Invasive species can disrupt food webs by altering the abundance of prey species or integrating into the food web themselves. In the Gulf of Maine, there have been a suite of invasions that have altered the composition of the benthic ecosystem. These novel prey species can potentially benefit native predators depending on their nutritional value and relative abundance. We measured feeding instances of the native blood star, Henricia sanguinolenta, and changes in the seasonal abundances of invasive ascidian prey species. Results indicate that H. sanguinolenta forages optimally, as the blood star will prey on invasive ascidians when in high abundance, but feed on other species during periods of scarcity. Further, our study shows that blood stars prey on a wider variety of species than was previously known, such as small bivalves and barnacles. Additionally, we compared growth and reproduction of sea stars fed different combinations of invasive ascidians (Diplosoma listerianum or Botrylloides violaceus) or a native sponge (Haliclona oculata). Sea stars grew more on the native diet when compared with the invasive ascidian species, and D. listerianum appeared to be a superior quality food source when compared with B. violaceus. By comparing our data with historical data, we determined that there was a dramatic increase in sea star populations between 1980 and 2011, but then populations decreased by almost half from 2011 to 2016–2017. These data suggest that while invasive ascidians may have helped sea star populations at one point, sea stars are declining without their native food source.

Thirteen new genera and three new families of cheilostome Bryozoa are described from the New Zealand biogeographic region, centred on Zealandia, between 26.42° (northern Norfolk Ridge) and 54.02°S latitude (south-east Campbell Plateau) from coastal waters to bathyal depths (46‒1676 m). The new genera, comprising 15 new and one previously described Zealandian species, are: Elementella (Elementellidae n. fam.), Niwapora, Quasicallopora, Quitocallopora, Judyella (Calloporidae), Ellisantropora (Antroporidae), Rhizellisina (Ellisinidae), Radixenia (Calloporoidea incertae sedis), Granomurus (Granomuridae n. fam.), Carolanna (Bugulidae), Borioplebs (Borioplebidae n. fam.), Seabournea (Cribrilinidae) and Waeschenbachia (Romancheinidae). A new Recent species of the otherwise Eocene‒Miocene genus Vincularia is also described from deep water on the Three Kings Ridge. Two new combinations are created – Judyella precocialis (Gordon, 1984) and Ellisantropora aggregata (Gordon, 1984). Ellisantropora tilbrooki sp. nov. is also introduced for a species from Torres Strait. Four of the deep-sea genera (three from one station on the northern Norfolk Ridge, one from a station on the Three Kings Ridge) have species with plesiomorphies or distinctive skeletal characters that suggest they are relict. Almost half of the new species form spot-like colonies on hard substrata.

Of the five nominal species in the genus Caranx Lacepède 1801 distributed throughout the Eastern Central Pacific, Caranx caballus and Caranx sexfasciatus are the only two that have formal fish larval descriptions based on diagnostic characteristics (morphology, meristics and pigmentation). In this study, the diagnostic characteristics of three Caranx species larvae were validated using DNA barcoding analysis cytochrome c oxidase subunit I (COI; 651 bp). For the first time, the morphological taxonomic assignation of C. caballus fish larvae was confirmed using COI gene partial sequences of adults, with a genetic similarity between 99.8–100%. However, molecular evidence demonstrated that fish larvae previously described as C. sexfasciatus had high genetic similarity (99.7–100%) and low genetic distance (<1%) to Caranx caninus adults. An undescribed larval morphotype collected in the present study genetically matched (100%) with COI sequences of C. sexfasciatus adults. The diagnostic characteristics of this new morphotype were a lack of pigmentation in the supraoccipital crest, over the gut, and at the terminal region of the gut. The combination of diagnostic characteristics and DNA barcoding evidence allowed the discrimination and validation of C. caballus, C. caninus and C. sexfasciatus larvae. The diagnostic characteristics and COI sequences of Caranx lugubris and Caranx melampygus larvae, which are also distributed in the Eastern Central Pacific, remain to be investigated.

