Molluscs from the Gazul mud volcano and its adjacent areas in the northern Gulf of Cádiz were studied using different sampling methods. This mud volcano has vulnerable deep-sea habitats and a potential high biodiversity. A total of 232 species were identified from the taxocoenosis and thanatocoenosis, of which 86 are new records for the Spanish margin of the Gulf of Cádiz, three of them are new records for Spanish waters and two species are new to science. The high species richness observed could be related to the combination of different sampling methods, the study of the thanatocoenosis, the high habitat heterogeneity and the geographical location of the Gazul mud volcano between different biogeographical regions. The best-represented species were
Se estudiaron los moluscos del volcán de fango Gazul y sus zonas adyacentes, en el norte del Golfo de Cádiz, utilizando diferentes métodos de muestreo. Este volcán de fango destaca por la presencia de hábitats vulnerables de aguas profundas y una alta biodiversidad potencial. Se identificaron un total de 232 especies de la taxocenosis y la tanatocenosis, de las cuales 86 son nuevas citas para el margen español del Golfo de Cádiz, tres de ellas son nuevas citas para aguas españolas y dos especies son nuevas para la ciencia. La alta riqueza de especies detectada podría estar relacionada con la combinación de diferentes métodos de muestreo, el estudio de la tanatocenosis, la alta heterogeneidad del hábitat y la ubicación geográfica del volcán de fango Gazul entre diferentes regiones biogeográficas. Las especies mejor representadas fueron
Mud volcanoes (MVs) are submarine structures formed by the vertical migration of sediments and fluids saturated in hydrocarbons, mainly methane, which are extruded by high pressure and low temperature emissions (
The GoC is an important area of seepage activity at a global scale, with the presence of more than 70 MVs and MV/diapir complexes located in different fields of the Spanish, Portuguese and Moroccan continental margins (
Some of the species and habitats existing in the northern GoC are included in national and international conservation lists (e.g. Habitat Directive, EUNIS, OSPAR), such as vulnerable deep-sea habitats with high ecological value (e.g. cold-water coral banks and black coral gardens), while others are unique within the European context (e.g. chemosynthesis-based communities) (
Molluscs are one of the most diverse faunal groups in marine environments, representing important components of the benthic communities due to their different feeding strategies (e.g. filter feeders, deposit feeders, carnivores and parasites) and their contribution as an important food source for higher trophic levels (
The study area is the Gazul MV and its adjacent bottoms (36°33.53′N, 6°55.96′W), located in the northeastern sector of the shallow field of fluid expulsion of the Spanish margin of the GoC, within the site of community importance
Sampling was carried out in several areas of the Gazul MV (
Expedition | Sampling method | Sample code | Latitude start |
Longitude start | Depth start (m) | Latitude end |
Longitude end |
Depth end (m) | Area |
---|---|---|---|---|---|---|---|---|---|
INDEMARES/CHICA 0610
(R/V |
Beam-trawl | BT2 | 36°33.28′N | 06°56.72′W | 477 | 36°33.32′N | 06°57.45′W | 478 | Adjacent bottoms |
BT3 | 36°34.03′N | 06°56.28′W | 462 | 36°34.43′N | 06°56.68′W | 460 | Adjacent bottoms | ||
BT4 | 36°33.80′N | 06°56.52′W | 495 | 36°33.33′N | 06°56.32′W | 483 | Erosive depression | ||
BT5 | 36°33.82′N | 06°56.72′W | 487 | 36°33.33′N | 06°56.52′W | 478 | Erosive depression | ||
BT6 | 36°33.55′N | 06°56.12′W | 422 | 36°33.98′N | 06°55.98′W | 450 | MV edifice | ||
BT7 | 36°33.37′N | 06°55.85′W | 420 | 36°33.87′N | 06°55.60′W | 459 | MV edifice | ||
BT8 | 36°33.45′N | 06°56.02′W | 380 | 36°33.90′N | 06°55.73′W | 455 | MV edifice | ||
Benthic Dredge | DA2 | 36°33.57′N | 06°55.75′W | 402 | 36°33.58′N | 06°55.85′W | 451 | MV edifice | |
DA5 | 36°33.58′N | 06°56.10′W | 422 | 36°33.48′N | 06°56.13′W | 418 | MV edifice | ||
DA6 | 36°33.30′N | 06°56.75′W | 478 | 36°33.32′N | 06°56.90′W | 478 | Adjacent bottoms | ||
DA7 | 36°33.82′N | 06°56.58′W | 495 | 36°33.72′N | 06°56.53′W | 491 | Erosive depression | ||
DA8 | 36°33.73′N | 06°56.70′W | 486 | 36°33.60′N | 06°56.63′W | 487 | Erosive depression | ||
