Comparison of bryozoan assemblages from two contrasting Arctic shelf regions

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<ul><li><p>located at the same latitude and the samples were taken from similar depths; however, the regions differed in water temperature and oceanog-raphy. East Greenland, which has lower mean annual water temperatures, was found to be one third richer in taxa (86 species) than West Spits-bergen (59 species). Diversity (ShannoneWiener index e H0) and abundance were also higher on average in East Greenland (e.g. H0 2.49)than West Spitsbergen (e.g. H0 2.12). However for species richness, diversity and abundance there were no significant statistical differencesbetween means (ANOVA) from the two regions. In spite of these similarities the investigated assemblages differed to a large extent in bothspecies composition and dominance structure. There were 55 species that occurred only in East Greenland and 28 species that were presentonly in West Spitsbergen. There was higher proportion of species with an Arctic distribution in East Greenland (46%) than in West Spitsbergen(24%). Observed dissimilarities were concluded to be due to different hydrological conditions between the two regions. 2007 Elsevier Ltd. All rights reserved.</p><p>Keywords: biodiversity; water masses; Bryozoa; Arctic; East Greenland; West Spitsbergen</p><p>1. Introduction</p><p>Arctic hydrology is influenced by a complex of watermasses of different origin, thus environmental conditionsacross the Arctic marine system are not homogenous. Usuallythese water masses differ in seawater temperature, which af-fects annual longevity of ice cover, glacier retreat, freshwaterwater inflow and sedimentation into the marine ecosystem(e.g. Peterson et al., 2002). The shallow Arctic shelf is influ-enced to a large extent by the inflow of waters both fromdeeper parts of the oceans and by terrigenous waters fromthe continent. Thus these areas are controlled by ongoingchanges in both the terrestrial and marine environment.</p><p>Differences in physical conditions among Arctic localitiesare mirrored in the community structure of benthic faunal as-semblages. For instance, it was found that fish stocks of theBarents Sea follow fluctuations in seawater temperatures,with higher seawater temperatures favouring survival of thecritical early life stages of the fish (Ottersen et al., 2006).Analysis of annual photographs at a permanent rocky bottomstation on West Spitsbergen over a period of more than20 years revealed that diversity of the benthic biota is stronglylinked to sea water temperature e the higher the sea watertemperature the higher the biodiversity (Beuchel et al.,2006). On the other hand, there are examples where the pres-ence of warm water masses have an opposite effect on param-Comparison of bryozoan asseArctic she</p><p>Piotr Kuklinski a</p><p>a Institute of Oceanology, Polish Academy of Sciencesb University of Kiel, Institute of Geosciences,</p><p>Received 26 January 2007</p><p>Available onlin</p><p>Abstract</p><p>The structure of bryozoan assemblages from two Arctic regions (Ea</p><p>Estuarine, Coastal and Shelf Scienc* Corresponding author. Current address: Natural History Museum, Crom-</p><p>well Road, London SW7 5BD, UK.</p><p>E-mail addresses: (P. Kuklinski), (B. Bader).</p><p>0272-7714/$ - see front matter 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.ecss.2007.03.024mblages from two contrastinglf regions</p><p>,*, Beate Bader b</p><p>, ul. Powstancow Warszawy 55, Sopot 81-712, PolandLudewig Meyn Str 14, D-24118 Kiel, Germany</p><p>; accepted 29 March 2007</p><p>e 17 May 2007</p><p>st Greenland and West Spitsbergen shelf) was compared. Both areas are</p><p>e 73 (2007) like richness or biodiversity of Arctic biota. Aninvestigation of soft-bottom benthos at two Arctic locationsdiffering in seawater temperature has shown that the warmersite had lower species richness and biodiversity thana cooler site (Wlodarska-Kowalczuk and Weslawski, 2001).</p></li><li><p>aSeveral studies indicate that aquatic sessile organisms, bothindividually and collectively as assemblages, are good indica-tors of environmental conditions or long-term ecosystemchanges (Kroncke, 1995; Wlodarska-Kowalczuk and Weslaw-ski, 2001; Beuchel et al., 2006). In the Arctic, aquatic sessilecolonial invertebrates are one of the most diverse and abundantgroups among rocky bottom organisms (Gulliksen et al., 1999;Kuklinski and Bader, 2007). Their potential sensitivity tophysical parameters as well as high abundance make themgood candidates for comparative studies of locations differingin environmental conditions. This study focuses on bryozoanfaunal composition and assemblage structure on rocky sub-strates from two contrasting Arctic regions that differ in hy-drological conditions.