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\begin{document}

\title{Prey density drives diet shift of the invasive mysid shrimp, Limnomysis
benedeni}



\author[1]{Varsha Rani}%
\author[1]{Zsófia  Horváth}%
\author[2]{Jens Nejstgaard}%
\author[1]{Ádám  Fierpasz}%
\author[1]{Károly Pálffy}%
\author[1]{Csaba Vad}%
\affil[1]{Centre for Ecological Research}%
\affil[2]{Leibniz-Institute of Freshwater Ecology and Inland Fisheries in the Forschungsverbund Berlin eV Department 3 Experimental Limnology}%


\vspace{-1em}



  
  \date{May 19, 2024}


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\selectlanguage{english}
\begin{abstract}
Understanding the diet preferences and prey selection of invasive
species is crucial to better predict their impact on community structure
and ecosystem functioning. Limnomysis benedeni, a Ponto-Caspian invasive
mysid shrimp, is one of the most successful invaders in numerous
European river and lake ecosystems. While existing studies suggest
potentially strong trophic impact due to high predation pressure on
invaded plankton communities, little is known of its prey selectivity
between phyto- and zooplankton, under different prey concentrations.
Here, we therefore investigated the feeding selectivity of L. benedeni
on two commonly occurring prey organisms in freshwaters, the small
rotifer zooplankton Brachionus calyciflorus together with the
microphytoplankton Cryptomonas sp. present in increasing densities. Our
results demonstrated a clear shift in diet selection, with L. benedeni
switching from B. calyciflorus to Cryptomonas sp. already when the two
prey species were provided in equal biomasses. Different functional
responses were observed for each prey type, indicating somewhat
different foraging mechanisms for each prey type. These findings provide
experimental evidence on the feeding flexibility of invasive mysid
shrimps and potential implications for trophic interactions in invaded
ecosystems.%
\end{abstract}%



\sloppy


\textbf{Prey density drives diet shift of the invasive mysid
shrimp,\emph{Limnomysis benedeni}}

Varsha Rani\textsuperscript{1,2*}, Zs\selectlanguage{ngerman}ófia Horváth\textsuperscript{1},
Jens C. Nejstgaard\textsuperscript{3}, Ádám
Fierpasz\textsuperscript{1,2}, Károly Pálffy\textsuperscript{1} \& Csaba
F. Vad\textsuperscript{1}

\textsuperscript{1}Institute of Aquatic Ecology, Centre for Ecological
Research, Budapest, Hungary

\textsuperscript{2}Doctoral School of Biology, Institute of Biology,
ELTE, Eötvös Loránd University, Budapest, Hungary

\textsuperscript{3}Department of Plankton and Microbial Ecology, Leibniz
Institute of Freshwater Ecology and Inland Fisheries, Stechlin, Germany

*Corresponding author email: vysneha9@gmail.com

\textbf{Abstract}

Understanding the diet preferences and prey selection of invasive
species is crucial to better predict their impact on community structure
and ecosystem functioning. \emph{Limnomysis benedeni} , a Ponto-Caspian
invasive mysid shrimp, is one of the most successful invaders in
numerous European river and lake ecosystems. While existing studies
suggest potentially strong trophic impact due to high predation pressure
on invaded plankton communities, little is known of its prey selectivity
between phyto- and zooplankton, under different prey concentrations.
Here, we therefore investigated the feeding selectivity of \emph{L}
.\emph{benedeni} on two commonly occurring prey organisms in
freshwaters, the small rotifer zooplankton \emph{Brachionus
calyciflorus} together with the microphytoplankton \emph{Cryptomonas}
sp. present in increasing densities. Our results demonstrated a clear
shift in diet selection, with \emph{L. beneden} i switching from
\emph{B. calyciflorus} to\emph{Cryptomonas} sp. already when the two
prey species were provided in equal biomasses. Different functional
responses were observed for each prey type, indicating somewhat
different foraging mechanisms for each prey type. These findings provide
experimental evidence on the feeding flexibility of invasive mysid
shrimps and potential implications for trophic interactions in invaded
ecosystems.

Keywords: \emph{Limnomysis benedeni} , prey density-dependent foraging,
diet shift, invasive species, prey selectivity

\textbf{Introduction}

Diet shift and prey selectivity are among the most important aspects to
understand the impact of a predator on community structure and food web
functioning (Greene, 1983; Sailley et al., 2015). Prey selection is
influenced by multiple variables such as the predator's ontogenetic
stage, prey availability and size, and environmental factors such as
temperature (Divoky et al., 2021; Graeb et al., 2006; Greene, 1986).
According to the optimal foraging theory, the diet preference of an
animal is influenced by maximizing net energy gain and minimizing the
cost of obtaining the prey (Gooding \& Harley, 2015, Krebs et al.,
1977). At the same time, foraging behaviour can be adjusted in response
to changes in prey density (Murdoch \& Oaten, 1975). Usually, predators
choose habitat patches with high prey availability as it can increase
the chances of successful predation events (Ioannou et al., 2009;
Wellenreuther \& Connell, 2002). Besides quantity, diet preference can
be also influenced by the nutritional quality of their prey (Mayntz et
al., 2005; Schmidt et al., 2012). Along this trade-off, consuming
smaller and less nutritious prey may only be beneficial if it is present
in large quantities and/or if the higher quality prey is difficult to
capture (Langerhans et al., 2021). Omnivores can show higher foraging
flexibility and may switch between different diet items depending on
their availability. Their ability to exploit more than one trophic level
(Pimm \& Lawton, 1978) allow them to affect the dynamics of an ecosystem
through multiple pathways. Understanding the feeding behaviours of
omnivores, especially invasive species, can provide insight into their
functional roles, and be used to better predict population and ecosystem
dynamics.

The spread of multiple Ponto-Caspian invaders in numerous European
brackish and freshwater habitats and more recently in North American
Great Lakes received considerable attention in the past decades (Bij de
Vaate et al., 2002; Reid \& Orlova, 2002; Ricciardi \& MacIsaac, 2000).
The invasion was initially facilitated via unintentional means such as
migration through artificial canals, reservoirs acting as stepping
stones on rivers, and passive transport by ships (Ja\selectlanguage{polish}ż\selectlanguage{english}d\selectlanguage{polish}ż\selectlanguage{english}ewski, 1980). The
expansion was further supported by intentional introduction to improve
the fish food resources (Karpevich, 1975). Crustaceans, specifically,
amphipods, cladocerans, and mysids are among the most successful
Ponto-Caspian invaders (Lepp\selectlanguage{ngerman}äkoski et al., 2002; Leppäkoski \& Olenin,
2001; Ricciardi \& Rasmussen, 1998). They can influence native
communities by eliminating native species, decreasing functional
diversity, and ultimately altering the energy flow in ecosystems (Dick
\& Platvoet, 2000; Jazdzewski et al., 2004; Ketelaars et al., 1999;
Ojaveer et al., 2002).

