Deep Sea Research Part II: Topical Studies in Oceanography
Meiofauna assemblages of the Condor Seamount (North-East Atlantic Ocean) and adjacent deep-sea sediments
Introduction
Seamounts are topographic elevations of the deep-sea seafloor (Pitcher et al., 2007, Wessel et al., 2010, Yesson et al., 2011). Several seamounts contribute to create peculiar hydrological conditions, such as enhanced current flow, eddies, up- and down welling and closed retention cells (i.e. Taylor caps; White et al., 2007), which can provide enhanced food resources to benthic fauna (Piepenburg and Müller, 2004). Because of these characteristics, seamounts are considered hotspots of biodiversity and biomass of several macro- and megabenthic taxa (Samadi et al., 2006, Samadi et al., 2007, Rowden et al., 2010, Clark et al., 2010, Sautya et al., 2011, Tracey et al., 2011).
Despite an increasing knowledge on seamounts and their associated biodiversity, our knowledge about meiofaunal component is still limited (McClain, 2007, Vanreusel et al., 2010). Among the ca. 232 seamounts sampled world-wide, only 8 have been sampled for meiofauna (George, 2013). Due to difficulties encountered in seamounts sampling and the use of different sampling devices, meiofaunal studies remain mainly qualitative or focused only on specific taxa, thus preventing comparisons among seamounts and between seamounts and other deep-sea habitats (see George, 2013). The most detailed investigations on the biodiversity, community composition and distribution of meiofauna on seamounts have been carried out in the North Atlantic Ocean and in particular in the Great Meteor, Sedlo and Seine Seamounts (George, 2013 and references therein). Some of these studies have revealed the existence of highly diverse meiofauna assemblages living in sediments of seamounts when compared to those typical of the deep sea (Gad and Schminke, 2004) with several species and genera new to science (George, 2004, George, 2006, Gad, 2004a, Gad, 2004b). Others studies have suggested seamounts as potential areas of endemism also for meiofaunal species and as “stepping stone” for large-scale dispersal of some meiofaunal taxa such as nematodes and copepods (George and Schminke, 2002, George, 2004, Gad, 2009, Piepenburg and Müller, 2004, Mironov and Krylova, 2006).
The present study aims to compare meiofaunal assemblages in five sites on the Condor Seamount (Azores, North-East Atlantic Ocean) and in a nearby open slope site. We investigated variations in abundance, community structure, and biodiversity of benthic meiofauna and its relationship with environmental variables (including sediment grain size and available food resources) in order to answer to the following questions:
- (i)
Is there a difference between the meiofaunal biodiversity (expressed as richness of higher taxa) between seamount and open slope sites?
- (ii)
Is there a difference in meiofaunal biodiversity and assemblage structure among different seamount areas (summit, flanks and bases) and between the northern and southern slope?
- (iii)
Is the seamount summit a hotspot of meiofaunal abundance, biomass and diversity?
Section snippets
Study sites and samples collection
The main geomorphologic characteristics of the Condor Seamount are described in Tempera et al. (2012). Condor is a linear volcano located in the Azores (northeast Atlantic), 17 km to the southwest of Fayal Island. It is 39 km long, 23 km wide, and extends from more than 1800 m to 185 m water depth (Tempera et al., 2012). This seamount has a flat summit characterized by the presence of large rocky outcrops, boulders, gravels, and coarse bioclastic deposits and steep slopes mainly characterized by
Sediment grain size
Sediment characteristics of the investigated sites are reported in Table 2 and in Fig. 2. The Condor summit showed a different sediment grain composition compared to the other sites, being composed by a gravelly bioclastic sand rich in angular shell fragments (pteropods, gastropods, echinoids, bivalves), rounded pumex clasts, polished lava pebbles and planktonic foraminifera shells. The other sites showed in general poorly sorted sediment dominated by sand on the flanks and by silt at the base
Discussion
In this study, results of sediment grain-size distribution on the Condor Seamount supported the occurrence of strong water mixing. The summit of the Condor resulted to be characterized by coarse grained sediments, in accordance to Caetano et al. (2013), indicating an area swept by bottom currents where sediments are winnowed and reworked. Similar conclusions were also reported by Bongiorni et al. (this issue) who found low level of sediment organic matter on the seamount summit when compared to
Conclusion and final remarks
The Condor Seamount hosted a rich and diverse meiofaunal assemblage. The analysis of meiofauna in distinct physiographic sites of the Condor Seamount (its summit, the north and south flanks, the north and south bases) allowed answering to the following questions:
- (i)
Is there a difference between the meiofaunal biodiversity (expressed as richness of higher taxa) associated to a seamount and the one of the adjacent deep-sea sediments?
Although the highest number of taxa was recorded in the Condor
Acknowledgments
This work was funded by the Fundação para a Ciência e Tecnologia, Portugal (FCT Project BIOMOUNT, PTDC/MAR/105486/2008. COMPETE funds). The authors are indebted to the CONDOR project (Observatory for long term study and monitoring of Azorean ecosystem, EEA Grants PT0040/2008, Iceland, Liechtenstein). We are particular grateful to Dr. Gui Menezes, Dr. Eva Giacomello and Ricardo Medeiros. We thank captain and crew of the R.V. Noruega, and cruise participants from IMAR-DOP/University of the
References (68)
- et al.
Topographically induced circulation patterns and mixing over Condor seamount
Deep Sea Res. II.
(2013) - et al.
Metazoan meiofauna in deep-sea canyons and adjacent open slopes: a large-scale comparison with focus on the rare taxa
Deep-Sea Res. I
(2010) - et al.
Organic matter composition and macrofaunal diversity in sediments of the Condor seamount (Azores, NE Atlantic)
Deep-Sea Res. II.
(2013) - et al.
The Condor seamount at Mid-Atlantic Ridge as a supplementary source of trace and rare earth elements to the sediments
Deep- Sea Res. II
(2013) - et al.
Contrôle exercé par la dorsale médio-Atlantique et le Gulf Stream sur la sedimentation quaternaire sur le plateau des Açores. (Control of the Mid-Atlantic ridge and the Gulf Stream on the Quaternary sedimentation on the Azores Plateau)
C.R. Acad. Sci. Paris
(1999) - et al.
A three-year time series of elemental and biochemical composition of organic matter in subtidal sandy sediments of the Liguria Sea (northwestern Mediterranean)
Cont. Shelf. Res.
(1995) - et al.
Meiofauna and macrofauna community structure in relation to sediment composition at the Iberian margin compared to the Goban Spur (NE Atlantic)
Prog. Oceanogr.
(2002) The measurement of marine species diversity, with an application to the benthic fauna of the Norwegian continental shelf
J. Exp. Mar. Biol. Ecol.
(2000)- et al.
The influence of hydrodynamic regime on infaunal assemblages inhabiting carbonate sediments on central Pacific seamounts
Deep Sea Res.
(1989) - et al.
Organic matter composition, meiofauna and nematode biodiversity in deep-sea sediments surrounding two seamounts
Deep-Sea Res. II
(2009)