The snails' tale in deep-sea habitats in the Gulf of Cadiz (NE Atlantic)

Bridging the Atlantic and Mediterranean continental margins, the South Iberian region has recently been the focus for geological and biological investigations. In this region, the Gulf of Cadiz (GoC) encompasses a great variety of deep-sea habitats that harbour highly diverse biological communities. In this study, we describe the composition of gastropod assemblages obtained from in situ colonization experiments and benthic sampling of deep-sea habitats in the GoC. Gastropod distributional patterns, such as bathymetric ranges, bathymetric turnover, affinity to substrate types and abundance-occupancy relationships, are analysed and interpreted in relation to their inferred dispersal capabilities and substrate availability. Overall, the GoC comprises a high diversity of gastropods (65 species), and distinct assemblages were found in typical sedimentary environments at mud volcanoes and in association with carbonate and coral samples or organic substrata. The number of taxa peaked at the Carbonate Province in the middle slope (600–1200 m depth), a highly heterogeneous area with numerous mud volcanoes, carbonate mounds and corals. Darwin (1100 m) and Captain Arutyunov (1300 m) mud volcanoes harboured the most species-rich and abundant gastropod assemblages, respectively. Colonization experiments with organic substrata (wood and alfalfa grass) also yielded diverse and abundant gastropod assemblages. These organic inputs allowed the recruitment of local species but mainly of wood specialist taxa that were not previously known from the GoC. Our results suggest that the distribution of gastropod assemblages may be primarily determined by the occurrence of suitable habitats, probably due to the effect of the substrate type on the structural complexity of the habitat and availability and diversity of adequate food sources. The type of larval development is apparently not a limiting factor for colonization of deep-sea habitats. However, the predominance of non-planktotrophy, and especially lecithotrophy, suggests that a trade-off between more limited dispersal capability and higher potential for self-recruitment may be a recurrent pattern in gastropod species inhabiting reducing environments and other patchily distributed deep-sea habitats. A network of suitable habitats that ensures effective population connectivity would explain the predominance and relatively wide distribution of short-distance dispersing non-planktotrophic species in the GoC deep-sea habitats and other geographical regions

Bottom-trawling fisheries influence on standing stocks, composition, diversity and trophic redundancy of macrofaunal assemblages from the West Iberian Margin

Bottom-trawling fisheries operating in Portugal (West Iberian Margin) impose one of the largest footprints per unit of biomass landed in European waters at depths greater than 200 m, affecting the seafloor integrity and the associated benthic fauna. To investigate how trawling pressure is affecting the macrofaunal assemblages, we compared the standing stock (abundance and biomass), community structure and taxonomical and trophic diversity in areas subjected to varying trawling pressure along the SW Portuguese upper slope, between 200 and 600 m. In addition to trawling pressure, several environmental variables, namely depth, grain size and organic matter, were correlated with the biological component, which suggest that the longstanding trawling pressure presents cumulative effects to the habitat heterogeneity known to characterise the West Iberian Margin fauna. Furthermore, our results showed a depletion of macro-infaunal abundances in both the fishing ground and the adjacent area (up to 3 times lower), when compared to the area not trawled. The observed decrease in abundance with increasing trawling pressure was also associated with a loss of species and trophic richness, but univariate diversity indices related with community structure (i.e. Shannon-Wiener index, Pielou's evenness) failed to detect consistent differences across areas. Also observed was a decrease in the number of taxa – trophic guilds combinations of the core assemblage (i.e. characteristic, dominant or frequent taxa) with increasing trawling pressure. We suggest that, in disturbed sediments, the lower functional redundancy resulting from the loss of species within most feeding guilds increases the vulnerability of trophic interactions and therefore of the whole assemblage to further increases in natural and anthropogenic disturbance or their synergistic effects.publishe

An enigmatic kilometer-scale concentration of small mytilids (Late Miocene, Guadalquivir Basin, S Spain).

