With over a century of records, we present a detailed analysis of the spatial and temporal occurrence of marine turtle sightings and strandings in the UK and Ireland between 1910 and 2018. Records of hard-shell turtles, including loggerhead turtles (Caretta caretta, N = 240) and Kemp's ridley turtles (Lepidochelys kempii, N = 61), have significantly increased over time. However, in the most recent years there has been a notable decrease in records. The majority of records of hard-shell turtles were juveniles and occurred in the boreal winter months when the waters are coolest in the North-east Atlantic. They generally occurred on the western aspects of the UK and Ireland highlighting a pattern of decreasing records with increasing latitude, supporting previous suggestions that juvenile turtles arrive in these waters via the North Atlantic current systems. Similarly, the majority of the strandings and sightings of leatherback turtles (Dermochelys coriacea, N = 1683) occurred on the western aspects of the UK and the entirety of Ireland's coastline. In contrast to hard-shell turtles, leatherback turtles were most commonly recorded in the boreal summer months with the majority of strandings being adult sized, of which there has been a recent decrease in annual records. The cause of the recent annual decreases in turtle strandings and sightings across all three species is unclear; however, changes to overall population abundance, prey availability, anthropogenic threats and variable reporting effort could all contribute. Our results provide a valuable reference point to assess species range modification due to climate change, identify possible evidence of anthropogenic threats and to assess the future trajectory of marine turtle populations in the North Atlantic.

The first zoeal stages of the snapping shrimps Alpheus carlae and A. intrinsecus from Brazil were obtained from laboratory-hatched specimens and a detailed morphological description is provided. The morphological characteristics of both species are compared with available descriptions of other Alpheus species with a known first zoeal stage. Remarks from a semi-quantitative comparison of species belonging to A. armillatus species complex (A. carlae and A. brasileiro) and a comparison between larvae of A. intrinsecus from two localities in Brazil are presented. It was possible to distinguish first zoea of both species from the other congeners based on morphology. No intraspecific variability was detected between A. intrinsecus larvae obtained from two locations. Some structures showed differences between species of the A. armillatus complex. However, generalizations and conclusions based on larval morphology for taxonomic rearrangements at this point need to be made with caution and accuracy, since data of a sufficient number of species are not yet available for comparison.

The effects of flow velocity on the fitness-related behaviours of Mesocentrotus nudus remain largely unknown, greatly hampering the efficiency of stock enhancement. To explore the appropriate velocities for stock enhancement, we investigated dislodgement and immobilization velocities up to 90 cm s−1. The experimental results showed that M. nudus (test diameter of ~30 mm) were dislodged at 73.50 ± 7.7 cm s−1 and that M. nudus movement occurred only when the flow velocity was less than 33.40 ± 2.7 cm s−1. Three flow velocities less than 33.40 ± 2.7 cm s−1 (2, 10 and 20 cm s−1) were subsequently used to study the effects of flow velocities on covering behaviour and the righting response time of M. nudus. The downstream movement velocity of M. nudus was significantly larger than that upstream at 2 cm s−1 (P = 0.016) and 10 cm s−1 (P = 0.008), but not at 20 cm s−1 (P = 0.222). The righting response time of M. nudus was significantly longer at 20 cm s−1 than that at 2 cm s−1 (P = 0.015). The present study indicates that a flow velocity less than 20 cm s−1, preferably 2–10 cm s−1, is probably appropriate for the stock enhancement of M. nudus. Notably, the current study is a laboratory investigation without considering the hydrographic complexity in the field. Further studies should be carried out to investigate the long-term effects of water flow on feeding and growth of M. nudus both in the laboratory and the field.

