Experimental comparison of periphyton removal by chironomid larvae and Daphnia magna

Daphnia magna is a large pelagic cladoceran known to feed on phytoplankton. Our laboratory experiments demonstrate that it can also remove periphyton at rates similar to or higher than chironomid larvae, which are typical periphyton grazers. After a 2-week laboratory exposure at 20 °C, periphyton biomass (dominated by green algae) was significantly reduced by D. magna (38%). Similar periphyton removal was observed for a naturally associated invertebrate community dominated by chironomid larvae (33%) and chironomid larvae alone (37-62%). Periphyton removal rates of all tested grazers were comparable at the community level (360-540 mg dry weight [DW] m-2 d-1). The larger chironomid larvae had higher individual periphyton removal rates (0.12-0.17 mg DW ind.-1 d-1) than D. magna (0.03 mg DW ind.-1 d-1). Body mass-specific periphyton removal rates of D. magna (0.96 mg DW mg grazer DW-1 d-1) were 55% higher than those of chironomids. We suggest that the impact of D. magna on periphyton may be significant when phytoplankton concentrations are low, such as during the clear-water phase or in macrophyte beds where daphnids seek refuge from fish predation.&nbsp

Effects of water temperature on summer periphyton biomass in shallow lakes: a pan-European mesocosm experiment

Periphyton communities play an important role in shallow lakes and are controlled by direct forces such as temperature, light, nutrients, and invertebrate grazing, but also indirectly by planktivorous fish predation. We performed a pan-European lake mesocosm experiment on periphyton colonization covering five countries along a north/south geographical/temperature gradient (Estonia, Germany, Czech Republic, Turkey, and Greece). Periphyton biomass on artificial polypropylene strips exposed at 50 cm water depth at low and high nutrient regimes (with mean total phosphorus concentration of 20 and 65 µg L−1, respectively) was compared during mid-summer. No significant effect of nutrient loading on periphyton biomass was observed as nutrient concentrations in the mesocosms were generally above limiting values. Water temperature significantly enhanced summer periphyton biomass development. Additionally, direct and indirect top-down control of snails and fish emerged as a significant factor in periphyton biomass control

Two New Fish Records from the Mediterranean Sea, of the Libyan coast: The undulate ray Raja undulata (Lac´ep`ede,1802) and the Atlantic wreckfish, Polyprion americanus (Bloch and Schneider,1801)

  The discovery of new alien species in Libyan waters, whether introduced by Lessepsian migration from the Red Sea or the Atlantic Ocean, has recently received much attention. This shows that marine life is still thriving in Libyan waters. Raja undulata (SL: 47cm, TL: 51 cm), weighing 18 kg, was caught from Derna coast by a bottom trawl haul on 20th July 2022, at a depth of 100 m. On the other hand, a single Polyprion americanus specimen (SL: 79 cm, TL: 97 cm) weighing 16.447 kg was caught by longline on the coast of Tripoli on 19th June 2022, at a depth of 500 m. The present study aims to document the first record of Raja undulate and the second record of Atlantic wreckfish, Polyprion americanus, from Libyan waters. This observation is detailed in this note

Effects of trophic status, water level, and temperature on shallow lake metabolism and metabolic balance: A standardized pan‐European mesocosm experiment

Important drivers of gross primary production (GPP) and ecosystem respiration (ER) in lakes are temperature, nutrients, and light availability, which are predicted to be affected by climate change. Little is known about how these three factors jointly influence shallow lakes metabolism and metabolic status as net heterotrophic or autotrophic. We conducted a pan‐European standardized mesocosm experiment covering a temperature gradient from Sweden to Greece to test the differential temperature sensitivity of GPP and ER at two nutrient levels (mesotrophic or eutrophic) crossed with two water levels (1 m and 2 m) to simulate different light regimes. The findings from our experiment were compared with predictions made according the metabolic theory of ecology (MTE). GPP and ER were significantly higher in eutrophic mesocosms than in mesotrophic ones, and in shallow mesocosms compared to deep ones, while nutrient status and depth did not interact. The estimated temperature gains for ER of ~ 0.62 eV were comparable with those predicted by MTE. Temperature sensitivity for GPP was slightly higher than expected ~ 0.54 eV, but when corrected for daylight length, it was more consistent with predictions from MTE ~ 0.31 eV. The threshold temperature for the switch from autotrophy to heterotrophy was lower under mesotrophic (~ 11°C) than eutrophic conditions (~ 20°C). Therefore, despite a lack of significant temperature‐treatment interactions in driving metabolism, the mesocosm's nutrient level proved to be crucial for how much warming a system can tolerate before it switches from net autotrophy to net heterotrophy