Upper Miocene heterozoan carbonates crop out extensively in a NE-SW-trending belt (42 km long and 1.5-8 km wide) along the so-called El Alcor topographic high, from Carmona to Dos Hermanas (Seville, S Spain). These carbonates formed at the southern active margin of the Guadalquivir Basin, the foreland basin of the Betic Cordillera. They change to marls basinward (NE) and to sands landward (SE and SW). Therefore, carbonate production was constrained to a limited area in an otherwise siliciclastic shelf. The carbonates (up to 40 m thick) overlie a gradually coarsening-upward succession of marls followed by silts and sandstones. The carbonate sequence can be divided into three subunits corresponding, frombottom to top, to lowstand, transgressive, and highstand system tract deposits. The lower subunit, exhibiting extensive trough cross-bedding, is interpreted as a shallow-water bar deposit. The intermediate subunit onlaps underlying sediments and was deposited in deeper, lowturbulence conditions. The upper subunit deposits accumulated in a well-oxygenated outer platform based on benthic foraminiferal assemblages. The presence of hummocky and swaley cross-stratification in these latter deposits suggests that theywere affected by storms. Pervasive fluid-escape structures are also observed throughout the carbonates. The three subunits consist of bioclastic packstones to rudstonesmade up of abundant fragments of smallmytilids. Isotopic data from serpulid polychaete Ditrupa tubes show 13C-depleted values (up to −16.1¿), whereas δ18O yields normal marine values. Additional isotopic data on shells of scallops, oysters, and small mussels, as well as bulk sediment, show diagenetic alterations. Based on actualistic examples of massive concentrations of mussels, the nearly monospecific composition of the El Alcor deposits, together with negative δ13C values of Ditrupa tubes, indicates that cold seeps presumably promoted carbonate formation. However, the absence of typical features of cold-seep deposits, such as authigenic carbonatesmediated by anaerobic bacterial activity and the typical chemosynthetic shelly organisms, makes the large carbonate body of El Alcor an unusual cold-seep deposit

Effects of sample storage and shell orientation on LA-ICPMS trace element measurements on deep-sea mussels.

Geochemical markers are being increasingly applied to fundamental questions in population and community ecology in marine habitats because they allow inferences on individuals dispersal, but vital effects, small sample size and instrumental limitation are still challenging particularly in deep-sea studies. Here we use shells of the deep-sea bivalve Idas modiolaeformis to assess potential effects of sample storage, mineralogy, and valve orientation on LA-ICPMS measurements. Trace element concentrations of (24)Mg, (43)Ca, (88)Sr, (137)Ba, (208)Pb, and (238)U are not affected by the two most commonly used storage methods of biologic deep-sea samples (frozen at -20°C and fixed in 95% ethanol); thus combined analysis of differently preserved specimens is possible when the number of individuals is insufficient and distinct sample fixation is needed for multiple purposes. Valve orientation had a strong impact on quantification of trace elements in the calcitic but not in the aragonitic layer of adult shells. Hence, to enable comparisons between adult shells and entirely aragonitic embryonic shells, a reference map of site-specific signatures can potentially be generated using the aragonitic layer of the adult shells. Understanding ontogenetic changes and environmental effects in trace element incorporation is critical before geochemical fingerprinting can be used as a tool for larval dispersal studies in the deep-sea

A complex picture of associations between two host mussels and symbiotic bacteria in the Northeast Atlantic

Among chemosymbiotic metazoans found at deep-sea hydrothermal vents, cold seeps and organic falls, members of the mussel clade Bathymodiolinae (Bivalvia: Mytilidae) have evolved interactions with a higher diversity of bacterial lineages than other bivalve groups. Here, we characterized the bacteria associated with "Bathymodiolus" mauritanicus and Idas-like specimens from three sites in the Northeast Atlantic (two mud volcanoes in the Gulf of Cadiz and one seamount of the Gorringe Bank). Phylogenetic analysis of bacterial 16S rRNA-encoding gene sequences demonstrated that "B". mauritanicus has a dual symbiosis dominated by two phylotypes of methane-oxidising bacteria and a less abundant phylotype of a sulphur-oxidising bacterium. The latter was the dominant phylotype in a sympatric population of Idas-like mussels at the Darwin mud volcano. These results are the first report of a bacterial phylotype shared between two deep-sea mussels from divergent clades. This sulphur-oxidising bacterium was absent from Idas-like specimens from the other two sites (Gorringe Bank and Meknès mud volcano), in which bacterial clone libraries were dominated by other Gammaproteobacteria related to symbionts previously identified in Idas modiolaeformis from the Eastern Mediterranean. All Idas-like specimens studied herein are closely related and also related to I. modiolaeformis. However, they probably display different associations with bacteria, with the possible absence of both methane- and sulphur-oxidising symbionts at the Gorringe Bank. These results draw a very complex picture of associations between mussels and bacteria in the Northeast Atlantic, which could be highly variable depending on locale characteristics of the habitats

