© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at Bryozoans in polar latitudes: Arctic and Antarctic bryozoan communities and facies B. BADER & P. SCHÄFER Abstract: Bryozoan community patterns and facies of high to sub-polar environments of both hemi- spheres were investigated. Despite the overall similarities between Arctic/Subarctic and Antarctic ma- rine environments, they differ distinctly regarding their geological history and hydrography which cause differences in species characteristics and community structure. For the first time six benthic communi- ties were distinguished and described for the Artie realm where bryozoans play an important role in the community structure. Lag deposits resulting from isostatic uplift characterise the eastbound shelves of the Nordic Seas with bryozoan faunas dominated by species encrusting glacial boulders and excavated infaunal molluscs. Bryozoan-rich carbonates occur on shelf banks if terrigenous input is channelled by fjords and does not affect sedimentary processes on the banks. Due to strong terrigenous input on the East Greenland shelf, benthic filter feeding communities including a larger diversity and abundance of bryozoans are rare and restricted to open shelf banks separated from the continental shelf. Isolated ob- stacles like seamount Vesterisbanken, although under fully polar conditions, provide firm substrates and high and seasonal food supply, which favour bryozoans-rich benthic filter-feeder communities. In con- trast, the Weddell Sea/Antarctic shelf is characterised by iceberg grounding that causes considerable damage to the benthic communities. Sessile organisms are eradicated and pioneer species begin to grow in high abundances on the devastated substrata. Whereas the Arctic bryozoan fauna displays a low de- gree of endemism due to genera with many species, Antarctic bryozoans show a high degree of en- demism due to a high number of genera with only one or few species. However, the bryozoan growth forms of the Arctic seamount Vesterisbanken in the Central Greenland Sea show highest degree of cor- respondence with the Antarctic Weddell Sea shelf with a predominance of erect species. Key words: Bryozoa, polar marine environments, benthic communities. 1 Introduction In the Artie realm bryozoans are very of- ten the dominant component in benthic Apart from their polar position, low , • • « • i . . .. communities in boulder habitats and on epi- temperatures and the seasonal trends in irra- , , „„, ,. • . , i ji phytes (BARNES et al. 1996; LIPPERT et al. diance and ice cover, the north and south r ' polar benthos are strik.ngly different from 2001^ BARNES & KuKL1NSK1 2004>- AU each other. The Arctic bottom fauna con- thou8h the systematic work is quiet ad- sists of a small number of species of all ma- vanced> the role of bryozoans in ecosystems jor taxa. These species are mostly euryther- is wide'y unknown. KUKLINSKI (2004) con- mal and may have successfully invaded the ducted the first study on the quantitative North Polar waters from the boreal Atlantic composition and distribution of bryozoan or Pacific. In the Antarctic benthos, only a communities in Svalbard waters with a spe- few taxonomic groups have evolved into a cial focus on the Kongsfjorden ecosystem. large number of steno-thermal species, while the remainder of the higher taxa are Br^ozoa were found t0 be ver? sPecies' poorly represented on the Antarctic shelf. rich in the Arctic; the diversity is estimated Polar food webs show that annual primary t0 be wel1 above three hundred species production is poor and highly seasonal, the (KLUGE 1975) and they are amongst the benthos is largely de-coupled from the richest of the Arctic macrofauna (GULLIK- pelagic zone and the majority of polar ani- SEN et al. 1999). West Spitsbergen is proba- Denisia 16, zugleich Kataloge mals grow slowly and reproduce late. bly the best investigated of high Arctic sites, Neue Serie 28 (2005), 263-282 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at Fig. 1: Research vessel Polarstern