Mysid shrimps, including species such as \emph{Hemimysis anomala}
,\emph{Limnomysis benedeni} , \emph{Katamysis warpachowskyi} ,
and\emph{Paramysis lacustris} , have become prominent Ponto-Caspian
invaders. These species have successfully established in Europe
(Audzijonyte et al., 2008, 2009; Borza et al., 2019; Wittmann, 2008),
while \emph{H. anomala} also invaded the North American Great Lakes
(Audzijonyte et al., 2008). Traits such as wide environmental tolerance,
omnivory, high annual number of generations, and related ability to get
established quickly in new habitats likely contributed to their invasive
success (Borza, 2014; Borza et al., 2017). Mysid shrimps are small,
generally omnivorous crustaceans found in both marine and freshwater
environments (Mauchline, 1980). They are grazers and predators of
microorganisms and zooplankton (Viherluoto et al., 2000), and a primary
food source for many fish species, birds, and other aquatic animals
(Arrhenius \& Hansson, 1993; Möllmann et al., 2004; Moran \& Fishelson,
1971). They are facultative filter feeders, using their specialized
thoracic limbs to filter plankton from the water column (Borza et al.,
2023; Wittmann et al., 2014). By feeding on organisms from multiple
trophic positions, and representing food for higher trophic levels, they
occupy key positions in their ecosystems (Rakauskas, 2019). Therefore,
their establishment and changes in abundance can have cascading effects
on other organisms in the ecosystem (Kiljunen et al., 2020). To study
the functional roles and impacts of invasive Ponto-Caspian mysid shrimps
in invaded ecosystems, understanding their feeding interactions with
native communities is therefore of high importance. Consequently, there
are numerous studies exploring the feeding habits of native mysid shrimp
species. For instance, omnivorous nature, role of predator and prey
size, ontogenetic diet shift and seasonal migration to different aquatic
zones have been explored (Arba\selectlanguage{polish}č\selectlanguage{english}iauskas et al., 2013; Fink et al., 2012;
Lesutien\selectlanguage{polish}ė \selectlanguage{english}et al., 2007; Penk \& Minchin, 2014). However, limited data is
available on the feeding ecology, specifically on the diet shift as a
function of different prey types and densities in invasive Ponto-Caspian
mysid shrimps.

\emph{Limnomysis benedeni} is one of the most widespread omnivorous
invasive mysids in continental Europe, including main river systems like
the Danube, Rhine, neighbouring lakes and even some isolated lakes
(Audzijonyte et al., 2009; Borza, 2014; Borza et al., 2011; Wittmann,
2007). \emph{L. benedeni} feeds by actively selecting and capturing
small-sized zooplankton, while also passively filtering smaller
particles such as algal cells (Fink \& Harrod, 2013). It can feed in
both the benthic and pelagic zones which can affect the nutrient cycling
in the littoral zone (Hanselmann et al., 2013). Earlier studies found
that \emph{L. benedeni} is a selective predator of zooplankton, and also
suggested that prey density-dependent diet switching between
phytoplankton and zooplankton may have a significant impact on plankton
community structure and dynamics (Fink et al., 2012). However, the
occurrence and direction of this diet shift were so far not quantified
and studied in detail.

We aim to, through this study, yield a better understanding of the
impact of phytoplankton and zooplankton density on the diet preference
of \emph{L. benedeni} . To do this, we compared the ingestion rates
of\emph{L. benedeni} on food mixtures containing a rotifer and a
microalga, across increasing algal biomass. We expected the mysids to
feed on the larger and highly nutritious zooplankters preferentially,
and only switch to phytoplankton when present at sufficiently high
biomass, which consequently reduces predation on rotifers.

\textbf{Materials and Methods}

\textbf{Study organisms and culturing conditions}

Two different types of prey, a microalga and a microzooplankton species,
were used in the experiment. \emph{Cryptomonas} sp. (strain 26.80 of the
SAG Culture Collection, originally isolated from Lake Windemere, UK) was
grown in WC medium (Guillard, 1975) enriched with Vitamin B12 (0.135 g
L\textsuperscript{-1} ) (recipe available at UTEX culture collection of
algae, Texas website). The rotifer \emph{Brachionus calyciflorus}
(obtained from AQ4Aquaristics, Braunschweig, Germany) were cultivated in
aerated and filtered (by a JBL Cristal Profi e702 external aquarium
filter) tap water and were fed by\emph{Cryptomonas} sp. Individuals of
the mysid shrimp \emph{Limnomysis benedeni} were collected from the
littoral zone of Lake Balaton, Hungary, in March 2022 by a hand net.
They were subsequently reared in lab aquaria at 20, under a 16:8 light:
dark photoperiod, and gentle aeration. The population was fed with
\emph{Cryptomonas} sp. at saturating concentrations (\textgreater{}1 mg
C L\textsuperscript{-1}) three times per week. Three-fourths of the
volume (\textasciitilde{}3-4 litres) of the water in the aquaria was
replaced with fresh filtered tap water twice a week.

\textbf{Grazing experiment}

In order to estimate the individual dry mass and carbon mass
of\emph{Cryptomonas} sp. and \emph{B. calyciflorus} , we measured the
axial dimensions of 20 randomly selected individuals of each species.
The measurements were obtained using an inverted microscope (Zeiss Axio
Vert.A1) after the individuals had been preserved with 10\% Lugol's
iodine solution. The biovolume of \emph{Cryptomonas} sp. was
approximated by using the formula for a prolate spheroid (Hillebrand et
al., 1999). Afterwards, the carbon content of the algae was estimated
using the formula \(Cc\ (in\ pg/cell)=0.109.\ V^{0.991}\) where \emph{V} is the biovolume in
\selectlanguage{greek}µ\selectlanguage{english}m\textsuperscript{3}(Weisse et al., 2001). The biovolume of the
rotifers was estimated using the formula\(Vr\ (in\ um^{3})=\ \frac{4\Pi.l.w^{2}}{3}\) where
\emph{l} is the length (in \selectlanguage{greek}µ\selectlanguage{english}m) and \emph{w} is the width of the rotifer
(in \selectlanguage{greek}µ\selectlanguage{english}m) (Bottrell et al., 1976). The dry weight of the rotifers was
calculated by assuming it to be 10\% of the wet weight, which was
calculated using the assumption that 1 mm\textsuperscript{3} equals 1 mg
(Pace \& Orcutt Jr., 1981). The dry weight was then converted to carbon
content using a conversion factor of 0.48 (Work et al., 2005).

Prior to the grazing experiment, \emph{L. benedeni} specimens were
pre-acclimatised to the experimental conditions (temperature and light)
for 48 hours. We kept them in 200 ml glass jars with 160 ml of filtered
tap water in two water baths at a constant temperature of 21, with
gentle aeration and a 16:8 light and dark photoperiod. Each jar
contained three individuals of \emph{L. benedeni} , fed by a mixture
of\emph{Cryptomonas} sp. and \emph{B. calyciflorus} at saturating
densities (both at 1 mg C L\textsuperscript{-1}) during the first 24
hours, followed by exposing them to the experimental conditions (see
below) in the next 24 hours. We applied a third water bath with the same
treatments containing individuals of \emph{L. benedeni} used as backup,
in order to replace any dead individuals in the experimental jars to
keep experimental biomass constant.

After this 48-hours pre-acclimatisation period, \emph{L.
benedeni}individuals were carefully rinsed in filtered tap water to
remove any debris or food attached to them. To quantify grazing rates of
\emph{L. benedeni} on both prey types, we run a grazing experiment
consisting of four treatment levels with different algae biomasses
(corresponding to 0.1, 0.5, 1, and 1.5 mg C L\textsuperscript{-1},
ranging between \textasciitilde{} 2,000k to 32,000k cells
ml\textsuperscript{-1}), while rotifer biomass was kept constant (1 mg C
L\textsuperscript{-1}, \textasciitilde{} 3 rotifers
ml\textsuperscript{-1}) across them. This setup was replicated four
times. We applied two types of controls at each treatment levels: one
containing only \emph{Cryptomonas} sp. to measure the growth rate of
algae (applied in two replicates) and the second containing both
\emph{Cryptomonas sp.} and \emph{B. calyciflorus}to measure the
consumption rate of algae by rotifers at different algae biomass
treatments (applied in three replicates). The experiment was run for 14
hours under constant dim light (4000 K LED, overall light intensity
approx. 3 * 10\textsuperscript{14} photons /cm\textsuperscript{2}/s).
Other experimental conditions (i.e., medium, volume, temperature,
aeration) were the same as described above for the pre-acclimatisation
period. The few dead individuals (three) of \emph{L. benedeni} were
replaced with individuals from the backup cultures. At the end of the
experiment, 1 ml and 10 ml samples were taken from each jar after
thorough mixing to estimate the biomasses of\emph{Cryptomonas} sp. and
\emph{B. calyciflorus} . The samples were fixed with Lugol's iodine
solution and counting was done using a stereomicroscope (Zeiss Stemi
305) using a Sedgwick rafter cell counter (S50, Graticules Optics, UK)
for \emph{Cryptomonas} sp. and a Petri dish with grids for \emph{B.
calyciflorus} .