Arichlidon reyssi

<p> <i>Arichlidon reyssi</i> (Katzmann, Laubier & Ramos, 1974)</p> <p> <i>Bhawania reyssi</i> Katzmann, Laubier & Ramos, 1974: 313, fig. 1 (type locality: Adriatic Sea, 51–77 m; other localities: Catalan and Banyuls-sur-Mer coasts, 10 m).</p> <p> <i>Paleanotus heteroseta</i> – Rullier 1964: 142 (Cape Verde Islands, 20–100 m). [not Hartman, 1945]</p> <p> <i>Arichlidon reyssi</i> – Watson Russell 1998: 159, figs 4, 6 (Mediterranean, Red Sea, intertidal to 3947 m). — Watson <i>et al</i>. 2014: 317, fig. 4 (Senghor Seamount, Cape Verde Archipelago, 1000– 1651 m).</p> Material examined <p> SPAIN – <b>Bay of Biscay</b> • 1 af, 1 pf; tributary of Cap Breton Canyon; 43°31.74′ N, 02°45.60′ W; 221 m; St M84-5_633; DBUA 0002276.01 • 1 af; tributary of Cap Breton Canyon; 43°31.68′ N, 02°45.48′ W; 214 m; St M84-5_677; DBUA 0002276.02.</p> <p>PORTUGAL • 1 pf (cf); Gulf of Cadiz, Formosa Ridge; 36°10.263′ N, 07°43.819′ W; 1079 m; St TTR 12_AT388; DBUA 0000698.</p> Description <p>Both specimens from the Bay of Biscay are very small and extremely arched, and thus difficult to examine. The anterior fragment from station M84-5_633 (DBUA 0002276.01) has eleven chaetigers and measures approximately 1.17 mm long. Should the two fragments (anterior and posterior) belong to the same specimen, the total number of chaetigers would be 17 and the total length 1.94 mm. Prostomium with two pairs of coalescent dark eyes. Indistinct paired structure present ventrally at mouth level. Palaeal notochaetae bright and translucent, covering entire body and forming an acute mid-dorsal ridge. Paleae broadly rounded, distally with a small acute tip and strong serrate margins; dorsal surface with raised serrate ribs. Blades of compound neurochaetae long and spinigerous, in dorsalmost position becoming falcigerous and gradually shorter ventrally.</p> Remarks <p> <i>Arichlidon reyssi</i> has often been reported as occurring in large numbers at a given locality (e.g., Aguirrezabalaga <i>et al.</i> 1986, Cantabrian Sea, 100 m, numerous specimens; Watson Russell 1998, eastern Mediterranean, 196–199 m, 82 specimens; Watson <i>et al.</i> 2014, Senghor seamount, 102–133 m, 80 specimens). In the present study, only a couple of specimens were found at shelf-break depths in the Bay of Biscay and a dubious posterior fragment at a deeper station in the Gulf of Cadiz. These small and incomplete specimens possess lateralmost median paleae not clearly longer than the remaining ones, which is a distinguishing character for <i>A. reyssi</i> (Watson Russell 1998, 2000b). Apart from that, no other obvious morphological differences were found. The absence of tall lateralmost median paleae in some specimens was previously noted for the eastern Mediterranean, Red Sea and Egyptian populations, which were nonetheless considered as belonging to the same species (Watson Russell 1998). However, the known wide bathymetric range of this species suggests a possible complex of cryptic species in need of further study (see Watson <i>et al.</i> 2014).</p> Ecology and distribution <p> <i>Arichlidon reyssi</i> is distributed in the NE Atlantic from the Cantabrian Sea (Bay of Biscay) to the Cape Verde Archipelago, at 20–1651 m; in the Mediterranean from the Alboran Sea to the Levant Basin, from the intertidal to 3947 m (the deepest locations in the E Mediterranean); in the Red Sea from the intertidal to a depth of 757 m (Watson Russell 1998; San Martín 2004; Watson <i>et al.</i> 2014). <i>Arichlidon reyssi</i> usually occurs in hard substrates, e.g., coarse sediments with shell debris, rock, calcareous substrates, but also in mud at the deepest localities (Watson 1998; San Martín 2004). The material studied herein was collected together with samples of the scleractinian coral, <i>Dendrophyllia cornigera</i> (Lamarck, 1816), at the head of a Cap Breton Canyon tributary (Cantabrian Sea, Bay of Biscay) at 214–221 m and from inactive carbonate chimneys at Formosa Ridge (SW Iberian margin, Gulf of Cadiz) at 1079 m.</p>Published as part of <i>Ravara, Ascensão, Aguado, M. Teresa, Rodrigues, Clara F., Génio, Luciana & Cunha, Marina R., 2019, Description of a new genus and species of Chrysopetalidae (Annelida: Polychaeta) from the NE Atlantic, with some further records of related species, pp. 1-21 in European Journal of Taxonomy 539</i> on pages 7-9, DOI: 10.5852/ejt.2019.539, <a href="http://zenodo.org/record/3353542">http://zenodo.org/record/3353542</a&gt

