Search

The recent emergence of approaches based on functional traits allows a more comprehensive evaluation of the role of functions and interactions within communities. As phytoplankton size and shape are the major determinants of its edibility to herbivores, alteration or loss of some morpho-functional phytoplankton traits should affect zooplankton grazing, fitness and population dynamics. Here, we investigated the response of altered phytoplankton morpho-functional trait distribution to grazing by zooplankton with contrasting food size preferences and feeding behaviors. To test this, we performed feeding trials in laboratory microcosms with size-fractionated freshwater phytoplankton (3 size classes, >30 µm; 5–30 µm and <5 µm) and two different consumer types: the cladoceran Daphnia longispina, (generalist unselective filter feeder) and the calanoid copepod Eudiaptomus sp. (selective feeder). We observed no significant changes in traits and composition between the controls and grazed phytoplankton communities. However, community composition and structure varied widely between the small and large size fractions, demonstrating the key role of size in structuring natural phytoplankton communities. Our findings also highlight the necessity to combine taxonomy and trait-based morpho-functional approaches when studying ecological dynamics in phytoplankton-zooplankton interactions.

Biofilms in river sediments play a key role in P retention in aquatic ecosystems. Most studies in freshwater ecosystems focus mainly on the autotrophic component of biofilms but little is known about the role of heterotrophic components on P removal. It is known that DOC in some streams is of low bioavailability, hence, resulting in severe DOC and P co-limitation of heterotrophic biofilm growth which could then constrain P removal efficiency. How DOC limitation affects P removal efficiency in the benthic zone and how it modifies P thresholds (i.e. concentration from which the removal efficiency decreases) are still open questions. We performed an experiment in the MOBICOS (Streamside Mobile Mesocosms) in the Holtemme River (Germany) to study the role of labile DOC on P thresholds in P retention in the bed-sediment biofilm community. Our flume experiment followed a BACI design (before: no DOC addition; after: labile DOC addition at C:P molar ratios >100; control: basal P and DOC concentrations; impact: P concentrations ranging from 25 µg P/L to 420 µg P/L). Our results show that labile DOC increases the P removal efficiency of the system (i.e. P water mass balances in the flumes) and shifts P thresholds for P removal towards higher P concentrations meaning that at a given P concentration higher P removal efficiency is achieved if the system is supplied with labile DOC. Labile DOC activated the heterotrophic component in the flumes and benthic biofilms receiving labile DOC show higher bacterial density and higher P accumulation compared to the ones not receiving labile DOC. Our results demonstrate that the heterotrophic biofilm community plays a key role in in-stream phosphorus retention. As it relies on availability of labile DOC, the interaction of DOC and P dynamics need consideration in models for stream nutrient processing and retention.

A new cultivation system with the chlorophyte Monoraphidium contortum combined with a self-sustaining culture of the freshwater rotifer Brachionus calyciflorus was applied for Sander lucioperca (L.) larviculture. Survival, morphometrics, as well as fatty acid composition of pikeperch larvae were analyzed after a ten-day feeding period. By using the pseudo-green water technique with improved aeration and water movement at the surface, survival rates reached up to 94%, with a total larval length of 8.1 +/- 0.3 mm and a specific length growth rate of up to 4.1% day(-1) for S. lucioperca. The biochemical composition of B. calyciflorus and especially its contents in C18 PUFAs and suitable n-3/n-6 ratios met the nutritional requirements of pikeperch larvae. The high abundance of highly unsaturated fatty acids (HUFAs) in the diet appeared to be less important in the first feeding due to a possible retention of essential fatty acids, which originate from the yolk sac reserves, at adequate levels. Exponential growth of microalgae and zooplankton under the applied conditions was most effective when stocking M. contortum five days and B. calyciflorus three days before adding the fish larvae. Appropriate timing and sufficient live feed density allowed a successful integration of B. calyciflorus into pikeperch larviculture. We hypothesize that feeding pikeperch larvae with a self-sustaining Brachionus-culture under pseudo-green water conditions with minor disruptions during larviculture will improve survival and growth. This system is a first step towards pikeperch larviculture inside recirculated aquaculture systems (RAS) under continuous feed supply with live feed within the same aquaculture unit.

The nutritional quality of phytoplankton is essential for the fitness of herbivorous zooplankton and for efficient carbon fluxes in pelagic ecosystems. In freshwater lakes, cladocerans and calanoid copepods are the main pelagic herbivores in terms of both numbers and grazing impact. However, most studies focused on the easily cultivable cladocerans, while only few studies addressed the impact of the diet on freshwater calanoid copepods due to their more complex life cycle. We here supplied five different phytoplankton diets to the freshwater calanoid copepod Eudiaptomus sp. to investigate their dietary quality for the copepods' fitness traits over the copepod's entire life cycle. While all tested diets supported comparable reproductive success in adults, egg production, hatching success and survival rate differed markedly between diets. In the offspring generation, diet affected developmental and reproductive periods, size at first reproduction and clutch size. Eudiaptomus body fatty acid composition only partially reflected their diet, indicating that the copepods are able to selectively accumulate and interconvert certain essential fatty acids. This capability may allow them to cope with nutritional deficiencies and may thus be interpreted as an ecological adaptation strategy to the fluctuating environmental conditions and resource availabilities in freshwater plankton.