in the Weddell Sea in May 2000. new species are still being added even in shallow water (KuKLlNSKl & HAYWARD 2004). Bryozoans are a major component of the Antarctic benthos in many of the areas that have been studied (BULLIVANT 1961, 1967; WINSTON 1983; VOB 1988; WINSTON & HE- IMBERG 1988; GALERON et al. 1992; BARNES 1995a, b, BARNES & CLARKE 1998; MOYANO &. RlSTEDT 2000). The last few decades have seen a dramatic explosion of taxonomic and ecological work in southern polar waters. Many new Antarctic cheilostomatid bryo- zoan species and genera have been de- scribed, whilst the taxonomic status of many others has been elucidated (see HAYWARD 1995 and references therein). In contrast to other Antarctic shelf sites the bryozoan fau- na of the Weddell Sea is not well known. RlSTEDT (1995) presented a first description of the bryozoan fauna, ZABALA et al. (1997) a first taxonomic list of the Weddell Sea bryozoans. 2 Material and working areas Living bryozoans and bryozoan carbon- ates were collected during several cruises in the years 1989, 1990, 1994 and 2000 with the German research vessels "Meteor", "Lit- torina", "Polarstern" (Fig. 1) and the Nor- wegian research vessels "Ottar" and "Johan http:// www.cpc.ncep.noaa. Rud". The working areas are the Arctic do- Fig. 2: Study areas with the shelves of North Norway (1), Barents shelf / SW main with a main focus on the shelves of Spitsbergen (2), Central Greenland Sea (3) and the Weddell Sea (4). 264 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at North Norway, Northeast Greenland and In contrast to the Norwegian continen- Fig. 3: Preparation of an Agassiz trawl (A) the central Greenland Sea (Fig. 2, 4); and tal shelf, the East Greenland shelf is fed by and catch of an Aggassiz trawl (B) on board of Polarstern in April 2000 in the the Antarctic domain with the Weddell Sea water masses of polar origin (East Greenland Weddell Sea/Antartica. as study area (Fig. 2, 13). The material was Current) with year-round lowest tempera- sampled by means of grab, giant box corer, tures and salinities. Most of the year the and dredge (Fig. 3). The material was either shelf is covered by sea ice except of the dried or preserved in 70 % alcohol. Under- northern section, where the seasonally de- water video and camera was used to docu- veloped coastal Northeast-Water polynya ment distribution of the fauna and flora on brings open-water conditions during sum- the sea floor. mer months. This polynya affects Belgica Bank, an open shelf bank isolated from the 3 Bryozoan communities East Greenland shelf and surrounded by an anti-cyclonic spin-off of the East Greenland 3.1 Arctic and Current (Fig. 4). Fig. 4: Oceanographic current regime and location of study area with Belgica Subarctic communities Bank/North-East Greenland (1), Spitsbergen 3.1.2 Holocene history Bank/Barents Shelf (2a) and Westspitsbergen Shelf (2b), Seamount 3.1.1 Hydrography Due to Holocene eustatic sea level rise Vesterisbanken/central Greenland Sea (3), and isostatic uplift of the continental crust The temperate Atlantic waters in the Rakkfjord/North Norway shelf (4) and because of continental ice melting (Scandi- Trondheim Shelf/North Norway (5). East, the cold ice-covered Polar waters in the West and the seasonally ice-covered Arctic waters in between are the three ma- jor surface water masses in the Nordic Seas. They occur close together but are separated by steep oceanic gradients. The North Nor- wegian shelf is mainly affected by the Nor- wegian Coastal Current, which runs north- ward and parallel to the Norwegian Current (Fig. 4). Along the outer edge of the Barents Sea and the West Spitsbergen shelves, At- lantic waters of the Norwegian Current are separated from the polar water masses of the Spitsbergen Bank and the East Spitsbergen Currents by the Polar Front. In contrast, seamount Vesterisbanken in the central Greenland Sea and most of the Barents Shelf lie under polar water masses through- out the year. 265 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at amict started