation permit and are often based
on recommended best practices. However, the
prescribed maximum temperature difference of
3 K between water upstream and downstream
of the discharge can be – and often is – exceeded
due to permit exceptions (ROSE, pers. communi-
cation 2017). Within their thermal range, these
systems can provide suitable conditions for (sub)
tropical neobiota year-round.
While TIFs exist throughout Germany, most
studies analysing the distribution of non-native
species exempt TIFs from their surveys (e.g. WOL-
TER & RÖHR 2010). So far, the stream Gillbach in
the Rhine/Erft catchment is the only TIF with
established non-natives in Germany that has been
described in the scienti c literature (KEMPKES et
al. 2009; KLOTZ et al. 2013; JOURDAN et al. 2014;
EMDE et al. 2016; LUKAS et al. 2017). The Gillbach
is exclusively fed by a power plant’s coolant water
discharge and has received attention due to its
established non-native species assemblage (e.g.
Vallisneria spiralis, Neocaridina davidi, Macrobrachium
dayanum, Poecilia reticulata, Amatitlania nigrofasciata,
Oreochromis sp., Pelmatolapia mariae, Ancistrus sp.;
HÖFER & STAAS 1998; KEMPKES et al. 2009;
KLOTZ et al. 2013; JOURDAN et al. 2014; EMDE
et al. 2016; LUKAS et al. 2017). Among them are
species like the guppy and several cichlids, all of
which have a long invasion history all over the
world (WELCOMME 1988; CANONICO et al. 2005;
DEACON et al. 2011). The guppy exhibits parti-
cularly high propagule pressure (LINDHOLM et al.
2005) seeing that only one pregnant female is
needed to establish a whole population (DEACON
et al. 2011). Nevertheless, the Gillbach has been
identi ed as a rather localized phenomenon with
its (sub)tropical invaders being constrain ed by the
temperature gradient, which is only maintained
over a short distance (KLOTZ et al. 2013; JOURDAN
et al. 2014; LUKAS et al. 2017). However, there
are ecological consequences for the native ora
and fauna (e.g. introduction of non-native para-
sites; EMDE et al. 2016) that call for continuous
monitoring of the Gillbach and similar systems.
Outside of the scienti c community, infor mation
of (sub)tropical species are circulating – whether
it is the sensationalism of piranhas being landed
by anglers capturing the headlines of local press
(ANONYMOUS 2007) or sh enthusiasts sharing
video observations of feral aquarium sh found
in local creeks (see appx. 2). Also, the aquarium
magazine ‘DATZ – Die Aquarien- und Terrari-
enzeitschrift’ pub lished several articles about the
Gillbach (KEMPKES 2002, 2005, 2011; MENDAX
2011; ROSE 2012).
Given the novelty of the idea that thermally
in uenced freshwaters serve as hotspots for
non-native species (GOLLASCH & NEHRING 2006;
EMDE et al. 2016) and the scarcity of knowledge
we have about them, this study was designed to
(1) investigate whether more thermal refuges
for warm-adapted freshwater sh exist (or have
previously existed) throughout Germany. This
spatial and temporal baseline data could then be
used to further instigate long-term monitoring
efforts and management decisions. Further, we
wanted to engage the public and (2) raise aware-
ness for the issue of pet sh release by aquarium
hobbyists and its consequences.
2. Material and Methods
According to POCOCK et al. (2014a, b) citizen s
are motivated to participate in science through
interest, curiosity, fun or concern. Local natu-
ralists and conservation organisations (e.g. The
Nature and Biodiversity Conservation Union
‘NABU’) can easily be engaged, because they
16
already have a strong interest in invasive non-
native species and the management thereof.
Aquarium sh clubs and associations are equally
aware of the subject. Ornamental trade is a main
introduction pathway for non-natives (PADILLA
& WILLIAMS 2004; EMDE et al. 2016; LUKAS et
al. 2017), so many clubs are educating their
members that aquarium releases can be harmful
to the local ora and fauna and are prohibited
by Germany’s animal welfare laws (§3 Abs. 3,
4 TIERSCHG). Further, some aquarists harbour
a great curiosity for novelty strains, such as
feral populations of guppies ( g. 1) and other
ornamental sh, making them a great resource
in terms of biomonitoring.
