Macrofaunal assemblages from mud volcanoes in the Gulf of Cadiz: abundance, biodiversity and diversity partitioning across spatial scales

The Gulf of Cadiz is an extensive seepage area in the south Iberian margin (NE Atlantic) encompassing over 40 mud volcanoes (MVs) at depths ranging from 200 to 4000 m. The area has a long geologic history and a central biogeographic location with a complex circulation ensuring oceanographic connectivity with the Mediterranean Sea, equatorial and North Atlantic regions. The geodynamics of the region promotes a notorious diversity in the seep regime despite the relatively low fluxes of hydrocarbon-rich gases. We analyse quantitative samples taken during the cruises TTR14, TTR15 and MSM01-03 in seven mud volcanoes grouped into Shallow MVs (Mercator: 350 m, Kidd: 500 m, Meknes: 700 m) and Deep MVs (Captain Arutyunov: 1300 m, Carlos Ribeiro: 2200 m, Bonjardim: 3000 m, Porto: 3900 m) and two additional Reference sites (ca. 550 m). Macrofauna (retained by a 500 mu m sieve) was identified to species level whenever possible. The samples yielded modest abundances (70-1567 individuals per 0.25m(2)), but the local and regional number of species is among the highest ever reported for cold seeps. Among the 366 recorded species, 22 were symbiont-hosting bivalves (Thyasiridae, Vesicomyidae, Solemyidae) and tubeworms (Siboglinidae). The multivariate analyses supported the significant differences between Shallow and Deep MVs: The environmental conditions at the Shallow MVs make them highly permeable to the penetration of background fauna leading to high diversity of the attendant assemblages (H': 2.92-3.94; ES(100): 28.3-45.0; J': 0.685-0.881). The Deep MV assemblages showed, in general, contrasting features but were more heterogeneous (H': 1.41-3.06; ES(100): 10.5-30.5; J': 0.340-0.852) and often dominated by one or more siboglinid species. The rarefaction curves confirmed the differences in biodiversity of Deep and Shallow MVs as well as the convergence of the latter to the Reference sites. The Bray-Curtis dissimilarity demonstrated the high beta-diversity of the assemblages, especially in pairwise comparisons involving samples from the Deep MVs. Diversity partitioning assessed for species richness, Hurlbert's expected number of species and Shannon-Wiener index confirmed the high beta-diversity across different spatial scales (within MVs, between MVs, between Deep and Shallow MVs). We suggest that historical and contemporary factors with differential synergies at different depths contribute to the high alpha-, beta- and gamma-diversity of the mud volcano faunal assemblages in the Gulf of Cadiz

Are organic falls bridging reduced environments in the deep sea?: Results from colonization experiments in the Gulf of Cadiz

Organic falls create localised patches of organic enrichment and disturbance where enhanced degradation is mediated by diversified microbial assemblages and specialized fauna. The view of organic falls as “stepping stones” for the colonization of deep-sea reducing environments has been often loosely used, but much remains to be proven concerning their capability to bridge dispersal among such environments. Aiming the clarification of this issue, we used an experimental approach to answer the following questions: Are relatively small organic falls in the deep sea capable of sustaining taxonomically and trophically diverse assemblages over demographically relevant temporal scales Are there important depth- or site-related sources of variability for the composition and structure of these assemblages? Is the proximity of other reducing environments influential for their colonization? We analysed the taxonomical and trophic diversity patterns and partitioning (α- and β-diversity) of the macrofaunal assemblages recruited in small colonization devices with organic and inorganic substrata after 1-2 years of deployment on mud volcanoes of the Gulf of Cádiz. Our results show that small organic falls can sustain highly diverse and trophically coherent assemblages for time periods allowing growth to reproductive maturity, and successive generations of dominant species. The composition and structure of the assemblages showed variability consistent with their biogeographic and bathymetric contexts. However, the proximity of cold seeps had limited influence on the similarity between the assemblages of these two habitats and organic falls sustained a distinctive fauna with dominant substrate-specific taxa. We conclude that it is unlikely that small organic falls may regularly ensure population connectivity among cold seeps and vents. They may be a recurrent source of evolutionary candidates for the colonization of such ecosystems. However, there may be a critical size of organic fall to create the necessary intense and persistent reducing conditions for sustaining typical chemosymbiotic vent and seep organisms

