Metabolic and Oxidative Stress Responses of Cassiopea sp. to Environmental Stress : Towards a Better Physiological Understanding of Jellyfish's Tolerance

Jellyfish are commonly seen as robust, noxious and unwelcoming animals. In recent decades, reports concerning jellyfish outbreaks and invasions are increasing worldwide. Regardless of the debate about the underlying drivers of jellyfish blooms, climate change and anthropogenic activities are commonly perceived as the main drivers. There is, however, scarcity of strong evidences to support this perception, because only few manipulative experiments have addressed the physiological responses of jellies to varying environmental stressors. The overall aim of this thesis is to use manipulative experiments and field excursions to test hypotheses about tolerance of jellyfish to stressors associated with climate change and anthropogenic activities for better prediction of their fate in the future. Due to climate change, extreme weather conditions are becoming more frequent and severe. In chapters 2 and 3, I investigate the metabolic and oxidative responses of the upside-down jellyfish Cassiopea sp. (Cassiopea hereafter) medusae to sudden changes in seawater temperature (i.e., either rise or drop by 6 AdegreeC from the control temperature). Medusae responded in contrasting manners to drop and rise in seawater temperature. While medusae treated at low temperature (20 AdegreeC) looked unhealthy and showed signs of decreased physiological performance (i.e., in term of decreased body mass and size) after two weeks, medusae treated at high temperature (32 AdegreeC) gained in body mass and size, indicating an enhanced performance for the same period. At the cellular level, medusae treated at low temperature suffered from oxidative stress-induced cellular damage and elevated metabolic demand, while no oxidative stress or signs of increased energy demand were evident in medusae at higher temperature. The overall results of these two chapters suggest that Cassiopea medusae are more tolerant to temperature rise than drop. They might benefit from global warming to spread and expand their populations in the future as well. Coastal systems experience a variety of pollutants, nutrient loading and other burdens associated with anthropogenic activities. In chapter 4, I investigate the anaerobic potential and oxidative stress responses in Cassiopea medusae collected from anthropogenically impacted and protected marine coastal habitats. While medusae from all investigated locations did not show signs of oxidative stress-induced damage (e.g., lipid peroxidation), the medusae from polluted locations had more anaerobic potential (e.g., high PK and LDH activities). While the results of Chlorophyll-a (Chla) contents measurements did not show clear trends in medusae from the studied locations, it seems that medusae Chla content is more sensitive to water clarity than to pollution status in the studied sites. Overall these results suggest that Cassiopea seems to be robust to the level of pollution at the studied sites and they might be anaerobically poised to live and thrive at such habitats. Noteworthy to mention here is that while the studies conducted in this thesis could work as a framework for future studies aimed for better understanding of jellyfish physiological responses, the thesis findings do not claim ultimate proofs for tolerance or sensitivity in all jellies. However, this thesis, and for the first time, highlights the feasibility and importance of understanding the underlying mechanisms of jellyfisha s physiological tolerance/sensitivity to changing environmental conditions. By using the epibenthic jellyfish Cassiopea as a representative model for studying tropical jellyfisha s ecological roles and responses to environmental stressors, this thesis encourages doing further researches on this jellyfish

Metabolischer und oxidativer Stress Reaktionen von Cassiopea sp. zu Umweltstress : Auf dem Weg zu einem besseren physiologischen Verständnis der Toleranz der Qualle

Jellyfish are commonly seen as robust, noxious and unwelcoming animals. In recent decades, reports concerning jellyfish outbreaks and invasions are increasing worldwide. Regardless of the debate about the underlying drivers of jellyfish blooms, climate change and anthropogenic activities are commonly perceived as the main drivers. There is, however, scarcity of strong evidences to support this perception, because only few manipulative experiments have addressed the physiological responses of jellies to varying environmental stressors. The overall aim of this thesis is to use manipulative experiments and field excursions to test hypotheses about tolerance of jellyfish to stressors associated with climate change and anthropogenic activities for better prediction of their fate in the future. Due to climate change, extreme weather conditions are becoming more frequent and severe. In chapters 2 and 3, I investigate the metabolic and oxidative responses of the upside-down jellyfish Cassiopea sp. (Cassiopea hereafter) medusae to sudden changes in seawater temperature (i.e., either rise or drop by 6 AdegreeC from the control temperature). Medusae responded in contrasting manners to drop and rise in seawater temperature. While medusae treated at low temperature (20 AdegreeC) looked unhealthy and showed signs of decreased physiological performance (i.e., in term of decreased body mass and size) after two weeks, medusae treated at high temperature (32 AdegreeC) gained in body mass and size, indicating an enhanced performance for the same period. At the cellular level, medusae treated at low temperature suffered from oxidative stress-induced cellular damage and elevated metabolic demand, while no oxidative stress or signs of increased energy demand were evident in medusae at higher temperature. The overall results of these two chapters suggest that Cassiopea medusae are more tolerant to temperature rise than drop. They might benefit from global warming to spread and expand their populations in the future as well. Coastal systems experience a variety of pollutants, nutrient loading and other burdens associated with anthropogenic activities. In chapter 4, I investigate the anaerobic potential and oxidative stress responses in Cassiopea medusae collected from anthropogenically impacted and protected marine coastal habitats. While medusae from all investigated locations did not show signs of oxidative stress-induced damage (e.g., lipid peroxidation), the medusae from polluted locations had more anaerobic potential (e.g., high PK and LDH activities). While the results of Chlorophyll-a (Chla) contents measurements did not show clear trends in medusae from the studied locations, it seems that medusae Chla content is more sensitive to water clarity than to pollution status in the studied sites. Overall these results suggest that Cassiopea seems to be robust to the level of pollution at the studied sites and they might be anaerobically poised to live and thrive at such habitats. Noteworthy to mention here is that while the studies conducted in this thesis could work as a framework for future studies aimed for better understanding of jellyfish physiological responses, the thesis findings do not claim ultimate proofs for tolerance or sensitivity in all jellies. However, this thesis, and for the first time, highlights the feasibility and importance of understanding the underlying mechanisms of jellyfisha s physiological tolerance/sensitivity to changing environmental conditions. By using the epibenthic jellyfish Cassiopea as a representative model for studying tropical jellyfisha s ecological roles and responses to environmental stressors, this thesis encourages doing further researches on this jellyfish