Despite the high commercial value of the striped seabream Lithognathus mormyrus (Linnaeus, 1758) in the Gulf of Tunis, biological data on its age, growth and exploitation rate are lacking. With the aim of estimating growth parameters, 516 individuals, ranging from 6–27.5 cm total length and from 3.5–293.5 g total weight, were collected from the artisanal fishing fleet between February 2014 and July 2016. The somatic growth presented a positive allometry and was described by the equation TW = 6.54 10−3TL3.213. The monthly analysis of the marginal increment of the otoliths revealed that only one annulus was deposited per year. The estimated von Bertalanffy growth parameters were: L∞ = 30.18 cm, k = 0.303 year−1 and t0 = −1.42 years. Total and natural instantaneous rates of mortality were respectively Z = 0.784 year−1 and M = 0.698 year−1. Exploitation rate (E = 0.1) showed that the Gulf of Tunis stock of L. mormyrus is not overexploited. The estimated length class giving highest yield (Lopt) was 17.15 ± 1.71 cm.

The changes in abundance and biodiversity of deep-sea fish fauna are described based on an annual deep-water longline survey with data collected during the period 2015–2019 in the Basque Country continental Slope (ICES Division 8c). The sampling scheme included hauls in four 400 m strata, from 650–2250 m deep. The DST sensors installed in the main line have allowed us to set an accurate soak time for each haul, and they were used to calculate fishing effort and CPUE by haul. The catchability of the fishing gear indicated that 15% of the total hooks deployed in the five-year period were able to fish, and that the bottom longline was very effective in fishing a wide number of different species in all depth ranges. The fishing gear caught 14 different species of sharks (13 deepwater and one pelagic), two chimaeras and nine teleosts. The abundance and biomass registered on the hooks attached to the bottom were between three and four times higher than in the floating sections, and the highest CPUE and biomass were recorded between 1051–1450 m, from 2015 to 2017, and in the 1451–1850 m strata, but they do not show any clear trend throughout the five years of the series.

Hypleurochilus fissicornis is a resident species of the intertidal and subtidal zones of Mar del Plata, Argentina. The specific reproductive biology was studied by means of both microscopic and macroscopic analyses. A total of 212 males and 223 females were analysed. Specimens were dissected and their gonads and livers were removed. The gonadosomatic and hepatosomatic indexes and the condition factor were calculated on a monthly basis. Hypleurochilus fissicornis breeds in rocky intertidal areas, and exhibits low fecundity with benthic eggs and parental care. Size at first maturity (L50) was estimated at 53.66 and 55.83 mm total length for females and males, respectively. The spawning season takes place between December and April.

The demographic histories, genetic relationships and population structure of sedentary fish Pomatoschistus marmoratus (Risso, 1810), which was sampled from the north-eastern basin of the Mediterranean Sea (including the Turkish coasts of the Black Sea, Aegean Sea, Levantine Sea and Sea of Marmara), were investigated by mitochondrial cytochrome c oxidase subunit I (652 bp) and cytochrome b (526 bp) regions. It was found that the population groups had high haplotype diversity while the nucleotide diversity was quite low for both gene regions. Phylogeographic analyses of the haplotypes indicated that the Levantine population (LEV) were genetically different from other populations. Also, the gene flow between LEV and the other populations was very limited. The results of the analyses of neutrality and mismatch distributions that were applied to the population groups were evaluated as a whole. It was determined that the haplogroup that represents the Black Sea and Sea of Marmara populations (BLAMAR) was stable, but the Levantine population (LEV) was under the sudden demographic expansion model following the population bottleneck. The genetic variance indices indicated sudden demographic expansion following population contraction. This was supported by star-shaped haplotype networks. The reason for this limited gene flow and differentiation between the Levantine population (LEV) and the others was linked with wind-driven offshore transport of the larvae and surface currents in these sub-basins. The timing of the differentiation, demographic histories of populations associated with geological and palaeo-climatic events and current ecological conditions were discussed.

The introduction of non-native predator fish is thought to have important negative effects on native prey populations. Opsanus beta is a non-native toadfish that was originally described in the Gulf of Mexico, between the west coast of Florida and Belize. In the present study, we describe, for the first time, the occurrence of O. beta in Sepetiba Bay (22°55′S), south-eastern Brazil, probably brought into the bay through ships' ballast water. Thirteen specimens were recorded in this area near to Sepetiba Port. Similarly, three other records of this species in the Brazilian coast were also reported near to port areas at Rio de Janeiro (22°49′S), Santos (23°59′S) and Paranaguá (25°33′S) ports. To confirm the species identity, we employed DNA barcoding and compared our samples with sequences deposited on public databases, which indicated that our samples are highly similar (>99.9% of genetic similarity) to O. beta samples collected near its type locality. Several individuals were found in the capable spawning phase, according to histological analysis of the reproductive cell stages. The environmental plasticity of this species and the favourable local environmental conditions probably enabled the establishment of O. beta in this region. This raises concerns of potential high invasion impact due to this species' diet and reproductive capacity.