Moonshine worms are a popular bait species used for fishing. The taxon was not detected during surveys of the macrobenthos conducted in Knysna in the 1940s and 1990s, and was first reported as a harvested bait species in the mid-2000s, suggesting that it appeared for the first time in the estuary in the last three decades. A previous molecular analysis identified the worms as Diopatra aciculata, a species first described from Australia. This study provides an updated detailed morphological description of D. aciculata in South Africa to facilitate future identifications and also investigates the species' distribution and population size in the Knysna Estuary. Specimens were examined by scanning electron, stereo- and compound microscopes. Diopatra aciculata has tubes that protrude from the sediment in sandy areas, often decorated with algae and shell fragments; a large body size, up to 600 mm long and 11.5 mm wide. It has 10–18 rings on ceratophores; 5–10 teeth on pectinate chaetae; uni- and bidentate pseudo-compound falcigers and dorsal cirri approximately as long as branchiae. Diopatra aciculata was detected up to 12 km from the mouth of the Knysna Estuary with densities measured at 18 sampled sites. Statistical analysis retrieved high and low density groups that were significantly different from one another (Kruskal-Wallis H(14, 800) = 376.55; P = 0.01), but distribution of high density sites was patchy. We estimate that the population comprises 20–24 million individuals. Given the size of individual worms and the population estimate, this species can be expected to have significant ecological impacts in the estuary.

We investigated the seasonal occurrence and vertical distribution/migration of larval and juvenile northern smoothtongue, Leuroglossus schmidti (Pisces, Bathylagidae), in oceanic areas of the western subarctic Pacific. This species was the most abundant larval fish and one of the most abundant juvenile/adult fish at the study site. Larval recruitment of this species occurred in early March to mid-October. Larvae were found, however, throughout all seasons, suggesting that some had overwintered. The highest abundance (5.8 individuals m–2) of larvae was in summer. During summer and autumn, hatching mainly occurred at 100–150-m depth and larvae migrated toward the surface with growth. Once larvae reached about 20 mm in length, they moved below 100 m, and larger larvae (over 24 mm) exhibited diel vertical migration. The abundance of juveniles integrated through the water column was relatively constant (0.3 individuals m–2) throughout the study period. They were collected from below 300 m during the day, and part of the population (13–38%) swam into the epipelagic layer at night. The information on early stages of L. schmidti presented here provides a basis for future investigations of mesopelagic fish ecology in oceanic areas of the western subarctic North Pacific Ocean.

Paratectonatica tigrina employs three predatory tactics against bivalve prey: wall-drilling, edge-drilling and non-drilling (suffocation) tactics. In this study, we conducted laboratory experiments to examine the predator–prey interactions between the naticid gastropod P. tigrina and two species of bivalve prey, Ruditapes philippinarum and Meretrix lusoria, and to investigate how predatory tactics differ for the bivalve species. Predation success increased with the shell weight ratio between predator and prey, however, there was no significant difference among prey species. The shell weight ratio significantly differed (P < 0.05) between predatory tactics against R. philippinarum, but not against M. lusoria, implying that P. tigrina determines its predatory tactics based on the shell weight ratio for R. philippinarum. However, we observed that feeding duration was not influenced by shell weight ratio or prey species, even though data were separated for each predatory tactic. These results suggest that there is no difference in feeding efficiency based on shell weight ratio between prey species and between predatory tactics. Paratectonatica tigrina may alter its predatory tactics suitably depending on the prey species and the relative size difference, despite the same feeding efficiency.

Structure and diversity of sessile zoobenthic assemblages seem to be driven not only by chemical-physical constraints and biological interactions but also by substrate lithology and its surface features. Nevertheless, broadly distributed crustose epilithic corallines could mask the role of substrate on animal settling. To evaluate the direct influence of different rocky substrates, occurrence and coverage of several sessile species, growing on the dark (i.e. coralline-free) face of sublittoral limestone and granite boulders were compared in the Tavolara MPA (Mediterranean Sea). The analysis of photographic samples demonstrated significant differences in terms of species composition and coverage, according to lithology. Moreover, limestone boulders were widely bare, while the cover per cent was almost total on granite. The leading cause of observed patterns could be the different level of dissolution of the two types of rocks, due to their different mineral composition and textural characteristics. Limestone has previously been shown to have higher dissolution compared with granite, and consequently, a more unstable surface. Our results suggest that, in dark habitats, the absence of the crustose coralline layer allows more rock dissolution and consequent lower stability of the limestone compared with granite, which, in turn, reduces the zoobenthos colonization.