To reach our identi ed target audience, we
approached four of the most widely distributed
aquarium magazines in Germany with a pro-
posal for a citizen science project. Our project
was met with enthusiasm and three out of the
four editors contacted published a small article
stating our objectives and means of contact in
their upcoming issues. Within a span of three
months, our letter to the readership was printed
in the ‘Aquaristik Fachmagazin’ [Oct/Nov 2016
(LUKAS & BIERBACH 2016a)], ‘Amazonas’ [Sep/
Oct 2016 (LUKAS & BIERBACH 2016b)] and the
‘DATZ – Die Aquarienzeitschrift’ [Aug 2016 (LU-
KAS & BIERBACH 2016c)]. Each of these magazines
has a print run of approximately 20,000, 15,000
and 3,500 copies, respectively. Additionally, our
article was published in the newsletters of three
aquarium sh societies [Association of German
Clubs for Aquarium and Terrarium Care (VDA),
German Society for Livebearers (DGLZ) and
viviparos – the German Livebearer Working
group]. We chose the guppy (Poecilia reticulata
Peters, 1859) as an ambassador for our message
Fig. 1: Specimens of feral guppies retrieved from the Gillbach population in 2016. Both females (A) and
males (B) show a great variation in live coloration, typical for sh of the ornamental trade.
Abb. 1: Guppys, die im Jahr 2016 aus dem Gillbach entnommenen wurden. Weibchen (A) und Männchen
(B) zeigen ein großes Farbspektrum, typisch für Fische aus dem Aquarienhandel.
17
Bull. Fish Biol. 17 (1/2)
(also referred to as ‘ agship species’; VERÍSSIMO
et al. 2011; KALINKAT et al. 2017), seeing that the
species is very popular with aquarists, which is
directly linked to its invasion success worldwide
(FROESE & PAULY 2017). As a visual stimulus, we
included a picture of a pair of feral guppies ob-
tained from the Gillbach in the letter. We quickly
summarized the research previously conducted at
the Gillbach and its implications for research on
climate change and biological invasions. Further,
we stated our objective to gather information
about similar systems, which harbour non-native
species in Germany. As a call to action, we asked
readers to send in any information they might
have on feral populations of guppies and other
(sub)tropical sh via a mail address speci cally
activated for the project, associated with the
Leibniz-Institute of Freshwater Ecology and
Inland Fisheries. To further motivate readers and
incentivise reporting, we advertised a prize draw
of the popular aquarist books “Die Guppys”
volumes 1 and 2 by Michael KEMPKES (2010a, b).
Participants were considered in the price draw,
when their information was submitted to us via
mail by November 30th, 2016.
3. Results
In total, we received eight replies – fo ur were
sub mitted before the end of the deadline and
four additional reports were sent in afterwards
(as of August 2017; see tab. 1) –, all of which
varied greatly in detail and quality. We received
GPS coordinates to two extant guppy popula-
tions in Germany: a thermal spring in Baden-
Württemberg and a former coalmine in the
Saarland, which has been turned into a water
garden for tourism (see g. 2). The site now
includes a geothermal plant, whose discharge
heats the water garden before being returned to
the nearby creek at a more ambient temperature.
Two participants veri ed the establishment of
guppies in the Gillbach-Erft-system (see g.
1). Another writer provided us with historical
information of two sites: Wölfersheimer See
and a power plant outlet near Kornwestheim. In
the former, guppies and other neozoans such as
gold sh, clown loaches, cichlids, suckermouth
armoured cat sh and turtles could be found
until the early 1990s. Further, we did receive
information of guppy occurrences in Australia
Tab . 1 : Summary of feral guppy populations recorded in Germany. Adapted from observations compiled
by KEMPKES (2010a). Information received as a result of citizen science are indicated (CS).
Tab . 1 : Zusammenfassung der in Deutschland aufgezeichneten, wilden Guppypopulationen. In Anlehnung
an Ausführungen von KEMPKES (2010a). Informationen, die im Zuge der Citizen-Science-Studie gewonnen
wurden, sind gekennzeichnet (CS).
18
(1980s), Tanzania (1998) and Puerto Rico (cur-
rent). Notably, one participant did speci cally
point out that no (sub)tropical sh species had
established populations in any water bodies of
Lower Saxony.
4. Discussion
The enactment of the legislation on the “Pre-
venti on and management of the introduction
and spread of invasive alien species” (EUROPEAN
UNION 2014) poses an important milestone in
the prevention of their establishment. Yet, the
surveillance needed has to occur at spatial scales
beyond the reach of ordinary research efforts.
Citizen science provides the potential to collect
data across much larger spatio-temporal extents
than would otherwise be feasible. Rising in
prominence (SILVERTOWN 2009; DICKINSON et al.
2012), citizen science covers a wide range of taxa
(see DICKINSON et al. 2010 for review). Among
the most successful are targeted monitoring
projects, where species are prioritized based
on their taxonomy, endemic status, sensitivity
to threats and/or public interest (YOCCOZ et al.
