Mesoscale features within the Gulf of Mexico (GOM) are known to influence zooplankton dynamics. Here we describe the composition of the zooplankton assemblage off shelf during summer in relation to environmental conditions, with emphasis on hyperiid amphipods and salps. Zooplankton samples were collected in summer of 2015 and 2016 in the central and southern GOM and in the Yucatan Channel in 2015. Two anticyclonic gyres were present in the north and less intense coupled cyclonic-anticyclonic gyres in the south. Zooplankton abundances differed temporally and spatially. Copepods were the dominant group (>55% of total abundance), while several less abundant taxa contributed to inter-annual and spatial differences. Amphipods and salps comprised <3% and their abundances were positively correlated. Fifty-six hyperiid and 10 salp species were identified. The dominant amphipod species were: Lestrigonus bengalensis (summer 2015), Anchylomera blossevillei and Primno spp. juveniles (summer 2016). Dominant salp species were Ihlea punctata, Iasis cylindrica and Thalia spp. Lower salp and amphipod species richness and abundance were associated with anticyclonic structures. Spatial and temporal differences were partly associated with symbiotic relationships between the groups. This study supports previous evidence of high spatial and temporal variability in zooplankton abundance in off-shelf waters of the GOM.

Since the mid-1980s, swarms of the rhizostome Rhopilema nomadica have been an annual phenomenon in Israeli Mediterranean coastal waters during the summer months. Despite its annual prominence and the potential impact on food webs and ecosystem services, studies concerning its feeding ecology and its interactions with other biota in the marine food web have not been conducted. During summer 2015 gut contents of 41 R. nomadica were analysed as well as ambient plankton assemblages. More than 60% of the medusae diet was found to consist of microzooplankton <150 μm. Size correlations revealed that larger R. nomadica consumed faster swimming prey while smaller medusae relied more on the slower swimming taxa. The medusan diet reflected most of the ambient plankton taxa, but no statistically significant correlations between the relative abundance in diet and ambient plankton were found. As summer progressed, there was a gradual decrease in both mean medusa bell diameter (from 42.2–16 cm) and integrity of feeding structures. These findings suggest that R. nomadica, at least at the time of its appearance in Israeli coastal waters, may exert less predatory pressure on the plankton than we might otherwise expect.

The catostylid jellyfish, Crambionella annandalei was originally described by Rao (1932) based on a preserved specimen collected from the Andaman Sea. Since then, no detailed taxonomic studies have been conducted and the species is often misidentified. Here, we provide a detailed morphological re-description of C. annandalei from fresh material collected at a variety of locations along the east coast of India. The species can be distinguished from its congeners by a combination of morphological characters, the most important of which are the proportion of terminal club length to oral arm length (0.48 ± 0.031), the proportion of the distal portion of the oral arm to naked proximal portion (7.25 ± 0.268) and the body colour. The occurrence of intra-specific colour variation in fresh specimens was also observed in the present study.

In Thailand, two species of rhizostome jellyfish, Rhopilema hispidum and Lobonemoides robustus, are commercially harvested. The cnidomes, nematocyst size and toxicities were compared between these species. Rhopilema hispidum and L. robustus each had four types of nematocysts on their oral arms. For R. hispidum, these nematocyst types included two types of isorhiza and two types of rhopaloid, while in L. robustus, there were three types of isorhiza and one type of rhopaloid. For R. hispidum, tubule lengths of the largest nematocyst type (large round isorhiza; mean ± SD = 313.8 ± 62.2 μm) were significantly longer than those of L. robustus (large ellipsoid rhopaloid; 162.1 ± 38.5 μm). Using the freshwater shrimp, Palaemon paucidens, in a bioassay, we determined that the lethal nematocyst concentrations for R. hispidum and L. robustus were 5705.3 ± 1118.1 and 3408.3 ± 1032.9 unit g−1 wet weight, respectively, and that these concentrations were significantly higher in the former than in the latter.

