Latitudinal, longitudinal and bathymetric patterns of abundance, biomass of metazoan meiofauna: importance of the rare taxa and anomalies in the deep Mediterranean Sea

Abstract

Quantitative information on the spatial distribution of meiofaunal abundance, biomass and biodiversity (as richness of higher taxa) is summarised from 476 sites of the deep-Mediterranean Sea, at depths ranging from ca. 200 to 4617 m. Meiofaunal abundance (465 AE 31 and 306 AE 24 ind 10 cm À2 at 200-1000 and 1000-2000 m depth intervals) and biomass (125 AE 16 and 119 AE 20 mgC 10 cm À2 at 200-1000 and 1000-2000 m depth intervals) in the bathyal sediments of the Mediterranean Sea are similar to those reported in oceans worldwide but at much higher depths (abyssal or hadal). Meiofaunal abundance, biomass and richness of taxa displayed a common decreasing bathymetric pattern, but showed a steeper negative slope than in other oceanic regions. Latitudinal and longitudinal gradients revealed idiosyncratic patterns when different basins (Western, Central and Eastern) and habitats (open slope, canyon, deep basin and trench) were considered. The results of the non parametric multivariate multiple regression analyses revealed that, conversely to what expected, depth is not the key factor in explaining the variance of meiofaunal assemblages living down to 2000 m depth. The quality and quantity of food sources explained a larger fraction of the variance of meiofaunal variables (47, 25 and 33% for abundance, biomass and diversity, respectively) and the importance of food sources increased with increasing depth. However, most of the variance remains unexplained suggesting that other factors (such as episodic events, deep currents, other unexplored yet environmental characteristics) can act a key role in driving the observed meiofaunal spatial patterns. The analysis of rare taxa (on a data set of 183 samples), suggested that differences in the meiofaunal community were evident when dominating taxa (nematodes, copepods and polychaetes) were excluded. We report the presence of rare taxa exclusively present in open slope (amphipods) and canyon (cnidarians and decapod larvae) systems, whereas others are exclusively found in one of the two basins (e.g. gastrotrichs in the Western basin and amphipods and gastropods in the Eastern basin). The apparent preference of some rare taxa for a specific habitat or basin could have important implications for the identification of the hot spots of benthic diversity, for identifying the connectivity among systems and for an appropriate management of deep-sea habitats in the Mediterranean Sea.

Potter Cove, west Antarctic Peninsula, shallow water meiofauna: a seasonal snapshot

“…These values were much higher than those reported by Hong et al (2011) in the adjacent Marian Cove (King George Island). Biomass values were high (up to 2 mg C 10 cm -2 ), comparable to those found in temperate estuaries (Tietjen 1969), and up to two orders of magnitude higher than those reported for deep sea sites (Gambi et al 2010). When the two study sites were compared in terms of meiobenthic densities and community composition, they differed only in summer, with higher values and greater diversity in ST1.…”

Benthic communities in the deep Mediterranean Sea: exploring microbial and meiofaunal patterns in slope and basin ecosystems

“…As a consequence, higher faunal densities are anticipated for this area. The meiofaunal abundances reported in the present synthesis are indeed lower from those of similar depths in other oceans (for an extensive reference report see Gambi et al, 2010) but comparable to those recorded from similar Mediterranean deep-sea sediments (Tselepides and Lampadariou, 2004;Lampadariou and Tselepides, 2006;Lampadariou et al, 2009;Gambi et al, 2010), yet they fall within a wider range of values. Our data also confirms the prediction of higher faunal densities in the northern Aegean Sea, as the higher meiofaunal density was measured in this area.…”

“…Nonetheless, considerable work carried out over the last three decades on the deep Mediterranean meiofauna has advanced our knowledge on the smallest but most abundant metazoans of the sediments (extensive bibliographic references reported in Danovaro et al (2010) and Gambi et al (2010)). Following major trends in ecology, recent investigations have sought for latitudinal, longitudinal and bathymetric patterns of meiofauna (Lampadariou and Tselepides, 2006;Danovaro et al, 2009aDanovaro et al, , 2010Gambi et al, 2010), while few study differences in meiofaunal patterns among deep-sea habitats (Danovaro et al, 2009a, b;Vanreusel et al, 2010;Gambi et al, 2010). Danovaro et al (2009a), in a study including samples from Mediterranean slopes and basins, found that meiofaunal diversity in slopes was higher than in deep-sea plains.…”

Species richness, species turnover and functional diversity in nematodes of the deep Mediterranean Sea: searching for drivers at different spatial scales

“…However, recent evidence has suggested that this ecosystem is much more temporally and spatially variable than previously thought, with potentially important implications for biodiversity patterns (Lampitt et al, 2010;Pusceddu et al, 2010Pusceddu et al, , 2013Rex & Etter, 2010). Several mechanisms have been invoked to explain the spatial patterns of biodiversity: (1) sediment grain size and substrate/ habitat heterogeneity (Etter & Grassle, 1992;Danovaro et al, 2009Danovaro et al, , 2010Bongiorni et al, 2010;McClain & Barry, 2010;Vanreusel et al, 2010;Zeppilli et al, 2012); (2) productivity (Smith et al, 2008;Lampitt et al, 2010;Tittensor et al, 2011;McClain et al, 2012); (3) food resources (Danovaro et al, 2008b;Gambi et al, 2010); (4) oxygen availability (Diaz & Rosemberg, 1995); (5) water currents (Lambshead et al, 2001); and (6) occasional catastrophic disturbances (Levin et al, 2001;Pusceddu et al, 2010Pusceddu et al, , 2013. Nonetheless, all of these factors are subjected to strong scientific debate because they are often sitespecific and constrained by local (or regional) conditions (Levin et al, 2001).…”