Biology subjects

Vermiert, A.-M.

Publications and source records attributed to Vermiert, A.-M..

4 recordsLinked to original sources

bioRxiv2024

Fish predation induces drifting and emergence in an experimental stream mesocosm system

Predator-prey interactions are important drivers of adaptation in aquatic communities, shaping the behaviour of invertebrates with cascading effects on community dynamics. Behavioural responses, such as moving with the downstream current (drift) or altering the timing of emergence, can be initiated and reduces the risk of encountering predators. This study aimed to examine the effects of indirect and direct predation pressure on drift behaviour and emergence patterns of aquatic invertebrates. Using an experimental mesocosm setup (ExStream), we analysed how the number of drifting and emerging invertebrates changed with elevated levels of chemical cues from fish (indirect predation, Gasterosteus aculeatus and Cottus rhenanus) and subsequent additional direct predation by Cottus rhenanus over a 9-day period. Our findings show that most of the analysed invertebrate groups displayed noticeable responses to either indirect, direct, or both forms of predation. Furthermore, our study revealed a significant impact of predation on emergence patterns, reducing the number and the size of emergent invertebrates. Given the importance of drift and emergence in dispersion and in facilitating resource flows into terrestrial systems, our findings indicate a strong effect of predation on the communities.

ecology↗

bioRxiv2024

Multiple stressor effects on organic carbon degradation and microbial community composition in urban river sediments in a mesocosm experiment

Microorganisms in river sediments are the primarily responsible organisms for the turnover of dissolved organic carbon (DOC) in these systems and therefore are key players for river ecosystem functioning. Rivers are increasingly threatened by multiple stressors such as salinization and temperature rise, but little is known about how microbial DOC-degradation responds to these stressors and whether this function recovers after stressor release. Here, we investigated the direct and indirect effects of salinity and temperature increase and decrease on microbial communities and their ability to degrade DOC in river sediments using the outdoor experimental mesocosm system ExStream. Composition of sediment microbial communities was determined at the end of acclimatization, stressor, and recovery phase using 16S rRNA gene sequencing. At the same time points, DOC degradation rates were quantified in additional microcosm incubations based on isotopic changes of CO2 with the help of reverse stable isotope labelling. Our results showed that raising the salinity by 154.1 mg Cl- L-1 and temperature by 3.5 {degrees}C did not affect DOC degradation during the stressor phase but significantly increased DOC degradation in the recovery phase after stressors were released. Likewise, microbial community composition stayed constant during acclimation and stressor phase, but became more diverse in the recovery phase. The results indicate that microbial community composition and functioning were resistant towards both stressors, but responded to stressor release due to indirect effects of stressor increase and release on the riverine food web. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/602289v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@1074eccorg.highwire.dtl.DTLVardef@c634a1org.highwire.dtl.DTLVardef@a96182org.highwire.dtl.DTLVardef@40ae8e_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2024

Salinisation and warming disrupt predator-induced drift behaviour in aquatic predator-prey interactions

Predators act as a major selective force impacting biological communities in riverine ecosystems. Often predation risk is mediated by chemical cues upon which prey species display distinct morphological or behavioural defences. For stream invertebrates, predator-induced behaviours can be drifting and hiding. However, anthropogenic stressors increasingly impact freshwater ecosystems, with predicted consequences on the chemical information transfer, potentially affecting anti-predator behaviour. Despite this, knowledge and research on the extent to which these stressors may affect evolved predator-induced behaviour and subsequent ecosystems is scarce. Therefore, we conducted an outdoor mesocosm experiment (ExStream system) at a lowland stream in Germany, in which we investigated the effects of direct and indirect fish predation on invertebrate communities under different stressor conditions. As stressors, we tested elevated salinity (ambient vs + 136 mg/L NaCl), elevated temperature (ambient vs. + 3.4{degrees}C), and the combination of both. Our findings reveal distinct predator-induced drift behaviour, characterised by a greater number of drifting invertebrates and a concurrent reduction in overall invertebrate numbers in the communities. Increased salinity and temperature hampered the predator-induced drift behaviour. Our results support the possibility that stressors negatively impact the preys ability to perceive predators presence and respond appropriately. This disruption may alter predator-prey relationships, thereby affecting communities and potentially ecosystem functions. Highlights[vrecto] We hypothesised that anthropogenic stressors disrupt predator-induced behaviours in invertebrate prey species. [vrecto]Predator-induced drift behaviour was experimentally studied under ambient and elevated salinity and temperature conditions. [vrecto]Fish exposure elicited predator-induced drift behaviour, which decreased the number of invertebrate individuals of the communities. [vrecto]Elevated salt and elevated temperatures alone and in combination did not induce drift behaviour. [vrecto]We found that both stressors disrupted predator-induced drift behaviour, altering the anti-predator response of invertebrate prey. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=78 SRC="FIGDIR/small/601583v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@1eef03borg.highwire.dtl.DTLVardef@1ddda7corg.highwire.dtl.DTLVardef@332bdaorg.highwire.dtl.DTLVardef@1842dbb_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2024

Effects of temperature and salinity on microbial degradation of bacterial necromass in urban river sediments in outdoor mesocosm experiments

Microorganisms play a key role in the functioning of healthy river ecosystems because they consume carbon and nutrients from dead biomass derived from algae and other higher organisms, or "necromass", to feed it back into the food web. This so-called microbial loop is known to be substantial in aquatic systems, but it is so far unknown to which extent microorganisms perform self-recycling, i.e. recycling of necromass derived from microorganisms, and how this process is affected by multiple stressors such as increased temperature and salinity. In this study, we investigated microbial self-recycling in the sediment of the urban river Boye within a food-web context before, during, and after a period of increased temperature and salinity using the outdoor flow-through mesocosm system "ExStream". Rates of self-recycling were measured in additional microcosms with sediment and water from ExStream as an increase in 13CO2-concentration over time resulting from the microbial degradation of 13C-labelled microbial necromass, which was offered either in the form of intact but dead Escherichia coli cells, or lysed E. coli cells. The results showed that microbial self-recycling was highest in the first days of incubation suggesting that microbial necromass is an easily biodegradable carbon source. Increased salinity had no effect, but increased temperature or temperature and salinity strongly increased the rate of whole cell-necromass recycling compared to the unstressed control, while it had no effect on lysed cell-necromass recycling. After stressor removal, rates of self-recycling were not distinguishable from the unstressed control, showing the resilience of this community function. The compositions of the necromass-degrading communities were highly similar and little affected by stressor increase or release but changed during the course of the experiment. This indicated that both necromass types stimulated growth of the same organisms and that stressor levels were rather low for microorganisms and dominated by the effects of the seasonal variation in the Boye. The study suggests that microbial communities in urban rivers exposed to moderate levels of multiple anthropogenic stressors will be rather stressor-resistant and show fast recovery of community functioning.

microbiology↗