bioRxiv preprint doi: https://doi.org/10.1101/353060; this version posted June 21, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 1 2 3 4 Spatial distribution of benthic macrofauna in the Central Arctic Ocean 5 6 7 Andrey Vedenin1*, Manuela Gusky2, Andrey Gebruk1, Antonina Kremenetskaia1, 8 Elena Rybakova1, Antje Boetius2,3 9 10 11 12 1 P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, 13 Nakhimovsky Pr. 36, 117997 Moscow, Russia 14 15 2 Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 16 D-27570 Bremerhaven, Germany 17 18 3 Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, 19 Germany 20 21 Corresponding author 22 E-mail: [email protected] bioRxiv preprint doi: https://doi.org/10.1101/353060; this version posted June 21, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 23 Abstract 24 Permanent ice coverage and the low primary production in the mostly ice-covered Central Arctic 25 ocean basins result in significantly lower biomass and density of macrobenthos in the abyssal 26 plains compared to the continental slopes. However, little is known on bathymetric and regional 27 effects on macrobenthos diversity. This study synthesizes new and available macrobenthos data 28 to provide a baseline for future studies of the effects of Arctic change on macrofauna community 29 composition in the Arctic basins. Samples taken during three expeditions (in 1993, 2012 and 30 2015) at 37 stations on the slope of the Barents and Laptev Seas and in the abyssal of the Nansen 31 and Amundsen Basins in the depth range from 38 m to 4381 m were used for a quantitative 32 analysis of species composition, abundance and biomass. Benthic communities clustered in five 33 depth ranges across the slope and basin. A parabolic pattern of species diversity change with 34 depth was found, with the diversity maximum for macrofauna at the shelf edge at depths of 100- 35 300 m. This deviates from the typical species richness peak at mid-slope depths of 1500-3000 m 36 in temperate oceans. Due to the limited availability of standardized benthos data, it remains 37 difficult to assess the massive sea ice retreat observed in the past decade has affected benthic 38 community composition. The polychaete Ymerana pteropoda and the bryozoan Nolella sp. were 39 found for the first time in the deep Nansen and Amundsen Basins, as a potential first sign of 40 increasing productivity and carbon flux with the thinning ice. 41 bioRxiv preprint doi: https://doi.org/10.1101/353060; this version posted June 21, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 42 Introduction 43 The deepest parts of the Central Arctic, including the abyssal plains of the Nansen and 44 Amundsen Basins separated by the Lomonossov Ridge, are among the least studied areas of the 45 global oceans. Most surveys of Arctic benthos have been conducted on the shelf or upper slope, 46 whereas data from the deep basins remain rare and scattered in time and space. First data on the 47 deep-sea fauna of the Central Arctic were obtained in 1935 using trawls and dredges not suitable 48 for taking quantitative samples. Qualitative descriptions of the Central Arctic bathyal and abyssal 49 fauna were made by Soviet expeditions on the vessels Sadko in 1935-1937 and F. Litke in 1955 50 [1,2]. First quantitative data using mini-LUBS corer and “Okean” grabs were collected in the 51 1970s in the Canadian Basin from the American Fletcher’s Ice Island [3] and the Soviet drifting 52 station North Pole-22 [4]. The authors reported extremely low abundances at depths >1000 m of 53 a few individuals per m2 and hence a very low benthos biomass of around 0.04 g/m2. A recent 54 review of the Arctic macrobenthos confirms the strong decline in biomass by over an order of 55 magnitude from the outer shelves to the inner basins of the Arctic Ocean [5]. The Arctic deep- 56 sea benthos has likely evolved from shallow-water relatives inhabiting the large shelves, with 57 cold temperatures close to freezing point prevailing across the entire depth range. Till today, the 58 communities of the deep basins and the outer shelf share more than half of their taxa [5], and 59 food limitation seems to be the main factor structuring community composition [6]. 60 Today, when the rapid warming and sea ice decline are likely to change the Arctic 61 ecosystem in its entity, comparative analyses of macrofauna community composition, diversity 62 and abundance in space and time remain challenged by the paucity of quantitative, standardized 63 macrofauna data. Sampling surveys were made during expeditions of the research icebreakers 64 Ymer, Polarstern, Oden and Polar Sea in the 1990s and 2000s, but unfortunately not with 65 internationally standardized procedures [7-12]. Over 25 macrobenthic samples were retrieved in 66 1991 during the Polarstern expedition to the Nansen and Amundsen Basins [13,14], but the low 67 volume of sample obtained caused problems in diversity detection [15]. During the Polarstern bioRxiv preprint doi: https://doi.org/10.1101/353060; this version posted June 21, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 68 expeditions in 1993 and 1995, nine bathymetric transects were made at the northern slopes of 69 Barents, Kara and Laptev Seas from shelf to abyssal depths. Results of these surveys were partly 70 published by [11], [15] and [16]. The present study provides additional analyses of legacy 71 samples from these expeditions and adds a substantial number of new data from surveys during 72 the sea-ice minimum in 2012 [6,17]. 73 Patterns of bathymetric distribution of benthic fauna were previously reviewed for different 74 temperate and tropical ocean regions [18-23]. According to generally recognised patterns, the 75 density and the biomass of macrobenthos decrease with depth due to the declining flux of 76 particulate matter as main food supply. In contrast, species diversity shows a parabolic pattern 77 with a maximum at depths of 1500-3000 m [24-27]. In the Arctic, the known species diversity of 78 around 1100 taxa does not appear to follow this pattern, and no mid-depth peak of diversity was 79 yet detected, potentially due to the strongly limited food supply (summarised in [28]). 80 This hypothesis is supported by recent studies of horizontal distribution patterns of 81 macrofauna within the deep-sea Central Arctic. From the shelf to the deep-sea basins, food 82 supply is declining not only because of increasing water depth, but also because northwards, the 83 sun angle and the sea-ice conditions limit light availability to primary producers. A summary of 84 the abundance, biomass and modelled productivity of the Central Arctic macrofauna was 85 recently published by [6], covering samples from a 20-year period and a depth range of 520- 86 5420 m. It was shown that standing stock and production of the benthic communities are several 87 times higher under the seasonal ice than under the multiyear ice zones. This correlation was 88 explained by the different particle flux under the seasonally and permanently ice-covered areas 89 [6,17]. 90 In the present study we aimed at further testing the effect of location, water depth, sea ice 91 cover and phytodetritus flux for a large standardized data set of macrofauna at high taxonomical 92 resolution, focusing on the Eurasian slope and basin. [28] noted before, that analytic differences 93 among investigators make difficult or even impossible to synthesize species lists from different bioRxiv preprint doi: https://doi.org/10.1101/353060; this version posted June 21, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 94 studies. In our study the entire set of samples was identified by the same specialists. Another aim 95 was to test the entire data set available for any indication of decadal change in community 96 composition between the 1990s and today, i.e. before and after the significant sea ice decline in 97 this region [29]. We examined the bathymetric distribution patterns of macrofauna along the 98 Barents and Laptev Sea slopes and the spatial distribution pattern within central parts of the 99 Amundsen and Nansen Basins. Our hypotheses were the following: 1) Variations in 100 macrobenthos distribution are controlled by food availability; 2) Community similarity is high 101 across all depth zones; 3) Sea ice retreat leads to change in the community structure. 102 103 Materials and methods 104 Sampling 105 Material for this study was obtained from three expeditions. During the RV Polarstern 106 expedition ARK-IX/4 (August-September 1993), 44 benthic stations were sampled on northern 107 slopes of the Barents and Laptev Seas and adjacent shelf areas and the Nansen Basin.