Sardinella aurita has become an important source of fish protein-intake in NW African countries, where one stock is considered from Morocco to south Senegal, performing seasonal reproductive migrations along the coast. Although data are limited for the fisheries involved and for life-history knowledge of the species in the area, a precautionary approach is recommended to avoid overexploitation. Commercial landings of round sardinella produced by the European freezer-pelagic trawlers operating in Mauritanian waters were analysed between May 2004 and February 2012. The length-weight relationships (LWRs) (N = 40,725) did not show significant differences between sexes. Ripening round sardinellas were present throughout the year, but spawning effort rose between June and December. The length at first maturity for males and females was estimated at 27.7 cm TL (2.1 years) and 28.1 cm TL (2.2 years), respectively. Ages were interpreted from otoliths, varying from 0 to 8 years. Von Bertalanffy growth parameters resulted in non-statistically significant differences between sexes (P = 0.28). Natural mortality was estimated at ~0.63 year–1. The results provide important biological information for fisheries assessment of a species that plays an important key role in the current climate change scenario and for the economies of the riparian countries.

Mating strategy and sexual dimorphism of morphological traits of the leucosiid crab Pyrhila pisum were elucidated by analysing relative growth patterns of chelipeds and abdomen, and gonad development patterns. Male adults had long chelipeds compared with juvenile males and females. Among male adults, two phases with different slopes could be found in the regression lines; their chelipeds growth pattern changed from negative allometry to positive and longer chelipeds developed in large adults. The growth is more markedly expressed in the merus than in the propodus. Female adults had wider abdominal segments and a thicker body compared with juvenile females and males. Abdomen of females was greatly enlarged by a puberty moult. Male adults had well-developed gonads similar to female adults, and the weights of male gonads were often larger than those of females of the same body size. For adult males, a negative correlation was detected between carapace width and the weight ratio of their gonads, but no significant relationship was detected for adult females. Females had large and well-bloated seminal receptacles, whose weight was nearly equal to gonad weight. There was little difference in the amount of seminal receptacles regardless of the body size of females. There is a trade-off relationship in the development between chelipeds and gonads in adult males. Probably young adult males compensate for the disadvantageous condition of guarding by increasing the number of spermatozoids, and old adult males invest more of their energy to their chelae for guarding while decreasing investment in sperm production.

Marine hydroids, the polyp stage of hydrozoans, are assumed to be carnivores and play an important role in benthic-pelagic coupling processes by regulating zooplankton populations and transferring energy. The known hydroid diets mainly consist of zooplankton as well as some benthic diatoms and metazoans, almost all of which have smaller dimensions than the polyp. In the present study, a large-scale breeding failure of the early juveniles of the ivory shell Babylonia areolata (Mollusca: Gastropoda: Babyloniidae) was found in a local aquaculture farm in Fujian, China in July 2018. About 640,000 out of 800,000 early juveniles (80%) died due to predation by a millimetre-sized colonial hydroid species that was initially overlooked. The hydrozoan species was identified as Eirene sp. (Cnidaria: Hydrozoa: Eirenidae) via the integration of morphological and molecular data. A laboratory feeding experiment showed that the hydroid predation led to an overall mortality of ivory shell juveniles of up to 92.6% after 48 h. The predation process was observed in the laboratory and a video showing the entire process was prepared. This is the first report of hydroids preying on gastropod juveniles, revealing a previously unknown threat to mollusc aquaculture including ivory shells. Several management practices are suggested to mitigate this newly recognized threat.

Horizontal and vertical distribution of cephalopod paralarvae (PL) from the Mesoamerican Barrier Reef System (MBRS) in the Western Caribbean was studied during two oceanographic cruises in 2006 and 2007. A total of 1034 PL belonging to 12 families, 22 genera, 24 species, 5 morphotypes and a species complex were identified. Abralia redfieldi, Onychoteuthis banksii and Ornithoteuthis antillarum were the most abundant taxa. The taxonomic identification from these three species was corroborated with DNA barcoding (99.8–100% of similarity). Paralarvae of Octopus insularis were reported for the first time in the wild. Most PL occupied the Caribbean Surface Water mass in the 0–25 m depth stratum. Largest paralarval abundances were related to local oceanographic features favouring retention such as the Honduras Gyre and Cozumel eddy. No day-night differences were found in PL abundance, although Abralia redfieldi showed evidence of diel vertical migration. Distribution of PL in epipelagic waters of the MBRS was probably related to ontogenetic migration, hydrographic features of meso and subscale, and to the circulation regimes dominated by the Yucatan Current. The MBRS represents an important dispersion area for PL, potentially connecting a species-rich Caribbean community with the Gulf of Mexico and Florida waters.

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.