</p><p>We conducted our investigation in two regions: East Green-land and West Spitsbergen shelf. Both have conspicuousoceanographic features. The East Greenland location is thelargest and most northernly Arctic Polynya (usually an open-water region within an otherwise ice-covered sea) influencedby the cold East Greenland Current. Thus this region can beconsidered as cold Arctic, whereas West Spitsbergen isinfluenced by the Gulf Stream and has a milder climate com-pared to other areas of similar latitude, and may be consideredas warmer Arctic (Gammelsrod and Rudels, 1983; Loeng,1991; Bignami and Hopkins, 1997; Ritzrau, 1997). These re-gions provide a good model systems for testing hypothesesconcerning the influence of different water mass propertieson the Arctic biota.</p><p>The aim of the study was to investigate faunal structure anddifferences between assemblages of bryozoans from two sitesat similar latitude but differing in seawater temperature. Wepredict that these assemblages will differ in species composi-tion, richness, diversity and abundance. We also predict thatthe proportion of species of temperate origin or Arctic speciesthat range into warmer seas will be higher in warm Arcticsite. Our hypotheses are based on the assumption that differ-ences in seawater temperature or sea ice cover longevitybetween the sites should be mirrored in dissimilarities amongassemblage structure.</p><p>2. Materials and methods</p><p>2.1. Study area</p><p>Two regions in Greenland Sea were selected: East Green-land and West Spitsbergen shelf (Fig. 1). Both are at thesame latitude (79N), and samples were taken from approxi-mately the same range of depths (East Greenland 75e233 mdepth, West Spitsbergen 122e260 m). The study sites differin hydrology, distance from the land and size of the shelf.The East Greenland site is strongly influenced by the EastGreenland Current, which originates in the Arctic Ocean.The salinity regime varies from 32.3 to 35 psu, while the tem-perature range is from 1.7 C to 3 C (Bignami and Hopkins,1997). The area is characterised by ice-free zones or loose ice-</p><p>836 P. Kuklinski, B. Bader / Estuarine, Coastcover throughout the year, although it is greatly reduced insize during the winter (Minnett et al., 1997). The WestSpitsbergen region is influenced mainly by the West Spitsber-gen Current, a branch of the warm (4 C) and highly saline(35 psu) Norwegian Current (Loeng, 1991). The area is usu-ally ice-free throughout the year (Svendsen et al., 2002). Ow-ing to the vicinity of land and glaciers, the West Spitsbergensite is influenced by freshwater discharge during the summerwhich causes strong water mass stratification and high concen-trations of suspended sediment (Svendsen et al., 2002). TheEast Greenland shelf is four times wider (w400 km) thanthe West Spitsbergen shelf (w100 km). The sea bottom atboth regions consists of fine clastic sediment with dropstones(ice rafted debris) of variable size (Piepenburg, 1988).</p><p>2.2. Protocol</p><p>Assemblage comparisons require the use of strictly standar-dised methods and sample-processing and only similarhabitats should be compared (Gray, 2001). Stones offer a uni-form substrate that is an ideal model habitat for such compar-isons. Therefore, we focus only on bryozoans inhabitingdropstones. Samples of rocks were taken during cruiseANTXVI/2 of the R/V Polarstern (East Greenland) and R/YOceania as well as the R/V Jan Mayen (West Spitsbergen)in August 2000 (Fig. 1). Samples were collected by meansof dredges. From each region (East Greenland and West Spits-bergen) 100 rocks supporting bryozoans were collectedhaphazardly. Number of rocks collected at each station is indi-cated on Fig. 1. Surface areas and faunal percentage coverageof stones were estimated using an inelastic net marked ina grid of 1 cm2. All bryozoans were determined to the lowesttaxonomic level possible and counted. Each colony was con-sidered as one individual. All taxonomic identities were deter-mined using Kluges (1975) monograph of bryozoans.Bryozoan species were classified biogeographically into threecategories according to Gontar and Denisenko (1989): Arctic,Arctic-boreal and boreal. The number of species in eachbiogeographical category was expressed as a percentage valuefor each location.</p><p>Abundance was calculated as the number of colonies persquare metre of rock surface area. Diversity measures werecalculated using the PRIMER software package (Clarke andGorley, 2001), including species richness and ShannoneWiener H0 diversity index (log base e). All data (speciesrichness, ShannoneWiener H0 diversity and abundance) weresubjected to ANOVAwith region as a spatial factor.</p><p>The relative similarity of site assemblages was comparedand displayed using PRIMER software package followingfourth, square root transformed as well as untransformeddata. BrayeCurtis similarity measures were calculated (Brayand Curtis, 1957). The inter relationship between sampleswas mapped using the ordination technique, non-metric, mul-tidimensional scaling (nMDS).