Although marine phylogeographers have accumulated knowledge of the evolutionary history of various invertebrates, there is a large bias among the taxa regarding genetic data. The order Polycladida is a typical example for which little genetic information at population level is available. Here, we focused on the polyclad flatworm Stylochoplana pusilla, distributed in the Japanese Pacific coastal area. Stylochoplana pusilla is known to have commensal relationships with certain intertidal snails, using snails (mainly Monodonta confusa) as a refugee house. During low tide, S. pusilla hides in the mantle cavity of snails to protect themselves from desiccation and predation. Here, we investigated the genetic structure of S. pusilla using a mitochondrial Cytochrome Oxidase I marker and the species diversity of snails used by it. We found that S. pusilla has high genetic diversity of its populations. While S. pusilla showed a significant genetic differentiation among populations, it was relatively low. In addition, we also showed that S. pusilla used several intertidal snail species which inhabit various coastal environments. The present study suggests S. pusilla has sufficient dispersal ability to connect among its local populations. Also, the range of available snails for S. pusilla may help the connectivity among local populations. We provide important knowledge about this invertebrate taxon with a unique ecology, which has been insufficiently studied.

Rhamphobrachium (Rhamphobrachium) agassizii is reported from the Cantabrian Sea, Spain, from depths of 925–1207 m. This is its first record off the Iberian Peninsula and in European waters, representing its northernmost distribution in the North Atlantic Ocean to date. Previous reports of R. (R.) agassizii from the eastern and western North Atlantic demonstrate its apparent amphi-Atlantic distribution, which appears consistent with the distribution of the main Atlantic currents. It is a typical deep-water species with its deepest record at 2165 m from the Azores archipelago. The specimens were collected singly at two stations, attesting to the rarity of the species in contrast to its congener R. (Spinigerium) brevibrachiatum which was the most dominant polychaete species in a previous study.

Morphometric analysis is one of the tools widely used to quantify, analyse and describe the variations in the biological forms of animals. In this study, we examined the linear morphometric variations of the shell of the small intertidal gastropod Echinolittorina lineolata and compared the patterns to identify variations among populations and between sexes. The individuals were collected from latitudes 3°S, 14°S, 21°S and 23°S along the Brazilian coast. Traditional morphometric analysis was performed, and the morphometric variables of the shells, namely, the length and width of the shell and the length and width of the shell opening were obtained. The observed size pattern was influenced by latitude, as well as by local spatial responses to factors such as the substrate changing the morphometric variables of the snail. Of the morphometric variables, the length and the width of the shell were the most representative variables that influenced the gastropods in the different latitudes. These variables were also different in males and females, with females having larger shell lengths and widths across all latitudes.

This work aimed to test whether the colour variability featured by the European nudibranch Polycera quadrilineata is consistent with the concept of a single polychromatic species or may hide multiple lineages. Samples from across the geographic range of P. quadrilineata together with representatives from worldwide species with a focus on Atlantic diversity, were gathered and studied using an integrative taxonomic approach. Morpho-anatomical characters were investigated by light and scanning electron microscopy. Bayesian molecular phylogenetics using MrBayes, the Automatic Barcode Gap Discovery species delimitation method, and haplotype network analysis using the PopArt software were employed to help delimit species using the mitochondrial gene cytochrome c oxidase subunit I (COI). The results supported the existence of a second species, here described and named Polycera norvegica sp. nov., only known from Norway where it is sympatric with P. quadrilineata. The COI uncorrected p-genetic distance between the two species was estimated at 9.6–12.4%. Polycera norvegica sp. nov. differs by exhibiting a black dotted or patchy dotted pattern occasionally with more or less defined orange/brown patches, but never black continuous or dashed stripes as in P. quadrilineata. The two species share a common colouration with a whitish base and yellow/orange tubercles. Anatomically, P. norvegica sp. nov. has a weaker labial cuticle, a smaller radula with fewer rows, and only four marginal teeth, a reproductive system with a single lobed bursa copulatrix, shorter reproductive ducts, and a penis armed with two kinds of spines: needle-like and hook-shaped penile spines.

Moulting is essential for crustacean growth, but is one of the causes of mortality, because a crustacean cannot move during and just after its ecdysis. In the cases of ectosymbiotic crabs, escape from the host's hostile response may also be a problem during its own ecdysis. In this study, Sestrostoma sp. (Varunidae), an ectosymbiotic crab which clings to the ventral abdomen of upogebiid shrimps with legs that can walk, was studied to clarify how the crab moults and maintains association with the host. Five cases of crab ecdysis were observed, where the crab moulted with its legs clinging to the host abdomen, without detaching from the host body. Time required for moulting was 14–21 min. Shedding of the old exoskeleton (active phase) took only 40–59 s. Sestrostoma sp. detached from the host abdomen and waited in the burrow tube during shrimp ecdysis. The crab then reattached at the same location on the host when shrimp moulting was complete. Our results suggest that Sestrostoma sp. are able to maintain a symbiotic relationship with the same shrimp host after its own ecdysis as well after ecdysis of its host.

