Rising Temperature Is a More Important Driver Than Increasing Carbon Dioxide Concentrations in the Trait Responses of Enhalus acoroides Seedlings

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Effects of depth and ultraviolet radiation on coral reef turf algae

International audienceDespite the increasing dominance of turf algae in coral reefs, few studies have investigated their physiological and ecological responses to changes in abiotic factors. We tested the effects of depth and ultraviolet radiation on turf algae at different levels of successional stages using two experiments. Depth-related differences were found for all turf algal communities, characterized by a higher amount of the cyanobacteria taxon Dichothrix and the red filamentous genera Poly-/Herposiphonia in the shallow and the appearance of oscillating cyanobacteria in deeper waters. In the first experiment, cross-depth transplantation of 153 days old communities influenced percentage cover, biomass and taxa composition. Downward transplantation lowered overall biomass and abundance of the foraminifera Sorites, whereas the crustose green alga Pringsheimiella and filamentous cyanobacteria colonized the communities. A nearly reverse pattern was observed in upward transplanted communities. Overall we distinguished between sensitive taxa, like Oscillatoria, and taxa able to acclimate to alterations in their environment, like Pringsheimiella, Poly/Herposiphonia and Dichothrix. In the second experiment, algae grown for 285 days at 5 m were exposed together with a set of sterile settlement tiles to three UVR regimes at 2 m for 22 days. UVR had no effect on turf algal communities regardless of successional stage. This study highlights the presence of high light and UV tolerant species. The high UV tolerance of turf communities may confer a competitive advantage over other more sensitive coral reef biota, such as corals. This study demonstrates that turf algae are dynamic communities exhibiting species-specific resistance to environmental changes

The Chlorophytes of Curaçao (Caribbean): A revised checklist for the south-west coast

The global trend of unprecedented losses in coral reefs is particularly striking in the Caribbean, where dense algal assemblages are commonly replacing corals. So far, hardly anything is known about the ecology of the dominant algal groups. The present study compiled records of Chlorophytes from nine studies in the shallow reefs of Curaçao in the years preceding the onset of coral reef decline (1908–1978) and compared them with records from three recent (2007–2009) expeditions conducted at the same and nearby study locations along the south-west coast of the island. A total of 107 species were encountered, including seven new records for Curaçao (Anadyomene saldanhae, Bryopsis hypnoides, Chaetomorpha minima, Derbesia fastigiata, Ulva flexuosa subsp. paradoxa, Ulvella scutata and Ulvella lens). Sampled material revealed a higher species number during the dry seasons than during the wet seasons, indicating a seasonal variation in algal growth. Most species grew on hard substratum or were epibiotic, and 13 species were found growing on more than one substratum. Comparisons with earlier studies suggest an extension in depth range for nine species. The present work provides a comprehensive overview of the distribution of Chlorophytes of the island and can serve as an important baseline for further research on coral reef ecosystem changes.Fil: Fricke, Anna Lena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Leibniz Centre for Tropical Marine Research; AlemaniaFil: Titlyanova, Tamara V.. Far Eastern Branch of the Russian Academy of Sciences; RusiaFil: Teichberg, Mirta. Leibniz Centre for Tropical Marine Research; AlemaniaFil: Nugues, Maggy M.. Paris Sciences et Lettres Research University; Francia. Centre de Recherches Insulaires et Observatoire de l’Environnement; Polinesia Francesa. Caribbean Research and Management of Biodiversity; Antillas NeerlandesasFil: Bakai, Romina Vanesa. Universitat Bremen; Alemani

Predicted warming intensifies the negative effects of eutrophication on tropical seagrass: implementat sensitive indicator

World Seagrass Conference & International Seagrass Biology Workshop, WSC2022 & ISBW14, Annapolis, 7 - 12 August 2022N

Predicted warming intensifies the negative effects of nutrient increase on tropical seagrass: A physiological and fatty acid approach