Communication among marine organisms are generally based on production, transmission, and interpretation of chemical cues. Volatile organic compounds (VOCs) can act as infochemicals, and ocean acidification can alter their production in the source organisms as well as the interpretation of the information they drive to target organisms. Two diatoms (Cocconeis scutellum var. parva and Diploneis sp.) and a macroalga (Ulva prolifera), all common epiphytes of Posidonia oceanica leaves, were isolated and cultured at two pH conditions (8.2 and 7.7). Their biomass was collected, and the VOCs produced upon wounding were extracted and analyzed using gas chromatography. Chemotactic reactions of invertebrates triggered by VOCs were tested using a static choice experimental arena and a flow-through flume system. Odor choice experiments were performed on several invertebrates associated with P. oceanica meadows to investigate the modification of behavioral responses due to the growth of algae in acidified environments. Complex patterns of behavioral responses were recorded after exposure to algal VOCs. This study demonstrated that a) ocean acidification alters the bouquet of VOCs released by diatoms and macroalgae and b) these compounds act as infochemicals and trigger peculiar behavioral responses in benthic invertebrates. In addition, behavioral responses are species-specific, dose-dependent, and are modified by environmental constraints. In fact, the static diffusion in choice arenas produced different responses as compared to flow-through flume systems. In conclusion, we demonstrate that in future marine environments higher CO2 concentrations (leading to a pH 7.7 by the end of this century) will modify the production of VOCs by micro- and macroalgae as well as the recognition of these infochemicals by marine invertebrates.

Modern aquaculture practices fundamentally need upgrades under two aspects: i. eco-sustainability and ii. high quality of productions. Crustaceans may be both subjects of aquaculture productions and dangerous parasites of fish, to be chemically controlled in production plants. Salmon aquaculture, under this point of view, exhibits several issues, because of the high impacts of parasitic copepods: seventeen species of Caligidae copepods represent possible threats for fish and the environment. The drugs used to fight salmon louse are quite toxic and inefficient. For this reason, periodic treatments are needed to assure sufficient growth and survival of salmons, but they produce damages to the benthic and planktonic communities neighbour to the cages, in particular to crustacean’s communities. In addition, various economically important decapod crustaceans may be damaged by the presence of pesticides, so producing also an economic loss to the fishery activities. In this chapter, the main issues related to the use of pesticides in salmon aquaculture practices are reported, and the results of a newer investigation on natural compounds derived from cyanobacteria are exposed, as a promising tool to obtain an eco-sustainable control of parasitic copepods, maximizing the health of salmons and avoiding damage to other economically or ecologically important crustaceans.

Volatiles are important ‘infochemicals’ that play a crucial role in structuring life on our planet, fulfilling diverse functions in natural and artificial systems. Algae contribute significant quantities to the global budget of volatiles, but the ecological roles of aquatic volatiles are not well understood. In this review, we discuss the current knowledge of volatile compounds from freshwater and marine microalgae and marine macroalgae, with a focus on their ecological roles. We highlight the multiple reported functions of biogenic volatiles, ranging from intraspecific communication for reproduction, intra-bloom signalling and antioxidant functions, to various interspecific signal exchanges that may allow herbivores to locate them and function in defence against competitors and predators. Beyond reviewing our current understanding, we specifically highlight major knowledge gaps and emerging questions for algal volatile research. These novel perspectives have the potential to improve our understanding of aquatic ecosystems and thus need to be addressed in future research. Filling these gaps and addressing these questions will facilitate humanity's efforts to exploit aquatic volatiles in various applications.