Impact of nutrients and water level changes on submerged macrophytes along a temperature gradient: A pan-European mesocosm experiment

Submerged macrophytes are of key importance for the structure and functioning of shallow lakes and can be decisive for maintaining them in a clear water state. The ongoing climate change affects the macrophytes through changes in temperature and precipitation, causing variations in nutrient load, water level and light availability. To investigate how these factors jointly determine macrophyte dominance and growth, we conducted a highly standardized pan-European experiment involving the installation of mesocosms in lakes. The experimental design consisted of mesotrophic and eutrophic nutrient conditions at 1 m (shallow) and 2 m (deep) depth along a latitudinal temperature gradient with average water temperatures ranging from 14.9 to 23.9 degrees C (Sweden to Greece) and a natural drop in water levels in the warmest countries (Greece and Turkey). We determined percent plant volume inhabited (PVI) of submerged macrophytes on a monthly basis for 5 months and dry weight at the end of the experiment. Over the temperature gradient, PVI was highest in the shallow mesotrophic mesocosms followed by intermediate levels in the shallow eutrophic and deep mesotrophic mesocosms, and lowest levels in the deep eutrophic mesocosms. We identified three pathways along which water temperature likely affected PVI, exhibiting (a) a direct positive effect if light was not limiting; (b) an indirect positive effect due to an evaporation-driven water level reduction, causing a nonlinear increase in mean available light; and (c) an indirect negative effect through algal growth and, thus, high light attenuation under eutrophic conditions. We conclude that high temperatures combined with a temperature-mediated water level decrease can counterbalance the negative effects of eutrophic conditions on macrophytes by enhancing the light availability. While a water level reduction can promote macrophyte dominance, an extreme reduction will likely decrease macrophyte biomass and, consequently, their capacity to function as a carbon store and food source

Auswirkungen von Prädatoren (Top-down) und Ressourcen (Bottom-up) gesteuerten Prozessen auf die Nahrungskette in Flachseen, unter spezieller Berücksichtigung des Periphytons