2001). For example, citizen science data have
enabled researchers to identify areas harbou-
ring non-native birds in the continental United
States and Hawaii (STOHLGREN et al. 2006; CROWL
et al. 2008). In Europe, thermally in uenced
freshwaters have been identi ed as hotspot for
non-native sh species of (sub)tropical origin
(SPECZIÁR 2004; PIAZZINI et al. 2010; PETUTSCH-
NIG et al. 2008; MILENKOVIC et al. 2013; JOURDAN
et al. 2014; SAS-KOVACZ et al. 2015; LUKAS et al.
2017). By engaging the public and asking people
to participate in scienti c research, our aim was
to investigate how frequent these ‘hotspots’
are in Germany. When comparing print ratios
(ranging from 3,500 to 20,000 copies) to the
feedback we received (n = 8), the results of the
survey were slightly puzzling. Several questions
immediately arose:
(i) Are there no other sites with established
(sub)tropical sh species? Judging by the amount
of power plants currently employed that use
water as a cooling medium, it is highly likely that
more TIFs exist throughout Germany. In fact,
the cooling ponds of some power plants are
used commercially, rearing sh such as sturgeon,
carp, tench, pike and pikeperch to take advantage
of the elevated temperatures (e.g. power plants
Jänschwalde and Biblis [closed 2009]; KLUG
2009). However, the likelihood of (sub)tropical
sh persisting remains low, seeing that a species
must pass through a variety of environmental
lters to become successfully established in a
new habitat (e.g. VERMEIJ 1996; WILLIAMSON &
FITTER 1996; WILLIAMSON 2006; THEOHARIDES &
DUKES 2007). In aquarium sh, the display of
certain traits such as aggressive behaviour, rapid
Fig. 2: Map of Germany and the identi ed sites cur-
rently harbouring feral populations of (sub)tropical
non-native sh. A total of four TIFs with extant
populations of P. reticulata and other (sub)tropical
sh taxa were identi ed (gray; tab.1). Further, popula-
tions that are known to be extinct (†) or whose status
is unknown/could not be veri ed (?) are indicated.
Abb. 2: Deutschlandkarte und identi zierte Standor-
te, die derzeit wilde Populationen von gebietsfremden,
(sub)tropischen Fischen beherbergen. Es konnten
gegenwärtig vier thermisch belastete Gewässer mit
Populationen von P. reticulata und anderen (sub)
tropischen Fischarten identi ziert werden (grau; Tab.
1). Ferner sind ausgestorbene Populationen (†) und
solche, deren Status unbekannt ist/nicht veri ziert
werden konnte (?), aufgezeigt.
19
Bull. Fish Biol. 17 (1/2)
reproduction, large size or illness increases the
likelihood for intentional release by their owners
(PADILLA & WILLIAMS 2004; DUGGAN et al. 2006;
GERTZEN et al. 2008). Especially the former two
can assist the success of establishment, but to
survive sh must tolerate the environmental
conditions at the introduction site. Even within
a thermally in uenced system, water quality can
be an issue for stenoecious species. Further, they
must succeed in acquiring critical resources and
surviving interactions with natural predators and
competitors. For example, the guppy population
of the Zerkwitzer Kahnfahrt near Cottbus in
Eastern Germany (tab. 1) persisted for about
ten years before it broke down due to a combi-
nation of high predation pressure (most likely
European chub (Squalius cephalus), established
convict cichlids (Amatitlania nigrofasciata) and
several avian predators) and an accident that
caused the nearby power plant to shut down
temporarily (PAEPKE & HEYM 2002). In contrast,
the reported population in the Saarland appears
to be thriving (see appx. 2) and experience only
moderate predation (introduced convict cichlids
(Amatitlania nigrofasciata)). While this too seems
to be a very localized system, we do recommend
continuous monitoring due to its connectivity
to a natural creek and the consequential threat
of disease and parasite transmission.
(ii) Seeing that some TIFs harbour (sub)
tropical sh populations, why did they not get
reported? BLACKMORE et al. (2013) recommend-
ed in their Common Cause for Nature report
to not only communicate the objective (why?)
and methodology (how?) of a project, but also
the consequences of the cause (then what?).
