Abstract
Several seamounts are known as ‘oases’ of high abundances and biomass and hotspots of biodiversity in contrast to the surrounding deep-sea environments. Recent studies have indicated that each single seamount can exhibit a high intricate habitat turnover. Information on alpha and beta diversity of single seamount is needed in order to fully understand seamounts contribution to regional and global biodiversity. However, while most of the seamount research has been focused on summits, studies considering the whole seamount structure are still rather poor. In the present study we analysed abundance, biomass and diversity of nematodes collected in distinct physiographic sites and surrounding sediments of the Condor Seamount (Azores, North-East Atlantic Ocean). Our study revealed higher nematode biomass in the seamount bases and values 10 times higher in the Condor sediments than in the far-field site. Although biodiversity indices did not showed significant differences comparing seamount sites and far-field sites, significant differences were observed in term of nematode composition. The Condor summit harboured a completely different nematode community when compared to the other seamount sites, with a high number of exclusive species and important differences in term of nematode trophic diversity. The oceanographic conditions observed around the Condor Seamount and the associated sediment mixing, together with the high quality of food resources available in seamount base could explain the observed patterns. Our results support the hypothesis that seamounts maintain high biodiversity through heightened beta diversity and showed that not only summits but also seamount bases can support rich benthic community in terms of standing stocks and diversity. Furthermore functional diversity of nematodes strongly depends on environmental conditions link to the local setting and seamount structure. This finding should be considered in future studies on seamounts, especially in view of the potential impacts due to current and future anthropogenic threats.
Highlights
Seamounts are considered oases of the deep-sea life when compared with regular deep-sea environments [1]
Ii) Is the Condor summit an area of higher nematode standing stock and a hotspot of diversity compared to other seamount habitats such as flanks and bases?
This study is limited to one external area, when comparing the Condor Seamount with the off-mount sediments, we found higher nematode biomass at the seamount bases than in far-field site at comparable depth
Summary
Seamounts are considered oases of the deep-sea life when compared with regular deep-sea environments [1]. It has been suggested that seamounts support high abundance and biomass and exhibit high species richness representing hotspots of diversity because high nutrient and food concentrations are available [2]. In a study in the SW-Pacific Ocean, Rowden and colleagues [8] found four times higher epibenthic fauna biomass on seamounts than in adjacent slopes mainly due to the dominance of scleractinian corals. They concluded that besides their study provided some support for the seamount ‘oasis’ hypothesis, more investigations are needed targeting seamounts in less productive regions, with greater proportion of soft substrata and with less prevalent scleractinian corals population. In the Great Meteor Seamount Foraminifera occurred in very low densities compared with the surrounding area [11]
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