Deep-water sponge fauna from the mud volcanoes of the Gulf of Cadiz (North Atlantic, Spain)

Abstract

Mud volcanoes are singular seafloor structures classified as ‘sensitive habitats’. Here we report on the sponge fauna from a field of eight mud volcanoes located in the Spanish margin of the northern Gulf of Cadiz (North-eastern Atlantic), at depths ranging from 380 to 1146 m. Thirty-eight beam-trawl samplings were conducted (covering over 61,000 m2) from 2010 to 2012, in the frame of a EC-LIFE + INDEMARES grant. A total of 1659 specimens were retrieved, belonging to 82 species, from which 79 were in the Class Demospongiae and three in Hexactinellida. Two species were new to science (Jaspis sinuoxea sp. nov.; Myrmekioderma indemaresi sp. nov.) and three others recorded for the first time in the Atlantic Ocean (Geodia anceps, Coelosphaera cryosi and Petrosia raphida). Five additional species were ‘Atlantic oddities’, since this study provides their second record in the Atlantic Ocean (Lanuginella cf. pupa, Geodia cf. spherastrella, Cladocroce spathiformis, Cladocroce fibrosa and Haliclona pedunculata). Basic numerical analyses indicated a significant linear relationship between the species richness per m2 and the number of sponge individuals per m2, meaning that in most volcanoes many species occur in equivalent, moderate abundance. Likewise, sponge species richness increased with depth, while the abundance of hard substrata resulting from carbonate precipitation and the fishing activities around the volcanoes had no detectable effect on the sponge fauna. However, in the latter case, a negative trend – lacking statistical support – underlaid the analyses, suggesting that a more extensive sampling would be necessary to derive more definitive conclusions in this regard.

Methane Seeps on the US Atlantic Margin and Their Potential Importance to Populations of the Commercially Valuable Deep-Sea Red Crab, Chaceon quinquedens

“…Methane seeps are highly productive ecosystems where fluids enriched in methane and hydrogen sulfide "seep" out of the surface sediment, supporting chemoautotrophic production by both free-living and symbiotic microbes (Tunnicliffe et al, 2003;Torres and Bohrmann, 2014). Methane seeps are often characterized by symbiont-bearing megafauna (e.g., tubeworms and mussels), which form biogenic habitats that support a variety of additional species (Sibuet and Olu, 1998;Tunnicliffe et al, 2003;Govenar, 2010). Until recently, only three areas of methane seepage were recognized on the US Atlantic margin: a dense mussel community near Baltimore Canyon observed in the early 1980s (B. Hecker, cited in Prouty et al, 2016), and chemosynthetic communities associated with the Blake Ridge (Paull et al, 1995;Van Dover et al, 2003) and Cape Fear salt diapirs (Brothers et al, 2013;Wagner et al, 2013).…”

Molluscs from benthic habitats of the Gazul mud volcano (Gulf of Cádiz)

“…Molluscs are a good indicator for the biodiversity assessment in a particular area (Reyers et al 2000, Mellin et al 2011, so a species-rich area for molluscs will be indicative of a high-level of biodiversity for other taxa (Reyers et al 2000), and this would be the case of the Gazul MV (Díaz-del-Río et al 2014, Rueda et al 2016, Sitjà et al 2019. This high biodiversity of molluscs is striking, taking into account the small size of the study area (less than 5 km 2 ) and its location in the bathyal zone on the pathway of the MOW.…”

Influence of Water Masses on the Biodiversity and Biogeography of Deep-Sea Benthic Ecosystems in the North Atlantic

“…The MOW seems to represent one of the main water masses driving the distribution of CWCs across the NE Atlantic (Dullo et al, 2008;Somoza et al, 2014), promoting connectivity by the natural export of Mediterranean species and populations (Henry et al, 2014;Arnaud-Haond et al, 2017;Boavida et al, 2019). Several studies noted the presence of deep-sea suspension feeding species previously known only from the Mediterranean (e.g., the sponges Geodia anceps, Coelosphaera cryosi, and Petrosia raphida) at NE Atlantic locations, such as the Gulf of Cadiz (Spain; Palomino et al, 2016;Sitjá et al, 2018). This area is dominated by aggregations of scleractinians and gardens of large gorgonians and black corals (e.g., M. oculata, Acanthogorgia spp., Antipathes dichotoma, Leiopathes glaberrima; Figure 2) with particular locations, such as Gazul mud volcano, representing a biodiversity hotspot with more than 400 associated species (Rueda et al, 2016;Ramalho et al, 2018;Sitjá et al, 2018).…”

“…Several studies noted the presence of deep-sea suspension feeding species previously known only from the Mediterranean (e.g., the sponges Geodia anceps, Coelosphaera cryosi, and Petrosia raphida) at NE Atlantic locations, such as the Gulf of Cadiz (Spain; Palomino et al, 2016;Sitjá et al, 2018). This area is dominated by aggregations of scleractinians and gardens of large gorgonians and black corals (e.g., M. oculata, Acanthogorgia spp., Antipathes dichotoma, Leiopathes glaberrima; Figure 2) with particular locations, such as Gazul mud volcano, representing a biodiversity hotspot with more than 400 associated species (Rueda et al, 2016;Ramalho et al, 2018;Sitjá et al, 2018). The current distribution of living L. pertusa and M. oculata in the canyons of the Bay of Biscay coincides with the lower limit of the boundary between the ENACW and the MOW (De Mol et al, 2011), as does the distribution of carbonate mounds and CWC reefs in the Porcupine Seabight (De Mol et al, 2002, 2005White and Dorschel, 2010) and other contourite systems in the NE Atlantic (Van Rooij et al, 2007a,b;Hernández-Molina et al, 2009).…”