Food partitioning among coexisting species is often considered advantageous to minimize niche overlap and avoid inter-specific competition. Congeneric fish species such as the mullets Mugil curema and Mugil liza, which co-occur across marine and estuarine habitats, are good models to evaluate resource use and niche overlap or partitioning. We used stomach contents (SCA) and stable isotope analysis (SIA) to assess potential trophic shifts and changes in niche overlap associated with the mullets transitioning from marine to estuarine habitats. SIA included different fractions of organic matter in suspension and in the sediment to estimate the contribution of micro, nano and pico-organisms to the mullets’ diets. We hypothesized higher resource partitioning in the less resource-diverse system (marine surf-zone) than in the more diverse one (estuary). SCA showed diet differences between M. curema and M. liza according to the habitat. They showed distinct diets in the marine area (P < 0.001), but similar diets in the estuary (P = 0.226). A lower niche breadth was observed for both species in the marine area (M. curema = 0.03, M. liza = 0.06) compared with the estuary (M. curema = 0.14, M. liza = 0.16). Isotopic niches of both species were higher in the estuary (64.7%) compared with the marine area (0.7%). These findings corroborated our hypothesis of higher food partitioning in the marine surf-zone. We also demonstrated using SIA the shift from planktonic to benthic feeding following the recruitment of the mullets from the surf-zone into the estuary.

In this study, we investigated ontogenetic and sexual changes of the brain scaling as well as the scaling and the relative size of six major brain areas in the small-spotted catshark Scyliorhinus canicula from the Mediterranean Sea. The brain somatic index (0.31–1.25%) did not differ significantly between sexes but was significantly affected by size with smaller specimens exhibiting higher values. Brain growth exhibited negative allometry (allometric coefficient 0.634), not affected by sex or maturity status. The brain growth rate was found to be higher compared with a previous study from the Atlantic Ocean. Regarding the scaling of the brain areas, the olfactory bulbs scaled with positive allometry, the telencephalon and the diencephalon scaled with the same rate of negative allometry, the mesencephalon exhibited even higher negative allometry, while the cerebellum and the medulla oblongata both followed a close-to-isometric growth pattern. Immature S. canicula possessed a larger mesencephalon and diencephalon, highlighting the importance of vision in this life period, while mature specimens had enlarged olfactory bulbs, indicating that olfaction may be more important after the animal attains sexual maturity. In respect of sexual dimorphism, males had a larger cerebellum and medulla oblongata, while females had enlarged telencephalon and olfactory bulbs.

Anguillid leptocephali of three Congridae species (Conger conger, Ariosoma balearicum and Gnathophis mistax) were caught as bycatch of pelagic trawls during acoustic surveys targeting small pelagic fish species in the southern Adriatic Sea, carried out under the framework of the Italian MEDIAS project (western side) and its extension in the ambit of the FAO AdriaMed project (eastern side). Results refer to the findings of Congridae leptocephali during surveys conducted in 2011, 2014, 2015 and 2016. A total of 25 specimens were caught and analysed (morphological features and pigmentation patterns). Leptocephali of Conger conger were found in the range of 8.4–13.1 cm total length (TL) (between 50 and 132 m depth), Ariosoma balearicum from 9.7–12.2 cm TL (between 50 and 128 m depth) and for Gnathophis mystax in the range from 6.4–11.7 cm TL (between 40 and 79 m depth). The results indicate that the southern Adriatic Pit could be the spawning area of these species in the Adriatic Sea. Present data represent a contribution to existing knowledge about the ecology of leptocephali from the Congridae family in the southern Adriatic Sea, and also indicate the existence of differences in morphometric parameters between different areas, that is, the possibility of the existence of new geographic lines within the genus Ariosoma in the Adriatic Sea.

