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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.

We morphologically analyzed 79 cephalopod specimens from the North and Baltic Seas belonging to 13 separate species. Another 29 specimens showed morphological features of either Alloteuthis mediaor Alloteuthis subulata or were found to be in between. Reliable identification features to distinguish between A. media and A. subulata are currently not available. The analysis of the DNA barcoding region of the COI gene revealed intraspecific distances (uncorrected p) ranging from 0 to 2.13 % (average 0.1 %) and interspecific distances between 3.31 and 22 % (average 15.52 %). All species formed monophyletic clusters in a neighbor-joining analysis and were supported by bootstrap values of ≥99 %. All COI haplotypes belonging to the 29 Alloteuthis specimens were grouped in one cluster. Neither COI nor 18S rDNA sequences helped to distinguish between the different Alloteuthis morphotypes. For species identification purposes, we recommend the use of COI, as it showed higher bootstrap support of species clusters and less amplification and sequencing failure compared to 18S. Our data strongly support the assumption that the genus Alloteuthis is only represented by a single species, at least in the North Sea. It remained unclear whether this species is A. subulata or A. media. All COI sequences including important metadata were uploaded to the Barcode of Life Data Systems and can be used as reference library for the molecular identification of more than 50 % of the cephalopod fauna known from the North and Baltic Seas.

Identification of the two sympatric species, Alloteuthis media and Alloteuthis subulata , has long relied on a set of identifying morphometric parameters and descriptive guidelines. To resolve taxonomic status of Alloteuthis in the Eastern Adriatic, we used morphological and molecular approach on a dataset collected during MEDITS expeditions sampling the entire Eastern Adriatic over consecutive summers. Phylogenetic analyses inferred from mitochondrial DNA cytochrome oxidase I (COI) gene sequences confirmed presence of both species in the Eastern Adriatic, with A. subulata occurring only in its central and southern parts. Analyses of genetic diversity showed that A. subulata samples in the Eastern Adriatic shared a single haplotype while A. media showed high haplotype diversity. Comparison of Eastern Adriatic A. media samples and populations from other regions showed statistically significant genetic differentiation between the Atlantic haplotypes and each of the Adriatic, Aegean, and Ionian populations. Conversely, A. subulata had low genetic diversity with only two haplotypes present across samples collected globally. There was no single morphometric character with strong enough power to discriminate between species, however, when morphological traits were looked as a composite metric rather than in isolation, the majority of individuals were correctly classified into one of three groups ( A. media males or females and A. subulata ).

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.

Despite being landed in commercial cephalopod fisheries, species of Alloteuthis are not yet well defined, with A. subulata and A. media often confused. DNA barcoding combined with morphometric analyses has begun to clarify the distinction between these two morphologically similar species but has been limited in its geographic coverage to date. Herein, we provide DNA barcodes for 228 specimens collected from Guinea Bissau in the south, up the Atlantic coast, to the Irish shelf and North Sea. Employing species delimitation analyses, and with comparison to the literature, we identified 24 individuals of A. africana, 66 individuals of A. subulata and 138 individuals of A. media. We confirm that A. media has the northernmost distribution and is the only species identified by DNA sequencing from the Irish shelf and North Sea. We analysed morphometric measures and indices from 388 individuals from the North Sea, a subset of which (n = 58) were barcoded. The most useful traits for identification were tail length as a percentage of dorsal mantle length, and largest club sucker width as a percentage of head width. By comparison to other published data, we determined that A. media phenotypes vary substantially across the geographic range of this species. This partly explains the difficulties in morphological identification and suggests regional identification guides may be required in support of fisheries management. Interregional analyses suggest character displacement may occur where species co-exist.

Aim: Studies focussing on long-term changes in squid populations are rare due to limited availability of fisheries-independent data. However, squid play an important role as predator and prey in marine food-webs and have also become an increasingly important target for fisheries. Their short life history is thought to make them particularly sensitive to changes in the environment, potentially leading to strong fluctuations in population size. Here, we investigate whether squid have increased in the North Sea, in terms of distribution and abundance, and whether these patterns are related to variability in environmental and climatic factors. Location: North Sea, north-east Atlantic Ocean. Methods: We extracted squid catches from a unique 35-year time series of bottom trawl survey data in the North Sea (1980-2014), collected during late summer (August-September). Changes in distribution and abundance were compared with climatic variables known to be linked with various ecosystem components in the area. Results: We found that squid distribution across the North Sea increased over the 35-year time series. Loligo expanded southward from a predominantly north-easterly distribution, compared to northward expansions by Alloteuthis and the Ommastrephidae from their core distributions in the southern and central North Sea respectively. In addition, all squid species studied here displayed an overall increase in biomass over the time series and there were large annual fluctuations. Significantly positive relationships were found between this increase and climate variables for each of the dominant individual taxa studied and when all species were combined. Main conclusions: The results suggest a strong causal relationship between climate variability, notably warming sea temperatures, and squid populations. At least for the last 35 years, climate change appears to have been largely favourable for squid and with changes in climate set to continue, squid may end up beneficiaries where many finfish struggle.

Squid of the genus Alloteuthis from the Aegean Sea and eastern Mediterranean were identified as A. media. It is not possible to distinguish A. media from A. subulata by relative fin length. Both ‘species’ are probably intraspecific forms. Egg size varied from 1·5 to 2·3 mm. Oocyte maturation in the ovary occurs in batches. The potential fecundity is some 1000–4000 eggs, most of these being released during continuous spawning accompanied by female growth.

Demersal trawl fisheries generate large quantities of discards which temporarily increase the amount of carrion available to benthic communities and lead to a faster energetic turn-over. This study examines the availability of discarded material to the benthos, assesses consumption times of different items and identifies scavengers attracted to those invertebrates most frequently discarded from Clyde Sea Nephrops trawlers. In field and laboratory trials, heavy-shelled dead whelks (Buccinum undatum, Neptunea antiqua) sank faster than softer-bodied species like cephalopods (Allotheuthis subulata, Rossia macrosoma) or echinoderms (Ophiura ophiura, Asterias rubens), making most discards available to the benthos (at ca. -60 m CD [chart datum]) within minutes after discarding. SCUBA and time-lapse camera observations in the Clyde Sea and Loch Sween indicated bait utilisation times between 24 and 48 h. Fast-moving animals like brachyuran crabs were the first to arrive at discard bait piles whose composition mimicked typical discards from the Clyde Sea Nephrops fishery. Bimonthly deployments of traps baited with invertebrate discards in the north of the Clyde Sea showed that A. rubens, followed by Pagurus bernhardus, Liocarcinus depurator and whelks, were the most abundant megafaunal scavengers. Fine-meshed funnel traps deployed inside those creels yielded up to 2819 amphipods per trap, with Scopelocheirus hopei and Orchomene nanus accounting for most of the catch. Together with whelks, A. rubens and Carcinus maenas, O. nanus showed a clear preference for crustacean bait. By contrast, Pagurus bernhardus was more attracted to A. rubens and, in 1 trial, to O. ophiura bait. Traps deployed in the south of the Clyde Sea yielded generally lower numbers and species diversity in the catch, with Nephrops being the most abundant megafaunal scavenger. It showed a preference for L. depurator and conspecific bait. While the results show that a range of epibenthic species readily utilise invertebrates discarded from Clyde Sea Nephrops trawlers, it is unknown to what extent discards subsidise benthic communities as information on the ecological energetics of the species involved locally is currently lacking.