Meiofauna in the Gollum Channels and the Whittard Canyon, Celtic Margin—How Local Environmental Conditions Shape Nematode Structure and Function

Abstract

The Gollum Channels and Whittard Canyon (NE Atlantic) are two areas that receive high input of organic matter and phytodetritus from euphotic layers, but they are typified by different trophic and hydrodynamic conditions. Sediment biogeochemistry was analysed in conjunction with structure and diversity of the nematode community and differences were tested between study areas, water depths (700 m vs 1000 m), stations, and sediment layers. The Gollum Channels and Whittard Canyon harboured high meiofauna abundances (1054–1426 ind. 10 cm−2) and high nematode diversity (total of 181 genera). Next to enhanced meiofauna abundance and nematode biomass, there were signs of high levels of organic matter deposition leading to reduced sedimentary conditions, which in turn structured the nematode community. Striking in this respect was the presence of large numbers of ‘chemosynthetic’ Astomonema nematodes (Astomonema southwardorum, Order Monhysterida, Family Siphonolaimidae). This genus lacks a mouth, buccal cavity and pharynx and possesses a rudimentary gut containing internal, symbiotic prokaryotes which have been recognised as sulphur-oxidising bacteria. Dominance of Astomonema may indicate the presence of reduced environments in the study areas, which is partially confirmed by the local biogeochemical environment. The nematode communities were mostly affected by sediment layer differences and concomitant trophic conditions rather than other spatial gradients related to study area, water depth or station differences, pointing to small-scale heterogeneity as the main source of variation in nematode structure and function. Furthermore, the positive relation between nematode standing stocks, and quantity and quality of the organic matter was stronger when hydrodynamic disturbance was greater. Analogically, this study also suggests that structural diversity can be positively correlated with trophic conditions and that this relation is tighter when hydrodynamic disturbance is greater.

From microbes to macrofauna: an integrated study of deep benthic communities and their response to environmental variables along the Malta Escarpment (Ionian Sea)

“…Several studies have reported a strong influence of food availability not only on the meiofauna standing stock, but also on the diversity (e.g. Garcia et al 2007, Ingels et al 2011. Conversely, Hasemann and Soltwedel (2011) showed the same apparent lack of relationship between meiofauna and organic matter content as we see along the Malta Escarpment.…”

Characteristics of meiofauna in extreme marine ecosystems: a review

“…These processes act in concert to produce canyon sediments that are usually richer in organic matter (labile or refractory, depending on the active processes) compared to adjacent slope environments, although spatial and temporal changes can cause significant variability. The often high amounts of food (but not necessarily high quality/ availability; see Kiriakoulakis et al 2011) enriches the sedimentary standing stock, and disturbance regimes stimulate recolonisation processes on a regular basis, allowing biodiversity enrichment, at least for meiofauna (Snelgrove and Smith 2002;Ingels et al 2011c;. Whilst much of the literature supports the claim of canyons being meiofauna abundance 'hotspots', many studies also offer the view that meiofauna abundance in canyons can be extremely variable, with meiofauna densities ranging anywhere between 3 and 9457 ind.…”

“…These results argue for the importance of topographic features in the distribution of rare meiofauna taxa in the deep sea, but also highlight the importance of biodiversity turnover along continental margins and the contributions that canyons make to regional diversity. Whilst canyon local or alpha biodiversity is often lower than for adjacent slope areas [but there are exceptions; see Ingels et al (2011c) for the Whittard Canyon and Gollum Channels], high biodiversity turnover rates (beta diversity) have been observed between canyon areas and adjacent non-canyon areas in several studies, implying that canyon biodiversity contributes significantly to total regional or margin biodiversity Ingels et al 2011a;Leduc et al 2014). The fact that different meiofauna communities can be found in canyons compared to slope systems attests to the observation that canyons contribute to regional diversity (Danovaro et al , 2010a.…”

Is the meiofauna a good indicator for climate change and anthropogenic impacts?

“…They play an important role in benthic food webs, not only as consumers (feeding on detritus, diatoms and algae, and preying on other small metazoans; Pergent et al 1994;Duarte and Cebrian 1996;Gee and Somerfield 1997;Mateo and Romero 1997;Gwyther 2003;Torres-Pratts and Schizas 2007;Mascart et al 2013Mascart et al , 2015, but also as producers (being a food source for macrofauna and fish; Gerlach 1978; Lebreton et al 2011;Vinagre et al 2012;Carpentier et al 2014). The abundance, diversity, distribution and functional properties of meiofauna can be affected by several abiotic factors, including temperature, salinity, hydrodynamic and sedimentary processes, sediment grain size, oxygenation level and food availability (Ingels et al 2011;Lizhe et al 2012;Ngo et al 2013;Zeppilli et al 2013;Górska et al 2014;Pusceddu et al 2014b), and also, by biotic factors such as predation and competition (Tita et al 2000;Danovaro et al 2007;Nascimento et al 2011;Braeckman et al 2013;Boldina et al 2014). Meiofauna are characterised by a high sensitivity to environmental changes due to their short generation time and the lack of pelagic larval dispersion for the dominant meiofaunal groups (Bongers and Ferris 1999).…”