Natsushima bifurcata Miura & Laubier 1990

Natsushima bifurcata Miura & Laubier, 1990 Natsushima bifurcata Miura & Laubier, 1990: 322–323, fig. 2 (type locality: Sagami Bay, Japan, 1170 m; host: Acharax sp.). Natsushima bifurcata – Miura & Hashimoto 1996: 265–266 (Sagami Bay, 1114 m; host: Acharax johnsoni Dall, 1891). — Ravara et al. 2007: 96, fig. 1 (Gulf of Cadiz, 920–1105 m; host: Acharax sp.). Material examined MOROCCO – Gulf of Cadiz • 3 cs; Jesuz Baraza mud volcano; 35°35.439′ N, 07°12.264′ W; 1105 m; 9 Jul. 2002; inside mantle cavity of Acharax gadirae; St. TTR12 _AT391; DBUA 00711 • 1 af (damaged); Yuma mud volcano; 35°24.973′ N, 07°05.461′ W; 960 m; 2 Aug. 2004; inside mantle cavity of Acharax gadirae; St TTR14 _AT524; DBUA 00765 • 4 cs; Yuma mud volcano; 35°25.820′ N, 07°06.330′ W; 1030 m; 29 May 2006; inside mantle cavity of Acharax gadirae; St TTR16 _AT604; DBUA 00791.01 • 4 cs, 1 af; Yuma mud volcano; 35º25.046′ N, 07º05.450′ W; 975 m; 29 May 2006; inside mantle cavity of Acharax gadirae; St TTR16 _AT605; DBUA 00791.02 • 2 cs; Ginsburg mud volcano; 35°22.677′ N, 07°04.979′ W; 920 m; 29 May 2006; inside mantle cavity of Acharax gadirae; St TTR16 _AT607; DBUA 00791.03. Remarks Ravara et al. (2007) reported this species from cold seeps in the Gulf of Cadiz (Jesus Baraza, Yuma and Ginsberg MVs). The specimens were found in the mantle cavity of Acharax sp., which was later described as a new species, Acharax gadirae Oliver, Rodrigues & Cunha, 2011 (Bivalvia: Solemyidae) (Oliver et al. 2011). The bathymetric range of Acharax gadirae in the Gulf of Cadiz is 556–3902 m. However, only the populations from the mud volcanoes of the Western Moroccan field, located at depths of 920–1105 m, were infested by N. bifurcata. This species was originally found in the mantle cavity of Acharax johnsoni (Dall, 1891) from the Hatsushima and Okino-Yama cold seeps in Sagami Bay (E Pacific), at similar depths (1114–1170 m). Despite the great geographical distance, there were no substantial morphological differences between the specimens from the two localities that could justify the establishment of a new species. Aguado & Rouse (2011) obtained a COI sequence from one of the specimens from the Gulf of Cadiz (GenBank accession number JF304492). However, the preservation of the Japanese specimens did not allow DNA analysis, and thus a molecular comparison was not possible. Ecology and distribution East Pacific (Sagami Bay, Japan) and NE Atlantic (Gulf of Cadiz), living inside the mantle cavity of chemosynthesis-based bivalves of the genus Acharax, from cold seeps at depths of 920–1170 m (Miura & Laubier 1990; Ravara et al. 2007).Published as part of Ravara, Ascensão, Aguado, M. Teresa, Rodrigues, Clara F., Génio, Luciana & Cunha, Marina R., 2019, Description of a new genus and species of Chrysopetalidae (Annelida: Polychaeta) from the NE Atlantic, with some further records of related species, pp. 1-21 in European Journal of Taxonomy 539 on pages 11-12, DOI: 10.5852/ejt.2019.539, http://zenodo.org/record/335354