Without a clear statement, organisers and vo-
lunteers might pursue different agendas (NER-
BONNE & NELSON 2004), e.g. participants may
expect actions that are beyond the scope of the
project or, in contrast, may face a scenario they
nd unacceptable. In light of pan-European
bans for popular but invasive genera such as
the apple snails Pomacea sp. (EUROPEAN UNION
2012) or the marbled cray sh Procambarus fallax
f. virginalis (EUROPEAN UNION 2016), participants
may fear that a detection of feral populations
of aquarium sh will provoke similar legislative
acts. As a matter of fact, the fact that we receiv-
ed a curious reply solely stating the absence
of any feral sh populations in Lower Saxony
may further support this hypothesis. Another
potential explanation is that sites harbouring
guppies are not easily accessible by the public.
While many non-native species tend to invade
highly modi ed habitats and thus end up in
close proximity to the potential observer, on
average, people are less likely to spend time
around power plants for recreational purposes
such as bathing or hiking. On top, power plant
grounds are often enclosed by security fences,
thus obstructing the access to TIFs that po-
tentially contain non-native species. However,
TIFs can be quite popular among anglers (e.g.
SPIGARELLI 1974). An additional problem is that
potential catchers such as motivated aquarists
are legally hindered on catching sh without
a valid shing license and thus could only en-
counter potential feral populations of guppies
as by-catch when seeking for natural feed for
their pets (e.g. “Tümpelfutter”).
Ideally, a trigger (= event prompting involve-
ment) should neither be too common nor too
rare to avoid participants feeling overwhelmed
or disengaged (POCOCK et al. 2014a,b). In our
case, while spectacular, the trigger was most
likely too rare, so that most people in our target
audience simply did not possess the desired
information. Lastly, motivation for the project
could be lacking or the audience we engaged
with was too narrow (see GROVE-WHITE et al.
2007). Successful projects may resonate with
people for various reasons (see POCOCK et al.
2014a,b) and in our letter to the readership we
attempted to appeal to people’s sense of place
(“my area”), their pre-existing interest in sh
(especially aquarium sh) as well as their sense
of discovery (“I had no idea that feral guppies
existed in Germany”) and jeopardy (“My river
might be under threat”).
With hindsight comes insight, so (iii) how
could we improve and structure future projects?
Conservation enthusiasts and organisations
with similar interests (e.g. naturalist societies,
angling associations) have previously expressed
concerns about sightings of invasive non-native
20
species, so could easily be engaged with record-
ing them. Angling associations are already invol-
ved in citizen science, monitoring sh catches
and stocking efforts (e.g. ‘Besatz sch’, ‘Digitaler
Fischartenatlas’; see appx. 1), as well as assessing
invertebrate abundance and water quality (e.g.
‘River y Monitoring Intiative’; see appx. 1).
There may be potential for tapping into this,
seeing that anglers regularly visit shing spots
and are often well informed about the species
they encounter. Due to the licensing process,
anglers are trained to identify common sh
taxa that are of local interest and thus would be
able to identify non-native species more quickly
than laypeople. Furthermore, they often keep
extensive and detailed records, allowing us to
also access historical data. While reports of
anglers landing tilapia and even piranhas in the
Gillbach-Erft river system have made headlines
before, they are, however, unlikely to notice
smaller cichlids (e.g. Amatitlania nigrofasciata,
Hemichromis bimaculatus) or small livebearers such
as guppies, mollies and swordtails. National citi-
zen science project databases (e.g. ‘Portal Bee’,
see appx. 1) can also be useful in widening the
audience, allowing motivated people seeking a
worthy cause to get involved. Further, collabo-
rations with already existing programs can help
to successfully combine engagement and data
gathering to answer a question of shared interest
(see ‘Check, Clean, Dry’). One particularly inter-
esting candidate would be the ‘Ventus’ project
(see appx. 1) that gathers information on power
plants worldwide. They primarily map locations,
but also request other information concerning
carbon dioxide emission via simple form lling.
Adding a few questions about the surrounding
water bodies, their ora and fauna as well as
their temperature regime could provide valuable
insight for our mission. But even with abundant
data, new issues such as data veri cation, stor-
age and security arise. For example, an internet
source had reported a feral guppy population in
the thermal springs of Kaiserstuhl near Freiburg
(tab. 1), yet we were unable to verify this infor-
mation. One possible strategy is applied by the
North American Breeding Bird Survey, which
only codes a species “absent” when data on
other parameters or non-focal species has been
submitted for this site. In our case, the status
of this population remains unknown, but many
other TIFs could be eliminated if parameters
such as the water temperature or occurrence of
native species were recorded instead.
