The mojarras (Eucinostomus) are a widespread group of coastal fishes of controversial taxonomy because of similarities in their external morphology. In the present study, we assessed the genetic diversity of species and populations of Eucinostomus using DNA barcodes using a systematic and phylogeographic context. In total, 416 COI sequences of all valid Eucinostomus representatives were analysed based on public databases and collected specimens from the north-eastern coast of Brazil (Western South Atlantic). Several cases of misidentification were detected in the barcode dataset (E. argenteus, E. harengulus, E. gula, E. dowii and E. jonesii) that could account for the taxonomic issues in this genus. In contrast, we identified four molecular operational taxonomic units (MOTUs), with divergence above 2% in the Western Atlantic, that correspond to cryptic forms within E. argenteus, E. harengulus, E. gula and E. melanopterus. These data suggest that Plio-Pleistocene events (rise of the Panama isthmus, Amazonas outflow and sea-level fluctuations) played a major role in the diversification of mojarras. While subtle morphological differences have been used as proxies to discriminate Eucinostomus species, the genetic data proved to be efficient in differentiating them and revealing potentially undescribed taxa. Therefore, we recommend that further taxonomic studies in mojarras should incorporate DNA-based evidence.

Iranian coastal fishers targeting narrow-barred Spanish mackerel (Scomberomorus commerson) recently replaced their historical multifilament gillnets with those made from monofilament, evoking management concerns over potential increases in catch-per-unit-of-effort. During 20 fishing days, we compared catches from replicate surface-set gillnets that were identical in terms of mesh size (140 mm stretched opening), length (180 m), depth (30 m), hanging ratio (0.56) and spatio-temporal deployment, but had different materials: multifilament (1.8-mm diameter twisted twine) vs monofilament (0.8-mm diameter twine). Compared with the multifilament gillnet, there was a trend of greater catches (up to 1.3×) of S. commerson and another retained species, mackerel tuna (Euthnus affinis), along with one discarded species, giant catfish (Netuma thalassina) by the monofilament gillnet. However, statistical significance was restricted to E. affinis catches and a bias towards smaller S. commerson. These differences were attributed to species-specific catching mechanisms within gillnet material, with larger S. commerson retained by their teeth in the multifilament and all E. affinis more securely retained by their deeper bodies in the monofilament. Gillnet materials require regulation to preclude excessive effort on fully exploited stocks of species such as S. commerson.

The present study investigated the effects of a fish weir, a fixed trap used by artisanal fisheries, on the intertidal macrobenthic infauna of a macrotidal sandy beach on the Amazon coast. Biological and sediment samples were collected from within the weir and at five points of increasing distance (10 cm, 50 cm, 1 m, 2 m, 5 m and 50 m) from the external portion of the trap. The sediments from the weir and at 10 cm were dominated by mud, with a gradual decline in fine grains, water content and organic matter with increasing distance from the weir to 50 m (control). Taxon abundance and richness were significantly higher in the weir and at 10 cm than at the other sampling points. There was a trend of decreasing density and richness of the infauna from the weir to 1 m (which was a point of transition between the muddy and sandy sediments), after which the biological descriptors tended to increase once again. A shift was also observed in the dominant trophic groups, with a decrease in the abundance of the deposit feeders with increasing distance from the weir. By contrast, predators were more abundant at the points further from the weir. Our results indicate that fish weirs alter the associated sedimentary habitats, due to the increased protection from the action of waves and currents, with a micro-scale (from a few centimetres to 1–2 m) influence on the local macrofauna.

A new species of ampithoid amphipod, Sunamphitoe gigantea sp. nov., is described from Katsurakoi, Hokkaido, Japan. The new species most closely resembles S. eoa, but can be distinguished from it by the shorter flagellum of antenna 1, the maxilla 1 inner plate that bears two slender setae, the short dactylus of male gnathopod 2, and the presence of a group of long setae on anterior margins of pereopods 3 and 4 bases. Nucleotide sequences of mitochondrial cytochrome c oxidase subunit I obtained from the type specimens also differentiated this new species from the congeners. Ontogenetic morphological changes of the male gnathopod 2 are briefly discussed.

Ocean warming and acidification are expected to influence the biology of the ecologically and economically important red king crab, Paralithodes camtschaticus. We investigated transcriptome responses of adult, larval and juvenile red king crab to assess sensitivity to reduced pH and elevated temperature. In adults, gill tissue (but not heart or cuticle) responded to reduced pH by differentially regulating many genes involved in metabolic, membrane and cuticular processes, but not ionic or acid/base regulation. In larval crabs, we found little evidence for a strong transcriptomic response to pH, but did observe large differences in the transcriptomes of newly hatched and one-week old larvae. In juvenile crabs, we found that there was a strong transcriptomic response to temperature across all pH conditions, but that only extreme low pH caused transcriptomic shifts. Most of the genes in juveniles that were differentially expressed were for cuticular and calcification processes. While inferences regarding the specific biological responses associated with changes in gene expression are likely to change as resources for red king crab genomics enabled studies continue to improve (i.e. better assemblies and annotation), our inferences about general sensitivities to temperature and pH across the life stages of red king crab are robust and unlikely to shift. Overall, our data suggest that red king crab are more sensitive to warming than acidification, and that responses to acidification at the transcriptomic level occur at different levels of pH across life stages, with juveniles being less pH sensitive than adults.