List of Tables…………………………………………………………………. 6 List of Figures………………………………………………………………… 8 Summary……………………………………………………………………… 11 Zusammenfassung…………………………………………………………….. 13 Thesis Outline………………………………………………………………… 15 Chapter I. General Introduction I.I. Shallow lake periphyton……………………………………………………………... 17 I.II. Factors effecting periphyton growth………………………………………………… 18 I.II.I. Bottom-up forces (nutrient dynamics)……………………………………….… 18 I.II.II. Top-down forces (grazing vs. fish)……………………………………………. 20 I.II.III. Effect of temperature on periphyton biomass………………………………… 22 I.III. Threshold-driven shifts in two copepod species……………………………………. 23 I.IV. Aims of the thesis…………………………………………………………………… 24 Chapter II. Climate change effects on shallow lakes: Design and preliminary results of a cross-European climate gradient mesocosm experiment……………………….. 26 Chapter III. The effect of top-down and bottom-up control factors on periphyton growth in shallow lakes: a continental-scale mesocosm experiment………………………….. 50 Chapter IV. Experimental comparison of periphyton removal by chironomid larvae and Daphnia magna……………………………………………………………………. 67 Chapter V. Threshold-driven shifts in two copepod species: Testing ecological theory with observational data…………………………………………………………………. 81 Chapter VI. General Discussion…………………………………………………………. 105 VI.I. Effects of water temperature on periphyton biomass…………………………. 106 VI.II. Effects of nutrients on periphyton biomass………………………………….. 107 VI.III. Effects of direct and indirect top-down control on periphyton biomass……. 107 VI.IV. Interactions between periphyton and its limiting factors…………………… 108 VI.V. Remarks on applied methodology…………………………………………… 109 VI.VI. Conclusions…………………………………………………………………. 111 References…………………………………………………………………….. 113 Statement of academic integrity………………………………………………. 122 Acknowledgements…………………………………………………………… 123 Arabic summary (الملخص العربى)………………………………………………. 124 Curriculum vitae……………………………………………………………… 126The main objective of the current thesis was to determine the ecological relevance of top-down (predator driven) and bottom-up forces (nutrient driven) processes in shallow lake food webs with specific interest on periphyton ecology. We used three different methodological approaches: small scale laboratory microcosm experiments, lake based mesocosms experiments, and analysis of long-term field records. In the lake based mesocosm experiments we manipulated nutrient dynamics by establishing two nutrient scenarios and temperature by performing the same periphyton experiments across a temperature gradient in 5 European countries (Estonia, Germany, Czech Republic, Turkey, and Greece). In laboratory microcosms experiments we investigated the role of invertebrate grazers for periphyton removal. Finally, in long-term records we analyzed underlying mechanisms driving the abrupt changes of two coexisting copepod species in the context of regime shift- and intraguild predation theory. Periphyton communities play important roles in shallow lakes and are controlled by direct forces, such as temperature, light, nutrients, invertebrate predation and indirectly by cascading fish predation effects. We manipulated nutrient dynamics by establishing two nutrient scenarios; (clear, 25µg TPL-1) and (turbid, 200µg TP L-1) and used the temperature gradient across the 5 European countries. All mesocosms contained a layer of sediment; (10 cm thickness); macrophytes (Myriophyllum spicatum), planktivorous fish, and phyto- and zooplankton species assembles, which were collected from 5 different lakes in each country. Periphyton biomass was colonized 4 weeks on artificial strips exposed at 50 cm mesocosm water depth during mid-summer (July and August 2011). The results indicated that water temperature plays an important positive role for the summer periphyton biomass development. The slope of the regression between water temperature and periphyton biomass suggests that for every degree increase in water temperature, summer periphyton biomass was stimulated positively. Even though, our nutrient loading (TP) was implemented in low and high nutrient treatments (20 µg TP L-1, 65 µg TP L-1, respectively), there was no significant nutrient effect on periphyton biomass. We found indirect positive top-down effects by fish on periphyton biomass (chl a) due to the control of periphyton scraping invertebrates grazers. The slope of the regression between fish biomass and periphyton chl a adjusted to water temperature suggests the top-down control of invertebrate grazers by fish. In laboratory experiments, we compared the effect of D. magna on periphyton removal with a naturally associated invertebrate community dominated by chironomid larvae and chironomid larvae only. The impact of pelagic Daphnia magna, which migrates into the littoral zone to seek refuge from fish predation, on periphyton removal is still unknown. Periphyton biomass was significantly reduced by D. magna, the natural grazer community, as well as by chironomids during a two-week laboratory experiment performed at 20°C. In accordance with allometric theory, the larger chironomid larvae had higher individual periphyton removal rates than D. magna, whereas body mass specific periphyton removal rates of D. magna was 58%; higher than that of chironomids. We concluded that the role of large planktonic cladoceran such as D. magna for periphyton removal can be significant and deserves further attention. We studied the long-term dynamics (30 years) of two cyclopid copepod species (Cyclops vicinus and Cyclops kolensis) along a declining gradient in trophic state in a shallow, eutrophic lake. We showed that while under high nutrient conditions and thus high algal biomass the larger C. vicinus is the superior competitor, it looses its advantages under medium productivity levels, because it is a less effective exploiter of algal resources. We further predicted that the release of the smaller C. kolensis from the competition and predation pressure by C. vicinus enabled its sudden and conspicuous dominance of the winter cyclopoid community. We further accessed the threshold density of the competitor necessary for this shift to happen. Underlying mechanisms of that non-linear threshold