Large Spatial Scale Variability in Bathyal Macrobenthos Abundance, Biomass, α- and β-Diversity along the Mediterranean Continental Margin

Abstract

The large-scale deep-sea biodiversity distribution of the benthic fauna was explored in the Mediterranean Sea, which can be seen as a miniature model of the oceans of the world. Within the framework of the BIOFUN project (“Biodiversity and Ecosystem Functioning in Contrasting Southern European Deep-sea Environments: from viruses to megafauna”), we investigated the large spatial scale variability (over >1,000 km) of the bathyal macrofauna communities that inhabit the Mediterranean basin, and their relationships with the environmental variables. The macrofauna abundance, biomass, community structure and functional diversity were analysed and the α-diversity and β-diversity were estimated across six selected slope areas at different longitudes and along three main depths. The macrobenthic standing stock and α-diversity were lower in the deep-sea sediments of the eastern Mediterranean basin, compared to the western and central basins. The macrofaunal standing stock and diversity decreased significantly from the upper bathyal to the lower bathyal slope stations. The major changes in the community composition of the higher taxa and in the trophic (functional) structure occurred at different longitudes, rather than at increasing water depth. For the β-diversity, very high dissimilarities emerged at all levels: (i) between basins; (ii) between slopes within the same basin; and (iii) between stations at different depths; this therefore demonstrates the high macrofaunal diversity of the Mediterranean basins at large spatial scales. Overall, the food sources (i.e., quantity and quality) that characterised the west, central and eastern Mediterranean basins, as well as sediment grain size, appear to influence the macrobenthic standing stock and the biodiversity along the different slope areas.

Exploring the Relationship between Macrofaunal Biodiversity and Ecosystem Functioning in the Deep Sea

“…Moreover, there was no correlation between predator number (ind m −2 ) and their biomass (R 2 = 0.03, p > 0.05); in particular, the wM slope systems were characterized by a large number of predators and a high EPR (20) , whereas their biomass values were lower than those measured in the Atlantic slope area. Mediterranean benthic organisms have been reported to have a generally smaller size than those inhabiting the Atlantic Ocean (Sardà et al, 2004;Tecchio et al, 2011;Pape et al, 2013), and significantly lower macrobenthic biomass values have been described in the Mediterranean basin compared with the Atlantic sector (Tselepides et al, 2000;Coll et al, 2010;Baldrighi et al, 2014). The bioturbation activity of organisms can affect both the abiotic and biotic components of a system (Quéiros et al, 2015), and is one of the functional traits of benthic organisms that may sustain mutualistic interactions on the basis of BEF relationships (Loreau, 2008).…”

“…The Mediterranean open-slope systems selected for the present study are characterized by a high percentage of silt sediment at all depths. Bottom-water temperature and salinity increase significantly from west to east, with values ranging respectively from 13.1 • C and 38.5 • C in the wM area to 14.7 • C and 38.8 • C in the Eastern Mediterranean basin (Baldrighi et al, 2014; Table S1). At each station, sampling involved 3 independent box-corer deployments for macrofauna (entirely sieved) and 3 deployments for meiofauna, microbial components, and environmental variables (n = 3 replicate samples for each parameter).…”

“…Data of macrofaunal abundance, biomass and diversity as well as data of environmental parameters characterizing the Mediterranean basin from west to east have previously been shown in Baldrighi et al (2014). Data of meiofauna abundance, structural and functional diversity from the Mediterranean basin have been presented in Baldrighi and Manini (2015) and the relationship with macrofaunal structural and functional diversity has been investigated.…”

“…The two fractions (>63 µm, sand; <63 µm, silt and clay) were dried in an oven at 60 • C and weighed. Data were expressed as a percentage of the total sediment dry weight (Baldrighi et al, 2014).…”

Functional response to food limitation can reduce the impact of global change in the deep‐sea benthos

“…For instance, previous studies conducted over the continental margins of the Mediterranean Sea reveal that some deep‐sea species can be particularly abundant at specific bathymetric intervals (e.g., Bathypterois mediterraneus and deep‐sea red shrimp Aristeus antennatus ; D'Onghia, Lloris, Sion, Capezzuto, & Labropoulou, ; D'Onghia et al, ; Sardà et al, ). These species, thus, can influence the observed patterns of megafaunal abundance and biomass along bathymetric gradients (Baldrighi, Lavaleye, Aliani, Conversi, & Manini, ; Company et al, ; Sardà et al, ).…”