Deep-sea habitat heterogeneity influence on meiofaunal communities in the Gulf of Guinea

Abstract

To estimate the degree of spatial heterogeneity of benthic deep-sea communities, we carried out a multiple-scale (from m's to 200 km) investigation in the Congo-Angola margins (Equatorial West African margin, 3150-4800 m) in which we examined the metazoan meiofauna at a variety of habitats along the Congo Channel system and in the associated cold seep. We investigate the structure, density, vertical distribution patterns in the sediment and biomass of meiofaunal communities in the Gulf of Guinea and how they are controlled by hydrologic and biogeochemical processes. The meiofaunal communities in the Gulf of Guinea were shaped by heterogeneous conditions on the margin, and reflect the multiple-scale spatial variability that corresponds with different identified habitats. The two control sites, located at >100 km away from the canyon, were inhabited by very dense and the most diverse meiobenthic communities. Similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep. Sites located along the Congo Channel were obviously affected by the local high-velocity bottom currents and unstable sedimentary conditions in this active submarine system. Extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites. The ROV Victor 6000 provided images of the cold seep, showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa (Mytilidae, Vesicomyidae and Siboglinidae). These cold seep sediments were colonised by a unique meiobenthic community, characterised by a high small-scale (m's) patchiness, low species richness and the prominent dominance of two large-sized nematode species: Sabatieria mortenseni, which is a cosmopolitan nematode known from littoral habitats, and an undescribed Desmodora species. The high individual body weight of Sabatieria mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites. In addition, the vertical A c c e p t e d m a n u s c r i p t 2 nematode profiles, with maximum proportions in subsurficial layers, points to a chemosynthesis-based meiobenthic community in this cold seep, in contrast to the phytodetritus-based communities at the control sites and at the transition zone.

Worldwide Analysis of Sedimentary DNA Reveals Major Gaps in Taxonomic Knowledge of Deep-Sea Benthos

“…Deep-sea habitat heterogeneity at larger spatial scales is poorly understood but is believed to play an important role in the maintenance of benthic biodiversity on the ocean floor (e.g., Levin et al, 2001;Van Gaever et al, 2009;Vanreusel et al, 2010;Durden et al, 2015). Our data suggest a considerable degree of taxonomic differentiation, and hence biogeographic patterning, between the soft-sediment benthic communities that are represented by our eDNA samples (Figures 6, 7).…”

Characteristics of meiofauna in extreme marine ecosystems: a review

“…In the Congo Channel, the active system with high-speed currents resulted in meiofauna abundances as low as 3 ind. 10 cm −2 (Van Gaever et al 2009b). Other explanations for reduced abundance and biomass may be high levels of sedimentation and burial, leading to oxygen stress.…”

“…In this context, the observed dominance of nematode genera, such as Sabatieria, has often been linked to oxygen stress and sediment disturbance in general (Garcia et al 2007;Schratzberger et al 2009;Leduc et al 2014), whilst the presence of Microlaimus, for instance, can indicate sediment disturbance and recolonisation processes (Lee et al 2001;Van Gaever et al 2009b;Leduc et al 2014). Several authors have claimed that canyons are harsh environments and that only opportunistic organisms can survive in these habitats (e.g.…”

“…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. 10 cm −2 (values from the Congo Channel and head of the Mississippi Trough, respectively; Baguley et al 2006;Van Gaever et al 2009b). de Bovée et al (1990), for instance, reported 2-3-fold abundance variations for similar depths and 10-15-fold variation in meiofauna abundance along the entire depth range studied in the Gulf of Lions; even twin branches or areas within the same canyon branch can exhibit large abundance variation (Bianchelli et al 2008;Ingels et al 2009Ingels et al , 2011a.…”

An insight into the feeding ecology of deep-sea canyon nematodes — Results from field observations and the first in-situ 13C feeding experiment in the Nazaré Canyon

“…The abundance of meiobenthic communities in canyons reflects the prevailing current regime to an extent, with often very low 20 densities in areas where sediments are disturbed regularly and hydrodynamic activity is greatest, e.g. in the axis of a canyon (Bianchelli et al, 2008;Garcia et al, 2007;Ingels et al, 2009;Van Gaever et al, 2009). Although strong near-bottom flow can reduce the abundance and alter the assemblage of both meiofauna and macrofauna in the deep sea (Thistle and Levin, 1998), meiofauna appear to recover more quickly than macrofauna with regards to physical disturbance (Lee et al, 2001a;Lee et 25 al., 2001b;Thistle et al, 1999).…”