DA9 | 36°34.02′N | 06°56.27′W | 458 | 36°34.10′N | 06°56.33′W | 456 | Adjacent bottoms | ||
DA10 | 36°33.57′N | 06°55.95′W | 390 | 36°33.43′N | 06°56.02′W | 410 | MV edifice | ||
DA11 | 36°33.70′N | 06°56.32′W | 461 | 36°33.85′N | 06°56.32′W | 462 | Erosive depression | ||
Shipek grab | SK1.1 | 36°33.72′N | 06°56.32′W | 461 | Erosive depression | ||||
SK1.2 | 36°33.72′N | 06°56.30′W | 459 | Erosive depression | |||||
SK1.3 | 36°33.72′N | 06°56.32′W | 461 | Erosive depression | |||||
SK2.1 | 36°33.78′N | 06°56.53′W | 494 | Erosive depression | |||||
SK2.2 | 36°33.78′N | 06°56.52′W | 494 | Erosive depression | |||||
SK2.3 | 36°33.77′N | 06°56.52′W | 495 | Erosive depression | |||||
SK3.1 | 36°33.75′N | 06°56.70′W | 486 | Erosive depression | |||||
SK3.2 | 36°33.75′N | 06°56.70′W | 486 | Erosive depression | |||||
SK3.3 | 36°33.75′N | 06°56.72′W | 486 | Erosive depression | |||||
Box-corer | BC6.1 | 36°33.53′N | 06°55.95′W | 370 | MV edifice | ||||
BC6.2 | 36°33.50′N | 06°55.98′W | 371 | MV edifice | |||||
BC6.3 | 36°33.52′N | 06°55.97′W | 369 | MV edifice | |||||
BC8.1 | 36°33.52′N | 06°55.72′W | 419 | MV edifice | |||||
BC8.2 | 36°33.52′N | 06°55.72′W | 418 | MV edifice | |||||
BC8.3 | 36°33.50′N | 06°55.70′W | 427 | MV edifice | |||||
BC9.1 | 36°33.58′N | 06°55.53′W | 454 | MV edifice | |||||
BC9.2 | 36°33.58′N | 06°55.55′W | 457 | MV edifice | |||||
BC9.3 | 36°33.58′N | 06°55.55′W | 449 | MV edifice | |||||
BC10.1 | 36°33.92′N | 06°56.15′W | 462 | Adjacent bottoms | |||||
BC10.2 | 36°33.93′N | 06°56.18′W | 461 | Adjacent bottoms | |||||
BC10.3 | 36°33.98′N | 06°56.23′W | 461 | Adjacent bottoms | |||||
BC11.1 | 36°33.28′N | 06°56.67′W | 477 | Adjacent bottoms | |||||
BC11.2 | 36°33.28′N | 06°56.72′W | 477 | Adjacent bottoms | |||||
BC11.3 | 36°33.28′N | 06°56.67′W | 477 | Adjacent bottoms | |||||
IND./CHICA 0412
R/V |
Box-corer | BC1 | 36°33.52′N | 06°55.95′W | 362 | MV edifice | |||
ATLAS/MEDWAVES
0916
R/V |
Box-corer | BC1_MED | 36°33.78′N | 06°55.87′W | 444 | Adjacent bottoms | |||
BC2_MED | 36°33.87′N | 06°55.86′W | 450 | Adjacent bottoms | |||||
BC3_MED | 36°33.92′N | 06°55.86′W | 446 | Adjacent bottoms |
Additionally, for some species, comparative material from the expeditions of the R/V
Beam-trawl and benthic dredge samples were sieved on board over mesh sizes of 10, 5 and 1 mm to separate large and small specimens. Moreover, box-corer/Shipek grab samples were sieved on board with a 0.5 mm sieve in order to retain the small species while eliminating the sandy and muddy sediment. The samples were mainly preserved in 70% ethanol. In the laboratory, species of each sample were separated from the remaining sediment by large groups (mainly molluscs, crustaceans, annelids and echinoderms) using a stereomicroscope (Leica MZ12), and mollusc specimens were identified to the lowest possible taxonomic level. Scientific names follow the nomenclature of the WoRMS (
The number of live-taken specimens of each mollusc species was quantified in each sample, while for the species of the thanatocoenosis a rank system was applied (except in the beam-trawl samples, in which hardly any sediment was collected, so the thanatocoenosis could not be studied) (1, 1 shell; 2, 2 to 5 shells; 3, 6 to 30 shells; 4, 31 to 100 shells; 5, more than 100 shells). Although, admittedly, shells may be displaced in space and time, we took into account the thanatocoenosis because we are also convinced that it provides a much more complete account of the species composition than the live-taken specimens only. We believe that the loss of accuracy using shells is outweighed by the gain in the amount of information on the faunal composition (
Photographs were taken for the most representative or less common species using a Nikon DXM camera mounted on a stereomicroscope, and some characteristic details (e.g. microsculptures and protoconchs) were examined with scanning electron microscopy (JEOL JCC 1100 equipment). Several views focusing on different image planes were taken and assembled using the CombineZ software (