The genera Ophiophragmus and Amphiodia are amphiurids that are considered taxonomically difficult due to their great resemblance, few diagnostic characters and synonymy problems. Our aim is to redescribe the species using scanning electron microscopy and morphometry of diagnostic structures, and to provide new information for the identification of these Ophiuroidea. Five Amphiodia spp. and six Ophiophragmus spp. recorded in Brazil were rigorously redescribed. The descriptions include new diagnostic characters derived from external morphology, arm microstructures and morphometry. We also provided comparative analyses of species with shared characters such as Amphiodia riisei and Amphiodia trychna. The geographic and bathymetric distributions of the studied species were updated, and new records are provided. All the information presented may be used in taxonomic, ecological and phylogenetic studies, helping to fill gaps in the knowledge of the biodiversity, ecology and evolution of these Ophiuroidea. Conclusively, all the tools applied here assisted in the identification of genera and species and could be useful in other taxonomic studies of Echinodermata.

The goal of this study was to study the distribution of potential habitat markers (Sr/Ca, Ba/Ca, Mn/Ca and Li/Ca) in water from the Paranaguá Estuarine Complex (Brazil) and to study habitat use patterns of Cathorops spixii through ontogeny employing otolith microchemistry. Fish were caught from three sampling sites while water samples were collected at eight stations covering a salinity range from 4.5–33. Elemental concentrations in otolith and water were determined by LA-ICP-MS and ICP-MS, respectively. When the relationship between salinity and elements or ratios in water was studied, significant positive relationships were found for Sr, Li, Ca, Sr/Ca, and negative for Ba, Mn, Ba/Ca and Mn/Ca (P < 0.05). No relationship was observed between water Li/Ca and salinity. A significant positive correlation was found between otolith edge Sr/Ca and salinity (r = 0.63; P < 0.05), positioning this ratio as the best natural tag for reconstructing environmental histories of C. spixii. Change point analysis (CPA) based on otolith Sr/Ca signature through ontogeny revealed potential migrations between environments with different salinity. According to CPA, the number of displacements among different salinities ranged from 3–9 (6.1 ± 1.9), suggesting high plasticity in the migratory patterns. Ba/Ca, Li/Ca and Mn/Ca peaks were observed on the outer margin of the primordium, and could be influenced by physiological, environmental and maternal factors.

Estuarine habitats are major nurseries for the European flounder Platichthys flesus, with different year classes sharing food and space resources. Hence, an understanding of feeding strategies that optimize resource use and maintain carrying capacity is fundamental for sustainable and successful ecosystem management. The main feeding areas of juvenile European flounder (including 0-group and 1-group age classes) in the Lima estuary (northern Portugal) nursery ground were investigated by integrating stomach content analyses with stable isotopic values (δ13C and δ15N) and fish condition indices (Fulton K and RNA:DNA ratio). The 0-group flounder that were associated with the upstream section of the estuary presented the lowest δ13C value (−25.58 ± 1.86‰), while 1-group flounder exhibited a higher δ13C value (−22.59 ± 2.51‰), indicating use of the more saline areas of the estuary (lower and middle sections). The two age groups did not differ in terms of δ15N (0-group: 13.93 ± 0.29‰; 1-group: 13.50 ± 0.96‰), indicating similar trophic levels. The low salinity upper estuary was the main feeding area of 0-group flounder (74%), while 1-group flounder fed along the estuary both upstream (52%) and downstream (48%). Juvenile flounder showed high individual condition based on the Fulton K index (0-group: 1.05 ± 0.08; 1-group: 1.07 ± 0.05) and RNA:DNA (0-group: 1.70 ± 0.70; 1-group: 1.41 ± 0.47). These indices deal with fish health, and hence indicate nursery habitat quality. It is concluded that in this temperate nursery habitat, different feeding strategies sustained the condition of the European flounder juveniles, compared with other flounder populations.