driven response of both copepod species were tested by using two scenarios of regime shift theory in the context of intraguild predation theory. Not before the larger competitor, which exhibit higher requirements for algal resources, declined below a critical threshold in abundance the coexisting smaller copepod species, exhibiting lower needs for algal prey, was able to thrive in the low algal food niche. Finally, I provide some critical remarks on the advantages and drawbacks of the different methods applied in my thesis which ranged from small to large scale experiments to decadal long-term field studies. Small scale laboratory experiments have the advantage of full control of the tested driving forces, by lacking the inherent complexity of interactions within ecosystems. Some of that complexity was met in our enclosure experiments by including sediment, macrophytes and fish in our tanks. Long-term ecological research has the advantage that the outcome of any seen dynamic results from the complex interplay of external and internal driving forces. The challenge here is, however, to disentangle the multifarious overlapping driving forces.Das Ziel dieser Arbeit ist es, die ökologische Relevanz von Top-down (Räuber- gesteuerten) und Bottom-up (Nährstoff-gesteuerten) Prozessen in der Nahrungskette von Flachseen zu erfassen, insbesondere mit Blick auf die Ökologie des Periphytons. Dafür haben wir drei verschiedene Methoden benutzt: Mikrokosmen-Laborexperimente, Mesokosmen-Experimente im See und die Analyse von Langzeitdaten des Müggelsees. Die Mesokosmen Experimente im See wurden unter zwei Nährstoffszenarien (niedrig/hoch) und entlang eines Temperaturgradienten über fünf Europäische Staaten (Estland, Deutschland, Tschechien, die Türkei und Griechenland) durchgeführt. Mit den Mikrokosmen- Experimenten im Labor haben wir das Beweiden von Periphyton durch verschiedene Invertebraten quantifiziert. Die Zeitreihenanalyse wurde u.a. genutzt um ökologische Theorien mit empirischen Felddaten zu testen; in diesem Fall wurde die Regime Shift Theorie mit den Zeitreihenverläufen zweier Copepoden Spezies getestet. Periphytongemeinschaften spielen eine wichtige Rolle in der Nahrungskette von Flachseen, und die Periphytonbiomasse wird direkt von Faktoren wie Temperatur, Nährstoffangebot oder Beweidung durch Invertebraten beeinflusst. Die Periphytonbiomasse wird außerdem auch indirekt durch die Anwesenheit von zooplanktivoren und benthivoren Fischen (trophische Kaskade) beeinflusst. Um den Einfluss von diesen direkten und indirekten Faktoren zu untersuchen, wurden in Mesokosmen-Experimenten je zwei Nährstoffszenarien (klar, 25µg TP L-1; trüb, 200µg TP L-1) entlang des Nord-Süd Europäischen Temperaturgradienten durchgeführt. Jeder Mesokosmos wurde mit einer 10 cm tiefen Lage Sediment versehen und mit Makrophyten (Myriophyllum spicatum), Dreistacheligen Stichlingen (Gasterosteus aculeatus) und lokalen Phyto- und Zooplanktongesellschaften bestückt. Die lokalen Planktongesellschaften wurden aus Populationen von je fünf verschiedenen Seen pro Land gemischt. Um den Bewuchs von Periphyton zu erfassen wurden im Sommer (Juli und August 2011) Plastikstreifen in 50 cm Tiefe in jeden Mesokosmos exponiert. Die Wassertemperatur spielte eine Hauptrolle bei der Entwicklung von Periphytonbiomasse im Sommer. Eine Regressionsanalyse zeigte, dass die Sommer Periphytonbiomasse um 42 % pro 1 °C Temperaturanstieg zunahm, während für die unterschiedlichen Nährstoffkonzentrationen kein signifikanter Effekt auf die Biomasse festgestellt werden konnte. Des Weiteren fand ich einen positiven indirekten Effekt des Fischbestandes auf die Entwicklung der Periphytonbiomasse (gemessen als Chlorophyll a), aufgrund der trophischen Kaskade von Stichlingen auf periphytonweidende Invertebraten. Eine Vorhersage der Effekte von interagierenden Faktoren erweist sich als sehr schwierig, da die Effekte der Interaktionen nicht immer der Summe der Effekte der einzelnen Faktoren entsprechen. Periphytonbiomasse wird direkt durch weidende Invertebraten wie zum Beispiel Wasserflöhe (Cladocera) und/oder Larven der Zuckmücken (Chironomidae) entfernt (als Sammelbegriff für Beweidung und Turbulenz induzierte Entfernung von Biomasse). Die Rolle von pelagischen Wasserflöhen wie Daphnia magna (die in der Litoralzone Schutz vor Frassfeinden suchen) bei der Entfernung von Periphyton ist ungeklärt. In Laborexperimenten haben wir die Rate der Periphytonreduktion durch verschiedene Weidegänger wie D. magna, Chironomidenlarven und die im Feld mit Periphyton assoziierteWeidegängergesellschaft (meist dominiert von Chironomiden Larven) quantifiziert und verglichen. Nach zwei Wochen Expositionszeit und bei einer Temperatur von 20 °C hatte jeder der getesteten Weidegänger die Periphytonbiomasse signifikant reduziert. Entsprechend ihrer größeren Körpermasse hatten Chironomidenlarven individuenbasiert eine höhere Periphytonreduktionsrate als D. magna Körpermassenspezifisch erreichte D. magna jedoch 58 % höhere Periphytonreduktionsraten. Daraus lässt sich schließen, dass große, planktische Wasserflöhe wie D. magna eine wichtige Rolle bei der Reduktion von Periphyton spielen können. Eine Analyse der 30 Jahre langen Verläufe von zwei Ruderfusskrebsspezies (cyclopoide Copepoden; Cyclops vicinus und Cyclops kolensis)zeigte dass die größere Art C. vicinus der überlegene Konkurrent unter einem hohen Nahrungsangebot war, da C. vicinus höhere Ansprüche an die Menge der vorhandenen Ressourcen hat. Des Weiteren konnten wir zeigen, dass die kleinere Art C. kolensis von der Reduktion der Konkurrenz um gemeinsame Resourzen- und des Räuberdrucks durch C. vicinus profitierte. Dies erklärt die plötzliche Zunahme und Dominanz von C. kolensis unter Bedingungen reduzierter Algenbiomasse und gleichzeitiger Abnahme von C. vicinus unterhalb einer kritischen Abundanzgrenze. Das nichtlineare Antwortverhalten der beiden Copepodenarten folgte der Vorhersage zweier Szenarien aus der Regimesshift Theorie. Durch Regressionsanalysen und durch die Anwendung dieser Regimeshift-Szenarien im Kontext der Intraguilt- Predation-Theorie konnten wesentliche zugrundeliegende Treiber der gegenläufigen Entwicklung der beiden Copepodenarten quantifiziert werden