(iv) How feasible is such an effort in this
particular case? It is noteworthy, that citizen
science is not free. To make a project successful,
it requires investment in recruiting, motivating
and retaining volunteers, as well as managing and
analysing the data that are produced. Germany’s
goal is to switch off all of its nuclear reactors by
2022 (FEDERAL GAZETTE 2011). In its mission to
signi cantly reduce greenhouse gas emis sions,
the German government aims to generate 80%
of its electricity from renewables by 2050 (BMWI
2016). Further, many stakeholders call for stricter
regulations on thermal pollution in light of cli-
mate change and recent ecological assessments
(BUND 2009). Current proposals would force
many power plants to return their coolant water
at a temperature equal to the point of collection.
With the future of German TIFs unknown, a
comparison with a similar scenario that occurred
after the German reuni cation suggests itself.
In the years subsequent to 1989, many Eastern
German power stations were unable to compete
and either went of ine or where substituted by
newer models that were more ef cient and water
conserving. Consequently, guppy and swordtail
populations that had inhabited outlets of these
power plants (e.g. Lübbenau, Trattendorf; tab.
1) all broke down shortly after. The population
of Lake Wölfersheim met a similar fate as the
power plant Wölfersheim stopped its operations
in 1991. In view of previous developments,
thermal refuges and their non-native inhabitants
are likely to be impacted by the German energy
revolution. With anthropogenic TIFs becoming
increasingly scarcer (WIKIPEDIA 2017), the basis
for the survival of sh species from warmer
regions may no longer be a given.
5. Conclusion
With the newest EU legislatio n concerning the
regulation and management of invasive species
21
Bull. Fish Biol. 17 (1/2)
(EUROPEAN UNION 2014), the obligation has
been placed on EU member states to assess key
introduction pathways and develop action plans
for preventive measures. Yet, among the top
challenges faced by this endeavour are insuf ci-
ent funding and a lack of awareness (CAFFREY et
al. 2014). Citizen science can be a powerful tool
to improve community awareness of biological
invasions and support biomonitoring efforts.
To be successful, however, each project needs
to be carefully tailored to the speci c issues and
audience it is designed to address. In addition
to the array of studies that have employed
citizen science successfully, several guidelines
and manuals exist that can provide detailed
recommendations and assist in putting projects
into practice (see ROY et al. 2012; TWEDDLE et
al. 2012; POCOCK et al. 2014a, b).
We believe that our study not only high-
lights some of the strengths and limitations
of a citizen science approach, but also gives
more insight to an often overlooked refuge
for (sub)tropical neobiota. Our data – while
sparse – do further support the assumption
that these systems are very localized pheno-
mena (KLOTZ et al. 2013; JOURDAN et al. 2014;
LUKAS et. al. 2017). Historical records of feral
guppies provided us with new examples of
population collapses after thermal pollution
ceased (tab. 1). In light of Germany’s energy
revolution and stricter regulations on thermal
pollution, this seems to be a likely future
scenario for the feral guppy population of
the Gillbach. In place of thermal pollution,
however, climate change might become the
main driver of species’ range shifts and adap-
tive responses. Thus, we call for continuous
monitoring to allow for a timely reaction if
new invaders or detrimental impacts to the
native ora and fauna are detected. Further,
we want to encourage more research to take
advantage of these systems, which provide
a unique opportunity to study the impacts
of climate change and species invasion on a
small geographical scale. Lastly, we hope our
efforts could contribute in raising awareness
for the ongoing threat of pet releases and its
implication for the endemic ora and fauna.
Acknowledgement
First and fo remost, the authors would like to
thank all the participants, who have contributed
to the study. Further, we express our gratitude
to the editors and aquarium sh associations
for supporting the project and publishing our
request. We are grateful to Hans-Joachim PAEP-
KE and Holm ARNDT for their detailed records
and invaluable comments. Lastly, we thank the
anonymous reviewers for their careful reading
and insightful suggestions to our manuscript.
This study received funding by the Gesellschaft
für Ichthyology e.V. (German Ichthyological
Society).
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Bull. Fish Biol. 17 (1/2)
Appendix 1: Table of the aforementioned citizen science projects.
Anhang 1: Au istung der genannten Citizen-Science-Projekte.
Appendix 2: List of public video observations of feral populations of (sub)tropical sh in Germany. All
videos were accessed on 31-08-2017.
Anhang 2: Liste mit öffentlichen Videoaufnahmen von wilden, (sub)tropischen Fischpopulationen in
Deutschland. Alle Quellen wurden am 31.08.2017 eingesehen.
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... In Germany, tropical fishes have established populations in several artificially heated stream systems (Lukas et al., 2017b), the most investigated being the Gillbach near Cologne (see Figure 1A, Jourdan et al., 2014;Lukas et al., 2017a;Kempkes et al., 2018). To estimate seasonal fluctuations in temperatureassociated abiotic and biotic conditions within the sampled range of the stream, we continuously recorded water temperatures with submerged data-loggers. ...