The specific growth rates, h\textsuperscript{-1} (\emph{k} ) of both
prey types were calculated using formula suggested by Frost (1972):

\(\ k\ =\frac{ln(\ C2)\ -ln(\ C1)}{t2-t1\ }\ \)

The grazing coefficients, h\textsuperscript{-1} (\emph{g} ) of \emph{L.
benedeni} were calculated by

\(g=kprey-\frac{[ln(C*2)-\ ln(C*1)]}{t2-t1}\)

where \emph{C\textsubscript{1}} and \emph{C\textsubscript{2}} are
initial and final prey abundances (algal cells or rotifer individuals
mL\textsuperscript{-1} ) in the control jars at
times\emph{t\textsubscript{1}} and \emph{t\textsubscript{2}}
and\emph{C*\textsubscript{1}} and \emph{C*\textsubscript{2}} are initial
and final prey abundances (individuals mL\textsuperscript{-1}) in the
jars with predators at times \emph{t\textsubscript{1}}
and\emph{t\textsubscript{2}} . The mysid filtration and ingestion rates
of mysids were calculated using formulae by Marin et al. (1986) and
Nejstgaard et al. (2001).

\textbf{Data analysis}

We ran multiple models, including linear models, generalized linear
models, and generalized additive models to test how different algal
densities affect the ingestion rates of \emph{L. benedeni}
on\emph{Cryptomonas sp.} and \emph{B. calyciflorus} . Model selection
was then based on the Akaike Information Criterion (AIC), which selected
generalized additive models (GAM) to be the relative best-fit models
(Burnham \& Anderson, 2004). Ingestion rates on algae or rotifers were
used as response variables, plotted against treatment levels (i.e.,
biomass of\emph{Cryptomonas} sp.) respectively with k=4. We used the
`anova.gam' of the `mgcv' R package to test the significance of the
smooth term, treatment levels (Wood et al., 2016). Model assumptions
(normality, heterogeneity of variances across treatments) were visually
assessed via diagnostic plots (histogram of model residuals, residuals
versus fitted values, normal Q-Q plots) and no deviations were found.
All statistical tests were performed using R studio version 4.1.1 with
nlme, mgcv, and ggplot2 packages (Jos\selectlanguage{ngerman}é Pinheiro et al., 2022; R Core
Team, 2021; Wickham H, 2009; Wood et al., 2016). Besides, to quantify
the preference of \emph{L. benedeni} for different prey items with
respect to their relative biomass, we calculated Ivlev's index
(e\textsubscript{i}) for each prey type across treatments (Ivlev, 1961;
Jacobs, 1974). Here, a positive score indicates a preference for a
particular food item while a negative score may indicate inaccessibility
or avoidance of the food item (Jacobs, 1974). We also calculated and
plotted the relative biomasses (mean of three replicates with 95\%
confidence intervals) ingested from each prey against their relative
availability. Here any deviations from the 1:1 line indicate
preferential feeding and a change in preference can be used to reveal
prey switching (Cuthbert et al., 2018; Hughes \& Croy, 1993).

\textbf{Results}

Ingestion rates of \emph{L. benedeni} on \emph{Cryptomonas} sp.
increased in a slightly sigmoidal pattern with an increase in algae
biomass (Fig. 1A). Parallel to this, ingestion rates on \emph{B.
calyciflorus} decreased following a clear sigmoidal pattern, with an
abrupt decline occurring between the algae concentrations 0.5 and 1.0 mg
C L\textsuperscript{-1} (Fig. 1A). The models explained 99.8\% (adj.
R\textsuperscript{2} = 0.998) and 97.8\% (adj. R\textsuperscript{2} =
0.978) variance for algae and rotifer consumption as a function of algae
biomass. Consumption of \emph{Cryptomonas} sp. or \emph{B.
calyciflorus}by mysids were found to have a strong association with the
experimental treatment levels (edf= 2.977 (for algae),
p\textless{}0.001, edf= 2.948 (for rotifers), p \textless{}0.001). The
total carbon biomass ingestion rate (i.e., the sum of ingested
\emph{Cryptomonas} sp. and \emph{B. calyciflorus} carbon biomass) by
\emph{L. benedeni} increased with an increase in algae biomass. The
relationship was non-linear, with a steeper increase above 1 mg C
L\textsuperscript{-1} than below (Fig. 1B).

The Ivlev's electivity index suggested a treatment-specific (i.g. algae
biomass dependent) preference for \emph{Cryptomonas} sp. and \emph{B.
calyciflorous} (e\textsubscript{i}\textgreater{}0). At lower algae
biomass (0.1 mg C L\textsuperscript{-1} and 0.5 mg C
L\textsuperscript{-1}), index values showed a preference for \emph{B.
calyciflorus} (e\textsubscript{i} = 0.02 and 0.08) vs
\emph{Cryptomonas}sp. (e\textsubscript{i} = -0.09 to -0.6). However, at
higher algae biomass (1 mg C L\textsuperscript{-1} and 1.5 mg C
L\textsuperscript{-1}) the pattern shifted to the opposite, with higher
e\textsubscript{i} values for \emph{Cryptomonas} sp. (0.18 to 0.25) than
for \emph{B. calyciflorous} (ranging from -0.2 to -0.9).

The pattern of the relative contribution of \emph{Cryptomonas} sp.
and\emph{B. calyciflorus} biomass to the total ingested biomass also
confirmed treatment-specific preferential feeding. When rotifers were
present in higher biomass than algae (i.e., 90.1\% and 66.7\% of total
available biomass), their share in the ingested biomass was higher than
could be expected in the case of non-preferential feeding, while lower
in treatments with equal to or higher biomasses of \emph{Cryptomonas}sp.
Consequently, the pattern found for \emph{Cryptomonas} sp. was similar,
but mirrored (Fig. 2).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Figure 1: \emph{Limnomysis benedeni} (A) ingestion rates (\selectlanguage{greek}µ\selectlanguage{english}g C
h\textsuperscript{-1}) on \emph{Cryptomonas} sp. (dark green)
and\emph{B. calyciflorus} (orange) across treatments (i.e., increasing
initial biomass of \emph{Cryptomonas} sp.). Solid lines represent fitted
generalized additive models with coloured bands representing 95\%
confidence intervals. (B) Total ingested plankton biomass (sum of
ingested \emph{Cryptomonas} sp. and \emph{B. calyciflorus} carbon
biomasses, \selectlanguage{greek}µ\selectlanguage{english}g C L\textsuperscript{-1}) with the increasing original
biomass of \emph{Cryptomonas} sp.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

Figure 2: Relative contribution of prey carbon biomass to the total
ingested biomass by \emph{Limnomysis benedeni} plotted as a function of
the relative contribution of each prey to total available carbon
biomass. Prey types used are \emph{Cryptomonas} sp. (dark green)
and\emph{B. calyciflorus} (orange). Solid dots represent samples while
error bars indicate the 95\% confidence intervals. The dashed 1:1 line
represents where \emph{L. benedeni} would be consuming a prey
proportional to its availability, meaning random food uptake (neither
preference, nor avoidance).

