A Unique Assemblage of Epibenthic Sessile Suspension Feeders with Archaic Features in the High-Antarctic
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ARTICLE IN PRESS Deep-Sea Research II 53 (2006) 1029–1052 www.elsevier.com/locate/dsr2 A unique assemblage of epibenthic sessile suspension feeders with archaic features in the high-Antarctic Josep-Maria Gilia,Ã, Wolf E. Arntzb, Albert Palanquesa, Covadonga Orejasb, Andrew Clarkec, Paul K. Daytond, Enrique Islaa, Nuria Teixido´a, Sergio Rossia, Pablo J. Lo´pez-Gonza´leze aInstitut de Cie`ncies del Mar (CMIMA-CSIC), Passeig Marı´tim de la Barceloneta 37-49, 08003 Barcelona, Spain bAlfred-Wegener-Institut fu¨r Polar- und Meeresforschung, Columbusstrasse, 27568 Bremerhaven, Germany cBritish Antarctic Survey, NERC, High Cross, Madingley Road, Cambridge CB3 0ET, UK dScripps Institution of Oceanography, La Jolla, CA 92093-0227, USA eDepartamento de Fisiologı´a y Zoologı´a, Universidad de Sevilla, Av Reina Mercedes 6, 41012 Sevilla, Spain Received 17 April 2005; accepted 3 October 2005 Available online 21 July 2006 Abstract We suggest that the epibenthic communities of passive suspension feeders that dominate some high-Antarctic seafloors present unique archaic features that are the result of long isolation, together with the effects of environmental features including reduced terrestrial runoff and favourable feeding conditions. These features probably originated during the Late Cretaceous, when the high-Antarctic environment started to become different from the surrounding oceans. Modern Antarctic communities are thus composed of a mixture of Palaeozoic elements, taxa that migrated from the deep ocean during interglacial periods, and a component of fauna that evolved from common Gondwana Cretaceous ancestors. We explore this hypothesis by revisiting the palaeoecological history of Antarctic marine benthic communities and exploring the abiotic and biotic factors involved in their evolution, including changes in oceanic circulation and production, plankton communities, the development of glaciation, restricted sedimentation, isolation, life histories, and the lack of large predators. The conditions favouring the retention of apparently archaic features in the Antarctic marine fauna remain to be fully elucidated, but high-Antarctic communities are clearly unique and deserve special conservation. r 2006 Elsevier Ltd. All rights reserved. Keywords: Benthic communities; Epibenthos; High-Antarctic; Suspension feeders; Paleozoic fauna; Palaeoecology 1. Introduction (Clarke and Johnston, 2003). There is, however, also significant spatial heterogeneity generated by Antarctic benthic communities have a predomi- variations in ice cover, sediment dynamics, and local nantly circumpolar distribution, probably related to hydrodynamic and trophic factors (Clarke and the powerful Antarctic Circumpolar Current Crame, 1989). Current data suggest that the continental shelves of the Weddell and Ross seas ÃCorresponding author. Fax: +34 93 221 7340. exhibit the greatest diversity and the highest E-mail address: [email protected] (J.-M. Gili). biomass levels in the Antarctic (Dayton et al., 0967-0645/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr2.2005.10.021 ARTICLE IN PRESS 1030 J.-M. Gili et al. / Deep-Sea Research II 53 (2006) 1029–1052 1974; Arntz et al., 1994; Gutt and Starmans, 1998). Bryozoa, Brachiopoda, and both solitary and Indeed these habitats, extending from the edge of colonial Ascidiacea. The mobile epifauna includes: the continental ice sheet beyond the shelf edge, often Echinodermata (regular Echinoidea, Asteroidea, to depths greater than 600 m, are among the richest Ophiuroidea, Holothurioidea); Peracarida (Amphi- in terms of sessile fauna in the world ocean (Dayton, poda, Isopoda, Tanaidacea, Mysidacea, Cumacea), 1990). These high-Antarctic benthic ecosystems are Ostracoda, Caridea, Teleostei, Selachii (Rajidae), unusual in a number of ways, notably in the depth Prosobranchia, Opisthobranchia, Polyplacophora, of the shelf, the dominance of sessile suspension Bivalvia, Cirripedia (Balanidae, rare and Scalpelli- feeders, and the development of complex three- dae), Scleractinia (solitary), Turbellaria, Nemerti- dimensional biogenic structures on soft bottoms. nea and Pterobranchia. The sparse infauna includes: Although the Antarctic shelf fauna contains a recent Polychaeta, Bivalvia, Prosobranchia, Echiurida, component, which probably arrived along shallow- Priapulida, Sipunculida, irregular Echinoidea, Sca- water routes, it also contains relict taxa whose phopoda and Solenogastres (Arntz et al., 1994; evolutionary history can be traced back in some Fogg, 1998; Gutt et al., 2000, 2004). The dominant cases to the Palaeozoic (Feldmann and Crame, taxa can vary over short distances (Teixido´et al., 1998). Here we argue that the