Dugno bendrijų struktūra besitraukiančio ledyno pakraštyje vakarų Svalbarde, Arktyje

Šio darbo tikslas buvo nustatyti tirpstančio ledyno poveikyje esančių sublitoralės makrozoobentoso bendrijų struktūros dėsningumus vakarų Svalbardo įlankose. Darbo metu, iš vakarų Svalbardo įlankose surinktos 3h trukmės vaizdo medžiagos buvo sukurtos 148 vaizdo įrašų mozaikos iš kurių, pasitelkus Arkties floros ir faunos taksonomijos ekspertų pagalbą, buvo identifikuoti 33 biologiniai ir biofiziniai požymiai. Pagal identifikuotus biologinius ir biofizinius požymius, kurie darbe taip pat įvardijami kaip morforūšys, buvo lyginamos Isjordeno ir Hornsundo fjordų įlankos esančios ledyno tirpsmo zonoje (Borebukta, Burgerbukta) su įlankomis esančiomis laisvoje nuo ledynų zonoje (Gipsvika, Adriabukta). Gauti rezultatai parodė, jog Adriabuktos, Burgerbuktos, ir Gipsvikos įlankose dominuoja iš dalies judrūs filtratoriai, o Borebuktoje dominuoja judrūs organizmai bei maitėdos. Didžiausius skirtumus tarp įlankų nulemia 8 tyrimų rajone dominuojančios morforūšys: Ceriantharia, dvigeldžiai, Sabellidae, ofiūros, bioturbuojančios kirmelės, krevetės, samangyviai Alcyonidium sp. ir Bryozoa undet individai. Burgerbuktos (54 ± 84 ind. trans-1), Adriabuktos (49 ± 68 ind. trans -1) ir Gipsvikos (25 ± 34 ind. trans-1) įlankose dominuoja daugiašerės Sabellidae, įlankose sudarydamos > 50 % bendro santykinio individų gausumo įlankoje, o Borebuktoje – ofiūros (76 ± 169 ind. trans-1), sudarydamos 78,4 % bendro santykinio individų gausumo įlankoje. Nustatyta, jog įlankos pagal bendrijas skiriasi tarpusavyje (Global ANOSIM R: 0,758; p = 0,001), o tirpstančio ledyno zona lemia didesnius skirtumus (Global ANOSIM R: 0,501; p = 0,001), nei Isjordeno ir Hornsundo fjordų geografinė padėtis (Global ANOSIM R: 0,398; p = 0,001). Pagal morforūšių dominavimą įlankų transektose buvo išskirtos 4 bendrijos: Sabellidae, bioturbuojančios kirmelės, samangyvių ir dvigeldžių bendrija, bei ofiūrų bendrija.

For the last decades' temperatures in the Arctic, fjords increased dramatically. Due to the warming climate, glaciers in Svalbard are not forming fast enough during winter, which leads to a winter ice area loss trend close to 10 percent per decade since 1979 (Onarheim et al., 2014). Increased melting and retreat of glaciers on Svalbard leads to the release of coastal marine habitats in the upper sublittoral for colonization by benthic macroorganisms where ice scouring was a limiting factor (Węsławski et al. 2011). Benthic communities near retreating glaciers are also being affected by sediment stability, larger inorganic particle concentration, sedimentation rate, and amount of organic matter in sediments (Wlodarska-Kowalczuk, Pearson, 2004). The study of the benthic structure under these pressures is important for understanding the processes occurring in the Arctic. The majority of benthic studies in the Arctic, including Svalbard, were done in deeper depths (100-1000m), with the main focus on easily accessible large fjords and bays using large ships and traditional sampling techniques. However, complex bottom topography and the presence of floating ice significantly complicates the use of traditional sampling methods, forcing us to look for alternative approaches. One such technique is underwater visual technology, which has grown in popularity in recent decades based on its effectiveness in hard-to-reach places. In this work, it will be demonstrated that the use of an underwater video mosaic based on video filming along transects in the upper sublittoral can be a reliable method for identifying communities of visible macro-fauna. This work aimed to assess the structure of benthic communities on the West coast of Svalbard in melting ice and ice-free zones and to determine the regularities of the structure of these communities or functional groups in terms of the melting glacier and geographical location. Underwater video filming was carried out in July-August 2018-2019 in the upper sublittoral (2 –65 m) of Hornsund and Isfjord areas (western Svalbard), representing two ice-free (Gipsvika, Adriabukta) and two glaciated sites (Borebukta, Burgerbukta). Almost 3 hours of video materials were obtained using an ROV and "drop-down" video cameras. Video footage was transformed into 148 video mosaics, from which 33 biological features (morphospecies) were identified to the lowest possible taxonomic level, which were further ascribed to benthic functional groups (feeding type and mobility mode), and those were used for further analysis of benthic communities. The study showed that benthic communities in Borebukta which is located near retreating glaciers are largely dominated by mobile fauna (79,8 %) and scavengers (78,5 %), while communities in ice-free sites - Gipsvika (98,8 %), Adriabukta (64,2 %), and in one of the retreating glacier sites - Burgerbukta (90,4 %) are dominated by discretely mobile individuals. Suspension feeders were dominating in Gipsvika (63,5 %), Adriabukta (98,1 %) and Burgerbukta (91,0 %). In the West Svalbard study area 8 morphospecies was dominating: tube-dwelling anemone Ceriantharia, bivalves, feather duster worms Sabellidae, brittle stars, bioturbating polychaetes, shrimps, bryozoa Alcyonidium sp. and unidentified Bryozoa undet. individuals. In Burgerbukta (54 ± 84 ind. trans-1), Adriabukta (49 ± 68 ind. trans-1), and Gipsvika (25 ± 34 ind. trans-1) bays feather duster worms Sabellidae were the most dominant one, forming up to 50 % of total relative individual abundance, in Borebukta bay Ophiurida (76 ± 169 ind. trans-1) comprised 78,4 % of total relative individual abundance. Morphospecies richness, Shannon-Wiener diversity, and Pielou evenness indices did not show any significant differences between ice-free and glaciated sites. Nevertheless, the Hulbert index showed significant differences between Adriabukta (5,33 ± 1,52) and Gipsvika (1,6 ± 0,89) sites. MDS and ANOSIM analysis showed that benthic communities were statistically different in all bays (Global ANOSIM R: 0,758; p = 0,001) also that bays geographical allocation determined larger similarities between bays (Global ANOSIM R: 0,398; p = 0,001) than presence of melting ice (Global ANOSIM R: 0,501; p = 0,001). Finally, 4 benthic communities were distinguished. Sabellidea community which was most dominant in retreating glacier site Burgerbukta, and in Gipsvika which is affected by riverine discharge; bioturbating polychaetes (a most likely feature of sandworm Arenicola marina) which was most dominant in shallow riverine bay transects of Gipsvika; brittle stars community dominated in Borebukta and Bryozoans together with bivalves that were dominant in ice-free site Adriabukta. After these results, it is evident that melting ice is impacting the distribution of the sublittoral macrozoobenthic community structure in the study area.