... Here, feral guppies (Poecilia reticulata) are highly abundant and as successful global invaders (Deacon et al., 2011) they are well-suited to investigate the expression of behavioral traits across time and space. First records of guppies at the Gillbach date back to 1978 and the population has existed continuously for a conservative minimum of 10 years (Lukas et al., 2017b;Kempkes et al., 2018). The Gillbach population likely originated from a small number of released domesticated guppies (see Supplementary Figure 4, Jourdan et al., 2014;Lukas et al., 2017b), and thus would have undergone a demographic bottleneck (i.e., founders' effect) with potential consequences on genetic diversity. ...
... First records of guppies at the Gillbach date back to 1978 and the population has existed continuously for a conservative minimum of 10 years (Lukas et al., 2017b;Kempkes et al., 2018). The Gillbach population likely originated from a small number of released domesticated guppies (see Supplementary Figure 4, Jourdan et al., 2014;Lukas et al., 2017b), and thus would have undergone a demographic bottleneck (i.e., founders' effect) with potential consequences on genetic diversity. The Gillbach has since been subject to repeated introduction of guppies through intentional release (personal observation of JL, GK, FWM and DB). ...
Article
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Understanding the linkage between behavioral types and dispersal tendency has become a pressing issue in light of global change and biological invasions. Here, we explore whether dispersing individuals exhibit behavioral types that differ from those remaining in the source population. We investigated a feral population of guppies (Poecilia reticulata) that undergoes a yearly range shift cycle. Guppies are among the most widespread invasive species in the world, but in temperate regions these tropical fish can only survive in winter-warm freshwaters. Established in a thermally-altered stream in Germany, guppies are confined to a warm-water influx in winter, but can spread to peripheral parts as these become thermally accessible. We sampled fish from the source population and a winter-abandoned site in March, June and August. Fish were tested for boldness, sociability and activity involving open-field tests including interactions with a robotic social partner. Guppies differed consistently among each other in all three traits within each sample. Average trait expression in the source population differed across seasons, however, we could not detect differences between source and downstream population. Instead, all populations exhibited a remarkably stable behavioral syndrome between boldness and activity despite strong seasonal changes in water temperature and associated environmental factors. We conclude that random drift (opposed to personality-biased dispersal) is a more likely dispersal mode for guppies, at least in the investigated stream. In the face of fluctuating environments, guppies seem to be extremely effective in keeping behavioral expressions constant, which could help explain their successful invasion and adaptation to new and disturbed habitats.
... Th e established populations of guppies in Poland seem to be one of the northernmost populations in the world, recorded in the thermally polluted waters of Nowa Huta heating channel in Krakow and thermally polluted waters of Żerań CHP plant in Warsaw (Witkowski, 1989;Nowak et al., 2008;Maciaszek et al., 2019). Until 2018 only one established population has been described for Germany, residing in the thermally altered Gillbach-Erft river system near Cologne (Lukas et al., 2017). As thermal power plants use water as a cooling medium, thus increasing the probability that more thermally infl uenced freshwater systems (TIFs) exist across Germany, two new established populations of guppies were found in heated water garden near Reden (Lower Saxony) and thermal springs near Bad Sauglau (Baden-Württemberg) (Lukas et al., 2017). ...
... Until 2018 only one established population has been described for Germany, residing in the thermally altered Gillbach-Erft river system near Cologne (Lukas et al., 2017). As thermal power plants use water as a cooling medium, thus increasing the probability that more thermally infl uenced freshwater systems (TIFs) exist across Germany, two new established populations of guppies were found in heated water garden near Reden (Lower Saxony) and thermal springs near Bad Sauglau (Baden-Württemberg) (Lukas et al., 2017). Th e "wild" guppies' populations in Kyiv at the Bortnychi aeration station in warm drains are also of the same age as those registered in more northern countries (Kutsokon et al., 2012;Nekrasova et al., 2021Nekrasova et al., , 2022. ...