Sediment characterization of each study zone was performed using the box-corer and Shipek grab samples of the INDEMARES/CHICA and ATLAS/MEDWAVES expeditions. After oven-drying of sediment samples at 60°C to constant weight, samples were wet-sieved in a 63 μm mesh sieve, giving a coarse fraction (>63 μm) and a fine fraction (<63 μm) composed of mud, whose quantity was obtained by weighing the total sample before and after sieving. The coarse fraction was subsequently dry-sieved in a column of sieves and each retained fraction was weighed and transformed into weight percent to characterize the texture of the sediment. The organic matter and carbonate content were estimated in samples stored at -20°C and, after oven-drying and grinding in an agate mortar, the “loss on ignition” method was performed by combustion at 550°C for organic matter and at 950°C for carbonates (
The near-bottom temperature in each sampling area was obtained by a CTD in the INDEMARES/CHICA 0211 expedition in February 2011. Although collected in a different season, these data are taken as representative of the near-bottom conditions because these have been found to have little seasonal variation below 250-300 m depth, under the influence of the MOW (
A data matrix containing the abundance of live-taken species was constructed for each sampling method. Results were standardized to 2000 m2 for the beam-trawl data, 300 m2 for the benthic dredge data and 1 m2 for the box-corer and Shipek grab data. Another data matrix was constructed with ranks for dead-collected species (shells or valves). Parameters and ecological indexes were calculated using the PRIMER v.6 software (
A multivariate analysis based on qualitative (presence/absence of live-taken species) similarities (Bray-Curtis measure) among all samples was carried out to identify molluscan assemblages on the Gazul MV and adjacent bottoms. To test for differences between the identified assemblages, an analysis of similarity (ANOSIM) was performed. The identification of the species characterizing each assemblage was performed through a similarity percentage analysis (SIMPER) with a 90% cut-off for low contributions. Finally, the relationships between molluscs and environmental and fishery parameters were contrasted using the BIOENV (BIOtic and ENVironmental linking) analysis. Prior to this, a Spearman correlation analysis was carried out, and those highly correlated parameters (more than 0.9) were not further considered (e.g. medium sand and salinity). Environmental data expressed as percentage (percentage of gravels, coarse sand, fine sand, mud and organic matter in sediment) were log(x+1) transformed. These multivariate analyses were performed with the PRIMER 6 software (
A total of 232 molluscan species were found at the Gazul MV and adjacent bottoms, and 213 were identified to species level. This number includes two species that are new to science and are described in the present study. A total of 2324 live-taken individuals (ind.) corresponding to 91 species (spp.) (
Family | Species | A | B | C | Previous records | BC/SK (12 samples) | DA (8 samples) | BT (7 samples) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Taxocoenosis | Thanat. | Taxocoenosis | Thanat. | Taxocoenosis | ||||||||||||||
N | %D | %F | Rank | %F | N | %D | %F | Rank | %F | N | %D | %F | ||||||
Neopilinidae | 1 | 8.3 | ||||||||||||||||
Neomeniidae | 1 | 1 | 1 | 0.91 | 8.3 | 1 | 1.15 | 14.3 | ||||||||||
Leptochitonidae | 1 | 0.91 | 8.3 | 130 | 6.09 | 75 | ||||||||||||
Hanleyidae | 4 | 0.19 | 12.5 | |||||||||||||||
Lepetidae | 1 | 1 | 1 | ALL (SM17) | 1 | 25 | ||||||||||||
Cocculinidae | 1 | LEBA | 1 | 8.3 | ||||||||||||||
Lepetellidae | 1 | 1 | ESAL | 1 | 12.5 | |||||||||||||
Lepetellidae | 1 | ESAL. LEBA | 1-3 | 75 | 1-3 | 62.5 | ||||||||||||
Addisoniidae | 1 | NOR, ESAL, LEBA | 1 | 12.5 | ||||||||||||||
Anatomidae | ESAL | 1-3 | 25 | |||||||||||||||
Anatomidae | 1 | 1 | ESAL | 2 | 1.82 | 8.3 | 1-5 | 75 | 3-4 | 50 | ||||||||
Fissurellidae | ESAL, CAN | 1 | 8.3 | 7 | 0.33 | 25 | 1 | 25 | 1 | 1.15 | 14.3 | |||||||
Fissurellidae | 1 | 1 | 8.3 | 10 | 0.47 | 25 | 1 | 25 | 1 | 1.15 | 14.3 | |||||||
Fissurellidae | 1 | 1 | 8.3 | 4 | 0.19 | 12.5 | 1 | 37.5 | 1 | 1.15 | 14.3 | |||||||
Fissurellidae | 2 | 8.3 | 1-3 | 50 | ||||||||||||||
Fissurellidae | ESAL, LEBA, CAN | 1 | 8.3 | 1-2 | 37.5 | |||||||||||||
Chilodontaidae | 1 | 1 | 0.91 | 8.3 | 1-2 | 41.7 | 24 | 1.12 | 50 | 1-3 | 75 | 1 | 1.15 | 14.3 | ||||
Trochidae | 1 | 1 | 3 | 0.14 | 12.5 | 2 | 12.5 | |||||||||||
Trochidae | 1 | 1-3 | 66.7 | 28 | 1.31 | 37.5 | 1-4 | 87.5 | 1 | 1.15 | 14.3 | |||||||
Solariellidae | 1 | 1 | 1-4 | 50 | 2-3 | 50 | ||||||||||||
Seguenzioidea | 1 | CAN | 1-3 | 16.7 | 1 | 12.5 | ||||||||||||
