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| Gaidropsarus mauritanicus Knorrn, Beuck, & Freiwald, in Knorrn, Beuck, Barros-García, Fernández-Peralta et Freiwald, 2024. DOI: 10.1111/jfb.15859 |
Abstract
Gaidropsarus mauritanicus sp. nov. is described from one specimen collected using a grab sample from the Tanoûdêrt Canyon (ca. 20° N) off Mauritania at a depth of 595 m. The new species was further observed during eight remotely operated vehicle (ROV) dives along the Mauritanian slope southwards down to the Tiguent Coral Mound Complex (~17° N) in a bathymetric range between 613 and 416 m. It can be distinguished from congeners by a combination of characteristics, including large eyes (38.1% head length [HL]), large head (25.8% standard length [SL]), elongated pelvic fins (35.7% SL), low number of vertebrae (44), and coloration (pinkish with a dorsal darker brownish hue and bright blotches along the dorsal-fin base). A species-delimitation analysis performed with available cytochrome c oxidase subunit 1 (COI) sequences affiliated to the genus Gaidropsarus additionally supported the validity of the new species. Video analyses showed a deep-water coral-associated and protection-seeking behavior, which may explain why the species has remained undescribed until now. Additional ROV footage from separate deep-water coral sites in the North Atlantic and Mediterranean Sea further highlights the ecological behavior and hidden diversity of bathyal three-bearded rocklings. Here, we additionally discuss the biogeographical distribution of all genetically verified Gaidropsarus spp. in combination with genetic data and morphological characters. G. mauritanicus sp. nov. is closely related to a species from Tasmania (43° S), a geographical point furthest among the studied samples, which may hint to an important influence of (paleo-) oceanography on the distributions of Gaidropsarus species.
Keywords: deep-water coral habitat, micro-CT, NE Atlantic, NW Africa, phylogenetics, species delimitation, Tanoûdêrt canyon, X-ray, Mauritania
Class: Osteichthyes Huxley, 1880.
Order: Gadiformes Goodrich, 1909.
Family: Gaidropsaridae Jordan & Evermann, 1898.
Genus: Gaidropsarus Rafinesque, 1810.
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| Photograph showing in vivo coloration of the holotype of Gaidropsarus mauritanicus sp. nov. in seawater after sampling. (a) Overview, dorso-lateral side. (b–d) Details, dorsal view: (b) cephalic region, (c) first and second dorsal fins, and (d) left pectoral fin. |
Gaidropsarus mauritanicus sp. nov. Knorrn, Beuck, & Freiwald, 2024.
Species identification:
The specimen can be affiliated with the genus Gaidropsarus Rafinesque 1810 as it displays the morphological characters previously described by Cohen et al. (1990). These characteristics include the presence of three barely separated dorsal fins, with the first possessing only one single thickened and unsegmented ray, the second having several small and unsegmented rays in a fleshy elongated groove, and the third with segmented rays in an elongated fin. Additionally, the species has three prominent barbels: one located on the chin and one at each anterior nostril on the snout, in addition to a prominent anal fin and an interrupted lateral line running along the entire length of the body.
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Diagnosis: G. mauritanicus sp. nov. differs from all other 13 valid Gaidropsarus species by the combination of the following characteristics: large eyes (38.1% HL) versus small eyes, relatively large head (25.8% SL), elongated pelvic fin (35.7% SL) versus medium-sized pelvic fin, small pectoral fin (13.8% SL) versus enlarged pectoral fin, 44 vertebrae, coloration (pinkish with a darker brownish hue around the dorsal side and brighter dots around the dorsal-fin bases), and habitat preference (deep-water coral ecosystems). For detailed comparisons between the species, see Tables 2 and 3.
Etymology: The species name “mauritanicus” is derived from the Latin name of the Islamic Republic of Mauritania, known for its species-rich marine ecosystems, among them the most extensive known “chain”-shaped, habitat-forming deep-water coral ecosystem, to which this species is associated.
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| Representative remotely operated vehicle (ROV) images of Gaidropsarus mauritanicus sp. nov. in its habitat (copyright Tomas Lundälv from the Sven Lovén Centre for Marine Infrastructure of the University of Gothenburg, Sweden). (a) A small individual—similar in size to holotype—between coral rubble (Banda Coral Mounds, 523-m water depth). (b) Inside a coral garden (Swiftia phaeton), sheltered between dead coral framework fragments and rubble (Timiris Coral Mounds, 492-m water depth). (c) Hiding inside a dead coral framework, see red arrow (Tanoûdêrt Canyon, 610-m water depth). (d) Coexistence with cf. Japonoconger africanus inside live Desmophyllum pertusum framework (red arrow) (Tamxat Coral Mounds, 501-m water depth). (e) Below protective “canopy” of live Madrepora oculata (Tiguent Coral Mounds, 418 m). (f) Two individuals next to a dead scleractinian framework, which is colonized by sponges and various octocorals, among Swiftia phaeton (Tamxat Coral Mounds, 535-m water depth; see also Video S3). (g) Next to a framework fragment, which is colonized by a branched bryozoan (Celleporina cf. lucida); note the whitish marks on the skin (Tamxat Coral Mounds, 479-m water depth). (h) Adult individual finds shelter next to hardground (geology term) ledge; note the slightly varying coloration with respect to young individuals (Tiguent Coral Mounds, 434-m water depth). |
CONCLUSION:
The existence of G. mauritanicus sp. nov. as a new species is morphologically confirmed by the presence of only 44 vertebrae, a conspicuously long pelvic fin (35.7% SL), the large eyes (38.1% HL), medium-sized pectoral fin (13.8% SL), and the pinkish coloration with several brighter dots along the base of the dorsal fin, as well as genetically confirmed by several independent species delimitation analyses. Furthermore, ROV and lander surveys reveal insights into the ecology and behavior of deep-water coral-associated Gaidropsarus species, suggesting that these species are territorial and protective. Genetically supported distribution data show clear patterns in the biogeographical and bathymetrical distribution of the different Gaidropsarus species. Recent and ancient oceanography seems to be an important factor in terms of larval distribution and phylogenetic relationships, such as the first evidence of G. mauli as a basal member of the boreal Gaidropsarus species. Further, the genetic and distribution data also indicate possible misidentifications between G. macrophthalmus and G. mediterraneus. This highlights the urgent need for a comprehensive taxonomic identification key and a complete scientific collection. There still remains a great knowledge gap concerning the Gaidropsarus species of the Southern Hemisphere, which should be the focus of future investigations.
Alexander H. Knorrn, Lydia Beuck, David Barros-García, Lourdes Fernández-Peralta and André Freiwald. 2024. Gaidropsarus mauritanicus (Gadiformes, Gaidropsaridae) A New three-bearded Rockling from A Deep-water Coral Ecosystem with a genetically verified biogeographical distribution of the genus and notes to its ecology and behavior. Journal of Fish Biology. DOI: doi.org/10.1111/jfb.15859