Article
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This paper presents the original data on studies of populations of guppies on the territory of Ukraine on the example of those of them surviving for many years in the drainage system of Kyiv. For 10 years, wild populations of guppies and their morphological features were studied in the warm water flows of the Bortnychi aeration station in Kyiv (2011–2020). During this period, the original “key” was developed to describe the morphology of their coloration peculiarities, which includes: total length, the number of pattern and coloration elements (4 types, 9 elements), pigmented area (light — orange, dark, pigmentation index), the shape and pigmentation of the tail (6 types) and its asymmetry At present, in the countries of Eastern Europe, the species is not adapted to any waters in the wild due to low winter temperatures, but these fish have become well established in sewage and other warm water bodies in urbanized areas (cities, towns, factories, etc.). We described the places where this invasive species had been found for many years, highlighting its key features. Thanks to GIS modelling, it was revealed that the existence of wild populations of guppies in Ukraine and Latvia is possible only in warm waters (currently mainly sewage systems of big cities) within anthropogenic territories. Such a key and study of relatively isolated populations of invasive species will provide a deeper understanding of micro-evolution of their morphological features (coloration) in isolation, help to track distribution of invasive species in a changing climate and provide material for comparison with possible similar invasions in areas heavily affected by military actions.
... One use of charismatic IAS as flagship species that can be beneficial is for monitoring programs and citizen-science initiatives, as they can help to motivate volunteers to become engaged in sampling or monitoring activities (Figure 2d; Lukas et al. 2017). ...
... (c) IAS charisma contributes to societal acceptance of IAS: Opuntia species in Spain have become iconic symbols in the landscape, and have been depicted on stamps and postmarks. (d) IAS charisma can contribute to volunteer involvement in citizen-science projects: guppies (Poecilia reticulata) were promoted as flagship species of a citizen-science project directed at monitoring alien fish species in thermally polluted waters in Germany(Lukas et al. 2017). ...
Article
Commonly used in the literature to refer to the “attractiveness”, “appeal”, or “beauty” of a species, charisma can be defined as a set of characteristics – and the perception thereof – that affect people’s attitudes and behaviors toward a species. It is a highly relevant concept for invasion science, with implications across all stages of the invasion process. However, the concept of invasive alien species (IAS) charisma has not yet been systematically investigated. We discuss this concept in detail, provide a set of recommendations for further research, and highlight management implications. We review how charisma affects the processes associated with biological invasions and IAS management, including species introductions and spread, media portrayals, public perceptions of species management, research attention, and active public involvement in research and management. Explicit consideration of IAS charisma is critical for understanding the factors that shape people’s attitudes toward particular species, planning management measures and strategies, and implementing a combination of education programs, awareness raising, and public involvement campaigns.
... Ao contrário do carisma das espécies ameaçadas que tem um efeito positivo nos esforços de gerenciamento, peixes ornamentais não-nativos carismáticos (Lukas et al., 2017;Ferraz et al., 2019), podem representar um obstáculo ao gerenciamento (Jarić et al., 2020). O carisma que peixes ornamentais não-nativos proporcionam ao ser humano pode reduzir o apoio do público leigo às tentativas de gerenciamento pelas autoridades ambientais (e.g., proibição/recolhimento de espécies populares) e assim, contribuir para impedir estas medidas (Jarić et al., 2020). ...
... Knowledge of the presence of self-sustaining tropical fish populations in temperate areas is thus not only representing research opportunities but is also mandatory for management actions to be taken (Latombe et al. 2017). In Germany, there are 3 recent sites known that harbor stable, self-sustaining populations of tropical fish species (Jourdan et al. 2014, Lukas et al. 2017a, Lukas et al. 2017b, Kempkes et al. 2018, Lukas et al. 2021). Here we report on a newly discovered population of feral guppies close to but independent of the well-reported Gillbach population in western Germany (Jourdan et al. 2014). ...
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Feral populations of tropical fish species in temperate climates like Central Europe are a rare but repeatedly observed phenomenon. Due to the influence of industrial or geothermal heated water, released tropical fish may be able to survive harsh winter conditions. Here we characterize a newly discovered thermally polluted river, with an established population of the guppy ( Poecilia reticulata ) co-occurring with native species. Through a mark-recapture approach, we estimated the population size of the guppies close to the warm water inflow to be around 2000 individuals during summer and we further provide descriptive demographics of this population which allow us to assume it is well established in that river. Further, we found some of the sampled specimen being parasitized by Camallanus roundworms, thus showing the guppies’ host potential for this genus of internal parasites. The popularity and widespread distribution of guppies as ornamental fish often leads to their intentional or unintentional release into the wild where they are often pioneer species in anthropogenically heavily modified habitats. Guppies threaten native species through niche competition and transmission of diseases. Accordingly, early awareness and knowledge on the status of non-native populations is crucial for effective management strategies.