Seguenzioidea | 1 | 1 | 1 | ESAL, LEBA, CAN | 1-2 | 16.7 | ||||||||||||
Seguenzioidea | 1 | 1 | 8.3 | |||||||||||||||
Skeneidae | 1 | 1 | 1 | 1 | 0.91 | 8.3 | 1-5 | 58.3 | 1 | 0.05 | 12.5 | 1-4 | 75 | |||||
Skeneidae | ESAL, LEBA, CAN | 2 | 16.7 | |||||||||||||||
Skeneidae | 1-3 | 33.3 | ||||||||||||||||
Skeneidae | 1-2 | 25 | ||||||||||||||||
Pendromidae | ESAL | 1 | 8.3 | |||||||||||||||
Colloniidae | 1 | 1 | 1-2 | 33.3 | 21 | 0.98 | 25 | 1-3 | 25 | |||||||||
Cerithiidae | 1 | 1 | 1 | 0.91 | 8.3 | 1-5 | 100 | 2-5 | 87.5 | |||||||||
Turritellidae | 1 | 1-2 | 16.7 | 2-4 | 37.5 | |||||||||||||
Triphoridae | 1-2 | 37.5 | ||||||||||||||||
Triphoridae | ALL | 2 | 16.7 | |||||||||||||||
Triphoridae | ESAL, LEBA, CAN | 1 | 12.5 | |||||||||||||||
Triphoridae | 1 | 1 | 1 | 1-2 | 25 | |||||||||||||
Triphoridae | 1 | 16.7 | ||||||||||||||||
Triphoridae | Triphoridae (unidentified) | 6 | 0.28 | 12.5 | 1-3 | 25 | ||||||||||||
Newtoniellidae | 1 | 1 | 25 | 2-3 | 50 | |||||||||||||
Newtoniellidae | 1 | 1 | 1 | 1 | 12.5 | |||||||||||||
Cerithiopsidae | 1 | ESAL, CAN (SM17) | 1 | 8.3 | 1-3 | 50 | ||||||||||||
Cerithiopsidae | ESAL, LEBA, CAN | 2 | 12.5 | |||||||||||||||
Cerithiopsidae | 2 | 16.7 | 2 | 25 | ||||||||||||||
Cerithiopsidae | 1-2 | 16.7 | 1-3 | 62.5 | ||||||||||||||
Cerithiopsidae | 1 | 12.5 | ||||||||||||||||
Cerithiopsidae | 1 | 1 | ESAL, CAN (SM17) | 1-3 | 16.7 | 2-3 | 62.5 | |||||||||||
Epitoniidae | 1 | 1 | ESAL, LEBA, CAN | 1 | 0.91 | 8.3 | 1 | 8.3 | 1 | 12.5 | ||||||||
Epitoniidae | 1 | 1 | 1-2 | 41.7 | 22 | 1.03 | 62.5 | 1-3 | 50 | |||||||||
Epitoniidae | 1 | ALL | 1-2 | 41.7 | 1-3 | 37.5 | ||||||||||||
Epitoniidae | 1 | ESAL, LEBA, CAN | 2 | 12.5 | ||||||||||||||
Epitoniidae | 1 | 1 | 1 | ESAL, LEBA | 1 | 16.7 | 1 | 12.5 | ||||||||||
Epitoniidae | 1-3 | 16.7 | ||||||||||||||||
Epitoniidae | 1 | NOR | 1-2 | 16.7 | 1-3 | 37.5 | ||||||||||||
Epitoniidae | 1 | 1 | CAN | 1 | 8.3 | |||||||||||||
Epitoniidae | 1 | 1 | 1 | ESAL, CAN (SM17) | 1 | 25 | 1 | 0.05 | 12.5 | 1-3 | 75 | |||||||
Eulimidae | 1 | ESAL, LEBA (SM17) | 1 | 8.3 | 1 | 12.5 | ||||||||||||
Eulimidae | 1-2 | 16.7 | 2-3 | 37.5 | ||||||||||||||
Eulimidae | 1 | ALL | 1 | 0.91 | 8.3 | 1-2 | 33.3 | 3 | 0.14 | 12.5 | 2-3 | 62.5 | ||||||
Eulimidae | Eulimidae (unidentified) | 12 | 0.56 | 12.5 | ||||||||||||||
Eulimidae | NOR, ESAL, CAN | 2-3 | 41.7 | |||||||||||||||
Eulimidae | 1-2 | 16.7 | 3 | 0.14 | 12.5 | 1-3 | 62.5 | |||||||||||
Eulimidae | 1 | ESAL, LEBA | 1 | 8.3 | ||||||||||||||
Eulimidae | ESAL, CAN | 1 | 12.5 | |||||||||||||||
Eulimidae | 1 | 1 | 1 | ESAL, LEBA | 1 | 8.3 | 2 | 12.5 | ||||||||||
Eulimidae | 1 | 1 | NOR, ESAL, LEBA | 1 | 33.3 | 1-2 | 25 | |||||||||||
Eulimidae | ESAL, CAN | 1 | 8.3 | |||||||||||||||
Rissoidae | 1 | 1 | 1 | 4 | 3.64 | 16.7 | 1-5 | 100 | 6 | 0.28 | 12.5 | 2-5 | 87.5 | |||||
Rissoidae | 1 | 5 | 4.55 | 16.7 | 1-4 | 83.3 | 2-4 | 62.5 | ||||||||||
Rissoidae | 1 | 1-3 | 33.3 | 1 | 12.5 | |||||||||||||
Rissoidae | 1 | 9 | 8.18 | 25 | 1-5 | 83.3 | 3-5 | 62.5 | ||||||||||
Rissoidae | 1 | 1 | 1 | 0.91 | 8.3 | 1-3 | 58.3 | 1-4 | 75 | |||||||||
Rissoidae | 1 | ESAL | 1 | 0.91 | 8.3 | 1-3 | 41.7 | 2-3 | 37.5 | |||||||||
Rissoidae | 1 | 1 | 3 | 8.3 | ||||||||||||||
Rissoidae | 1-2 | 16.7 | 2 | 12.5 | ||||||||||||||
Rissoidae | 1 | 1 | NOR, ESAL, CAN | 1-3 | 16.7 | 1 | 12.5 | |||||||||||
Vanikoridae | 1 | 1 | 1-2 | 25 | 1 | 12.5 | ||||||||||||
Calyptraeidae | 1 | 25 | ||||||||||||||||
Capulidae | 1-2 | 37.5 | ||||||||||||||||
Eratoidae | 1 | 8.3 | 1-2 | 37.5 | ||||||||||||||
Triviidae | 1 | 25 | ||||||||||||||||
Naticidae | 1 | 1 | 8.3 | 4 | 0.19 | 25 | 1 | 12.5 | ||||||||||
Naticidae | Naticidae (unidentified) | 1-2 | 41.7 | 6 | 0.28 | 12.5 | 2-4 | 87.5 | ||||||||||
Naticidae | NOR, ESAL, CAN (SM17) | 9 | 0.42 | 25 | 1-2 | 25 | ||||||||||||
Cassidae | 1 | 2 | 16.7 | 1 | 12.5 | 2 | 2.30 | 28.6 | ||||||||||
Ranellidae | 1 | 1 | 1 | 25 | 3 | 3.45 | 42.9 | |||||||||||
Atlantidae | ALL | 1 | 8.3 | 1 | 12.5 | |||||||||||||
Muricidae | ALL | 18 | 0.84 | 12.5 | 1-2 | 25 | 1 | 1.15 | 14.3 | |||||||||
Muricidae | 1 | 1 | 1 | ALL (SM17) | 1-2 | 50 | 13 | 0.61 | 37.5 | 1-3 | 75 | |||||||
Muricidae | 1 | 1 | ESAL | 1 | 0.91 | 8.3 | 1-3 | 58.3 | 16 | 0.75 | 25 | 2-5 | 100 | |||||
Fasciolariidae | 1 | 12.5 | ||||||||||||||||
Buccinidae | 1 | 2 | 12.5 | |||||||||||||||
Buccinidae | 1 | 1 | (SM17) | 2 | 8.3 | 2-3 | 37.5 | |||||||||||
Buccinidae | 1 | 12.5 | ||||||||||||||||