Unveiling the potential of marine-derived diterpenes from the order Alcyonacea as promising anti-obesity agents

Metabolic syndrome (MS) represents a global health challenge characterized by various metabolic disorders, including HOMA-IR (insulin resistance), obesity, dyslipidemia, and hypertension. In our pursuit of identifying natural alternatives for the development of effective and safe anti-obesity medications, we examined the potential of the methanolic extract of the Red Sea derived soft coral Sarcophyton glaucum, where serum levels of glucose, insulin, HOMA-IR, lipid profile, fetuin A and B, PTP1Β (Protein tyrosine phosphatase 1B), adropin and omentin were determined. Furthermore, the expression of the UCP1 (Uncoupling protein 1) and PPARGC1A (Peroxisome proliferator–activated receptor-g coactivator-1a) genes have been assessed, to evaluate the anti-obesity potential of S. glaucum organic extract. Our findings demonstrated a significant decrease in glucose, HOMA-IR, cholesterol, triglyceride, LDL-C, fetuin A and B, and PTP1Β levels, accompanied by a significant increase in insulin, HDL-C, adropin, omentin, UCP1, and PPARGC1A expression after treatment with the soft coral extract. These promising outcomes can be attributed to the remarkable ingredients present in the extract, which were further supported by histopathological findings. In addition, a virtual screening protocol including molecular docking (MDock) and Structure-Activity Relationships (SARs) of 27 marine diterpenes was also explored to identify potential PTP1Β inhibitors targeting simultaneously the catalytic site and allosteric site, as well as fetuin A modulators. Moreover, the six most promising predicted marine diterpenes (4, 8, 9, 10, 13 and 14) were investigated for their pharmacokinetic properties, druglike nature and medicinal chemistry friendliness using the SwissADME platform. Of these, four marine diterpenes (4, 8, 9, and 10) were predicted to exhibit the appropriate drug-like properties