Increased numbers of great cormorants (Phalacrocorax carbo) in the Baltic Sea may have local impacts on fisheries and salmonid hatcheries. We studied spatial and temporal variability in cormorant diet, and potential consumption of hatchery salmonids, by analysing knee subcutaneous adipose tissue fatty acids (FA) of specimens (N = 77) collected along Swedish and Finnish coasts in different seasons during 2013–2017. The FA profiles of the subspecies sinensis and carbo were similar, with large individual variation. The proportion of C18 polyunsaturated FAs (PUFAs) was the largest in the north, whereas the proportion of C20–22 monounsaturated FAs (MUFAs) increased towards the south, reflecting diminishing freshwater and increasing marine food web characteristics towards the south. As an exception, the C20–22 MUFA percentage was high in sinensis collected in June 2017 from the northern Baltic Sea. The source of C20–22 MUFAs was probably hatchery salmonids, raised on ocean fish hatchery feed and released 10 days before, near the cormorant capture site. The FA profiles of northern and southern cormorants differed from each other both in early and late summer samples, suggesting spatially different diets. The largest individual variation was found in 22:1n-11, characteristic of ocean zooplanktivorous fish, and likely originating from Atlantic wild or Baltic Sea hatchery-reared fish. This study shows that adipose tissue FA profiles can be used as proxies for seabird diet monitoring and indicators of predation on hatchery-reared fish. Obtaining quantitative estimates on the proportions of dietary fish species requires future feeding experiments, allowing calibration between the FA compositions and diet.

Elasmobranchs in the Gulf of California have been found with malformations, probably originated during embryonic development or caused by environmental anomalies and pollution associated with intense mining activity in the region. Clasper malformations are reported for the first time in two specimens of Pseudobatos buthi, a species recently described from the Gulf of California. The function of the claspers was not affected by the size difference, because specimens presented the distinctive characteristics of an adult individual. The reproductive system did not show any malformation, with symmetrical testes. Histological analysis of the testes revealed a normal spermatogenic development. To elucidate the causes and to detect a possible effect of the morphological malformations due to high levels of heavy metals, trace concentration values (cadmium, copper, iron, manganese, silver, lead and zinc) were determined in muscle and liver. Cadmium and lead concentrations in the muscle of the two specimens were below the permissible limit for human consumption (<0.05 mg kg−1); however, iron and zinc presented high values (0.455, 4.024 mg kg−1 in muscle and 21.931, 3.694 mg kg−1 in liver respectively). Mining activity and heavy metal pollution in the sampling area may have caused the malformations, which might be attributed to the high values of iron and zinc discovered in the muscle and liver.

The Pacific sleeper shark Somniosus pacificus is one of the largest predators in deep Suruga Bay, Japan. A single individual of the sleeper shark (female, ~300 cm in total length) was observed with two baited camera systems deployed simultaneously on the deep seafloor in the bay. The first arrival was recorded 43 min after the deployment of camera #1 on 21 July 2016 at a depth of 609 m. The shark had several remarkable features, including the snout tangled in a broken fishing line, two torn anteriormost left-gill septums, and a parasitic copepod attached to each eye. The same individual appeared at camera #2, which was deployed at a depth of 603 m, ~37 min after it disappeared from camera #1 view. Finally, the same shark returned to camera #1 ~31 min after leaving camera #2. The distance between the two cameras was 436 m, and the average groundspeed and waterspeed of the shark were 0.21 and 0.25 m s−1, respectively, which were comparable with those of the Greenland shark Somniosus microcephalus (0.22–0.34 m s−1) exhibiting the slowest comparative swimming speed among fish species adjusted for size. The ambient water temperature of the Pacific sleeper shark was 5.3 °C, which is considerably higher than that of the Greenland shark (~2 °C). Such a low swimming speed might be explained by the ‘visual interactions hypothesis’, but it is not a consequence of the negative effects of cold water on their locomotor organs.

There are limited data regarding the reproductive biology of the scalloped hammerhead (Sphyrna lewini) in Ecuadorian waters, which limits the development of appropriate management measures of its populations. A total of 1664 S. lewini specimens were recorded in Manta, Ecuador in 2003–2009. Specimens were caught by local commercial fisheries and measured between 50–310 cm total length (TL). Females were more frequently caught, with a sex ratio of 1M:1.8F. The median size at maturity was 178.1 cm TL for males and 219.4 cm TL for females, which was larger compared with other localities. Gravid females, which measured 246–298 cm TL, contained 16–22 embryos. Embryos, which were observed from October–July, measured between 11.1–54.6 cm TL and the available data agreed with a gestation period of 10–11 months that starts in September and ends in June/July. Size at birth was 47–55 cm TL. Sampling data indicated that most fishing activity occurred in nearshore and around seamounts in the central-eastern Pacific Ocean, with much of the landed catch comprising immature individuals. This study documents the reproductive biology of S. lewini in the central-eastern Pacific Ocean and provides additional information to improve management and conservation measures for this species.