Buccinidae | 1 | 1-2 | 25 | |||||||||||||||
Buccinidae | NOR | 1-2 | 25 | |||||||||||||||
Nassariidae | ESAL (SM17) | 1-2 | 16.7 | 18 | 0.84 | 25 | 1-4 | 50 | ||||||||||
Columbellidae | 1 | 1 | 1 | ALL (SM17) | 1-2 | 25 | 1-3 | 50 | ||||||||||
Columbellidae | ESAL (SM17) | 4 | 0.19 | 12.5 | 1 | 25 | ||||||||||||
Columbellidae | NOR, ESAL, CAN (SM17) | 1 | 8.3 | 14 | 0.66 | 37.5 | 1-2 | 25 | ||||||||||
Marginellidae | 3 | 0.14 | 12.5 | 1-3 | 50 | |||||||||||||
Granulinidae | 1 | 1 | 1 | 0.91 | 8.3 | 1-5 | 58.3 | 3-4 | 50 | |||||||||
Granulinidae | 1 | ESAL, LEBA, CAN | 1 | 25 | ||||||||||||||
Cystiscidae | 1 | ESAL, LEBA (SM17) | 6 | 5.45 | 25 | 1-4 | 75 | 11 | 0.52 | 12.5 | 2-3 | 62.5 | ||||||
Volutidae | 1 | 1 | 25 | |||||||||||||||
Cancellariidae | 1 | 1 | 12.5 | |||||||||||||||
Drilliidae | 1 | 1 | ESAL (SM17) | 1-2 | 50 | 7 | 0.33 | 25 | 2-5 | 62.5 | ||||||||
Borsoniidae | 1 | 1 | ESAL, LEBA (SM17) | 1-2 | 16.7 | 1-3 | 62.5 | |||||||||||
Borsoniidae | 1 | 1 | ALL (SM17) | 1 | 0.05 | 12.5 | 1-2 | 62.5 | ||||||||||
Mangeliidae | 1 | 1 | 12.5 | |||||||||||||||
Raphitomidae | 1 | 1 | ESAL, LEBA, CAN | 2-3 | 25 | |||||||||||||
Raphitomidae | 1 | 1 | ESAL, CAN (SM17) | 1 | 8.3 | 1 | 12.5 | |||||||||||
Raphitomidae | 1 | 16.7 | ||||||||||||||||
Raphitomidae | 1 | 1 | ALL (SM17) | 1 | 0.91 | 8.3 | 1-2 | 50 | 1-4 | 62.5 | ||||||||
Architectonicidae | 1 | ESAL, LEBA | 1 | 12.5 | ||||||||||||||
Architectonicidae | 1 | ESAL, LEBA, CAN | 1 | 0.05 | 12.5 | 1 | 12.5 | |||||||||||
Mathildidae | 1 | ESAL, LEBA, CAN | 1 | 8.3 | 1 | 0.05 | 12.5 | 1-3 | 50 | |||||||||
Mathildidae | 1 | ESAL | 1 | 8.3 | 4 | 0.19 | 12.5 | 1-2 | 25 | |||||||||
Mathildidae | ESAL, LEBA, CAN | 2-3 | 25 | |||||||||||||||
Cimidae | 1 | 8.3 | ||||||||||||||||
Cimidae | 1 | 1 | 1-2 | 16.7 | ||||||||||||||
Amathinidae | 1-3 | 58.3 | 1 | 12.5 | ||||||||||||||
Pyramidellidae | ESAL, LEBA, CAN | 1-2 | 16.7 | |||||||||||||||
Pyramidellidae | 1 | 1-2 | 25 | 1-3 | 50 | |||||||||||||
Pyramidellidae | ESAL | 1 | 8.3 | 1 | 12.5 | |||||||||||||
Pyramidellidae | CAN | 2 | 12.5 | |||||||||||||||
Pyramidellidae | LEBA, CAN | 1 | 8.3 | 2 | 12.5 | |||||||||||||
Pyramidellidae | 1 | 16.7 | 2 | 12.5 | ||||||||||||||
Pyramidellidae | 1-2 | 33.3 | ||||||||||||||||
Pyramidellidae | 1 | 1 | 1-2 | 25 | ||||||||||||||
Pyramidellidae | ESAL, LEBA, CAN | 1 | 0.91 | 8.3 | 1-2 | 25 | 1-2 | 50 | ||||||||||
Pyramidellidae | 1 | 25 | ||||||||||||||||
Pyramidellidae | 1-2 | 16.7 | ||||||||||||||||
Pyramidellidae | 1 | 1 | 2 | 16.7 | 1-3 | 37.5 | ||||||||||||
Pyramidellidae | 1 | 1 | 1 | 1-4 | 66.7 | 2-3 | 50 | |||||||||||
Pyramidellidae | 2 | 12.5 | ||||||||||||||||
Pyramidellidae | CAN | 1 | 8.3 | |||||||||||||||
Pyramidellidae | 1 | 1 | 8.3 | 1-2 | 25 | |||||||||||||
Pyramidellidae | 1 | 1 | 1 | 12.5 | ||||||||||||||
Pyramidellidae | 1 | 1 | 2 | 16.7 | 1-3 | 37.5 | ||||||||||||
Pyramidellidae | ESAL, LEBA | 1 | 8.3 | |||||||||||||||
Tjaernoeiidae | ESAL | 1 | 8.3 | |||||||||||||||
Acteonidae | 1 | 1 | 12.5 | |||||||||||||||
Acteonidae | 1 | 1 | 1 | 1-3 | 66.7 | 1-4 | 75 | |||||||||||
Ringiculidae | 1 | 8.3 | 2 | 12.5 | ||||||||||||||
Ringiculidae | 1 | NOR | 1 | 0.05 | 12.5 | 2-3 | 25 | |||||||||||
Philinidae | 1 | ALL | 1 | 8.3 | 1 | 12.5 | ||||||||||||
Philinidae | LEBA | 1 | 12.5 | |||||||||||||||
Cylichnidae | 1 | 1 | 0.05 | 12.5 | 1 | 25 | ||||||||||||
Retusidae | 1 | 1 | 1 | 12.5 | ||||||||||||||
Scaphandridae | 1 | 1 | 8.3 | |||||||||||||||
Cavoliniidae | 1 | 1 | 1-4 | 83.3 | 1-3 | 50 | ||||||||||||
Cavoliniidae | ESAL, LEBA, CAN | 1-2 | 16.7 | 1 | 37.5 | |||||||||||||
Cavoliniidae | ESAL, LEBA, CAN | 1 | 8.3 | |||||||||||||||
Cavoliniidae | 1 | 2-4 | 25 | 2-3 | 25 | |||||||||||||
Cliidae | 1 | ESAL, LEBA, CAN | 1-2 | 16.7 | ||||||||||||||
Cliidae | 1 | 1 | ALL | 1-3 | 16.7 | 1-3 | 12.5 | |||||||||||
Creseidae | ESAL, LEBA, CAN | 2 | 8.3 | |||||||||||||||
Limacinidae | 1 | 1-4 | 41.7 | |||||||||||||||
Limacinidae | 1 | ALL | 1 | 16.7 | ||||||||||||||
Limacinidae | 1 | ESAL, LEBA, CAN | 1-2 | 16.7 | ||||||||||||||
Limacinidae | 1 | 1 | 12.5 | |||||||||||||||
Peraclidae | 1 | 1 | 16.7 | |||||||||||||||
Tylodinidae | 1 | 1 | ESAL | 1-2 | 16.7 | 1-2 | 37.5 | |||||||||||
Pleurobranchaeidae | 1 | 1.15 | 14.3 | |||||||||||||||
Discodorididae | ALL | 2 | 2.30 | 14.3 | ||||||||||||||
Nuculidae | ESAL | 1 | 8.3 | |||||||||||||||
Nuculidae | 1 | 1 | 2 | 1.82 | 8.3 | 1-3 | 50 | 12 | 0.56 | 25 | 1-2 | 37.5 | ||||||