around 12.6 ka on the North Norwegian shelf (SCHÄFER et al. 1996). In- vasion by the marine benthos reached the Barents Shelf (Spitsbergen Bank) around 8.6 ka (HENRICH et al. 1997) and West- Spitsbergen shelf around 9.1 ka (AN- DRULE1T et al. 1996). Due to isostatic uplift after melting of the continental ice sheet, shelf banks uplifted, the endofauna was washed out and the lag deposit colonised by a diverse epifauna including bivalves, bryo- zoans and balanid cirripedians at around 2.0 ka (Northern Norway), at 2.8 ka (Spits- bergen Bank), and at 2.6 ka (West-Spits- bergen shelf)- In contrast, the Greenland shelf with its still prominent ice cover became less uplift- ed; therefore, the shelf break remains in a water depth of 500 to 600 m. Shelf banks are covered by silts and muds, prominent lag de- posits are mostly lacking. Bank with lag de- posits and coarse-grained sediments such as the Belgica Bank in the Northeast Water polynya are rare and completely separated from the continental hinterland. 3.1.3 Fjordic environments Fjords in subpolar latitudes are charac- terised by nearly vertical walls and water depths from intertidal down to 200 m. Sea floor in deeper parts of the fjords is covered by fine mud. Shallow sites on trough shoul- ders and fjord sills, however, display a rela- tively large variety of communities in which bryozoans are important constituents. Two distinct bryozoan communities can be dis- tinguished: Red algae - bryozoan - Fig. 5: Free living rhodolith of navia, Barents Sea, Greenland) the subpo- polychaet communities Lithothamnium boreale (A), L. boreale lar shelves surrounding the Nordic Seas en- encrusted with weakly calcified bryozoan Dense consortia of coralline and non- countered a very complex geologic history. Dendrobeania spp. (B). Scale bar = 1 cm. coralline red algae and bryozoans fixed to- The North Norwegian Shelf, the Barents gether by polychaete tubes occur in the Shelf and the West Spitsbergen shelf ran Rakkfjord, Troms, North Norway, in about through several transgressions and regres- 10 m water depth. The red alga Lithothamni- sions, the shelf break is in about 200 water urn boreale forms free living rhodoliths with depths, and the shelves are covered by car- an open branch structure; the bryozoans are bonate-lag deposits. During Holocene his- mostly erect, often articulated and weakly tory, shelves were affected by the interplay calcified anascans such as Dendrobeania mur~ of eustatic sea-level rise and isostatic uplift rayana, D. pseudomurrayana, D. frucucosa, resulting in erosion of an early Holocene Scrupoceliaria sabra, and Notopiites normanni bivalve endofauna forming a carbonate lag (Fig. 5). The consortium forms a rich habi- deposit. Colonisation of a late glacial di- tat housing a high diversity of delicate bryo- 266 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at zoans (Caüopora craäcula, Tegella araka and others) and serpulids (Spirorbis sp.). The fil- ter feeders benefit from the elevated posi- tion above the sea floor formed by the rhodoliths. Chlamys islandica - banks Fouling communities are well-defined ecosystems with narrow limitations in time and space. Larval recruitment and competi- tion for space are considered to be the major factors that control the adaptive success of colonial and solitary organisms within this highly stressed environment. The boreal-Arctic pectinid bivalve Chlamys islandica lives in great abundance in a water depth of 20 to 70 m in the outer fjords of Troms, North Norway. The living clams are heavily fouled by bryozoans asso- ciated with barnacles, serpulids, hydrozoans, sponges, small molluscs and brachiopods, crustose coralline algae, and foraminifers (SCHÄFER 1994,1997). Clams are attached by byssus (young in- dividuals) or are free living (adults) on the builds the largest colony and is considered Fig. 6: Chlamys islandica with sea bottom with their left valves turned up- to have higher growth rates than others. Dendrobeania spp., encrusting bryozoans, wardly and with their right valves