\textbf{Discussion}

Our results clearly showed that the diet preference of \emph{L.
benedeni} depends on the relative (C) biomass concentration of prey
types, by shifting from microzooplankton to phytoplankton prey with
increasing phytoplankton prey biomass. The patterns of consumption rates
in response to relative prey biomass differed between the prey types
suggesting slightly different functional responses for the
microzooplankton and phytoplankton prey. While both resembled a
sigmoidal pattern (Fig. 1A), the ingestion rate on \emph{B.
calyciflorus} followed a type III functional response more clearly,
which usually indicates either prey switching or efforts to modify
foraging behaviour in response to the prey density (Holling, 1959;
Ki\selectlanguage{ngerman}ørboe et al., 2018; Thomas et al., 1996). In the case
of\emph{Cryptomonas} sp. after a slower increase at low densities, the
pattern was closer to linear and did not show saturation within the
tested biomass range during the experiment, overall resembling a type I
functional response (Holling, 1959), suggesting that consumption of
\emph{Cryptomonas} sp. is primarily a function of density.

The decreasing consumption rates on rotifers with increasing algae
concentration illustrated how the presence of alternative prey items in
sufficient densities can lead to decreased predation pressure on another
type of prey. If more than one alternative food source is present,
predators can select based on prey-specific encounter rates to optimize
foraging time and energy intake (Krebs et al., 1977). Specifically, the
relative attack rate is a function of relative density and the switching
can happen only if the likelihood of attacking the last eaten species is
higher than attacking other species (Oaten \& Murdoch, 1975). In our
case, the cost-to-benefit ratio changes in favour of algae at higher
algae densities. Indeed, we found that algae consumption increased in
comparison to rotifer consumption for biomass equal to or higher than 1
mgC L\textsuperscript{-1}. This is also supported by Ivlev's index
results which point towards the flexibility in the feeding behaviour of
\emph{L. benedeni} depending on algal density. The Ivlev's indices
indicate a preference for rotifers in the presence of low algae biomass
and avoidance of algae and vice versa with high algal biomass.

Predators typically select their diet based on size, nutritional
quality, and escape responses of the prey (Cotonnec et al., 2001; Frost,
1972; Viitasalo \& Rautio, 1998). They would try to increase their
fitness by acquiring prey with easier access and lower cost-to-benefit
ratio (MacArthur \& Pianka, 1966; Pyke et al., 1977; Stephens \& Krebs,
1986). Earlier studies suggest that \emph{L. benedeni} is not an
optically-oriented predator but selects its food based on size (Fink et
al., 2012). Here we provided \emph{L. benedeni} with two types of food
with very different sizes. Purely from a size-based perspective, feeding
on the smaller prey is only beneficial when available in sufficient
densities, which was indeed confirmed by our results, with \emph{L.
benedeni}showing a gradual shift to the smaller prey with its increasing
quantity.

Prey nutritional quality can also affect the development of consumers
and influence their dietary choices (Gulati \& Demott, 1997; Meunier et
al., 2016). For instance, algae generally have a higher
carbon-to-nutrient ratio than animal prey (Elser et al., 2000; Sterner
\& Hessen, 1994). In the case of \emph{Cryptomonas} SAG 26.80, a C:P
ratio of \textasciitilde{}150 and a C:N ratio of \textasciitilde{}22
were reported during the exponential growth phase (i.e. when nutrients
are not limiting growth; Vad et al., 2020). For \emph{B. calyciflorus} ,
C:P ratios are relatively constant around \textasciitilde{}92, while C:N
are \textasciitilde{}4 (Jensen \& Verschoor, 2004), which is very close
to the body stoichiometry of omnivorous crustaceans such as mysids
(C:P\textasciitilde{}90 and C:N \textasciitilde{}4) (Arba\selectlanguage{polish}č\selectlanguage{english}iauskas et
al., 2013). Therefore, based on a purely elemental stoichiometric point
of view (Laspoumaderes et al., 2010), rotifers would be the preferred
prey. The higher C to nutrient ratios of algae may explain the pattern
we found in the case of total ingested carbon biomass, which instead of
steadily increasing showed an accelerating increase at the highest
\emph{Cryptomonas} sp. biomass level. This may indicate that \emph{L.
benedeni} needs to increase overall food uptake when feeding on algae,
to obtain sufficient amounts of nutrients.

Other factors such as essential fatty acids (Ahlgren et al., 1990; Brett
\& M\selectlanguage{ngerman}üller-Navarra, 1997; Ramlee et al., 2021; Trommer et al., 2019), or
vitamins (Fridolfsson et al., 2018, 2019; Hessen, 1992) can also
influence food quality.\emph{Cryptomonas} sp. is considered to be a
high-quality algal food source based on the high cellular content of
essential fatty acids (Von Elert \& Stampfl, 2000; Weers \& Gulati,
1997). Consequently, the results may differ if the autotrophic food
quality is less cost-efficient for the predator than the heterotrophic
prey. For instance, had a `less favourable' algal food source, such as
green algae, been used, the preference for rotifers might have been more
pronounced. Nonetheless, a preference for green algae
(\emph{Chlamydomonas sp.} ) over zooplankton has been observed
previously at an algal biomass of 0.3 mg POC L\textsuperscript{-1} as
well (Fink et al., 2012).

Given that our study is based on a short-term experiment, there are some
aspects in which its results might differ from patterns arising in
natural communities. For instance, the container size in laboratory
studies is a factor that may influence predator behaviour (Bergström \&
Englund, 2004; Toonen \& Fu-Shiang, 1993). Therefore, a small-sized jar
could have increased the competition among mysids thus forcing them to
choose algae, a `costly prey', to consume maximum food to maintain their
energy budget. In addition, in this grazing experiment, we did not
include predators of mysids, though in natural ecosystems optimal
foraging strategy is based on a tradeoff between nutritional needs and
simultaneously minimising the risk of predation as described in the
unified foraging theories (e.g., Mangel \& Clark, 1986). Experiments
with another trophic level (e.g., small fish), carried out in larger
mesocosms, could therefore provide more specific predictions on these
tradeoffs in the future, including longer-term effects on ecosystem
stability.

Despite these limitations, our results provide important implications
for plankton community dynamics in natural ecosystems. Depending on the
relative biomasses of phyto- and zooplankton, mysid shrimps may act as
predators or competitors of zooplankton, being intraguild predators of
the latter. By always suppressing the more abundant planktonic prey,
they may reduce the amplitude of predator-prey oscillations, thereby
contributing to ecosystem stability. However, there are certainly other
possible scenarios as well, as illustrated by the effects of other
invasive omnivorous Ponto-Caspian mysids. For example, \emph{Hemimysis
anomala} and \emph{Paramysis lacustris} were both found to contribute to
the alteration of trophic pathways in their invaded habitats, due to
their strong predatory impact on zooplankton and benthic
macroinvertebrate communities (Evans et al., 2018; Ketelaars et al.,
1999; Rakauskas, 2019). For a better understanding of the potential
effects of omnivorous mysids on trophic cascades and food web stability,
studying their feeding mechanisms and diet selection is of high
importance. Field observations coupled with laboratory and mesocosms
studies could contribute to understanding the mechanisms underlying
community and ecosystem-level effects of these widespread (and still
spreading) invasive species.

\textbf{Acknowledgements}

This study was supported by the NKFIH-138215 project. We acknowledge the
valuable suggestions given by Pavel Kratina and Peter Borza.

