Abstract
Abstract. Previous work in the mud volcanoes from the Gulf of Cadiz (South Iberian Margin) revealed a high number of chemosymbiotic species, namely bivalves and siboglinid polychaetes. In this study we give an overview of the distribution and life styles of these species in the Gulf of Cadiz, determine the role of autotrophic symbionts in the nutrition of selected species using stable isotope analyses (δ13C, δ15N and δ34S) and investigate the intra-specific variation of isotope signatures within and between study sites. During our studies, we identified twenty siboglinidae and nine bivalve chemosymbiotic species living in fifteen mud volcanoes. Solemyid bivalves and tubeworms of the genus Siboglinum are widespread in the study area, whereas other species were found in a single mud volcano (e.g. "Bathymodiolus" mauritanicus) or restricted to deeper mud volcanoes (e.g. Polybrachia sp., Lamelisabella denticulata). Species distribution suggests that different species may adjust their position within the sediment according to their particular needs, and to the intensity and variability of the chemical substrata supply. Tissue stable isotope signatures for selected species are in accordance with values found in other studies, with thiotrophy as the dominant nutritional pathway, and with methanotrophy and mixotrophy emerging as secondary strategies. The heterogeneity in terms of nutrient sources (expressed in the high variance of nitrogen and sulphur values) and the ability to exploit different resources by the different species may explain the high diversity of chemosymbiotic species found in the Gulf of Cadiz. This study increases the knowledge on distributional patterns and resource partitioning of chemosymbiotic species and highlights how trophic fuelling varies on spatial scales with direct implications to seep assemblages and potentially to the biodiversity of continental margin.
Highlights
During our for several cold seep inveErteabrratthes,Sanydsctoenmfirmed by the obstudies, we identified twenty siboglinidae and nine bivalve chemosymbiotic species living in fifteen mud volcanoes
Chemosymbiotic species were identified from 15 mud volcanoes (MVs) with 11 bivalve species occurring at 13 MVs and 20 siboglinid species at 14 MVs (Table 1, Fig. 1 and Supplement Fig. S1)
The number of chemosymbiotic species found in the Gulf of Cadiz is high when compared with other seep locations such as the mud volcanoes in the Eastern Mediterranean Sea and the Gulf of Guinea (Hilario et al, 2010; Oliver et al, 2011)
Summary
Previous work in the mud volcanoes from the Gulf 1 Introduction of Cadiz (South Iberian Margin) revealed a high number of chemosymbiotic species, namely bivalves and siboglinid polychaetes. Solemyid bivalves and tubeworms of the genus Siboglinum otic relationship, the invertebrate host facilitates the access to are widespread in the study area, whereas other species inorganic carbon, oxygen and reduced sulphur-compounds, were found in a single mud volcano Chemosymbiotic bivalves and siboglinid tubeworms were sorted and identified; Siboglinum and Polybrachia specimens were ascribed to species according to Hilario et al (2010) or given new codenames consistent throughout the samples when they did not yet match a known species. The ground subsample for carbon analysis was acidified with HCl (1M) until no further bubbling occurred; it was re-suspended in distilled water, centrifuged and the supernatant was discarded, the subsample was dried at 60◦C and reground. The ground subsample for sulphur analysis was re-suspended in distilled water, shaken for 5 min, centrifuged and the supernatant was discarded; this procedure was repeated 3 times and the subsample was dried at 60◦C and reground
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