New advances in the study of the biodiversity of the SCI "Volcanes de fango del golfo de Cádiz" (southwestern Spanish Margin)

• ¹ Oceanographic Center of Málaga, Spanish Institute of Oceanography (IEO), Spain
• ² Instituto Español de Oceanografía (IEO), Centro Oceanográfico de Málaga, Spain
• ³ University of Málaga, Departamento de biología animal, Spain
• ⁴ Oceanographic Center of Cádiz, Spanish Institute of Oceanography, Spain
• ⁵ University of Málaga, Department of Animal Biology, Spain
• ⁶ Autonomous University of Madrid, Department of Zoology, Spain
• ⁷ University of Seville, Departamento de Zoología, Spain
• ⁸ Center for Advanced Studies of Blanes, Superior Council of Scientific Investigations, Spain
• ⁹ Department of Zoology, Faculty of Biology. University of Seville, Spain
• ¹⁰ Autonomous University of Madrid, Department of Zoology, Spain
• ¹¹ Federal University of Rio de Janeiro, Instituto de Pesquisas Jardim Botânico do Rio de Janeiro, Brazil
• ¹² University of Alicante, Centro de Investigación marina de Santa Pola (CIMAR), Spain

The Gulf of Cádiz represents an important seepage area with ca. 70 mud volcanoes (MV), of which one third are located in European waters (Spain and Portugal). Previous projects and expeditions resulted on a large amount of information on different aspects of MV of the Moroccan margin, which seem to have a higher seepage activity than those of the Iberian margin. Those studies mainly focused on their geological characteristics, whereas others offered novel information on their associated biota, especially the endosymbiont-bearing invertebrates as well as non-previously described species (Vanreusel et al., 2009). In 2014, the MV of the Spanish margin of the Gulf of Cádiz were included in the Natura 2000 network (Site of Community Importance - SCI "Volcanes de fango del golfo de Cádiz" - ESZZ12002) under the framework of the Life + project INDEMARES. Nowadays, the LIFE IP PAF INTEMARES project represents an opportunity for improving the knowledge on the biodiversity of this SCI. Samples and underwater images were obtained in MV and their adjacent bottoms from 300 to 1100 m water depth in the SCI, during the INDEMARES/CHICA and ISUNEPCA expeditions (Figure 1). Sampling was carried out using box-corer/Shipek, benthic dredge, beam-trawl and otter-trawl. Samples were sieved (10, 5, 1 and 0.5 mm) and individuals separated from the sediment, preserved in 70% Ethanol-4% Formaldehyde and identified. Transects with the ROV LIROPUS 2000 and photogrammetric sleds (APHIA 2012, HORUS) were done in different areas and completed the faunistic list with other species. More than 1000 species have been listed so far in the SCI, with molluscs displaying the highest number of species, followed by fishes, annelids, decapod crustaceans, cnidarians, sponges, echinoderms and bryozoans in decreasing order. Other groups are less represented such as brachiopods, sipunculids, nemerteans and ascidians or could not be studied yet (e.g. peracarid crustaceans). Recent revisions of some groups, mainly poriferans, bryozoans and molluscs, may result in the description of more than 10 new species to science such as the sponge Myrmekioderma indemaresi (dedicated to the INDEMARES project) (Sitjà et al., 2018) or the bryozoan Reteporella victori (dedicated to the mud volcano specialist Victor Díaz del Rio, Ramalho et al., 2018) (Fig. 2). Other species are new records for the area (the echinoderm Hacelia superba, the decapod crustacean Calliax lobata (García Raso et al., 2018), the molluscs Pseudosimnia flava, Neopycnodonte zibrowii, Solemya elarraichensis, Lucinoma asapheus, the fish Zenion hololepis, Opisthoproctus grimaldii). Around 20 species are included in local, national and international lists of threatened or vulnerable species, such as the cnidarians (Madrepora oculata, Dendrophyllia cornigera, Lophelia pertusa), echinoderms (Centrostephanus longispinus), molluscs (Charonia lampas) and fishes (Centrophorus granulosus). Also, an interesting ‘ascidian garden’ with the species Polycarpa mamillaris has been observed on carbonate structures, between 229 and 459 depth. Gazul, Pipoca and Chica displayed the highest species richness values, but Anastasya displayed low ones due to its extremophile sedimentary conditions with chemosynthetic-based communities and also the high trawling activity. The role of cold seeps and the formation of methane-derived authigenic carbonates for increasing biodiversity when compared to adjacent soft bottoms was noticeable in Gazul, Anastasya and Chica. A high number of species have been recorded in the SCI, as a result of the geological, geochemical, oceanographic and habitat heterogeneity of this area. The faunistic list of this area has increased considerably in 10 years from 30 spp. (Díaz-del-Río et al., 2009) to more than 1000 spp. (this study) due to the high sampling effort using different techniques targeting the infaunal, epifaunal and demersal species, new multidisciplinary sampling expeditions and the contribution of experienced taxonomists on different phyla, among other factors. Figure 1. Location of the Site of Community Importance "Volcanes de fango del golfo de Cádiz" and of the main fluid venting structures Figure 2. Some examples of the new species and records detected in the SCI. A) the bryozoan Reteporella victori Ramalho, López-Fé & Rueda, 2018; B) the gastropod Pseudosimnia flava; c) the decapod Calliax lobata; D) the sponge Myrmekioderma indemaresi Sitjà, Maldonado, Farias & Rueda, 2018.