Bioactive Steroids from the Red Sea Soft Coral Sinularia polydactyla

Six new (1, 2, 6, 8, 13, and 20) and twenty previously isolated (3–5, 7, 9–12, 14–19, and 21–26) steroids featuring thirteen different carbocycle motifs were isolated from the organic extract of the soft coral Sinularia polydactyla collected from the Hurghada reef in the Red Sea. The structures and the relative configurations of the isolated natural products have been determined based on extensive analysis of their NMR and MS data. The cytotoxic, anti-inflammatory, anti-angiogenic, and neuroprotective activity of compounds 3–7, 9–12, 14–20, and 22–26, as well as their effect on androgen receptor-regulated transcription was evaluated in vitro in human tumor and non-cancerous cells. Steroids 22 and 23 showed significant cytotoxicity in the low micromolar range against the HeLa and MCF7 cancer cell lines, while migration of endothelial cells was inhibited by compounds 11, 12, 22, and 23 at 20 µM. The results of the androgen receptor (AR) reporter assay showed that compound 11 exhibited the strongest inhibition of AR at 10 µM, while it is noteworthy that steroids 10, 16, and 20 displayed increased inhibition of AR with decreasing concentrations. Additionally, compounds 11 and 23 showed neuroprotective activity on neuron-like SH-SY5Y cells

Secondary Metabolites with Anti-Inflammatory Activity from <i>Laurencia majuscula</i> Collected in the Red Sea

The chemical investigation of the organic extract of the red alga Laurencia majuscula collected from Hurghada reef in the Red Sea resulted in the isolation of five C15 acetogenins, including four tricyclic ones of the maneonene type (1–4) and a 5-membered one (5), 15 sesquiterpenes, including seven lauranes (6–12), one cuparane (13), one seco-laurane (14), one snyderane (15), two chamigranes (16, 17), two rearranged chamigranes (18, 19) and one aristolane (20), as well as a tricyclic diterpene (21) and a chlorinated fatty acid derivative (22). Among them, compounds 1–3, 5, 7, 8, 10, 11 and 14 are new natural products. The structures and the relative configurations of the isolated natural products have been established based on extensive analysis of their NMR and MS data, while the absolute configuration of maneonenes F (1) and G (2) was determined on the basis of single-crystal X-ray diffraction analysis. The anti-inflammatory activity of compounds 1, 2, 4–8, 10, 12–16, 18 and 20–22 was evaluated by measuring suppression of nitric oxide (NO) release in TLR4-activated RAW 264.7 macrophages in culture. All compounds, except 6, exhibited significant anti-inflammatory activity. Among them, metabolites 1, 4 and 18 did not exhibit any cytostatic activity at the tested concentrations. The most prominent anti-inflammatory activity, accompanied by absence of cytostatic activity at the same concentration, was exerted by compounds 5 and 18, with IC50 values of 3.69 μM and 3.55 μΜ, respectively

Secondary Metabolites with Anti-Inflammatory Activity from Laurencia majuscula Collected in the Red Sea

The chemical investigation of the organic extract of the red alga Laurencia majuscula collected from Hurghada reef in the Red Sea resulted in the isolation of five C15 acetogenins, including four tricyclic ones of the maneonene type (1&ndash;4) and a 5-membered one (5), 15 sesquiterpenes, including seven lauranes (6&ndash;12), one cuparane (13), one seco-laurane (14), one snyderane (15), two chamigranes (16, 17), two rearranged chamigranes (18, 19) and one aristolane (20), as well as a tricyclic diterpene (21) and a chlorinated fatty acid derivative (22). Among them, compounds 1&ndash;3, 5, 7, 8, 10, 11 and 14 are new natural products. The structures and the relative configurations of the isolated natural products have been established based on extensive analysis of their NMR and MS data, while the absolute configuration of maneonenes F (1) and G (2) was determined on the basis of single-crystal X-ray diffraction analysis. The anti-inflammatory activity of compounds 1, 2, 4&ndash;8, 10, 12&ndash;16, 18 and 20&ndash;22 was evaluated by measuring suppression of nitric oxide (NO) release in TLR4-activated RAW 264.7 macrophages in culture. All compounds, except 6, exhibited significant anti-inflammatory activity. Among them, metabolites 1, 4 and 18 did not exhibit any cytostatic activity at the tested concentrations. The most prominent anti-inflammatory activity, accompanied by absence of cytostatic activity at the same concentration, was exerted by compounds 5 and 18, with IC50 values of 3.69 &mu;M and 3.55 &mu;&Mu;, respectively