Nuculidae | 1 | 1-2 | 16.7 | |||||||||||||||
Nuculidae | 1 | 25 | 2 | 12.5 | ||||||||||||||
Nuculidae | 1 | 0.91 | 8.3 | 1-3 | 50 | 20 | 0.94 | 25 | 1-4 | 62.5 | ||||||||
Nuculanidae | 1 | 1 | 1 | 1 | 0.91 | 8.3 | 1-3 | 83.3 | 11 | 0.52 | 37.5 | 2-5 | 87.5 | |||||
Nuculanidae | 1 | 12.5 | ||||||||||||||||
Nuculanidae | 1 | 0.91 | 8.3 | 1-3 | 58.3 | 1-3 | 37.5 | |||||||||||
Yoldiidae | 1 | 1 | 3 | 2.73 | 16.7 | 1-3 | 50 | 1-3 | 50 | |||||||||
Arcidae | 1 | 1 | 9 | 8.18 | 41.7 | 1-4 | 66.7 | 116 | 5.43 | 75 | 1-5 | 75 | 19 | 21.84 | 42.9 | |||
Arcidae | 1 | 1 | 1-4 | 83.3 | 23 | 1.08 | 37.5 | 1-4 | 87.5 | |||||||||
Arcidae | 1 | 1 | 1 | 25 | 22.73 | 75 | 1-5 | 83.3 | 1222 | 57.24 | 87.5 | 3-5 | 100 | 5 | 5.75 | 28.6 | ||
Limopsidae | 1 | 1 | 1-4 | 33.3 | 53 | 2.48 | 37.5 | 1-5 | 50 | 4 | 4.60 | 57.1 | ||||||
Limopsidae | 1 | 1 | 3 | 2.73 | 16.7 | 1-4 | 91.7 | 13 | 0.61 | 37.5 | 1-5 | 100 | 1 | 1.15 | 14.3 | |||
Limopsidae | 1 | 1 | 2-3 | 8.3 | 4 | 12.5 | ||||||||||||
Mytilidae | ESAL (SM17) | 5 | 4.55 | 33.3 | 1-2 | 50 | 9 | 0.42 | 25 | 1-3 | 37.5 | |||||||
Pinnidae | 2 | 12.5 | ||||||||||||||||
Pteriidae | 6 | 0.28 | 12.5 | 1 | 12.5 | |||||||||||||
Propeamussiidae | 1 | 1-3 | 25 | 3 | 12.5 | |||||||||||||
Propeamussidae | 1 | 1 | 0.91 | 8.3 | 1-4 | 66.7 | 10 | 0.47 | 25 | 1-5 | 87.5 | |||||||
Propeamussiidae | 1 | 1 | 0.91 | 8.3 | 1-4 | 75 | 1 | 0.05 | 12.5 | 2-3 | 37.5 | |||||||
Pectinidae | 1 | 12.5 | ||||||||||||||||
Pectinidae | 1 | 1 | 5 | 12.5 | ||||||||||||||
Pectinidae | 1 | 1-3 | 83.3 | 15 | 0.70 | 50 | 1-4 | 87.5 | 5 | 5.75 | 42.9 | |||||||
Pectinidae | 1 | NOR, ESAL, LEBA (SM17) | 1 | 12.5 | ||||||||||||||
Pectinidae | 1 | 1 | 1-3 | 25 | 10 | 0.47 | 37.5 | 1-4 | 50 | 17 | 19.54 | 28.6 | ||||||
Spondylidae | 1 | 1 | NOR, ESAL (SM17) | 1 | 8.3 | 6 | 0.28 | 12.5 | 1 | 12.5 | 1 | 1.15 | 14.3 | |||||
Anomiidae | 1 | 1-5 | 83.3 | 13 | 0.61 | 37.5 | 1-5 | 100 | 7 | 8.05 | 28.6 | |||||||
Limidae | 1 | 0.91 | 8.3 | 1-3 | 75 | 4 | 0.19 | 12.5 | 1-3 | 62.5 | ||||||||
Limidae | 1 | 1 | 2 | 1.82 | 8.3 | 1-4 | 91.7 | 14 | 0.66 | 50 | 2-4 | 75 | ||||||
Gryphaeidae | 1-2 | 16.7 | 1 | 12.5 | 2 | 2.30 | 14.3 | |||||||||||
Carditidae | 3 | 0.14 | 12.5 | 2 | 12.5 | |||||||||||||
Astartidae | 1 | 3 | 2.73 | 16.7 | 1-4 | 83.3 | 77 | 3.61 | 62.5 | 1-4 | 75 | |||||||
Lucinidae | 1 | 1 | 16.7 | |||||||||||||||
Thyasiridae | 1 | 1 | 1-2 | 16.7 | 1 | 25 | ||||||||||||
Thyasiridae | 1 | 1 | ESAL, LEBA (SM17) | 1 | 8.3 | 1 | 12.5 | |||||||||||
Thyasiridae | 1 | 1 | 2 | 1.82 | 8.3 | 1-4 | 75 | 2-3 | 62.5 | |||||||||
Galeommatidae | 1 | 1 | 1 | 8.3 | ||||||||||||||
Lasaeidae | 1 | 8.3 | ||||||||||||||||
Lasaeidae | 1 | 1-2 | 16.7 | |||||||||||||||
Lasaeidae | 1 | 1 | 1-2 | 50 | 1-2 | 25 | ||||||||||||
Lasaeidae | 1 | 2 | 16.7 | |||||||||||||||
Cardiidae | 1-2 | 16.7 | 2 | 37.5 | ||||||||||||||
Cardiidae | 1 | 1 | 1-5 | 91.7 | 13 | 0.61 | 37.5 | 1-5 | 100 | |||||||||
Mactridae | 1 | 16.7 | ||||||||||||||||
Tellinidae | 1 | 1 | 8.3 | 1 | 12.5 | |||||||||||||
Semelidae | 1 | 1 | 1 | 1-3 | 66.7 | 4 | 0.19 | 12.5 | 1-4 | 62.5 | ||||||||
Semelidae | 2 | 8.3 | 2 | 12.5 | ||||||||||||||
Kelliellidae | 1 | 1 | 0.91 | 8.3 | 1-4 | 58.3 | 1-2 | 50 | ||||||||||
Trapezidae | 10 | 0.47 | 25 | |||||||||||||||
Veneridae | 1 | 1 | 0.05 | 12.5 | 1-3 | 12.5 | ||||||||||||
Veneridae | 2 | 1.82 | 8.3 | 2 | 16.7 | 1 | 0.05 | 12.5 | 1-3 | 12.5 | ||||||||
Veneridae | 1 | 0.91 | 8.3 | 1 | 16.7 | |||||||||||||
Poromyidae | 1 | 1 | 8.3 | 13 | 0.61 | 25 | 1 | 12.5 | ||||||||||
Poromyidae | 1 | 1 | 0.91 | 8.3 | 1 | 16.7 | ||||||||||||
Hiatellidae | 1 | 1 | 0.91 | 8.3 | 2-4 | 41.7 | 18 | 0.84 | 37.5 | 1-5 | 87.5 | 4 | 4.60 | 28.6 | ||||
Verticordiidae | 1 | 1 | 8.3 | |||||||||||||||
Verticordiidae | 1 | 1 | 3 | 0.14 | 12.5 | |||||||||||||
Cuspidariidae | 1 | 1 | 25 | |||||||||||||||
Cuspidariidae | 1 | 1-2 | 33.3 | 2 | 12.5 | |||||||||||||
Cuspidariidae | 1 | 1 | 8.3 | |||||||||||||||
Cuspidariidae | 1 | 0.91 | 8.3 | 1 | 8.3 | 6 | 0.28 | 12.5 | ||||||||||
Dentaliidae | 2 | 1.82 | 8.3 | 1-2 | 8.3 | 3 | 50 | |||||||||||
Entalinidae | 1 | 1-3 | 25 | 1-3 | 25 | |||||||||||||
Gadilidae | 1 | 1 | 1 | 1-3 | 75 | 6 | 0.28 | 12.5 | 2-4 | 62.5 | ||||||||
Sepiolidae | 1 | 1 | 1.15 | 14.3 | ||||||||||||||
Sepiolidae | 4 | 4.60 | 42.9 | |||||||||||||||
Eledonidae | 1 | 1.15 | 14.3 | |||||||||||||||