Response of Benthic Foraminifera to organic matter quantity and quality and bioavailable concentrations of metals in Aveiro Lagoon (Portugal)

This work analyses the distribution of living benthic foraminiferal assemblages of surface sediments in different intertidal areas of Ria de Aveiro (Portugal), a polihaline and anthropized coastal lagoon. The relationships among foraminiferal assemblages in association with environmental parameters (temperature, salinity, Eh and pH), grain size, the quantity and quality of organic matter (enrichment in carbohydrates, proteins and lipids), pollution caused by metals, and mineralogical data are studied in an attempt to identify indicators of adaptability to environmental stress. In particular, concentrations of selected metals in the surficial sediment are investigated to assess environmental pollution levels that are further synthetically parameterised by the Pollution Load Index (PLI). The PLI variations allowed the identification of five main polluted areas. Concentrations of metals were also analysed in three extracted phases to evaluate their possible mobility, bioavailability and toxicity in the surficial sediment. Polluted sediment in the form of both organic matter and metals can be found in the most confined zones. Whereas enrichment in organic matter and related biopolymers causes an increase in foraminifera density, pollution by metals leads to a decline in foraminiferal abundance and diversity in those zones. The first situation may be justified by the existence of opportunistic species (with high reproduction rate) that can live in low oxic conditions. The second is explained by the sensitivity of some species to pressure caused by metals. The quality of the organic matter found in these places and the option of a different food source should also explain the tolerance of several species to pollution caused by metals, despite their low reproductive rate in the most polluted areas. In this study, species that are sensitive and tolerant to organic matter and metal enrichment are identified, as is the differential sensitivity/tolerance of some species to metals enrichment.CNPq [401803/2010-4]; [PEst-OE/CTE/UI4035/2014]info:eu-repo/semantics/publishedVersio

Comparison of rarefaction curves (Hurlbert’s expected number of species) for the assemblages assemblages recruited in the different experiments deployed in the El Arraiche field (A) and the Carbonate Province (B), pooled by substrate type (C) and pooled by sub-region (D).

<p>EA: El Arraiche field; CP: Carbonate Province; W: wood; A: alfalfa; C: carbonate; Mer: Mercator MV; Mek: Meknès MV; Dar: Darwin MV; 1: one year deployment; 2: 2 years deployment.</p

Trophic structure of the assemblages recruited in the different experiments: species richness and abundance of the different trophic groups.

<p>Symb: symbiotic; Ep: epibenthic feeding; Sr: surface feeding; Ss: sub-surface feeding; Pa: sectorial parasites; Su: suspension feeders; De: deposit feeders; Dt: detritivores; Gr: bacterial grazers; Gr(w): wood-specialist bacterial grazers; Pr(mei): predators feeding on meiofauna; Pr(mac): predators feeding on macrofauna; Pr(zoo): predators feeding on zooplankton; Sc: scavengers; Om: Omnivores (detailed information in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0076688#pone-0076688-t001" target="_blank">Table 1</a>). EA: El Arraiche field; CP: Carbonate Province; W: wood; A: alfalfa; C: carbonate; Mer: Mercator MV; Mek: Meknès MV; Dar: Darwin MV; 1: one year deployment; 2: 2 years deployment.</p

Species richness (bottom) and abundance (top) of the assemblages recruited in the different experiments.

<p>Numbers refer to 1 dm³ of initially deployed substrate. EA: El Arraiche field; CP: Carbonate Province; W: wood; A: alfalfa; C: carbonate; Mer: Mercator MV; Mek: Meknès MV; Dar: Darwin MV; 1: one year deployment; 2: 2 years deployment.</p

Partition of taxonomic (left) and trophic (right) diversity for different indices.

<p>S: number of species; H’: Shannon-Wiener diversity (ln-based); ES(30): Hurlbert expected number of species per 30 individuals; TG: number of trophic groups; ETG(30) Hurlbert expected number of trophic groups per 30 individuals; β₁: β-diversity within same substrate and same sub-region; β₂: β-diversity between different substrata in the same sub-region; β₃: β-diversity between sub-regions.</p

β-diversity analysis for species (top) and trophic groups (bottom) based on Bray-Curtis dissimilarity between all possible pairs of individual samples.

<p>Blue dots show the value of each pairwise comparison and black squares are the averages for each category. W: wood; A: alfalfa; C: carbonate.</p