Resource partitioning is important for species coexistence. Species with similar ecomorphological characters have a high potential for competition, especially when close phylogenetically. The diet and resource partitioning of four snappers (Lutjanus alexandrei, L. analis, L. jocu and L. synagris) was studied in the Tubarão River, north-eastern Brazil, between March and November 2012. Specimens were caught using a beach seine, and a total of 731 stomachs were analysed. The highest abundance of snappers was found near to vegetated habitats in the middle estuary. Crustaceans were dominant in the diet of all four species, being found in over 90% of the stomachs, followed by fish and molluscs. The species did not appear to compete for common resources, probably because there was not always spatial overlap, and differences in the proportions of consumption of items were observed. Ontogenetic comparisons of dietary compositions suggested differences among species, with changes in the diet related to changes in the mouth area as the body size increased. The changes were more evident in L. analis and L. synagris where microcrustaceans (Calanoida, Cyclopoida and Amphipoda) were dominant in the diet of the smaller size classes, and benthic crustaceans (Brachyura) and fish in the diet of larger individuals. The intra- and inter-specific differences in the dietary compositions, differences in the mouth area and feeding strategy contribute to allow the co-existence of these snappers in the study area.

The loggerhead turtle (Caretta caretta) is a circumglobal species and is listed as vulnerable globally. The North Pacific population nests in Japan and migrates to the Central North Pacific and Pacific coast of North America to feed. In the Mexican Pacific, records of loggerhead presence are largely restricted to the Gulf of Ulloa along the Baja California Peninsula, where very high fisheries by-catch mortality has been reported. Records of loggerhead turtles within the Sea of Cortez also known as the Gulf of California (GC) exist; however, their ecology in this region is poorly understood. We used satellite tracking and an environmental variable analysis (chlorophyll-a (Chl-a) and sea surface temperature (SST)) to determine movements and habitat use of five juvenile loggerhead turtles ranging in straight carapace length from 62.7–68.3 cm (mean: 66.7 ± 2.3 cm). Satellite tracking durations ranged from 73–293 days (mean: 149 ± 62.5 days), transmissions per turtle from 14–1006 (mean: 462 ± 379.5 transmissions) and total travel distance from 1237–5222 km (mean: 3118 ± 1490.7 km). We used travel rate analyses to identify five foraging areas in the GC, which occurred mainly in waters from 10–80 m deep, with mean Chl-a concentrations ranging from 0.28–13.14 mg m−3 and SST ranging from 27.8–34.4°C. This is the first study to describe loggerhead movements in the Gulf of California and our data suggest that loggerhead foraging movements are performed in areas with eutrophic levels of Chl-a.

In order to determine the sex of Chelonia mydas individuals found within one of the principal foraging areas of the Gulf of California during any given stage of ontogeny, 529 individuals were sampled in Bahía de los Ángeles from 1995–2012, and their morphometric data were collected. A principal component analysis (PCA) was performed for the morphometric variables, and two principal components were obtained that unambiguously separated sexes and ontogenetic stages. The first component was defined by straight carapace length (SCL), curve carapace length (CCL), plastron length (PL) and carapace depth (CD), while the second factor was represented by total tail length (TTL). Allometric models were fitted with the most important variables determined by the PCA. The model PL = αSCLβ was able to distinguish between adults and immature individuals. For adult organisms, the model that best separated males from females was TTL = αSCLβ. Adult females had SCL values of 66–96.7 cm and TTL values of 16.3–25 cm, while adult males had SCL values of 66.4–12.5 cm and TTL values > 25 cm. As the organisms were considered immature only if SCL < 77.3, we were able to determine the TTL values for immature individuals by using elemental mathematics and solving for SCL in the equation TTL = αSCLβ for each group (i.e. adult females, adult males and immatures). So, considering the mathematical approach and acknowledging the lack of background information, immature individuals may be considered potential females if the TTL value is between 7.04–17.8 cm and potential males if the TTL value > 17.8 cm.

In this paper a rare case of a double swordfish mortal attack against an adult blue shark (Prionace glauca) is reported. A female blue shark, with a total length of 3 m, was found stranded along the southern Sicilian coast (Strait of Sicily, Mediterranean Sea) on 30 May 2018. The analysis of this carcass revealed the presence of two swordfish bill fragments, impaled in the shark head; the former on the snout, the latter near the eye. The results of anatomical and computed tomography scanning analysis on the head of the blue shark showed that the larger bill fragment (19.7 cm) probably determined the death of this animal, having been impaled in a vital point, just behind the right eye. The analysis of both these events and other similar swordfish-shark interactions reported in the literature makes possible the hypothesis that young swordfish specimens put in place a precise defensive strategy against their potential predators or competitors, aimed at hitting vulnerable and vital points and delivering a mortal blow.