facing the hydrozoans and a balanid tube. Left valves, however, are exposed to a Scale bar = 1 cm. substrate. This specific orientation results in more complex physical environment where major environmental differences on left and water turbulence prevails. A larger diversity right valve surfaces that in addition to the of higher taxa occurs. It is indicated by a recruitment of pioneer taxa and competi- tion for space strongly influence the ecolog- dominance of barnacles, flexible bryozoans ical structure of the fouling communities. {Dendrobeania spp., Scrupocetiaria spp.) and hydrozoans, encrusting bryozoans (Poreüa Right valves roof a cryptic habitat and minuta, Microporelia ciliata, Escharelia immer- are mainly exposed to moderate, laminar sa, Tegella arctica, and Oncousoecia diasto- water currents. Encrusting bryozoans and poroides), and sponges (Fig. 6). "Unlimited calcareous polychaets dominate the fouling spaces" is available due to upright-flexible communities. Diversity of higher taxa is low. growth of anascan bryozoans resulting in Highest species diversity occurs on valves formation of a variety of ecological niches. with moderate encrustation. Limited space The communities are, therefore, more com- and same requirements for food and space of plex, distinctly tiered, and interacting. A the sessile-benthic organisms result in a dis- domination stage is rarely developed. tinct vertical succession of highly competi- tive but rather simple fouling communities 3.1.4 Open shelf banks finally dominated by a few species (Porelk eastern boundary shelves minuta, SchizomaveUa linearis) only. The lat- ter species switch from zooidal to multi- Open shelf banks of the Norwegian zooidal budding pattern when encountering shelf, the Barents shelf and West Spitsber- other colonies and, thus, have a competitive gen shelf are exposed to waves, and to strong advantage against other species. The most tidal and bottom current. Here, solid rock, competitive species, Porella minuta, as well moraine boulders and coquinas serve as an as Celkporella hyalina, may even switch to ideal ground for larval settlement (Fig. 7). frontal budding. Additionally, Porella minuta Because of high water energies, multiserial- 267 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at encrusting species dominate today the bryo- :oan fauna on the shallow banks. Depend- ing on the kind and abundance of suitable substrate to colonise, epibenthic organisms vary in diversity and abundance. In more soft-bottom habitats, uniserial runners such as Hippothoa spp. dominate on isolated rock pebbles, while large pebbles and boulders are colonised by a diverse multiserial-en- crusting bryozoan community (Fig. 8A). They are associated with a few up- right/branching (Homera lichenouks, Myria- pora spp., Idmidronea atlanaca), massive-do- mal (Ceüepora spp.; Fig. 8B), fenestrate (Serteüa septendrionalis) and upright-flexible (Dendrobeania spp.) species. Competition for space among multiserial-encrusting species is distinctly higher than in uniserial colonies as well as in dendroid and fenes- trate deeper-water bryozoan communities. Western boundary shelves Belgica Bank off the Northeastern Greenland shelf is characterised by grain size and seabed heterogeneity and a diverse invertebrate fauna of mostly vagile epifaunal and endofaunal organisms (see PlEPENBURG et al. 1997) (Fig. 9). Large ripple fields with dead valves of the infaunal Mya truncata ac- cumulated in the ripple troughs indicate near-bottom currents. Larger fields of dead valves of M. truncata and living and dead Astarte sp. cover larger areas of the northern Ob Bank. The bryozoan fauna revealed 68 cheilostomate, 12 cyclostomate and 2 ctenostome species indicating a typically high-Arctic circumpolar character with few- er boreal elements. Bryozoans display a patchy distribution. Suitable substrates are smaller and larger ice-rafted boulders and glacigenic lag deposits (Fig. 9C, D). Species with upright branching colonies (Myriapora subgracilis, Homera lichenoides) and those