Eutrophierung, d. h. die erhöhte Produktion von meist einzelligen Algen, ist nach wie vor ein ernstes Problem in vielen Gewässern, welches signifikant zu dem Verfehlen von Qualitätszielen, z. B. der EU-Wasserrahmenrichtlinie, beiträgt. Während Eutrophierung in Seen vor allem durch planktische Algen getrieben wird, sind es in kleinen und mittelgroßen Fließgewässern insbesondere die benthischen Algen (auch „Periphyton“ oder „autotrophe Biofilme“ genannt), welche die Eutrophierung treiben. Als Hauptursache gilt die erhöhte Konzentration von Nährstoffen.Jedoch können auch andere Faktoren, z. B. die Beweidung durch wirbellose Tiere, maßgeblich die Eutrophierung steuern und so die negativen Effekte der Nährstoffbelastung für das Ökosystem zum Teil kompensieren – man spricht von „Top-down-Kontrolle“. Während diese Möglichkeit der Wissenschaft länger bekannt ist, stellt sich für die wasserwirtschaftliche Praxis die entscheidende Frage, wie die Top-down Kontrolle gesteuert wird und so potenziell im Gewässermanagement genutzt werden könnte. Unter welchen Bedingungen versagt diese Kontrolle und was kann getan werden, um diese natürlichen Gegenspieler der Eutrophierung zu fördern? Vor diesem Hintergrund war das Ziel dieses Vorhabens, die Rolle der Nährstoffe für die Steuerung der Top-down-Kontrolle zu analysieren. Dabei konnte in Experimenten gezeigt werden, dass Nährstoffe nicht nur zu einer erhöhten Algenbiomasse (und damit zu mehr Nahrung für die Weidegänger) führen, sondern auch die Qualität der Nahrung verändern. Kurzzeitig kommt es zu einer Erhöhung der Nahrungsqualität durch Eutrophierung (indem das Nährstoff- zu Kohlenstoffverhältnis der Algen steigt), während längerfristig eine sinkende Qualität festgestellt wurde (da es zu einer Verschiebung der Algengemeinschaft hin zu weniger geeigneten Blaualgen kommt).

Chemical communication via infochemicals plays a pivotal role in ecological interactions, allowing organisms to sense their environment, locate predators, food, habitats, or mates. A growing number of studies suggest that climate change-associated stressors can modify these chemically mediated interactions, causing info-disruption that scales up to the ecosystem level. However, our understanding of the underlying mechanisms is scarce. Evidenced by a range of examples, we illustrate in this opinion piece that climate change affects different realms in similar patterns, from molecular to ecosystem-wide levels. We assess the importance of different stressors for terrestrial, freshwater, and marine ecosystems and propose a systematic approach to address highlighted knowledge gaps and cross-disciplinary research avenues.

A new cultivation system with the chlorophyte Monoraphidium contortum combined with a self-sustaining culture of the freshwater rotifer Brachionus calyciflorus was applied for Sander lucioperca (L.) larviculture. Survival, morphometrics, as well as fatty acid composition of pikeperch larvae were analyzed after a ten-day feeding period. By using the pseudo-green water technique with improved aeration and water movement at the surface, survival rates reached up to 94%, with a total larval length of 8.1 ± 0.3 mm and a specific length growth rate of up to 4.1% day−1 for S. lucioperca. The biochemical composition of B. calyciflorus and especially its contents in C18 PUFAs and suitable n-3/n-6 ratios met the nutritional requirements of pikeperch larvae. The high abundance of highly unsaturated fatty acids (HUFAs) in the diet appeared to be less important in the first feeding due to a possible retention of essential fatty acids, which originate from the yolk sac reserves, at adequate levels. Exponential growth of microalgae and zooplankton under the applied conditions was most effective when stocking M. contortum five days and B. calyciflorus three days before adding the fish larvae. Appropriate timing and sufficient live feed density allowed a successful integration of B. calyciflorus into pikeperch larviculture. We hypothesize that feeding pikeperch larvae with a self-sustaining Brachionus-culture under pseudo-green water conditions with minor disruptions during larviculture will improve survival and growth. This system is a first step towards pikeperch larviculture inside recirculated aquaculture systems (RAS) under continuous feed supply with live feed within the same aquaculture unit.

Communication among marine organisms are generally based on production, transmission, and interpretation of chemical cues. Volatile organic compounds (VOCs) can act as infochemicals, and ocean acidification can alter their production in the source organisms as well as the interpretation of the information they drive to target organisms. Two diatoms (Cocconeis scutellum var. parva and Diploneis sp.) and a macroalga (Ulva prolifera), all common epiphytes of Posidonia oceanica leaves, were isolated and cultured at two pH conditions (8.2 and 7.7). Their biomass was collected, and the VOCs produced upon wounding were extracted and analyzed using gas chromatography. Chemotactic reactions of invertebrates triggered by VOCs were tested using a static choice experimental arena and a flow-through flume system. Odor choice experiments were performed on several invertebrates associated with P. oceanica meadows to investigate the modification of behavioral responses due to the growth of algae in acidified environments. Complex patterns of behavioral responses were recorded after exposure to algal VOCs. This study demonstrated that a) ocean acidification alters the bouquet of VOCs released by diatoms and macroalgae and b) these compounds act as infochemicals and trigger peculiar behavioral responses in benthic invertebrates. In addition, behavioral responses are species-specific, dose-dependent, and are modified by environmental constraints. In fact, the static diffusion in choice arenas produced different responses as compared to flow-through flume systems. In conclusion, we demonstrate that in future marine environments higher CO2 concentrations (leading to a pH 7.7 by the end of this century) will modify the production of VOCs by micro- and macroalgae as well as the recognition of these infochemicals by marine invertebrates.