\textbf{Author's contributions}

\begin{itemize}
\tightlist
\item
  Varsha Rani- Conceptualization (Equal), Methodology (Equal), Data
  curation (Lead), Formal analysis (Equal), Original draft of the paper
  (Lead), Revision of the paper (Equal)
\item
  Zsófia Horváth- Conceptualization (Supporting), Formal analysis
  (Equal), Revision of paper (Equal), Supervision (Supporting)
\item
  Jens C. Nejstgaard- Conceptualization (Equal), Methodology
  (Supporting), Revision of the paper (Equal)
\item
  Ádám Fierpasz- Methodology (Supporting), Revision of the paper
  (Supporting)
\item
  Károly Pálffy- Formal analysis (Equal), Revision of the paper (Equal)
\item
  Csaba F. Vad- Conceptualization (Equal), Methodology (Equal), Resource
  (Lead), Data curation (supporting), Formal analysis (Equal), Original
  draft of the paper (Lead), Revision of the paper (Equal), Supervision
  (Lead), Funding acquisition (Lead)
\end{itemize}

\textbf{Conflict of Interest Statement}

The authors declare no conflict of interest.

\section*{Data availability statement}

{\label{data-availability-statement}}

The data used to draw graphs in the study is available on Dryad
https://datadryad.org/stash/share/xURDH3d1npo2cOZhJ0oOr3EIF5Lxc2p1u2d0Zf1YE0w
.

\textbf{References}

Ahlgren, G., Lundstedt, L., Brett, M., \& Forsberg, C. (1990). Lipid
composition and food quality of some freshwater phytoplankton for
cladoceran zooplankters. \emph{Journal of Plankton Research},
\emph{12}(4), 809--818. https://doi.org/10.1093/plankt/12.4.809

Arba\selectlanguage{polish}č\selectlanguage{english}iauskas, K., Lesutien\selectlanguage{polish}ė, \selectlanguage{english}J., \& Gasi\selectlanguage{polish}ū\selectlanguage{english}nait\selectlanguage{polish}ė, \selectlanguage{english}Z. R. (2013). Feeding
strategies and elemental composition in Ponto-Caspian peracaridans from
contrasting environments: Can stoichiometric plasticity promote invasion
success?\emph{Freshwater Biology}, \emph{58}(5), 1052--1068.
https://doi.org/10.1111/fwb.12108

Arrhenius, F., \& Hansson, S. (1993). Food consumption of larval, young
and adult herring and sprat in the Baltic Sea. \emph{Marine Ecology
Progress Series},\emph{96}(2), 125--137.

Audzijonyte, A., Wittmann, K. J., Ovcarenko, I., \& V\selectlanguage{ngerman}äinölä, R. (2009).
Invasion phylogeography of the Ponto-Caspian crustacean Limnomysis
benedeni dispersing across Europe. \emph{Diversity and
Distributions},\emph{15}(2), 346--355.
https://doi.org/10.1111/j.1472-4642.2008.00541.x

Audzijonyte, A., Wittmann, K. J., \& Väinölä, R. (2008). Tracing recent
invasions of the Ponto-Caspian mysid shrimp Hemimysis anomala across
Europe and to North America with mitochondrial DNA. \emph{Diversity and
Distributions},\emph{14}(2), 179--186.
https://doi.org/10.1111/j.1472-4642.2007.00434.x

Bergström, U., \& Englund, G. (2004). Spatial scale, heterogeneity and
functional responses. \emph{Journal of Animal Ecology}, \emph{73}(3),
487--493. https://doi.org/10.1111/j.0021-8790.2004.00823.x

Bij de Vaate, A., Jazdzewski, K., Ketelaars, H. A. M., Gollasch, S., \&
Van der Velde, G. (2002). Geographical patterns in range extension of
Ponto-Caspian macroinvertebrate species in Europe. \emph{Canadian
Journal of Fisheries and Aquatic Sciences}, \emph{59}(7), 1159--1174.
https://doi.org/10.1139/f02-098

Borza, P. (2014). Life history of invasive Ponto-Caspian mysids
(Crustacea: Mysida): A comparative study. \emph{Limnologica}, \emph{44},
9--17. https://doi.org/10.1016/j.limno.2013.06.001

Borza, P., Czirok, A., Deák, C., Ficsór, M., Horvai, V., Horváth, Z.,
Juhász, P., Kovács, K., Szabó, T., \& Vad, C. F. (2011). Invasive mysids
(Crustacea: Malacostraca: Mysida) in Hungary: distributions and
dispersal mechanisms. \emph{North-Western Journal of Zoology},
\emph{7}(2).

Borza, P., Huber, T., Leitner, P., Remund, N., \& Graf, W. (2017).
Success factors and future prospects of Ponto--Caspian peracarid
(Crustacea: Malacostraca) invasions: Is `the worst over'?
\emph{Biological Invasions},\emph{19}(5), 1517--1532.
https://doi.org/10.1007/s10530-017-1375-7

Borza, P., Kovács, K., György, A., Török, J. K., \& Egri, Á. (2019). The
Ponto-Caspian mysid Paramysis lacustris (Czerniavsky, 1882) has
colonized the Middle Danube.\emph{Knowledge \& Management of Aquatic
Ecosystems}, \emph{420}, Article 420.
https://doi.org/10.1051/kmae/2018039

Borza, P., Rani, V., \& Vad, C. F. (2023). Niche differentiation among
facultative filter feeders: Insights from invasive Ponto-Caspian mysids.
\emph{Current Zoology}, zoad030. https://doi.org/10.1093/cz/zoad030

Bottrell, H. H., Duncan, A., Gliwicz, Z., Grygierek, E., Herzig, A.,
Hilbricht-Ilkowska, A., Kurasawa, H., Larsson, P., \& Weglenska, T.
(1976). Review of some problems in zooplankton production studies.
\emph{Norwegian Journal of Zoology}, \emph{21}, 477--483.

Brett, M., \& Müller-Navarra, D. (1997). The role of highly unsaturated
fatty acids in aquatic foodweb processes. \emph{Freshwater Biology},
\emph{38}(3), 483--499. https://doi.org/10.1046/j.1365-2427.1997.00220.x

Burnham, K. P., \& Anderson, D. R. (2004). Multimodel Inference:
Understanding AIC and BIC in Model Selection. \emph{Sociological Methods
\& Research},\emph{33}(2), 261--304.
https://doi.org/10.1177/0049124104268644

Cotonnec, G., Brunet, C., Sautour, B., \& Thoumelin, G. (2001).
Nutritive Value and Selection of Food Particles by Copepods During a
Spring Bloom of Phaeocystis sp. In the English Channel, as Determined by
Pigment and Fatty Acid Analyses. \emph{Journal of Plankton Research},
\emph{23}(7), 693--703. https://doi.org/10.1093/plankt/23.7.693

Cuthbert, R. N., Dickey, J. W. E., McMorrow, C., Laverty, C., \& Dick,
J. T. A. (2018). Resistance is futile: Lack of predator switching and a
preference for native prey predict the success of an invasive prey
species. \emph{Royal Society Open Science}, \emph{5}(8), 180339.
https://doi.org/10.1098/rsos.180339

Dick, J. T., \& Platvoet, D. (2000). Invading predatory crustacean
Dikerogammarus villosus eliminates both native and exotic species.
\emph{Proceedings. Biological Sciences}, \emph{267}(1447), 977--983.
https://doi.org/10.1098/rspb.2000.1099

Divoky, G. J., Brown, E., \& Elliott, K. H. (2021). Reduced seasonal sea
ice and increased sea surface temperature change prey and foraging
behaviour in an ice-obligate Arctic seabird, Mandt's black guillemot
(Cepphus grylle mandtii). \emph{Polar Biology}, \emph{44}(4), 701--715.
https://doi.org/10.1007/s00300-021-02826-3