with bifoliate fenestrate growth (Dipbsolen Fig. 7: Underwater photographs of Arctic epibenthic communities and carbonate deposits intricarius) were found on UW-photographs from Spitsbergen Bank, western Barents Sea taken during Meteor cruise M-21/4. A: Mya (Fig. 9B, C, D) and in the sediment. Small truncata lag-deposit with branched bryozoans (Myriapora sp., Celleporella sp.) (B) and numerous ophiuroids (black triangle), Mya truncata valves are grazed by and large boulders are encrusted by unilami- strongylocentroid echinoids (S). The siphones belong to M. truncata (black arrow). nar, bi- and multiserial bryozoan colonies. 74°34N, 21°00E, 101 m water depth, scale = 30 X 30 cm. B: Mya truncata-Hiatella arctica Densest overgrowth occurs at sides of larger belt with boulders and pebbles, which are intensely encrusted by large bushy hydrozoans boulders, whereas upper sides of boulders are (HY) and sponges (P). Branched bryozoans (Myriapora sp.) (B) and strongylocentroid echinoids (S) are quite abundant. 74°40'N, 20°47E, 79 m water depth. The long axis of the rarely colonised indicating a strong grazing Chlamys islandica (C) valve is 8 cm. Pictures from HENRICH et al. (1995). pressure by vagile carnivorous organisms. Be- sides bryozoans, sessile foraminifers, poly- 268 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at chaet tubes, rare balanids and siliceous sponges cover the boulders. Hemisessile and vagile crinoids (Heliometra giacilis), pectinids (Arcmuia greenhmdica) as well as sea urchins, brittle and sea stars use boulders to rest and feed. The overall encrustation pat- tern indicates the intensity of colonisation increases with the boulder sizes. The overall benthic colonisation pattern counts for a strong pelagobenthic coupling and its control over structuring of benthic communities (PlEPENBURG et al. 1997). It is presumed that also the bryozoans benefit from food-rich conditions along sea-ice mar- gins of the NE Water polynya over Belgica Bank and Ob Bank. Organic fluff covering Ob Bank indicates a pulse-like export of green algae to the sea bottom as it is typical for mainly physically controlled particle flux in the Greenland Sea (PEINERT et al. 2001). Small-scaled patchiness of bryozoan dis- tribution on individual boulders/dropstones in an otherwise muddy environment follows the concept of "mini-islands". Tiering oc- curs in 4 levels: tier (1) is occupied by en- crusting bryozoans (cyclostomids and cheilostomids). Tier (2) is structured by small, upright growing, mostly tubuliporid bryozoans (Tuimlipora spp., Entalopharoecia clavata, Idmidronea atlantica). Encrusting species can benefit from irregularities of the boulder surfaces. The sessile, suspension feeding foraminifer Rupertina stabilis may reach into the second tier. The pectinid Arctinula greenlandica mediates between the second and third tier. Tier (3) is occupied by upright branching bryozoans (Homera the spinous zooidal apertures characterising Fig. 8: Massive-domal bryozoan lichenoides, Myriapora graciks, Dipfosokn inrri-the colonies (SCHÄFER et al. 1991). Celleporella sp. (A); pebble encrusted with upright-flexible (Dendrobeania sp.) and carius), small sponges, hydrozoans, and the Bryozoans collected in August 2000 on encrusting bryozoans, balanids and cirriped Balanus balanus. Small epizoans serpulids (B). Scale bar = 1 cm. (e.g. foraminifers) use older parts of bry- Belgica Bank revealed a large number of ozoan colonies for life within this tier. Tier small, non-fertile colonies; however, also (4), finally, is characterised by large crinoids mature colonies with embryos in ovicells (Heliometra glacials) and large cylindrical (Amphibiestrum trifolium var. quadrata, Hip- sponges. Competition for spaces is rarely podiplosia borealis, Smittina peristomata) were found in this environment due to the sparse found. The number of empty ovicells, how- benthic colonisation. In general, cheilosto- ever, exceeded the number of ovicells with mids dominate over cyclostomes in monop- embryos. Comparable substrates on Barents olising colonisation of surfaces. The only shelf and North Norwegian shelf collected exception is the small-sized cyclostome Dis~ in the same season (July 1990 and August porella hispida successfully preventing over- 2000, resp.) showed a higher percentage of growth by other species. This is explained large colonies probably indicating a longer, by the broad confluent budding zones and several years life cycle. 