15 pages, 7 figures, 3 tables.-- Under a Creative Commons licenseThe Gulf of Aqaba (GoA; northern Red Sea) supports extensive seagrass meadows, dominated by the small tropical seagrass species, Halophila stipulacea. Due to its semi-closed structure, in the GoA, regional nutrient loading and global warming are considered the biggest threats to local seagrass meadows, and their combination can potentially amplify their negative impacts. Using a seagrass-dedicated mesocosm, we exposed two seagrass populations with different local “nutrient history” to control (27 °C) and simulated warming (31 °C), with and without nutrients (20 µM DIN). Following four weeks of these treatments (“stress phase”), all plants were returned to control conditions (“recovery phase”) for another three weeks. Results showed that exposure to only thermal stress favoured growth, compared to exposure to only nutrient increase that reduced Fv/Fm and growth but favoured algae proliferation. Exposure to the combined thermal and nutrient stress, negatively affected seagrass performance resulting in high mortality observed after four weeks of combined exposure. The negative effects of combined stressors were stronger in populations with low “nutrient history”. Additionally, we propose two novel fatty acid (FA) biomarkers, one based on FA unsaturation, 16:3n-3/16:2n-6, and the other on FA elongation processes, 18:2n-6/16:2n-6. Fatty acid analyses showed a significant decrease in 16:3n-3/16:2n-6 and 18:3n-3/18:2n-6 with increases in temperature and nutrients; a more drastic decline was found under the interaction of both stressors. Our results point out that C16 PUFAs, that are synthesized within the “prokaryotic pathway”, are more sensitive to thermal and the combined thermal + nutrients stressors than C18 PUFAs, which are synthesized within the “eukaryotic pathway”. In general, following a month of control conditions, a clear recovery of most of the seagrass descriptors was observed, highlighting the great capability of Halophila stipulacea to recover from stress conditions. Our results have important ecological and management implications to the seagrass meadows in the GoA and elsewhere. For seagrasses to survive climate change, managers must put efforts into limiting other stressors such as eutrophication that would potentially reduce the seagrass resilience to climate changeThis research and SEASTRESS project was funded by The Israeli Ministry of Science and Technology (MoST), Israeli-Italian binational Grant Number 3-15152 (GW, PBC) and ICA in Israel, Grant 03-16-06a (GW). This work was also supported by the SEANARIOS project (SEAgrass sceNARIOS under thermal and nutrient stress: FKZ 03F0826A), an Israeli-German Scientific Cooperation, funded by the German Federal Ministry of Education and Research (BMBF), jointly with the SEASTRESS project, an Israeli-Italian Scientific Cooperation, funded by the Ministry of Science and Technology of Israel (MOST). Lastly, this project was also supported by the project IN607B 2020/04 funded by Xunta de Galicia, Galician Agency for Innovation, GAIN (Spain)Peer reviewe

Predicting the combined effects of warming and nutrient increase on the tropical seagrass Halophila stipulacea

3rd Israel Conference for convervation Science (ICCS),Tel-Aviv, 18-20th October 2022Famous for its coral reefs, the Gulf of Aqaba also supports extensive seagrass meadows, dominated by Halophila stipulacea. Nutrient loading and warming are considered the biggest threats to seagrass meadows, and their combination can potentially amplify their negative effects. We exposed two seagrass populations with different eutrophication “history” to control (27ºC) and simulated warming (31ºC), with and without nutrients (20 μg DIN). While exposure to only thermal stress favoured growth, eutrophication only reduced Fv/Fm and growth but favoured algae proliferation. Combined effects negatively enhanced seagrass performance with the highest mortality rates observed after four weeks of combined exposure. Negative effects of combined stressors were stronger in populations with low eutrophication “history”. Lipidomic analyses showed stress decreased ratios of fatty acids 16:3n-3/16:2n-6 and 18:3n-3/18:2n-6 with bigger declines in these ratios following exposure to the interaction of both stressors. The GoA’s waters are warming faster than the average of the world’s coastal warming trends. While it might be difficult to directly control the effects of global warming, sources of eutrophication are usually on local scales. For seagrasses to survive climate change, managers must put efforts into limiting other stressors such as eutrophication which would reduce the resilience of meadows to other stressorsN