Elser, J. J., Fagan, W. F., Denno, R. F., Dobberfuhl, D. R., Folarin,
A., Huberty, A., Interlandi, S., Kilham, S. S., McCauley, E., Schulz, K.
L., Siemann, E. H., \& Sterner, R. W. (2000). Nutritional constraints in
terrestrial and freshwater food webs. \emph{Nature}, \emph{408}(6812),
Article 6812. https://doi.org/10.1038/35046058

Evans, T. M., Naddafi, R., Weidel, B. C., Lantry, B. F., Walsh, M. G.,
Boscarino, B. T., Johannsson, O. E., \& Rudstam, L. G. (2018). Stomach
contents and stable isotopes analysis indicate Hemimysis anomala in Lake
Ontario are broadly omnivorous. \emph{Journal of Great Lakes Research},
\emph{44}(3), 467--475. https://doi.org/10.1016/j.jglr.2018.03.003

Fink, P., \& Harrod, C. (2013). Carbon and nitrogen stable isotopes
reveal the use of pelagic resources by the invasive Ponto-Caspian mysid
Limnomysis benedeni.\emph{Isotopes in Environmental and Health Studies},
\emph{49}(3), 312--317. https://doi.org/10.1080/10256016.2013.808197

Fink, P., Kottsieper, A., Heynen, M., \& Borcherding, J. (2012).
Selective zooplanktivory of an invasive Ponto-Caspian mysid and possible
consequences for the zooplankton community structure of invaded
habitats. \emph{Aquatic Sciences}, \emph{74}(1), 191--202.
https://doi.org/10.1007/s00027-011-0210-y

Fridolfsson, E., Bunse, C., Legrand, C., Lindehoff, E., Majaneva, S., \&
Hylander, S. (2019). Seasonal variation and species-specific
concentrations of the essential vitamin B1 (thiamin) in zooplankton and
seston. \emph{Marine Biology}, \emph{166}(6), 70.
https://doi.org/10.1007/s00227-019-3520-6

Fridolfsson, E., Lindehoff, E., Legrand, C., \& Hylander, S. (2018).
Thiamin (vitamin B1) content in phytoplankton and zooplankton in the
presence of filamentous cyanobacteria. \emph{Limnology and
Oceanography}, \emph{63}(6), 2423--2435.
https://doi.org/10.1002/lno.10949

Frost, B. W. (1972). Effects of Size and Concentration of Food Particles
on the Feeding Behavior of the Marine Planktonic Copepod Calanus
Pacificus1.\emph{Limnology and Oceanography}, \emph{17}(6), 805--815.
https://doi.org/10.4319/lo.1972.17.6.0805

Graeb, B. D. S., Mangan, M. T., Jolley, J. C., Wahl, D. H., \& Dettmers,
J. M. (2006). Ontogenetic Changes in Prey Preference and Foraging
Ability of Yellow Perch: Insights Based on Relative Energetic Return of
Prey.\emph{Transactions of the American Fisheries Society},
\emph{135}(6), 1493--1498. https://doi.org/10.1577/T05-063.1

Greene, C. H. (1983). Selective Predation in Freshwater Zooplankton
Communities.\emph{Internationale Revue Der Gesamten Hydrobiologie Und
Hydrographie},\emph{68}(3), 297--315.
https://doi.org/10.1002/iroh.19830680302

Greene, C. H. (1986). Patterns of Prey Selection: Implications of
Predator Foraging Tactics.\emph{The American Naturalist}, \emph{128}(6),
824--839.

Guillard, R. R. L. (1975). Culture of Phytoplankton for Feeding Marine
Invertebrates. In W. L. Smith \& M. H. Chanley (Eds.), \emph{Culture of
Marine Invertebrate Animals: Proceedings---1st Conference on Culture of
Marine Invertebrate Animals Greenport} (pp. 29--60). Springer US.
https://doi.org/10.1007/978-1-4615-8714-9\_3

Gulati, R., \& Demott, W. (1997). The role of food quality for
zooplankton: Remarks on the state-of-the-art, perspectives and
priorities. \emph{Freshwater Biology}, \emph{38}(3), 753--768.
https://doi.org/10.1046/j.1365-2427.1997.00275.x

Hanselmann, A. J., Hodapp, B., \& Rothhaupt, K.-O. (2013). Nutritional
ecology of the invasive freshwater mysid Limnomysis benedeni: Field data
and laboratory experiments on food choice and juvenile growth.
\emph{Hydrobiologia},\emph{705}(1), 75--86.
https://doi.org/10.1007/s10750-012-1382-8

Hessen, D. O. (1992). Nutrient Element Limitation of Zooplankton
Production. \emph{The American Naturalist}, \emph{140}(5), 799--814.

Hillebrand, H., Dürselen, C.-D., Kirschtel, D., Pollingher, U., \&
Zohary, T. (1999). Biovolume Calculation for Pelagic and Benthic
Microalgae. \emph{Journal of Phycology}, \emph{35}(2), 403--424.
https://doi.org/10.1046/j.1529-8817.1999.3520403.x

Holling, C. S. (1959). The Components of Predation as Revealed by a
Study of Small-Mammal Predation of the European Pine Sawfly. \emph{The
Canadian Entomologist},\emph{91}(5), 293--320.
https://doi.org/10.4039/Ent91293-5

Hughes, R. N., \& Croy, M. I. (1993). An Experimental Analysis of
Frequency-Dependent Predation (Switching) in the 15-Spined Stickleback,
Spinachia spinachia.\emph{Journal of Animal Ecology}, \emph{62}(2),
341--352. https://doi.org/10.2307/5365

Ioannou, C. C., Morrell, L. J., Ruxton, G. D., \& Krause, J. (2009). The
Effect of Prey Density on Predators: Conspicuousness and Attack Success
Are Sensitive to Spatial Scale. \emph{The American Naturalist},
\emph{173}(4), 499--506. https://doi.org/10.1086/597219

Ivlev, V. S. (1961).\emph{Experimental ecology of the feeding of
fishes}. Yale University Press, New Haven.

Jacobs, J. (1974). Quantitative measurement of food selection.
\emph{Oecologia},\emph{14}(4), 413--417.
https://doi.org/10.1007/BF00384581

Ja\selectlanguage{polish}ż\selectlanguage{english}d\selectlanguage{polish}ż\selectlanguage{english}ewski, K. (1980). Range Extensions of Some Gammaridean Species in
European Inland Waters Caused by Human Activity. \emph{Crustaceana.
Supplement}, \emph{6}, 84--107.

Jazdzewski, K., Konopacka, A., \& Grabowski, M. (2004). Recent drastic
changes in the gammarid fauna (Crustacea, Amphipoda) of the Vistula
River deltaic system in Poland caused by alien invaders. \emph{Diversity
and Distributions}, \emph{10}(2), 81--87.
https://doi.org/10.1111/j.1366-9516.2004.00062.x

Jensen, T. C., \& Verschoor, A. M. (2004). Effects of food quality on
life history of the rotifer Brachionus calyciflorus Pallas.
\emph{Freshwater Biology},\emph{49}(9), 1138--1151.
https://doi.org/10.1111/j.1365-2427.2004.01255.x

Jos\selectlanguage{ngerman}é Pinheiro, R Core Team, Johannes Ranke, Bert Van Willigen, Siem
Heisterkamp, Deepayan Sarkar, Saikat DebRoy, \& Douglas Bates. (2022).
\emph{nlme: Linear and Nonlinear Mixed Effects Models version 3.1-162
from CRAN}. https://rdrr.io/cran/nlme/

Karpevich, A. F. (1975). \emph{Theory and practice of aquatic organisms
acclimatization. 432}.