</p><p>One-way analyses of similarities (ANOSIM; Clarke andGreen, 1988) were used to test a priori differences in assem-blages with region as a spatial factor. ANOSIM uses the test</p><p>l and Shelf Science 73 (2007) 835e843statistic R, which is calculated using average rank similaritiesamong pairs of replicates within each of two groups (e.g. East</p></li><li><p>GreenlandeWest Spitsbergen), minus the average rank simi-larity of replicates between groups, and is scaled to givea value between 1 and 1. Thus, R 1 when all similaritieswithin groups are less than any similarity between groups,R &gt; 0.75 when the groups are well differentiated, R &gt; 0.5when groups overlap but are clearly different, R &lt; 0.25when groups are barely separable, and R 0 when replicateswithin and between groups are equally similar (Clarke andGorley, 2001).</p><p>3. Results</p><p>In total 114 bryozoan taxa were recognized on 200 rocks(100 from each region) with a total surface area of18,764 cm2 (East Greenland rocks: 9140 cm2, West Spitsber-gen; 9624 cm2). The East Greenland sample was one thirdricher in taxa (86 species) than the West Spitsbergen sample(59 species). Species number at the East Greenland samplingsites ranged from seven (G3) to 48 (G1) species, with an aver-</p><p>(S2) to 44 (S1), with an average value for all sites of 19(Fig. 2).</p><p>Diversity (ShannoneWiener index e H0) at the East Green-land region varied from 0.91 (G3) to 3.32 (G1), with an aver-age value for all sites of 2.49, while on West Spitsbergen itranged from 0.77 (S3) to 2.88 (S1) with an average valuefor all sites of 2.12 (Fig. 2).</p><p>Total abundance (sum of number of individuals from eachsite) for both regions was 14,922 individuals m2. Abundanceat the East Greenland sites ranged from 180 (G3) to 1521 in-dividuals m2 (G4), with an average value for all sites of 843.West Spitsbergen bryozoan abundance varied from 532 (S6) to1464 (S1), with an average value for all sites of 821 (Fig. 2).</p><p>In all cases (species richness, diversity and abundance)there was no significant statistical difference between meansfrom the two regions (ANOVA, Fig. 2).</p><p>In spite of the similarities of the two sites for all the param-eters measured (species richness, diversity and abundance), theassemblages at the two regions differed significantly in species</p><p>Fig. 1. The study area with marked sampling sites and indication of currents directions (gray arrows e cold East Greenland Current, black arrows e warm Nor-wegian Current, in brackets number of rocks collected at each of the sites).P. Kuklinski, B. Bader / Estuarine, Coasage value across all sites of 26 species per site (Fig. 2). OnWest Spitsbergen the number of species ranged from four837tal and Shelf Science 73 (2007) 835e843composition and dominance structure (Table 1). For example,in the East Greenland biota the most common bryozoan was</p></li><li><p>the cheilostome bryozoan Smittina belli (Dawson) [8% of totalabundance], while the West Spitsbergen assemblage was dom-inated by the cyclostome bryozoan Oncousoecia diastoporides(Norman) [23% of total abundance] (Table 1). Fifty five spe-cies occurred only in East Greenland, and 28 species only in</p><p>Fig. 2. Mean values SE of species richness (A); diversity (B); and abun-dance (C) for East Greenland (EG) and West Spitsbergen (WS) assemblages.</p><p>838 P. Kuklinski, B. Bader / Estuarine, CoastWest Spitsbergen site. Thirty one species occurred at both re-gions. A higher proportion of species with entirely Arcticdistributions was recorded in East Greenland (46%) thanWest Spitsbergen (24%) (Fig. 3). Quantitative differencesbetween bryozoan species composition were confirmed bymultivariate analysis (nMDS) showing sites to be clusteredinto two distinct groupings: East Greenland and West Spitsber-gen (Fig. 4). Multivariate analyses of untransformed, squareand fourth root transformed data showed the same splitbetween East Greenland and West Spitsbergen samples. Sim-ilarly the ANOSIM (R 0.677, p 0.001) statistic indicatesthat the East Greenland bryozoan biota is clearly differentfrom West Spitsbergen.</p><p>4. Discussion</p><p>Several Arctic studies have indicated that annual changesin temperature of water masses at one particular location ora number of locations influence diversity, biomass and abun-dance of benthic organisms (e.g. Bahr and Gulliksen, 2001;Beuchel et al., 2006). Analysis of annual photographs ata permanent rocky bottom station on West Spitsbergen overa period of more than 20 years revealed that diversity andabundance of the benthic biota fluctuated with the tempera-ture of the local water mass (Beuchel et al., 2006). A similartrend was observed by Bahr and Gulliksen (2001). Speciesrichness and diversity of benthic communities from northernNorway were higher during years with increased sea watertemperature. There are also examples where the abundanceof organisms increased in spite of decreasing sea water tem-perature (e.g. Hagberg and Tunberg, 2000). This pattern wasattributed to the influx of nutrients from cold bottom watermasses.</p><p>The current study has revealed no statistical significant dif-ferences in assemblage parameters, including mean values ofspecies richness, diversity and abundance, between two re-gions (cold Arctic [East Greenland] and warm Arctic[West Spitsbergen]) from the same latitude and with similardepths yet differing in sea water temperature and salinity(Fig. 2). Our prediction that species richness, d...</p></li></ul>


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