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The common octopus Octopus vulgaris Cuvier, 1797, once considered a cosmopolitan species, is a species complex composed by six species: O. tetricus, O. cf tetricus and O. sinensis in the Pacific; type I and II, in the West Atlantic; and type III in the Indian Ocean around South Africa. The tropical western central Atlantic is an important octopus fishing ground targeting O. maya, O. insularis, and a cryptic species considered to be O. vulgaris type I. In order to clarify the identification of this octopod, phylogenetic analyses were carried out with mitochondrial (COI and 16S) and nuclear (rhodopsin) genes, together with morphological analyses of 16 specimens caught in the northeastern continental shelf of Yucatan (Mexico). The main morphological traits differing from O. vulgaris were the presence, position and size of enlarged suckers and hectocotylus sucker number in males. Genetic distances and haplotype networks of the species complex were estimated using 285 COI sequences of nine Octopus species from 14 different locations around the world. The octopod sequences from Yucatan clustered within a monophyletic group that included sequences of O. vulgaris type II for the three genes analyzed. Phylogenetic distances with other members of the complex ranged between 2.71 and 3.89% using COI data. These genetic results support the presence of Octopus americanus Monfort, 1802 (formerly known as O. vulgaris type II) along the Yucatan continental shelf, a new octopod extending from the north of Argentina to the northwest coast of the USA.

Our knowledge of the diet of wild octopus paralarvae, Octopus vulgaris, is restricted to the first 2 weeks of its planktonic phase when they are selective hunters found near the coastline. These small paralarvae, bearing only three suckers per arm, are transported by oceanic currents from the coast towards offshore waters, where they complete the planktonic phase over 2 months. Here, we have investigated the trophic ecology of O. vulgaris paralarvae in two contrasting upwelling sub-regions of the Iberian Canary current (ICC) eastern boundary upwelling system and have evaluated dietary change as paralarvae develop (inferred by counting the number of suckers per arm, ranging from three to 15) along the coastal-oceanic gradient during their planktonic phase. Using high-throughput amplicon sequencing, we have characterised the diet of 100 paralarvae collected along the Northwest Iberian Peninsula (n = 65, three to five suckers per arm) and off the west coast of Morocco (n = 35, three to 15 suckers per arm), identifying up to 87 different prey species. The diet of paralarvae varied along the ICC, with crabs (53.4%), siphonophores (12.2%), copepods (12.3%), cnidarians (8.4%) and pteropods (3.7%) accounting for 90% of the variability detected off NW Iberian Peninsula, whereas off W Morocco, crabs (46.2%), copepods (23.1%), cnidarians (12.9%), krill (9.3%) and fishes (4.2%) explained 95.6% of the variability observed using frequency of observance (FOO%) data. Ontogenetic changes in the diet based on groups of paralarvae with similar numbers per arm were evidenced by the decreasing contribution of coastal meroplankton and an increase in oceanic holoplankton, including siphonophores, copepods, pteropods and krill. Trophic niche breadth values ranged from 0.06 to 0.67, with averaged values ranging from 0.23 to 0.33 (generalist = 1 and specialist = 0), suggesting that O. vulgaris paralarvae are selective predators through their ontogenetic transition between coastal and oceanic environments.

Understanding genetic diversity and population connectivity in marine organisms is essential for fisheries management. In the present study, we examined the population genetics of the European squid, Loligo vulgaris , along the western Iberian Peninsula at two genetic resolutions using the mitochondrial cytochrome oxidase subunit I gene (COI) and genomic markers obtained via double digest restriction-site associated DNA sequencing (ddRADseq). The results obtained revealed 79 haplotypes out of 160 COI sequences, while the SNP data set included 86,431 loci after filtering for 38 individuals with 86,319 neutral data. Mitochondrial COI analyses revealed high haplotype (0.961) and nucleotide (0.010) diversities, and the haplotype network reveals complex sub-structure in Turkish waters within a panmictic population. Both Tajima’s D and Fu’s Fs tests suggest that the population of L. vulgaris analysed is evolving neutrally. Pairwise F st for neutral SNPs were low (0 < F st <0.002) and not significant showing high homogeneity among populations, while pairwise comparations for candidate adaptive SNPs (112 loci) showed F st values ranging from 0.026 to 0.234. While neutral SNPs showed admixture, the candidate adaptive SNPs showed a moderate significant structure with a latitudinal discrimination. Overall, both genetic approaches showed homogeneity and strong genetic flux identifying a unique population along the Western Iberian Peninsula.