Ketelaars, H. A. M., Lambregts-van de Clundert, F. E., Carpentier, C.
J., Wagenvoort, A. J., \& Hoogenboezem, W. (1999). Ecological effects of
the mass occurrence of the Ponto--Caspian invader, Hemimysis anomala
G.O. Sars, 1907 (Crustacea: Mysidacea), in a freshwater storage
reservoir in the Netherlands, with notes on its autecology and new
records.\emph{Hydrobiologia}, \emph{394}(0), 233--248.
https://doi.org/10.1023/A:1003619631920

Kiljunen, M., Peltonen, H., Lehtiniemi, M., Uusitalo, L., Sinisalo, T.,
Norkko, J., Kunnasranta, M., Torniainen, J., Rissanen, A. J., \&
Karjalainen, J. (2020). Benthic-pelagic coupling and trophic
relationships in northern Baltic Sea food webs. \emph{Limnology and
Oceanography}, \emph{65}(8), 1706--1722.
https://doi.org/10.1002/lno.11413

Kiørboe, T., Saiz, E., Tiselius, P., \& Andersen, K. H. (2018). Adaptive
feeding behavior and functional responses in zooplankton.
\emph{Limnology and Oceanography},\emph{63}(1), 308--321.
https://doi.org/10.1002/lno.10632

Krebs, J. R., Erichsen, J. T., Webber, M. I., \& Charnov, E. L. (1977).
Optimal prey selection in the great tit ( Parus major). \emph{Animal
Behaviour},\emph{25}, 30--38.
https://doi.org/10.1016/0003-3472(77)90064-1

Langerhans, R. B., Goins, T. R., Stemp, K. M., Riesch, R., Araújo, M.
S., \& Layman, C. A. (2021). Consuming Costly Prey: Optimal Foraging and
the Role of Compensatory Growth. \emph{Frontiers in Ecology and
Evolution},\emph{8}.
https://www.frontiersin.org/articles/10.3389/fevo.2020.603387

Laspoumaderes, C., Modenutti, B., \& Balseiro, E. (2010). Herbivory
versus omnivory: Linking homeostasis and elemental imbalance in copepod
development.\emph{Journal of Plankton Research}, \emph{32}(11),
1573--1582. https://doi.org/10.1093/plankt/fbq077

Leppäkoski, E., Gollasch, S., Gruszka, P., Ojaveer, H., Olenin, S., \&
Panov, V. (2002). The Baltica sea of invaders. \emph{Canadian Journal of
Fisheries and Aquatic Sciences}, \emph{59}(7), 1175--1188.
https://doi.org/10.1139/f02-089

Leppäkoski, E., \& Olenin, S. (2001). The Meltdown of Biogeographical
Peculiarities of the Baltic Sea: The Interaction of Natural and Man-made
Processes.\emph{AMBIO: A Journal of the Human Environment},
\emph{30}(4), 202--209. https://doi.org/10.1579/0044-7447-30.4.202

Lesutien\selectlanguage{polish}ė, \selectlanguage{english}J., Gorokhova, E., Gasi\selectlanguage{polish}ū\selectlanguage{english}nait\selectlanguage{polish}ė, \selectlanguage{english}Z. R., \& Razinkovas, A.
(2007). Isotopic evidence for zooplankton as an important food source
for the mysid Paramysis lacustris in the Curonian Lagoon, the
South-Eastern Baltic Sea. \emph{Estuarine, Coastal and Shelf Science},
\emph{73}(1), 73--80. https://doi.org/10.1016/j.ecss.2006.12.010

MacArthur, R. H., \& Pianka, E. R. (1966). On Optimal Use of a Patchy
Environment. \emph{The American Naturalist}, \emph{100}(916), 603--609.
https://doi.org/10.1086/282454

Marin, V., Huntley, M. E., \& Frost, B. (1986). Measuring feeding rates
of pelagic herbivores: Analysis of experimental design and methods.
\emph{Marine Biology},\emph{93}(1), 49--58.
https://doi.org/10.1007/BF00428654

Mauchline, J. (1980).\emph{The biology of mysids and euphausiids}.
Academic Press.

Mayntz, D., Raubenheimer, D., Salomon, M., Toft, S., \& Simpson, S. J.
(2005). Nutrient-Specific Foraging in Invertebrate Predators.
\emph{Science},\emph{307}(5706), 111--113.
https://doi.org/10.1126/science.1105493

Meunier, C. L., Boersma, M., Wiltshire, K. H., \& Malzahn, A. M. (2016).
Zooplankton eat what they need: Copepod selective feeding and potential
consequences for marine systems. \emph{Oikos}, \emph{125}(1), 50--58.
https://doi.org/10.1111/oik.02072

M\selectlanguage{ngerman}öllmann, C., Kornilovs, G., Fetter, M., \& Köster, F. W. (2004).
Feeding ecology of central Baltic Sea herring and sprat. \emph{Journal
of Fish Biology},\emph{65}(6), 1563--1581.
https://doi.org/10.1111/j.0022-1112.2004.00566.x

Moran, SH., \& Fishelson, L. (1971). Predation of a sand-dwelling mysid
crustacean Gastrosaccus sanctus by plover birds (Charadriidae).
\emph{Marine Biology}, \emph{9}(1), 63--64.
https://doi.org/10.1007/BF00348818

Murdoch, W. W., \& Oaten, A. (1975). Predation and Population Stability.
In A. MacFadyen (Ed.), \emph{Advances in Ecological Research} (Vol. 9,
pp. 1--131). Academic Press.
https://doi.org/10.1016/S0065-2504(08)60288-3

Nejstgaard, J., Naustvoll, L., \& Sazhin, A. (2001). Correcting for
underestimation of microzooplankton grazing in bottle incubation
experiments with mesozooplankton. \emph{Marine Ecology Progress Series},
\emph{221}, 59--75. https://doi.org/10.3354/meps221059

Oaten, A., \& Murdoch, W. W. (1975). Switching, Functional Response, and
Stability in Predator-Prey Systems. \emph{The American Naturalist},
\emph{109}(967), 299--318. https://doi.org/10.1086/282999

Ojaveer, H., Leppäkoski, E., Olenin, S., \& Ricciardi, A. (2002).
Ecological Impact of Ponto-Caspian Invaders in the Baltic Sea, European
Inland Waters and the Great Lakes: An Inter-Ecosystem Comparison. In E.
Leppäkoski, S. Gollasch, \& S. Olenin (Eds.), \emph{Invasive Aquatic
Species of Europe. Distribution, Impacts and Management} (pp. 412--425).
Springer Netherlands. https://doi.org/10.1007/978-94-015-9956-6\_41

Pace, M. L., \& Orcutt Jr., J. D. (1981). The relative importance of
protozoans, rotifers, and crustaceans in a freshwater zooplankton
community1. \emph{Limnology and Oceanography}, \emph{26}(5), 822--830.
https://doi.org/10.4319/lo.1981.26.5.0822

Penk, M. R., \& Minchin, D. (2014). Seasonal migration of a glacial
relict mysid (Crustacea) into the littoral zone and its co-occurrence
with an introduced competitor in Lough Derg (Ireland).
\emph{Hydrobiologia},\emph{726}(1), 1--11.
https://doi.org/10.1007/s10750-013-1744-x

Pimm, S. L., \& Lawton, J. H. (1978). On feeding on more than one
trophic level.\emph{Nature}, \emph{275}(5680), Article 5680.
https://doi.org/10.1038/275542a0

Pyke, G. H., Pulliam, H. R., \& Charnov, E. L. (1977). Optimal Foraging:
A Selective Review of Theory and Tests. \emph{The Quarterly Review of
Biology}, \emph{52}(2), 137--154. https://doi.org/10.1086/409852

R Core Team. (2021).\emph{R: A language and environment for statistical
computing.}{[}Computer software{]}. R~ Foundation for Statistical
Computing,. http://www.rstudio.com/