composition of the 2002), and this pattern is largely determined by modern communities in the Weddell Sea, and other iceberg scour (Gutt and Starmans, 1998). In the high-Antarctic areas, is the result of a low-sedimen- Weddell Sea this community ranges over depths tation environment, which was also characteristic of from ca. 70 m down to about 400 m, and lives well Cretaceous epicontinental seas (Leckie et al., 2002). within the zone of iceberg scour. These benthic The evolutionary pattern followed by these communities display a key characteristic that communities has differed from the pattern in other differentiates them from most other shelf ecosys- oceans because of the very different ecological tems extant today in that they are dominated by influences to which they have been exposed. In sessile suspension feeders living mostly on soft many respects these conditions are akin to the substrata. conditions existing in the oceans at the beginning of The principal difference between the faunal the Palaeocene (Dingle and Lavelle, 2001). Our assemblages of modern Antarctic continental hypothesis thus is that this similarity of certain shelves and those in other oceans is that these environmental conditions might have resulted in the three-dimensional communities cover large sections development of communities with life forms con- of the Antarctic continental shelves, whereas else- vergent on Cenozoic rather than Palaeozoic faunas. where they are found only on rocky substrata or are In this review we examine the apparently archaic confined to specific areas such as deep coral banks features in the structure and morphotypes of the (Mortensen and Buhl-Mortensen, 2004). In recent benthic communities of high-Antarctic shelf in the years, detailed studies carried out in the Weddell Weddell Sea (Gutt and Starmans, 1998), Ross Sea Sea and other regions of the high-Antarctic (Dayton et al., 1974; Dearborn, 1977), and other continental shelf have demonstrated clearly the areas (Dell, 1972), and attempt to explain these richness and high degree of heterogeneity of features. communities dominated by sessile suspension fee- ders, many of which extend continuously over 1.1. Composition of benthic communities in the high kilometres (Gutt, 2000; Teixido´et al., 2002). Antarctic 1.2. High-Antarctic communities at shallower and Although the shallow-water communities of the deeper depths Antarctic continental shelf have a distinctly archaic, deep-sea character, the taxa themselves are not True shallow-water communities are missing in necessarily ancient or primitive, and many are those parts of the high-Antarctic where ice shelves highly derived (Aronson et al., 1997). The main cover all shallow-water sites. This is true for the components of the sessile suspension-feeding com- Weddell and Lazarev Sea coasts, and to a lesser munities in the high-Antarctic are: Porifera (De- degree for the Ross Sea coast. Here, however, there mospongia, Hexactinellida, Calcaria), Gorgonaria, are sites within diving depths (e.g. around McMur- Pennatularia (mostly deeper), Alcyonaria, Stoloni- do Sound: Dayton et al., 1974, and Terra Nova Bay: fera, Hydrozoa (incl. Milleporidae), Actiniaria, Cattaneo-Vietti et al., 2000). The shallowest site in ARTICLE IN PRESS J.-M. Gili et al. / Deep-Sea Research II 53 (2006) 1029–1052 1031 the high-Antarctic Weddell Sea is the unique Four described by Dayton and Oliver (1977), which has Seasons Bank, which reaches as shallow as 60 m a canopy of only a few centimetres. below the sea surface (Ragua´-Gil et al., 2004). The Below the archaic community in the high- community at this site, which is exposed to strong Antarctic Weddell Sea there is a level-bottom currents, is also dominated by suspension feeders community dominated numerically by ophiuroids, but on very coarse sand, gravel and boulders. The which, surprisingly, have their highest species fauna includes dense populations of Hydrozoa and numbers (15–17) between 300 and 350 m, at the Stolonifera together with a motile epifauna mainly same depth as the asteroids (19–21 species; Arntz of regular echinoids, small gastropods and peracar- et al., 2005). Truly archaic species (such as the id crustaceans (Gili et al., 1999; Ragua´-Gil et al., stalked crinoid Bathycrinus aldrichianus, see Ma- 2004)(Fig. 1). This is somewhat similar to the curda and Meyer, 1976) have been collected only on extremely dense soft-bottom infaunal/shallow epi- the Antarctic deep slope (1500 m) (D. Gerdes, faunal community of McMurdo East Sound, personal observation). Fig. 1. Epibenthic assemblage on hard substratum at the 60–70 m deep hilltop of Four Seasons Inlet (East of the Weddell Sea) (drawing by Jordi Corbera Barcelona). ARTICLE IN PRESS 1032 J.-M. Gili et al. / Deep-Sea Research II 53 (2006) 1029–1052 1.3. Other macrofaunal benthic communities in the sediment