TOTAL | 86 species new for GoC (of which 3 new for Spain), 2 n. sp. | 75 | 87 | 67 | 108 | 2130 | 86 |
This diverse fauna includes 160 gastropods (47 of them as live-taken spp. with 334 ind.), 62 bivalves (36 as live-taken spp. with 1839 ind.), three scaphopods (2 as live-taken spp. with 8 ind.), three cephalopods (6 ind.), two polyplacophorans (135 ind.), one monoplacophoran (1 shell) and one solenogastre (2 ind.). Regarding the live-collected molluscs, the most diverse gastropod families were Rissoidae (5 spp.), Fissurellidae and Muricidae (3 spp. each), and Arcidae (3 spp.) among bivalves.
The most dominant live-collected species were
Taxocoenosis spp. | N | %D | Thanatocoenosis spp. | Max. rank |
---|---|---|---|---|
1252 | 53.71 | 5 | ||
144 | 6.18 | 5 | ||
131 | 5.62 | 5 | ||
80 | 3.43 | 5 | ||
57 | 2.45 | 5 | ||
29 | 1.24 | 5 | ||
27 | 1.16 | 5 | ||
26 | 1.12 | 5 | ||
23 | 0.99 | 5 | ||
23 | 0.99 | 5 | ||
22 | 0.94 | 5 | ||
21 | 0.90 | 4 | ||
21 | 0.90 | 4 | ||
20 | 0.86 | 4 | ||
20 | 0.86 | 4 |
The most representative species found in the thanatocoenosis included
Multivariate analysis of the live-taken molluscan fauna based on qualitative data of all samples showed two main groups of samples, one collected on the MV edifice and one collected in the erosive depression and on the adjacent bottoms (
The first assemblage is associated with the MV edifice, where MDACs with live cold-water corals (e.g.
Sampling method | Area | S (±SE) | N (±SE) | J’ (±SE) | H’ (log2) (±SE) |
---|---|---|---|---|---|
Beam-trawl | MV | 7.3 (±0.9) | 9 (±1) | 0.976 (±0.002) | 2.786 (±0.163) |
Dep | 5 (±1) | 17 (±6) | 0.806 (±0.140) | 1.889 (±0.557) | |
Adj | 4.5 (±1.5) | 14 (±11) | 0.799 (±0.201) | 1.565 (±0.021) | |
Benthic dredge | MV | 22 (±6.7) | 418 (±228.3) | 0.717 (±0.061) | 3.029 (±0.220) |
Dep | 19.7 (±2.7) | 382.7 (±59.5) | 0.466 (±0.120) | 1.952 (±0.432) | |
Adj | 6 (±1) | 54 (±24) | 0.620 (±0.078) | 1.609 (±0.350) | |
Box-corer/Shipek grab | MV | 5 (±1.7) | 128.7 (±56) | 0.952 (±0.031) | 1.972 (±0.502) |
Dep | 6.3 (±3.9) | 91.3 (±71.2) | 0.941 (±0.048) | 2.680 (±0.555) | |
Adj | 4.8 (±1) | 136.3 (±26.4) | 0.958 (±0.019) | 2.289 (±0.187) |
Mud volcano edifice | ||||
---|---|---|---|---|
Taxocoenosis | N | %D | Thanatocoenosis | Max. rank |
531 | 45.50 | 5 | ||
87 | 7.46 | 5 | ||
57 | 4.88 | 5 | ||
51 | 4.37 | 5 | ||
36 | 3.08 | 5 | ||
25 | 2.14 | 5 | ||
24 | 2.06 | 5 | ||
22 | 1.89 | 5 | ||
19 | 1.63 | 5 | ||
19 | 1.63 | 5 | ||
18 | 1.54 | 5 | ||
16 | 1.37 | 4 | ||
16 | 1.37 | 4 | ||
14 | 1.20 | 4 | ||
14 | 1.20 | 4 | ||
Erosive depression | ||||
Taxocoenosis | N | %D | Thanatocoenosis | Max. rank |
678 | 67.33 | 5 | ||
72 | 7.15 | 5 | ||
35 | 3.48 | 5 | ||
34 | 3.38 | 5 | ||
21 | 2.09 | 4 | ||
18 | 1.79 | 4 | ||
13 | 1.29 | 4 | ||
Unidentified |
12 | 1.19 | 4 | |
10 | 0.99 | 4 | ||
10 | 0.99 | Unidentified |
4 | |
9 | 0.89 | 4 | ||
8 | 0.79 | 4 | ||
8 | 0.79 | 4 | ||
8 | 0.79 | 4 | ||
6 | 0.59 | 4 | ||
Adjacent bottoms | ||||
Taxocoenosis | N | %D | Thanatocoenosis | Max. rank |
43 | 29.66 | 5 | ||
23 | 15.86 | 5 | ||
20 | 13.79 | 5 | ||
9 | 6.21 | 4 | ||
6 | 4.14 | 4 | ||
5 | 3.45 | 4 | ||
3 | 2.07 | 3 | ||
3 | 2.07 | 3 | ||
2 | 1.38 | 3 | ||
2 | 1.38 | 3 | ||
2 | 1.38 | 3 | ||
2 | 1.38 | 3 | ||
2 | 1.38 | 3 | ||
2 | 1.38 | 3 | ||
2 | 1.38 | 3 |
The second group of samples corresponds to a mollusc assemblage linked to the western depression area, and to the assemblage of the adjacent bottoms. Within the depression, there are mainly coarse sediments mixed with hard substrates (e.g. MDACs slabs), and therefore this area included both hard-bottom and soft-bottom species. This assemblage was composed of 45 species (15 of them exclusive, such as
The parameters retained for the BIOENV analysis were the percentages of gravel (%G), coarse sand (%CS), fine sand (%FS) and organic matter (%OM); the water temperature (T, °C); the dissolved oxygen concentration (O2, mg l–1); the near-bottom current speed (cm s–1); the availability of MDACs (quantified as a rank) and the bottom-trawling activity (qualified as a rank).
The BIOENV analysis (
Sampling method | Number of parameters | Parameters combination | ρw |
---|---|---|---|
BT | 4 | T, O2, %OM, MDAC | 0.65 |
3 | T, %OM, MDAC | 0.64 | |
4 | T, %OM, MDAC, TA | 0.64 | |
DA | 3 | %G, %CS, TA | 0.46 |
4 | %G, %CS, %OM, TA | 0.41 | |
3 | %G, %CS, T | 0.41 | |
BC/SK | 3 | %G, %OM, TA | 0.63 |
4 | %G, %CS, %OM, TA | 0.62 | |