Craseoschema thyasiricola Ravara & Aguado & Rodrigues & Génio & Cunha 2019, sp. nov.

<i>Craseoschema thyasiricola</i> Ravara & Aguado sp. nov. <p>urn:lsid:zoobank.org:act: 146CA9DD-11B3-46F0-81A8-2E6B085458C0</p> <p>Figs 3–5</p> Diagnosis <p>Chaetous neuropodia and dorsal and ventral cirri present on the first segment. Notopodial lobes poorly developed. Notochaetae stick-like, with denticulated tips. Neurochaetae compound, with serrated blades and denticulated tips.</p> Etymology <p> The species name is derived from the host bivalve genus <i>Thyasira</i>, with the Latin suffix <i>-cola</i> denoting ‘inhabiting’.</p> Material examined <p> <b>Holotype</b></p> <p> PORTUGAL • 1 af, 1 pf, several mf; Gulf of Cadiz, Carlos Ribeiro mud volcano; 35°47.238′ N, 08°25.272′ W; 2200 m; specimen found inside mantle cavity of <i>Thyasira vulcolutre</i> (Bivalvia, Thyasiridae); St TTR16_AT615; ANEA NHMUK 2019.7339 • 2 mf; same locality; 1 slide and 1 SEM stub; DBUA 0002275.</p> Description <p> Only one fragmented specimen was found, inside the mantle cavity of a bivalve of the species <i>Thyasira vulcolutre</i> Rodrigues & Oliver, 2008. The anterior fragment has three chaetigers, the posterior nine chaetigers; largest median fragment with seventeen chaetigers, 5.82 mm long. Body elongate, tapering at anterior and posterior ends, arched dorsally and flattened ventrally, rectangular in crosssection (Fig. 5A). Colour in ethanol white. Prostomium very short, broadly rounded anteriorly, fused to first chaetiger (Figs 3A, 4A). Eyes absent. Paired antennae cirriform, with basal swelling, inserted dorsolaterally (Figs 3A, 4A). Palps as low mound structures, inserted ventrally just anterior to mouth (Fig. 3B). Pharynx strongly muscularised; jaws not examined (specimen not dissected in order to keep its integrity as holotype). Parapodia much shorter on first segment than on following ones (Fig. 3A–B). Dorsal and ventral cirri digitiform, present from first chaetiger. Notopodia clearly present from segment 4, rounded, with straight notoacicula and dorsal cirri inserted distally; neuropodia much longer and conical, neuroacicula with bent tips (Fig. 4D), ventral cirri inserted close to base (Figs 3 C–D, 4B, 5B).</p> <p>Notochaetae simple, stick-like, laddered basally, with a few rows of small spines subdistally, and ending in blunt and slightly curved tips with several denticles (only visible in SEM; Figs 3E, 5 C–D); absent in first three segments, up to 15 present in median and posterior segments; a single notochaeta in last segments. Neurochaetae compound falcigers, with long, laddered shafts and short, finely serrated blades (Figs 3 F–G, 4E, 5E–H). Neurochaetae longer in dorsalmost position, gradually shortening ventrally, and present in greater numbers than notochaetae in all segments. Blades of dorsalmost neurochaetae with two rows of longitudinal spines and numerous denticles distally, with a worn appearance under compound microscope (Fig. 5 E–F); blades of ventralmost neurochaetae with longer spines arranged in two longitudinal rows that are wider apart distally, resembling a spaghetti-spoon (Fig. 5 G–H). Pygidium button-like, with terminal anus and no appendages (Fig. 4C).</p> Remarks <p> Carlos Ribeiro is the deepest and most active mud volcano among the five mud volcanoes from where chrysopetalid specimens are recorded in this study. Two species of thyasirid bivalves, <i>Thyasira vulcolutre</i> (3 specimens) and <i>T. obsoleta</i> (Verrill & Bush, 1898) (1 specimen), were collected in the crater of this mud volcano (Rodrigues <i>et al</i>. 