The diet and feeding habits of the pelagic thresher shark Alopias pelagicus were analysed based on 104 stomachs (N = 84 females, 20 males) collected off Santa Rosa de Salinas, in the Ecuadorian Pacific. The sharks were caught between February 2008 and January 2009 in artisanal fisheries. The trophic spectrum of A. pelagicus included 19 prey items (10 cephalopods and 9 teleost fishes), the main four prey were the red flying squid Ommastrephes bartramii, jumbo squid Dosidicus gigas, the purpleback flying squid Sthenoteuthis oualaniensis and the South Pacific hake Merluccius gayi. The trophic niche was narrow (Bi = 0.2), thus the pelagic thresher could be considered a specialist predator. The analysis of dietary overlap showed high similarity between the diets of females and males (Cλ = 0.99), immature and mature females (Cλ = 0.81), immature and mature males (Cλ = 0.72), sizes of 141–230 cm TL and 231–321 cm TL (Cλ = 0.97), as well as sharks in rainy season and dry season (Cλ = 0.77). Using canonical of correspondence analysis (CCA), we found similarities in the diet for all categories recorded (sex: canonical r = 0.38, P = 0.97; sexual maturity stage: canonical r = 0.54, P = 0.31; sizes: canonical r = 0.55, P = 0.26; seasons of the year: canonical r = 0.61, P = 0.75). The trophic level estimated for A. pelagicus was 5.0, which is typical of top predators (quaternary consumers or tertiary carnivores).

Marine traffic has both short- and long-term effects on cetacean behaviour, yet fishing vessels present a unique situation as they disturb cetaceans whilst potentially offering alternative foraging opportunities. The Istanbul Strait is a key area for the study of anthropogenic disturbance on cetaceans due to heavy human pressure in a narrow space where at least three cetacean species are regularly encountered. The present study investigated changes in behaviour of bottlenose dolphins, common dolphins and harbour porpoises in relation to the presence of purse seiners using Markov chains analysis. The results revealed increased foraging in bottlenose and common dolphins' behavioural budgets and a decrease in the time spent foraging by harbour porpoises. Moreover, a loglinear model was used to analyse the effect of possible confounding variables on observed behaviours. The only variables found to be affecting behaviour were the previous recorded behaviour, seiner presence and marine traffic density. Consequently, the presence of purse seine vessels leads bottlenose and common dolphins to change their behaviour and are related with a decrease of energy intake in porpoises. The results of this study reveal that there is an effect of purse seine vessel presence on the cetaceans found in the Istanbul Strait with potentially significant impacts on their behaviour, therefore we suggest more research is needed in the area to identify the long-term impacts of these observed behavioural changes.

The coast of Aragua is a home of bottlenose dolphins (BND), Atlantic spotted dolphins (ASD) and fishermen (FIS) from four towns. A photo-identification study was carried out on BND to estimate their home ranges. From 2004 to 2008, 100 field surveys were carried out along 30 km of coastline (92.12 km2). In each sighting of BND, information regarding date, time, latitude/longitude and photographs were registered (ASD and FIS were registered without photography). The data were analysed using a Geographic Information System to estimate Minimum Convex Polygon (MCP) and Fixed Kernel (FK) at 95%. The home ranges of BND were estimated for seven individuals. This included three females (29–31 sightings) with estimated areas ranging from 33.90–39.90 km2 with MCP (36.79–43.31% of the study area) and from 80.47–101.31 km2 with FK (109.97–104.26%). For the remaining four dolphins (14–20 sightings) the estimated areas ranged from 9.67–22.34 km2 (MCP), the predominant depth of these home ranges varied from 51–100 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). For the pods of ASD the estimated area ranged 75.23 km2 with MCP (81.66%) and 119.86 km2 with FK (130.11%) with predominant depths of 101–200 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). The area used by FIS ranged 93.27 km2 by MCP and 228.49 km2 by FK. Finally, the overlap area of BND, ASD and FIS ranged 24.75 km2 (26.86%). We point out this locality presents important oceanographic and ecological aspects which deserve to be the subject of application of management plans for the conservation of its habitat and species.