Within the context of global climate change and overfishing of fish stocks, there is some evidence that cephalopod populations are benefiting from this changing setting. These invertebrates show enhanced phenotypic flexibility and are found from polar regions to the tropics. Yet, the global patterns of species richness in coastal cephalopods are not known. Here, among the 370 identified-species, 164 are octopuses, 96 are cuttlefishes, 54 are bobtails and bottletails, 48 are inshore squids and 8 are pygmy squids. The most diverse ocean is the Pacific (with 213 cephalopod species), followed by the Indian (146 species) and Atlantic (95 species). The least diverse are the Southern (15 species) and the Arctic (12 species) Oceans. Endemism is higher in the Southern Ocean (87%) and lower in the Arctic (25%), which reflects the younger age and the “Atlantification” of the latter. The former is associated with an old lineage of octopuses that diverged around 33 Ma. Within the 232 ecoregions considered, the highest values of octopus and cuttlefish richness are observed in the Central Kuroshio Current ecoregion (with a total of 64 species), followed by the East China Sea (59 species). This pattern suggests dispersal in the Central Indo-Pacific (CIP) associated with the highly productive Oyashio/Kuroshio current system. In contrast, inshore squid hotspots are found within the CIP, namely in the Sunda Shelf province, which may be linked to the occurrence of an ancient intermittent biogeographic barrier: a land bridge formed during the Pleistocene which severely restricted water flow between the Pacific and Indian Oceans, thereby facilitating squid fauna differentiation. Another marked pattern is a longitudinal richness cline from the Central (CIP) towards the Eastern Indo-Pacific (EIP) realm, with central Pacific archipelagos as evolutionary dead ends. In the Atlantic Ocean, closure of the Atrato Seaway (at the Isthmus of Panama) and Straits of Gibraltar (Mediterranean Sea) are historical processes that may explain the contemporary Caribbean octopus richness and Mediterranean sepiolid endemism, respectively. Last, we discuss how the life cycles and strategies of cephalopods may allow them to adapt quickly to future climate change and extend the borealization of their distribution.

Knowledge of recruitment to a fishery is particularly important in short-lived species, like most cephalopods, in which there is a complete turnover of individual every 1 or 2 years. In this study, age, body length, statolith length and growth rates of loliginid paralarvae ( Alloteuthis media , A. subulata and Loligo vulgaris ) were determined to evaluate the form of the growth curve and differences between species and hatching seasons. A total of 222 paralarvae collected in zooplankton samples along the Galician coast (NW Spain) were used to determine relationships between dorsal mantle length (DML), statolith length (SL) and the number of increments (NI)) deposited in the statolith. The paralarvae of L. vulgaris were between 1 and 35 days old, while both Alloteuthis species ranged in age from 1 to 54 days . Generalised additive models (GAMs) revealed non-linear growth in DML, with L. vulgaris exhibiting higher DML-at-age than Alloteuthis species. The best parametric model fit for these data was obtained using exponential regressions. The SL–NI relationship also differed between species, with L. vulgaris having larger statolith length at age . The paralarvae of L. vulgaris and A. media had two well-differentiated hatching peaks, one in late spring-early summer (beginning of the upwelling season) and another peak in late autumn (end of the upwelling season). Alloteuthis subulata had an earlier hatching peak in spring than in the other two loliginid species—and the second peak in autumn was barely visible, possibly because this species occurs further north in areas not sampled in autumn.

Octopuses are amongst the most fascinating animals in our oceans; however, while their intricate behaviours are often studied in laboratory settings, basic aspects of their movement ecology remain unstudied in the wild. Focusing on the socio-economically important common octopus ( Octopus vulgaris ), this study employs, for the first time, acoustic tracking techniques to address knowledge gaps regarding the species spatial ecology within a marine protected area. A total of 24 wild O. vulgaris (13 males, 11 females) were tagged in 2022 in the National Park Maritime-Terrestrial of the Atlantic Islands of Galicia, Spain. Acoustic transmitters were externally attached to the third arm, after testing other body parts (mantle cavity). Males were on average detected on 10 times more occasions than females (49 days in males and five in females). The average activity space in the study area was large in comparison to that determined in similar studies, with 0.16 km 2 . Activity space between males and females as well as day and night were comparable. Tagged octopuses displayed a crepuscular activity pattern. The location of dens could be established for 15 out of 24 individuals, from which octopuses were observed to undertake regular daytime excursions. Several individuals were also found to occupy more than one den and/or switch their main dens throughout the study duration. First implications and benefits of this approach are discussed.