2008), but only one large specimen of <i>T. vulcolutre</i> was infested. This thyasirid species was also reported to occur in higher abundance on Captain Arutyunov MV (37 spms) and Sagres MV (32 spms). These mud volcanoes were also reported as active cold seeps in the deepwater field, but none of the small-sized specimens collected from them (at depths of 1321 m and 1562 m, respectively) were infested. In the Gulf of Cadiz, Thyasiridae are represented by nine species collected from 10 different mud volcanoes, but only two are recognized as chemosymbiotic and both occur in MVs of the Deep Field: <i>Thyasira vulcolutre</i> (Captain Arutyunov, Sagres and Carlos Ribeiro MVs) and <i>Spinaxinus sentosus</i> Oliver & Holmes, 2006 (Captain Arutyunov MV) (Rodrigues <i>et al.</i> 2013). Another two species are mixotrophic and occur across a wider bathymetric range: <i>Axinulus croulinensis</i> (Jeffreys, 1847) (Mercator, Meknès, Captain Arutyunov, Bonjardim and Porto MVs; 350–3900 m) and <i>Thyasira granulosa</i> (Monterosato, 1874) (Mercator, Meknès, Chechaouen, Darwin and Captain Arutyunov MVs; 350–1321 m) (Rodrigues <i>et al.</i> 2013 and unpublished data). Except for the large specimen of <i>T. vulcolutre</i> from Carlos Ribeiro MV, all the other thyasirid specimens were not infested.</p> Ecology and distribution <p> NE Atlantic (Gulf of Cadiz), on Carlos Ribeiro MV, at a depth of 2200 m. Found in the mantle cavity of the chemosynthesis-based bivalve <i>Thyasira vulcolutre</i> Rodrigues & Oliver, 2008.</p>Published as part of <i>Ravara, Ascensão, Aguado, M. Teresa, Rodrigues, Clara F., Génio, Luciana & Cunha, Marina R., 2019, Description of a new genus and species of Chrysopetalidae (Annelida: Polychaeta) from the NE Atlantic, with some further records of related species, pp. 1-21 in European Journal of Taxonomy 539</i> on pages 13-16, DOI: 10.5852/ejt.2019.539, <a href="http://zenodo.org/record/3353542">http://zenodo.org/record/3353542</a&gt

Description of a new genus and species of Chrysopetalidae (Annelida: Polychaeta) from the NE Atlantic, with some further records of related species

Five chrysopetalid species are reported from samples collected at bathyal depths in three NE Atlantic regions: the Bay of Biscay, the Horseshoe Abyssal Plain and the Gulf of Cadiz. Arichlidon reyssi (Katzmann et al., 1974), Dysponetus caecus (Langerhans, 1880) and D. profundus Böggemann, 2009 are free-living forms found mainly on biogenic substrates (e.g., coral and sunken wood). A brief description and taxonomical remarks are given for each of these species and their geographical distributions and habitat records were updated accordingly. Natsushima bifurcata Miura & Laubier, 1990 and Craseoschema thyasiricola gen. et sp. nov. are symbionts inhabiting the mantle cavity of chemosynthesis-based bivalves known from four mud volcanoes from the Gulf of Cadiz. Craseoschema thyasiricola gen. et sp. nov. was found inside a thyasirid bivalve and presents mixed morphological characteristics of free-living and symbiotic forms within Calamyzinae Hartmann-Schröder, 1971. A full description of the new species is given together with DNA sequences of the genes COI, 16S and H3 that were used in a phylogenetic analysis to indicate the position of the new genus within the family