269 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at Fig. 9: Underwater photographs (scale = 1 m2) of Arctic epibentic communities from 3.1.5 Seamounts Belgica Bank, North Greenland taken during Polarstern cruise ARK III. A: Muddy facies The submarine, intra-plate volcano with some pebbles and crinoids (C). 78°46'N, 06°26'W, 270 m water depth. B: Muddy facies with ophiurids (0) and an upright branching bryozoans (Myriapora sp.) (B). 79°02'N, Vesterisbanken lies in the central Green- 07°44'E, 190 m water depth. C: Pebble field with ophiurids, upright branching bryozoans land Sea. A nearly year-round sea-ice cover, {Myriapora sp.) (B). 79°60'N, 14°0TW, 80 m water depth. D: Muddy field with pebbles and which retreats only during two months, very ophiurids (O), upright branching bryozoans (Myriapora sp.) (B) and echinoids (S). 79°59'N, low temperatures (-1 to 0 °C), and salinity 11 "33^, 80 m water depth. Pictures courtesy of D. Piepenburg (Institute of Polar Ecology, of 34-5 %o are recorded at nearly constant University Kiel). values over the entire water column (HEN- RICH et al. 1992). Despite this polar environment, a rich and diverse benthic community dominated 270 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at by siliceous sponges and bryozoans have colonised the various habitats of the seamount down to more than 2000 m water depth (Fig. 10). The topography of the seamount, the limited terrigenous input, and the seasonal increase of nutrients by down-welling enables the predominance of filter feeders to occur with high diversity and population densities down to great wa- ter depths. The top and flanks of the volcano dis- play a pronounced depth zonation of benth- ic communities. An almost continuous bio- genic mat composed of small demosponge- bryozoan-polychaet mounds and hedges covers the summit in 130 to 260 m water depth (Fig. 10A). In 260 to 400 m water depth, pectinid bivalves and polychaets dominate the substrate covered by volcanic ashes. Locally, demosponge-bryozoan-ser- pulid mounds are developed on volcanic el- evations. The extremely steep slopes below 400 m reveal various kinds of sponge-bry- ozoan mounds, sponge mounds, and a typi- cal hexactinellid sponge-crinoid assemblage on coarse volcaniclastics and firm lava ground (Fig. 10B, C). Fig. 10: Underwater photographs (scale = 2 m2) of Seamount Vesterisbanken communities from Central Greenland Sea taken during Polarstern cruise ARK VII. A: A section of a bryozoan-sponge thicket in the crest facies. A dense bryozoan thicket covers the substrate completely. Bryozoans (BRY) are dominated by Sertella elongata which forms erect reticulate fans. Poecilosclerid Clathria (PCL), actinians (A), and serpulids live in this thicket. OFOS track 21880-7, 197 m water depth. B: A section of a sponge-bryozoan mound in the deep slope facies. The core of these deep slope mounds are Thenea (TH) and Geodia (G). The mound surface is colonised by large poecilosclerid Clathria (PCL), yellow poecilosclerid crusts (Mycalel) (PY), Schaudinnia (S), fan-type bryozoan colonies (BRY), and serpulids. OFOS track 21891-1A, 450 m water depth. C: A section of bryozoan thicket in the deep slope facies. The deep slope bryozoan thickets (BRY) are dominated by slender, dichotomously branching and reticulate growth forms, probably Idmidronea atlantica var. gracillima and Sertella elongata. The bryozoan thickets are associated with geodiid sponges (G), actinians (A), and large, blue ascidians (AS). OFOS track 21891-1C, 1008 m water depth. Pictures from HENRICH et al. (1992) 271 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at 272