The trophic ecology of Octopus vulgaris paralarvae collected in 2008 off the Ría de Vigo, NW Spain (42° 12.80′ N–9° 00.00′ W), was approached by both morphological and molecular methods. External digestion of prey and posterior suction of the liquefied contents by wild O. vulgaris paralarvae made the morphological identification of gut contents impossible. Thus, a PCR-based method using group-specific primers was selected to identify prey consumed by O. vulgaris paralarvae in the pelagic realm. The mitochondrial ribosomal 16S gene region was chosen for designing group-specific primers, which targeted a broad range of crustaceans and fishes but avoided the amplification of predator DNA. These primers successfully amplified DNA of prey by using a semi-nested PCR-based approach and posterior cloning. Homology search and phylogenetic analysis were then conducted with the 20 different operational taxonomic units obtained to identify the putative organisms ingested. The phylogenetic analysis clustered ingested prey into 12 families of crustaceans (11 belonging to the order Decapoda and 1 to the order Euphausiacea) and two families of fishes (Gobiidae and Carangidae). According to the Czekanowski’s Index (CI), the trophic niche breadth of O. vulgaris paralarvae is low (CI = 0.13), which means that these paralarvae are specialist predators at least during the first weeks of their life cycle. It is the first time that natural prey has been identified in O. vulgaris paralarvae collected from the wild, and such knowledge may be critical to increasing the survival of O. vulgaris hatchlings in captivity, a goal that has been actively pursued since the 1960s by aquaculture researchers.

Accurate species classification is essential to understand complete life cycles of cephalopods. Identifying freshly caught or fixed loliginid paralarvae to species level with the traditional taxonomic guides is challenging. Therefore, the aim of this work was to identify genetically loliginid paralarvae captured in NW Spain (a region where at least three loliginid species are known to coexist) during 2012, 2013, and 2014, and to seek a means to distinguish the species from each other based on their morphometry. First, the barcoding region (COI gene) was amplified to identify each paralarva, and to obtain population molecular diversity indices and genetic structure for the different species. Afterwards, discriminant analysis (DA) was used to evaluate the performance of the selected morphometric measurements to distinguish among the species previously identified. Molecular analyses revealed three loliginid species (Alloteuthis media, A. subulata, and Loligo vulgaris), with different patterns of molecular diversity. DAs based on body morphometrics correctly categorised 75% of paralarvae to genus (Loligo and Alloteuthis) and 72% of Alloteuthis individuals to species level (A. media and A. subulata). When statolith measurements were included in the morphometric analysis, successful classification increased to 94 and 82%, respectively. The most useful variables for the discrimination of genus were hatching ring length and head width, while tentacle length helped to differentiate A. media from A. subulata. These discriminant functions should be tested with more paralarvae from different origins and seasons to account for body shape plasticity, but suggest a promising result to facilitate loliginid paralarvae identification for future research.

Several specimens of Alepisaurus ferox Lowe, 1833 were caught in the coastal Galician waters (Northwest Spain). From two preserved specimens, morphometric and meristic parameters, along with DNA barcoding, confirmed the identification of the specimens. Examination of the stomach contents revealed a diverse diet with up to 13 different preys with only three species in common (swimming crab, salps and the hyperiid amphipod pram shrimp). It is the first time that gadid fishes Micromesistius poutassou (Risso, 1827 ) and Trisopterus luscus (Linnaeus, 1758 ), crustaceans Polybius henslowi Leach, 1820 [in Leach, 1815–1875 ] and Pasiphaea sivado (Risso, 1816 ), and parasitic nematodes of the genus Anisakis Dujardin, 1845 are reported in the stomach of this species. Histological examination of the gonads showed a simultaneous hermaphrodite strategy, with both ovary and testis in immature phase in the same gonad, but well differentiated. These results contribute to a better knowledge of this pelagic and mainly offshore fish species in coastal areas.