5 | %G, %FS, O2, %OM, TA | 0.61 |
Species which represent new or otherwise noteworthy records for the area, and the two which have been considered new to science, are illustrated in Figures 3-6. New records of species represented by live-taken individuals or shells are marked in
Class GASTROPODA
Family RISSOIDAE
Genus
(type species:
(
LSID:
Other deep-sea species described for the Mediterranean Sea (revised by
Family EULIMIDAE
Genus
(type species:
Family BUCCINIDAE
Genus
(type species:
Family MARGINELLIDAE
Genus
(type species:
The living animal of this species was observed at the Balgim sampling station 75 (352 m). It is colourless except for a more opaque white zone bordering the front edge of the propodium. It has a thick, cylindrical siphon and slender, parallel-sided cephalic tentacles and black eyes bulging on the outer side of the tentacles. The foot of the crawling animal is about the same length as the shell, is truncated anteriorly and broadly rounded posteriorly.
This is the first record of this species in both Spanish waters (the material from the Gazul MV) and Moroccan waters (the unpublished localities from “Vanneau” 1923 and Balgim 1984).
Class BIVALVIA
Family LUCINIDAE
Genus
(type species:
Family LASAEIDAE
Genus
(type species:
Family CUSPIDARIIDAE
Genus
(type species:
LSID:
This is the first detailed work on the malacofauna associated with a MV and its adjacent areas within the European context. In the present study, a total of 232 molluscan species has been found, increasing the faunal list of molluscs known for the Spanish part of the GoC with 86 species that had not been cited previously (some of them preliminary reported in
Molluscs are a good indicator for the biodiversity assessment in a particular area (
Less than half of the species collected on the Gazul MV belong to species listed in the World Register of Deep-Sea Species (
The high number of species found in the analysed samples could be linked to several factors: 1) the combination of several types of sampling gears, which obtain species from different ecosystemic compartments such as the box-corer or the Shipek grab for capturing endofaunal micro molluscs, the benthic dredge targeting infaunal and epibenthic micro and macrofaunal species, and the beam-trawl collecting mainly epibenthic macrofauna and some demersal components such as cephalopods (
Many molluscs found on the Gazul MV are associated with bathyal hard substrates and/or macro-organisms that can reach high abundance on such substrates (e.g. corals, gorgonians and sponges). These hard substrates are composed of MDACs, which are unearthed from the sediment and exhumed by the action of bottom currents (
The finding of shell remains of the bivalve
The number of species in the thanatocoenosis (221) is 2.43 times the number of live-collected species, which is in good agreement with the 2 to 3 times stated as “typical” by
Finally, several environmental parameters analysed in this study were identified as playing a significant role in species and assemblage distribution. For infaunal species (mostly collected with the benthic dredge, box-corer and Shipek grab), it was found that the sediment texture, the percentage of organic matter in sediment and the bottom-trawling activity seem to be the main environmental and anthropogenic parameters linked to the distribution of the molluscan assemblages in the area. On the other hand, for epibenthic and demersal megafauna (mostly collected with the beam-trawl), the environmental parameters influencing species distribution were seawater temperature, the percentage of organic matter in sediment and the presence of MDACs. These results indicate that the type and nature of soft bottoms are important factors regarding the distribution of species, with many aspects of sediments to which animals (in this case molluscs) may respond, including sediment texture (some species are characteristically associated with a given sedimentary habitat), organic content of bottom sediments (a dominant food source for deposit feeders and, indirectly for suspension feeders) and sediment stability (some organisms or biological structures produce sediment-stabilizing effects that allow other animals to colonize the substrate), among others (
We thank the many people who have helped us at different stages of this work: the captains and all the crews of the R/V