Description: The transit of RV SONNE from Las Palmas (departure: 11.12.2021) to Guayaquil, Ecuador (arrival: 11.01.2022) is directly related to the international collaborative project SO287-CONNECT of GEOMAR in cooperation with Hereon and the University of Bremen, supported by the German Federal Ministry of Education and Research (BMBF) between October 15 2021 and January 15 2024. The research expedition was conducted to decipher the coupling of biogeochemical and ecological processes and their influence on atmospheric chemistry along the transport pathway of water from the upwelling zones off Africa into the Sargasso Sea and further to the Caribbean and the equatorial Pacific. Nutrient-rich water rises from the deep and promotes the growth of plant and animal microorganisms, and fish at the ocean surface off West Africa. The North Equatorial Current water carries the water from the upwelling, which contains large amounts of organic material across the Atlantic to the Caribbean, supporting bacterial activity along the way. But how the nutritious remnants of algae and other substances are processed on their long journey, biochemically transformed, decomposed into nutrients and respired to carbon dioxide, has so far only been partially investigated. Air, seawater and particles were sampled in order to provide new details about the large cycles of carbon and nitrogen, but also of many other elements such as oxygen, iodine, bromine and sulfur. Inorganic and organic bromine and iodine compounds are generally emitted naturally from the ocean into the atmosphere, promote cloud formation and affect climate, and some even reach the stratosphere where they contribute to ozone depletion. We measured how much of these compounds are released from the ocean, and at what locations and how they are transformed in the ocean and in the atmosphere. Sargassum algae, which have become a nuisance on beaches in the western and eastern Atlantic, support life and contribute to carbon cycling in the middle of the Atlantic, the Sargasso Sea and in the Caribbean, while their contribution to halogen cycling and marine bromine and iodine emissions was previously unknown. We investigated the influence of various natural parameters such as temperature and solar radiation on the biogeochemical transformation processes in order to understand the influence of climate change on these processes in incubation experiments with seawater and algae. We investigated how anthropogenic signals such as shipping traffic influence the nitrogen and sulphur cycle in the ocean, as well as the impact of nitrogen oxides from ship exhaust and sulphurous, acidic and dirty water from purification systems on organisms and biochemical processes. Plastic debris was sampled from the surface waters to investigate its contribution to global biogeochemical transformation processes. The working hypotheses of the research program were:  Bioavailability of dissolved organic carbon in surface waters decreases along the productivity gradient and transport pathway from the Eastern to the Western Tropical North Atlantic.  Nutrient gradients from East to West constrain the microbial utilization of organic matter- contributing to an accumulation of C-rich organic matter due to a) limited mineralization and b) enhanced exudation- also leading to gel-like particles accumulation in the western tropical North Atlantic and Sargasso Sea.  Tropospheric and stratospheric ozone are strongly impacted by biogeochemical and ecological processes occurring around and in the NA gyre system related to marine iodine and bromine cycles.  The long-range transport of natural and anthropogenic organic matter in water and of gases and aerosols in the air impact carbon-export, biogeochemical cycles in the water column, and the release of gases and particles from the ocean significantly. 4 SONNE -Berichte, SO287, Las Palmas - Guayaquil, 11.12.2021 - 11.01.202 The data and samples obtained specifically target carbon, nutrient and halogen cycling, the composition of phytoplankton, bacteria, the transport and sequestration of macro algae and the air-sea exchange processes of climate relevant gases and aerosols. The influence of ecological and transport processes, as well as anthropogenic impacts on the North Atlantic gyre system, specifically in the Sargasso Sea and the influence of ship emissions throughout the Atlantic towards the west and into the Pacific will be investigated with the data.