Rakauskas, V. (2019). The impact of introduced Ponto-Caspian mysids
(Paramysis lacustris) on the trophic position of perch (Perca
fluviatilis) in European mesotrophic lakes. \emph{Knowledge \&
Management of Aquatic Ecosystems},\emph{420}, Article 420.
https://doi.org/10.1051/kmae/2019030

Ramlee, A., Chembaruthy, M., Gunaseelan, H., Yatim, S. R. M., Taufek,
H., \& Rasdi, N. W. (2021). Enhancement of nutritional value on
zooplankton by alteration of algal media composition: A review.
\emph{IOP Conference Series: Earth and Environmental Science},
\emph{869}(1), 012006. https://doi.org/10.1088/1755-1315/869/1/012006

Reid, D. F., \& Orlova, M. I. (2002). Geological and evolutionary
underpinnings for the success of Ponto-Caspian species invasions in the
Baltic Sea and North American Great Lakes. \emph{Canadian Journal of
Fisheries and Aquatic Sciences}, \emph{59}(7), 1144--1158.
https://doi.org/10.1139/f02-099

Ricciardi, A., \& MacIsaac, H. J. (2000). Recent mass invasion of the
North American Great Lakes by Ponto--Caspian species. \emph{Trends in
Ecology \& Evolution},\emph{15}(2), 62--65.
https://doi.org/10.1016/S0169-5347(99)01745-0

Ricciardi, A., \& Rasmussen, J. B. (1998). Predicting the identity and
impact of future biological invaders: A priority for aquatic resource
management.\emph{Canadian Journal of Fisheries and Aquatic Sciences},
\emph{55}(7), 1759--1765. https://doi.org/10.1139/f98-066

Sailley, S. F., Polimene, L., Mitra, A., Atkinson, A., \& Allen, J. I.
(2015). Impact of zooplankton food selectivity on plankton dynamics and
nutrient cycling.\emph{Journal of Plankton Research}, \emph{37}(3),
519--529. https://doi.org/10.1093/plankt/fbv020

Schmidt, J. M., Sebastian, P., Wilder, S. M., \& Rypstra, A. L. (2012).
The Nutritional Content of Prey Affects the Foraging of a Generalist
Arthropod Predator.\emph{PLOS ONE}, \emph{7}(11), e49223.
https://doi.org/10.1371/journal.pone.0049223

Stephens, D. W., \& Krebs, J. R. (1986). \emph{Foraging Theory}.
Princeton University Press.

Sterner, R. W., \& Hessen, D. O. (1994). Algal Nutrient Limitation and
the Nutrition of Aquatic Herbivores. \emph{Annual Review of Ecology and
Systematics},\emph{25}, 1--29.

Thomas, K., E, S., \& M, V. (1996). Prey switching behaviour in the
planktonic copepod Acartia tonsa. \emph{Marine Ecology Progress Series},
\emph{143}, 65--75. https://doi.org/10.3354/meps143065

Toonen, R. J., \& Fu-Shiang, C. (1993). Limitations of laboratory
assessments of coelenterate predation: Container effects on the prey
selection of the Limnomedusa, Proboscidactyla Flavicirrata (Brandt).
\emph{Journal of Experimental Marine Biology and Ecology},
\emph{167}(2), 215--235. https://doi.org/10.1016/0022-0981(93)90032-J

Trommer, G., Lorenz, P., Lentz, A., Fink, P., \& Stibor, H. (2019).
Nitrogen enrichment leads to changing fatty acid composition of
phytoplankton and negatively affects zooplankton in a natural lake
community. \emph{Scientific Reports}, \emph{9}(1), Article 1.
https://doi.org/10.1038/s41598-019-53250-x

Vad, C. F., Schneider, C., Luki\selectlanguage{polish}ć, \selectlanguage{english}D., Horv\selectlanguage{ngerman}áth, Z., Kainz, M. J., Stibor,
H., \& Ptacnik, R. (2020). Grazing resistance and poor food quality of a
widespread mixotroph impair zooplankton secondary production.
\emph{Oecologia},\emph{193}(2), 489--502.
https://doi.org/10.1007/s00442-020-04677-x

Viherluoto, M., Kuosa, H., Flinkman, J., \& Viitasalo, M. (2000). Food
utilisation of pelagic mysids, Mysis mixta and M. relicta, during their
growing season in the northern Baltic Sea. \emph{Marine Biology},
\emph{136}(3), 553--559. https://doi.org/10.1007/s002270050715

Viitasalo, M., \& Rautio, M. (1998). Zooplanktivory by Praunus flexuosus
(Crustacea: Mysidacea): functional responses and prey selection in
relation to prey escape responses. \emph{Marine Ecology Progress
Series}, \emph{174}, 77--87. https://doi.org/10.3354/meps174077

Von Elert, E., \& Stampfl, P. (2000). Food quality for Eudiaptomus
gracilis: The importance of particular highly unsaturated fatty
acids.\emph{Freshwater Biology}, \emph{45}(2), 189--200.
https://doi.org/10.1046/j.1365-2427.2000.00671.x

Weers, P., \& Gulati, R. (1997). Effect of the addition of
polyunsaturated fatty acids to the diet on the growth and fecundity
ofDaphnia galeata. \emph{Freshwater Biology}, \emph{38}(3), 721--729.
https://doi.org/10.1046/j.1365-2427.1997.00237.x

Weisse, T., Karstens, N., Meyer, V., Janke, L., Lettner, S., \&
Teichgräber, K. (2001). Niche separation in common prostome freshwater
ciliates: The effect of food and temperature. \emph{Aquatic Microbial
Ecology}, \emph{26}, 167--179. https://doi.org/10.3354/ame026167

Wellenreuther, M., \& Connell, S. D. (2002). Response of predators to
prey abundance: Separating the effects of prey density and patch size.
\emph{Journal of Experimental Marine Biology and Ecology},
\emph{273}(1), 61--71. https://doi.org/10.1016/S0022-0981(02)00145-4

Wickham H. (2009).\emph{ggplot2: Elegant Graphics for Data Analysis.}
(1st ed.). Springer New York, NY.
https://doi.org/10.1007/978-0-387-98141-3

Wittmann, K. J. (2007). Continued massive invasion of Mysidae in the
Rhine and Danube river systems, with first records of the order
Mysidacea (Crustacea: Malacostraca: Peracarida) for Switzerland.
\emph{Revue Suisse de Zoologie}, \emph{114}, 65--86.
https://doi.org/10.5962/bhl.part.80389

Wittmann, K. J. (2008). Weitere Ausbreitung der pontokaspischen
Schwebgarnele (Crustacea: Mysida: Mysidae) Katamysis warpachowskyi in
der oberen Donau: Erstnachweis für Deutschland. \emph{Lauterbornia},
\emph{63}, 83--86.

Wittmann, K. J., Ariani, A. P., \& Lagardère, J.-P. (2014). Orders
Lophogastrida Boas, 1883, Stygiomysida Tchindonova, 1981, and Mysida
Boas, 1883 (also known collectively as Mysidacea). In \emph{Treatise on
Zoology---Anatomy, Taxonomy, Biology. The Crustacea, Volume 4 Part B}
(pp. 189--396). Brill. https://doi.org/10.1163/9789004264939\_006

Wood, S. N., Pya, N., \& Säfken, B. (2016). Smoothing Parameter and
Model Selection for General Smooth Models. \emph{Journal of the American
Statistical Association}, \emph{111}(516), 1548--1563.
https://doi.org/10.1080/01621459.2016.1180986

Work, K., Havens, K., Sharfstein, B., \& East, T. (2005). How important
is bacterial carbon to planktonic grazers in a turbid, subtropical lake?
\emph{Journal of Plankton Research}, \emph{27}(4), 357--372.
https://doi.org/10.1093/plankt/fbi013

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