Description: Epibacterial communities on seaweeds are affected by several abiotic factors such as temperature and acidification. Due to global warming, surface seawater temperatures are expected to increase by 0.5–5 °C in the next century. However, how epibacterial communities associated with seaweeds will respond to global warming remains unknown. In this study, we investigated the response of epibacterial communities associated with the invasive Gracilaria vermiculophylla exposed to 3 °C above ambient temperature for 4 months using a benthocosm system in Kiel, Germany, and 16S rRNA gene amplicon sequencing. The results showed that elevated temperature affected the beta-diversity of the epibacterial communities. Some potential seaweed pathogens such as Pseudoalteromonas, Vibrio, Thalassotalea, and Acinetobacter were identified as indicator genera at the elevated temperature level. Thirteen core raw amplicon sequence variants in the elevated temperature group were the same as the populations distributed over a wide geographical range, indicating that these core ASVs may play an important role in the invasive G. vermicullophylla. Overall, this study not only contributes to a better understanding of how epibacterial communities associated with G. vermiculophylla may adapt to ocean warming, but also lays the foundation for further exploration of the interactions between G. vermiculophylla and its epimicrobiota.

Description: In temperate and subarctic regions of the Northern Hemisphere, green algae of the genus Blidingia are a substantial and environment‐shaping component of the upper and mid‐supralittoral zones. However, taxonomic knowledge on these important green algae is still sparse. In the present study, the molecular diversity and distribution of Blidingia species in the German State of Schleswig‐Holstein was examined for the first time, including Baltic Sea and Wadden Sea coasts and the off‐shore island of Helgoland (Heligoland). In total, three entities were delimited by DNA barcoding, and their respective distributions were verified (in decreasing order of abundance: Blidingia marginata, Blidingia cornuta sp. nov. and Blidingia minima). Our molecular data revealed strong taxonomic discrepancies with historical species concepts, which were mainly based on morphological and ontogenetic characters. Using a combination of molecular, morphological and ontogenetic approaches, we were able to disentangle previous mis‐identifications of B. minima and demonstrate that the distribution of B. minima is more restricted than expected within the examined area. Blidingia minima, the type of the genus name Blidingia, is epitypified within this study by material collected at the type locality Helgoland. In contrast with B. minima, B. marginata shows a higher phenotypic plasticity and is more widely distributed in the study area than previously assumed. The third entity, Blidingia cornuta sp. nov., is clearly delimited from other described Blidingia species, due to unique characters in its ontogenetic development and morphology as well as by its tufA and rbcL sequences.

Description: Invited lecture about Arctic kelp forests and fieldwork in Kongsfjorden in the lecture series “Meeresforschung früher, heute und in Zukunft” of the Bremen Society for Natural Sciences on the occasion of the “UN-Dekade der Meeresforschung für nachhaltige Entwicklung 2021 – 2030”: “Bunte Vielfalt – Arktische Makroalgen im Wandel”

Description: Macroalgae are major primary producers and ecosystem engineers along rocky shores of the Arctic. With Svalbard being a hotspot of global warming, macroalgal species distribution and biomass is undergoing rapid changes, presumably affecting all associated life forms. The overall retreat of the yearly ice cover is only the centerpiece in a complex interplay of environmental drivers noticeably altering light availability, disturbance regimes and nutrient supply for Arctic seaweeds. Between 1996/1998 and 2012/2013 ecosystem changes were observed at our study site Hansneset in Kongsfjorden, as algal biomass in the littoral zone doubled and the macroalgal biomass peak, as well as the lower distribution limit of most dominating kelp species, shifted upwards by several meters. In summer 2021, we seek to complement these datasets. Our interdisciplinary group will repeat the quantitative monitoring study to examine how the community pattern of seaweeds and their associated fauna has changed since the last expedition. In detail, we will quantify macroalgal biomass and biodiversity, the age structure and fertility of kelp species, and the biomass and biodiversity of associated animals along a depth gradient between 0 and 15 m. Incorporated into the European Horizon 2020 project FACE-IT and two associated Svalbard Science Forum field grants, our superior aim is to analyse the response of benthic macroalgal assemblages to observed cryosphere changes in a broad context. In this poster, we will share the first results from this year’s field samplings and show how abundances, biomass and species diversity of macroalgae have changed over the last decades at our investigation site and what this means in general for the development of macroalgae on Arctic coasts.