Description: A review is presented of ongoing research on the oligosaccharide signals involved in cell-cell recognition in the Chondrus crispus-Acrochaete operculata host-pathogen association. In this pathosystem, the host gametophytes are resistant to the pathogen, whereas the sporophytic generation is susceptible to infection. The virulence of the green algal pathogen is mediated by the recognition of carrageenan oligosaccharides released from its red algal host: kappa-carrageenan oligosaccharides inhibit A. operculata virulence while lambda carrageenan oligosaccharides enhance its pathogenicity. It appears that the recognition of A. operculata by C. crispus also involves an oligosaccharidic signal. This signal is present in the non-virulent form of the pathogen whereas it is absent from the virulent form. Altogether this pathosystem offers a unique model to investigate the recognition of oligosaccharide signals in plant-pathogen interactions. The possible applications of this research to develop new strategies for disease control in maricultured algal crops are discussed.

Description: A backfiring weapon: The release of H2O2 by an amino acid oxidase is the early defensive reaction of the red alga Chondrus crispus against the endophytic green algal pathogen Acrochaete operculata (see scheme). This reaction can be induced by L-asparagine, which is released by the attacker when it recognises host cell-wall κ-carrageenan oligosaccharides. The induced signal of the attacker thus serves directly as the substrate for the production of the defensive metabolite.

Description: The red alga Gracilaria chilensis is commercially farmed for the production of agar hydrocolloids, but some susceptible algae in farms suffer from intense epiphyte growth. We investigated the induced chemical defense response of G. chilensis against epiphytes and demonstrated that an extract of an epiphyte-challenged alga can trigger a defense response. The hormonally active metabolites were purified by RP-HPLC. Treatment with the extract or the purified fraction changed the chemical profile of the alga and increased resistance against epiphyte spores. Semi-quantitative RT-PCR and enzyme assays demonstrated that this metabolic response occurs after an increase in lipoxygenase and phospholipase A2 activity. Although this suggests the involvement of regulatory oxylipins, neither jasmonic acid nor the algal metabolite prostaglandin E2 triggers comparable defense responses.

Description: Combined phylogenetic, physiological, and biochemical approaches revealed that differences in defense-related responses among 17 species belonging to the Gracilariaceae were consistent with their evolutionary history. An oxidative burst response resulting from activation of NADPH oxidase was always observed in two of the subgenera of Gracilaria sensu lato (Gracilaria, Hydropuntia), but not in Gracilariopsis and in species related to Gracilaria chilensis (“chilensis” clade). On the other hand, all species examined except Gracilaria tenuistipitata var. liui and Gracilariopsis longissima responded with up-regulation of agar oligosaccharide oxidase to an challenge with agar oligosaccharides. As indicated by pharmacological experiments conducted with Gracilaria chilensis and Gracilaria sp. “dura,” the up-regulation of agar oligosaccharide oxidase involved an NAD(P)H-dependent signaling pathway, but not kinase activity. By contrast, the activation of NADPH oxidase requires protein phosphorylation. Both responses are therefore independent, and the agar oligosaccharide-activated oxidative burst evolved after the capacity to oxidize agar oligosaccharide, probably providing additional defensive capacity to the most recently differentiated clades of Gracilariaceae. As demonstrated with Gracilaria gracilis, Gracilaria dura, and Gracilariopsis longissima, the different responses to agar oligosaccharides allow for a fast and nondestructive distinction among different clades of gracilarioids that are morphologically convergent. Based upon sequences of the chloroplast-encoded rbcL gene, this study suggests that at least some of the samples from NW America recorded as Gs. lemanaeiformis are probably Gs. chorda. Moreover, previous records of Gracilaria conferta from Israel are shown to be based upon misidentification of Gracilaria sp. “dura,” a species that belongs to the Hydropuntia subgenus.

Description: “Infochemicals” (information‐conveying chemicals) dominate much of the underwater communication in biological systems. They influence the movement and behavior of organisms, the ecological interactions between and across populations, and the trophic structure of marine food webs. However, relative to their terrestrial equivalents, the wider ecological and economic importance of marine infochemicals remains understudied and a concerted, cross‐disciplinary effort is needed to reveal the full potential of marine chemical ecology. We highlight current challenges with specific examples and suggest how research on the chemical ecology of marine organisms could provide opportunities for implementing new management solutions for future “blue growth” (the sustainable use of ocean resources) and maintaining healthy marine ecosystems.