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

• Published in: Biogeosciences
• Main Authors: Cunha, M. R., Rodrigues, C. F., Genio, L., Hilario, A., Ravara, Ascensão, Pfannkuche, O.
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union 2013
• Subjects: Bray; Kidd; North Atlantic
• Online Access: http://hdl.handle.net/10773/13388; https://doi.org/10.5194/bg-10-2553-2013

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 hydrocarbonrich 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, Mekn`es: 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 μm sieve) was identified to species level whenever possible. The samples yielded modest abundances (70–1567 individuals per 0.25m2), 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 (H0: 2.92–3.94; ES(100): 28.3–45.0; J 0: 0.685–0.881). The Deep MV assemblages showed, in general, contrasting features but were more heterogeneous (H0: 1.41–3.06; ES(100): 10.5–30.5; J 0: 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 -diversity of the assemblages, especially in pairwise comparisons involving samples from ...