... They manage to survive and settle at temperatures (Chung, 2001;Reeve et al., 2014) and salinities (Chervinski, 1984) that are distant from those of their native environment. For example, guppies can be found in unusual locations such as the Moscow sewer (Zhuikov, 1993) and the River Lee in Essex, England (Wheeler, 1998); or in Germany where temperature can drop to 12 • C (Lukas et al., 2017), in these places artificial heating effluents keep the water temperature high enough for them to survive. The guppy is also a very social species that performs most of its vital tasks in groups (Magurran, 1999(Magurran, , 2005 and one of the characteristics that is thought to have favored guppies' invasion in the Mexican Central Plateau (MCP) is their tendency to associate with native Goodeids, which translates into benefits such as locating food faster or acquiring information on food availability (Camacho-Cervantes et al., 2014a, 2015. ...
Article
Full-text available
Invasive species are one of the greatest threats to biodiversity. Behavioral traits are recognized as key to promote individual’s survival in changing conditions. For social species being part of a group is key to carry out vital activities. Heterospecific social environments could provide exotic species with the opportunity to join groups and gain the advantages of being part of a larger population. Short latency to exit a refuge is a behavioral response that could be linked to invasion success as it increases the chances of individuals to locate food sources and other resources in novel environments. The guppy (Poecilia reticulata ), a successful invader, has been found to take advantage of the presence of native species to reduce its refuge emergence latency and acquire information. The research was carried out in Mexico, we investigated the effect of heterospecific social contexts that include natives and other invasive viviparous fishes on guppies’ refuge emergence latency. We found that guppies’ emergence latency was shorter when accompanied by another guppy than when alone. Their latency was also shorter when with other invaders and when with native goodeids, but with one of the invaders ( Pseudoxiphophorus bimaculatus ) and with goodeids ( Skiffia bilineata ) latency reduction was not as high as when with conspecifics or with the invader Poecilia gracilis . Our experiment supports both the idea that already established invaders could provide benefits to new ones, and that native species also provide benefits but less than invaders. Increasing our knowledge about conspecific and heterospecific social interactions that could make an exotic species become invasive is key to assess the invasion risk of a community.
... Ao contrário do carisma das espécies ameaçadas que tem um efeito positivo nos esforços de gerenciamento, peixes ornamentais não-nativos carismáticos (Lukas et al., 2017;Ferraz et al., 2019), podem representar um obstáculo ao gerenciamento (Jarić et al., 2020). O carisma que peixes ornamentais não-nativos proporcionam ao ser humano pode reduzir o apoio do público leigo às tentativas de gerenciamento pelas autoridades ambientais (e.g., proibição/recolhimento de espécies populares) e assim, contribuir para impedir estas medidas (Jarić et al., 2020). ...
... Ao contrário do carisma das espécies ameaçadas que tem um efeito positivo nos esforços de gerenciamento, peixes ornamentais não-nativos carismáticos (Lukas et al., 2017;Ferraz et al., 2019), podem representar um obstáculo ao gerenciamento (Jarić et al., 2020). O carisma que peixes ornamentais não-nativos proporcionam ao ser humano pode reduzir o apoio do público leigo às tentativas de gerenciamento pelas autoridades ambientais (e.g., proibição/recolhimento de espécies populares) e assim, contribuir para impedir estas medidas (Jarić et al., 2020). ...
Article
Full-text available
Thermally abnormal waters represent safe sites for alien invasive plants requiring warmer conditions than provided by the ambient temperatures in the temperate zone. Therefore, such safe sites are frequently inhabited by tropical and sub-tropical plants. By performing a literature review we assessed that at least 55 alien aquatic plant taxa from 21 families were found in thermally abnormal waters in Europe. The majority of these taxa are submerged or rooted macrophytes. Six taxa are listed as quarantine pests according to EPPO. Among these, Pistia stratiotes is present in seven European countries, most of the records of this presence being recent. We studied P. stratiotes in a thermally abnormal stream where a persistent population was able to survive harsh winters. Models showed that the optimum temperature for P. stratiotes biomass was 28.8 +/- 3.5 °C. Here, we show that air temperatures had a higher influence on the photosynthetic efficiency of P. stratiotes, estimated by chlorophyll fluorescence measurements, than did water temperatures. Generally, growth, and consequently surface cover for free-floating plants, cannot be explained solely by thermally abnormal water temperatures. We conclude that even though the majority of thermophile alien plant occurrences resulted from deliberate introductions, thermally abnormal waters pose an invasion risk for further deliberate, accidental, or spontaneous spread, which might be more likely for free-floating macrophytes.
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An analysis and review of the ecological effects of power stations and other heated discharges on fresh and saline waters of the world. Includse effects of other temperature rises cause by hydro-electricity.. So far the only single author book on the topic. Little research has been done since the book was written so it is still very relevant though 25 years old.