Rapport
Résumé : The Belgica121 expedition (B121) ventured to explore the marine biodiversity of the West Antarctic Peninsula (WAP) to test the concept of using a nimble sampling platform, the R/V Australis, a steel hulled, fully rigged motor sailor. Named as a tribute to the first international scientific expedition in Antarctica lead by Adrien de Gerlache in 1897-99 (onboard the Belgica), B121 took place between February and March 2019, sampling 15 stations in 22 working days in an area extending from the Berthelot (65°19.751 S, 64°08.263 W) to the Melchior Islands (64°19.246 S, 62°55.375W). Deploying 20 different types of gear (both traditional and modern), the B121 team gathered over 1700 samples that will be brought back to Belgium for further identification (by taxonomic experts) and analyses (isotopes, population genetics or genomics...). The team focused on biodiversity assessments, from the intertidal to subtidal zone (20 m) in coastal areas with contrasting characteristics regarding their exposure to glaciers, oceanographic characteristics and intensity of touristic activities. Other projects included population genetics studies, trophic ecology, environmental DNA, microplastics surveys and more (see full report below for details).The use of R/V Australis for coastal studies deemed to be extremely efficient, in terms of environmental impact (ca. 150x less CO2 emissions than a Polar class icebreaker) and reactivity, allowing the team to adapt the sampling efforts in function of the weather or anchoring conditions. Fully devoted to the expedition, the ship allowed the B121 team to sample in shallow areas, not accessible to icebreaker and too far away from research stations, and which have been under sampled.Regarding the biodiversity census, the B121 expedition worked on various realms/taxonomic levels including the intertidal, soft sediments, macro- and megabenthos, fish, birds and marine mammals. Seven stations were investigated for the intertidal (MI, NH, UI, SK, HI, GR and FH) with a total of 121 measurements in quadrats. The average number of species per station was 18. Kidderia bicolor (bivalve), Obrimoposthia wandeli (flat worm) and Laevilitorina caliginosa (gastropod) were the most abundant organisms (up to thousands of individuals per m2).Sediment type (9 to 22 meters depth) ranged from complete silt in the anoxic inner basin at the anchorage site of Hovgaard Island or Neko Harbor, to sandier and well oxygenated sediments of Green Reef. At a first glance the macrofauna pre-sieved samples showed very poor communities in the anoxic sediments, with only small gastropods and few motile taxa such as amphipods, which were present in small numbers. A qualitative analysis of macrofauna will be carried out and biomass will be estimated for both soft sediment metazoan size classes and referred either to surface (for the core and Van Veen sampling) or to sediment volume (for the scooping sampling method).Regarding the mega/macro benthos (9 to 20 meters depth), 53 common species were identified. They were frequently observed directly in situ during the 38 dives performed at the nine sites, or after the dives when watching the 12 video transects... In total, 164 fish specimens were collected, most of them belonging to five species, i.e. Trematomus newnesi, Notothenia coriiceps, Harpagifer antarcticus, Trematomus bernacchii and Notothenia rossii. The spatial distribution of samples is patchy with most specimens collected at Føyn Harbor and Useful Island. Several localities yielded less than a dozen fish preventing spatial comparisons of fish catches. Fish samples collected represent a valuable collection of the Antarctic shallow water fish fauna, which is dominated by notothenioids. Regarding the birds and marine mammals, a total of 46 standard counts were carried out all along the cruise track (from the Beagle channel to the southernmost visited site of the cruise at Berthelot Islands along the Antarctic Peninsula and the Drake passage. 26 species of birds, 3 species of cetaceans and 4 species of pinnipeds were observed. Finally, several attempts (in 4 different locations) were unsuccessfully ran to sample snow petrel feathers for a project on this species phylogeography and taxonomy.Other projects were carried out during the expedition, focusing on habitat mapping, population genomics and eDNA sampling to gain further insights into the region’s biodiversity levels. Twelve video transects were carried out, one or two at each station, to characterize the shallow habitats. Although Antarctic shallow benthic communities are usually considered depauperated with very low biomass and abundances compared to deeper communities of the Antarctic continental shelf, preliminary results suggest the occurrence of highly diverse shallow communities depending on local conditions. A preliminary correspondence analysis of common taxon distribution suggests marked differences between the considered stations. An in- analysis of the video transects and the relative surface mapped will help further describe biotic interactions and community composition and diversity. The population genomics project was carried out to advance a technological pilot study undergoing in the framework of the RECTO project. A range of organisms were sampled for this purpose, including 83 ostracods, 227 amphipods, 65 bivalves, 16 sea stars and 81 fish.The pilot study focuses on the evaluation and optimization of reduced representation sequencing protocols, more specifically RADseq.. Eventually, RADseq should yield thousands of genotypes per specimen, which will help to identify any potential local adaptation patterns possibly linked to the contrasting environmental and community conditions. For the eDNA project, 8 sampling events were conducted at four major stations that correspond roughly to the widest spatial extent of the expedition. DNA will be extracted from the filters in dedicated eDNA lab spaces at the KU Leuven. Subsequent high-throughput sequencing of the obtained metabarcoding libraries should enable species-level presence-absence detection.Complimentary projects were ran during the expedition, including a microplastics survey, oceanographic measurements in selected sites, biogeochemistry and trophic ecology as well as macrophotography. For the microplastics survey, a total of 36 samples of sediment and organisms were taken at eight sites between 5m and 20m depth. Sea stars and filter feeding bivalve were sampled for the biotic part of this project. Analyses will be performed in collaboration with Heriot Watt University (Edinburgh, UK) as a part of a PhD thesis ongoing at the ULB Marine Biology Lab. With regards to the oceanographic measurements, 17 CTD casts were carried out in ten sites to characterize water masses parameters. A deep (400m) cast was carried out before Arctowski Peninsula (AP) in conjunction with an eDNA sampling effort. Biogeochemistry analysis will be carried out on soft sediment from the different sampling sites. Sediments will be characterized at the University of Ghent analyses to determine the granulometry (median grain size, size fraction%), total organic matter content (TOM), Total Organic Carbon (TOC%) content, Total nitrogen content (TN%), and pigments content. For trophic ecology, 156 samples counting 24 different species and over 650 specimens were collected at seven sites between 8m and 20m depth. Water and sediment samples were collected at each site. Specimens of seaweeds were sampled as potential food sources while other organisms were collected from different trophic guilds, among primary and secondary consumers, filter feeders, predators/scavengers and terminal consumers. Isotope analysis of ∂13C, ∂15N, and ∂34S will be carried out at the University of Liège. Trophic models will be developed to characterize species trophic niches and plasticity, as well as the main structures of trophic networks in shallow coastal habitats of the visited sites. Finally, 143 specimens were macro-photographed during the expedition. The most photographed phyla were Arthropoda (56 specimens) followed by Echinodermata (23), Mollusca (18), Polychaeta (14) and Chordata (10). Both overview and close up pictures of the specimens were captured.From the initial results, in terms of sampling diversity of projects and fuel efficiency, it appears that the B121 expedition was extremely successful. Further analysis is of course needed to better characterize the biodiversity and run the multiple analysis, but it is recommended that the concept of using a more nimble platform for shallow biodiversity works in the Southern Ocean should be more widely considered, as a complementary approach to traditional approaches which are either based in research station, or along logistics-driven polar icebreaker routes.

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