Illuminating Cassiopea jellyfish: biochemical revelations from metabolism to coloration under ultraviolet A and photosynthetically active radiation

Sunlight, including ultraviolet (UVA and UVB) and photosynthetically active radiation (PAR), is vital for the physiology of invertebrates with symbiotic Symbiodiniaceae. While the effects of UVB and PAR are well-studied, the impact of UVA remains underexplored. This study investigates the effects of varying UVA and PAR intensities on the metabolic, oxidative, and photosynthetic responses of Cassiopea andromeda jellyfish. Over 18 days, 24 medusae were exposed to four light treatments: low PAR (± low UVA) and high PAR (± high UVA). Results showed significant increases in jellyfish mass and umbrella diameter, with no differences between treatment groups. PAR intensity primarily drove aerobic respiration and photosynthesis, with reduced PAR enhancing ETS activity and chlorophyll-a concentration, while UVA had less effect. ETS activity was positively correlated with chlorophyll-a concentration but negatively with jellyfish size. Both high PAR and high UVA exposure increased lipid peroxidation (LPO), with the highest levels under combined high PAR and UVA. These findings show that UVA does not directly affect photosynthesis but might enhances oxidative stress when combined with high PAR, increasing LPO. Despite oxidative stress, jellyfish showed consistent growth and normal morphology, highlighting their resilience to varying light. Color changes linked to PAR exposure indicated shifts in algal symbiont density. This study highlights the adaptive capacity of C. andromeda jellyfish to fluctuating light, emphasizing PAR’s role in regulating metabolism and oxidative stress. It also offers new insights into UVA’s underexplored impact on jellyfish physiology, paving the way for future research on UVA’s broader effects on marine invertebrates

Aerobic respiration, biochemical composition, and glycolytic responses to ultraviolet radiation in jellyfish Cassiopea sp

The light-dependent zooxanthellate jellyfish Cassiopea sp. (the upside-down jellyfish) is invasive/exotic in many shallow and clear marine habitats, where the jellyfish might be exposed to high levels of ultraviolet radiation (UVR). Compared to other reef organisms, the sensitivity/resilience of the semi-transparent jellyfish to UVR exposure is overlooked. Therefore, we experimentally investigated the metabolic and physiological responses of Cassiopea sp. from the Red Sea to natural levels of underwater UVR following 16 days of exposure to three light treatments: 1) control group with only photosynthetically active radiation (PAR), 2) PAR+UV-B, and 3) PAR+UV-B+UV-A. While jellyfish body mass increased (by 40%) significantly in the control group, it did not increase in either of the UV treatments. However, both UV-exposed jellyfish had higher (98% to 120%) mitochondrial electron transport system (ETS) activity than the control group. Therefore, the results indicate elevated aerobic respiration rates in UV-exposed jellyfish (i.e., reflecting a higher energy cost of UVR exposure). Neither the lactate dehydrogenase (LDH) activity nor the available energy (Ea) exhibited different levels among UVR treatments compared to the control group. In contrast, pyruvate kinase activity was significantly lower (by 46%) in all UV-exposed jellyfish compared to the control group. Unchanged Ea and LDH activity combined with higher ETS activity indicates a high aerobic capacity of jellyfish, which might explain their ability to cope with UVR exposure-induced higher energy demands without inducing the onset of anaerobiosis. The results indicated that UV-A does not amplify or modulate jellyfish physiology and growth under UV-B exposure. In conclusion, the findings suggest that the jellyfish is more resilient (i.e., in terms of survival) to UVR than other cnidarians. This study on Cassiopea is the first to address its metabolic and physiological responses to UVR. Therefore, it could be used as a framework for further studies aiming to better understand jellyfish physiology.</jats:p

Photobiota of the Tropical Red Sea: Fatty Acid Profile Analysis and Nutritional Quality Assessments

Photosynthetic organisms are primary sources of marine-derived molecules, particularly &omega;3 fatty acids (FAs), which influence the quality of marine foods. It is reported that tropical organisms possess lower FA nutritional quality than those from colder oceans. However, the high biodiversity known for tropical areas may help compensate for this deficiency by producing a high diversity of molecules with nutritional benefits for the ecosystem. Here we addressed this aspect by analyzing the FA profiles of 20 photosynthetic organisms from the salty and warm Red Sea, a biodiversity hot spot, including cyanobacteria, eukaryotic microalgae, macroalgae, mangrove leaves, as well as three selected reef&rsquo;s photosymbiotic zooxanthellate corals and jellyfish. Using direct transesterification, gas chromatography-mass spectrometry, FA absolute quantification, and nutritional indexes, we evaluated their lipid nutritional qualities. We observed interspecific and strain-specific variabilities in qualities, which the unique environmental conditions of the Red Sea may help to explain. Generally, eukaryotic microalgae exhibited the highest nutritional quality. The previously unanalyzed diatoms Leyanella sp. and Minutocellus sp. had the highest eicosapentaenoic acid (EPA) contents. The bioprospected Red Sea photobiota exhibited pharmaceutical and nutraceutical potential. By sourcing and quantifying these bioactive compounds, we highlight the untapped rich biodiversity of the Red Sea and showcase opportunities to harness these potentials