Nematode diversity patterns at different spatial scales in bathyal sediments of the Mediterranean Sea

Abstract

Understanding biodiversity patterns and how they are driven at different spatial scales is a crucial issue in eco- logical studies. This is particularly evident for the deep sea, the largest biome of the biosphere, where information on the scales of spatial variation is very scant. Here, we investigated deep-sea nematodes species richness, turnover and func- tional diversity, and life strategies at different spatial scales (from local to macro-regional) to identify the factors that shape regional (γ) and macro-regional (ε) deep-sea diver- sity. This study was conducted in several deep-sea habitats (canyons, open slopes, deep-water corals, and bathyal plains) over > 2000 km across the whole Mediterranean Basin, at a bathymetric range comprised between ca. 600 and 1300 m. Our results indicate that the patterns of local (α) diversity across the deep Mediterranean follow the gradients of the trophic conditions, which decrease from the western to the eastern basins. For all of the sites and habitats, the α diversity is generally low. Conversely, the turnover diversity changes significantly among habitats (β diversity) and between re- gions (δ diversity), showing values of dissimilarity (based on species presence/absence matrixes) between 59 and 90 % for β diversity and between 81 and 89 % for δ diversity. This suggests that patterns and values of γ and ε diversities in the deep Mediterranean Sea are related to turnover diversity among habitats and between regions (β and δ diversities), rather than to the local biodiversity (α diversity). These re- sults indicate also that the differences in β and δ diversi- ties are even more important than those in α diversity for the comprehension of the drivers of biodiversity in the deep Mediterranean Sea. We conclude that the presence of differ- ent habitats and gradients in environmental conditions, by promoting a high turnover diversity across the Mediterranean Sea, may play a crucial role in the levels of γ diversity of deep-sea nematodes

Temperature impacts on deep‐sea biodiversity

“…If a majority of species have similar thermal performance curves, they will have optimum habitat ranges at similar mid–high temperatures, and thus species diversity will be higher at these temperatures. This prediction is supported by a nematode dataset (Danovaro et al ., ; Bongiorni et al ., ; Bianchelli et al ., ; Pusceddu et al ., ; R. Danovaro, unpublished data) covering a broad temperature range which shows a significant, unimodal, temperature–diversity relationship and also a rapid diversity decrease at the highest temperatures (Fig. C; see online Table S2).…”

“…time-series and palaeo-) (Danovaro et al, 2004). (C) Unified unimodal relationship from present-day Atlantic Ocean and Mediterranean Sea spatial dataset (Danovaro et al, 2009;Bongiorni et al, 2010;Bianchelli et al, 2013;Pusceddu et al, 2013;R. Danovaro, unpublished data; see online Table S2) (we used the data from 1000 to 4000 m water depth only: see online Fig.…”

“…S1. Data from Danovaro et al (2009), Bongiorni et al (2010, Bianchelli et al (2013), Pusceddu et al (2013), and R. Danovaro (unpublished data).…”

“…S1. Comparison of temperature–diversity relationships between (A) 1000–4000 m dataset and (B) whole dataset (including <1000 and >4000 m data) of present‐day North Atlantic Ocean and Mediterranean Sea nematode species diversity (Danovaro et al , ; Bongiorni et al , ; Bianchelli et al , ; Pusceddu et al , ; R. Danovaro, unpublished data; see online Table S2). Quadratic regression lines are shown.…”

Green Roof Ecosystems

“…While community and species ecologists are usually familiar with three levels of diversity described above, there are three additional measures of diversity related to landscape scale at the macro-and mega-levels (Magurran 1988;Bianchelli et al 2013). Delta (δ-diversity) is the change in large landscape diversity along major climatic or other physical or abiotic gradients.…”