The ocean quahog, Arctica islandica, is a commercially important bivalve in the eastern USA but very little is known about the recruitment frequency and rebuilding capacity of this species. As the longest-living bivalve on Earth, A. islandica can achieve lifespans in excess of 200 y; however, age determinations are difficult to estimate and age variability at size is extreme. Objectives for this study included the creation of an extremely large age-composition dataset to constrain age at length variability, development of reliable age-length keys (ALK), and descriptions of sex-based population dynamics for the quasi-virgin A. islandica population at Georges Bank (GB) within the greater US Mid-Atlantic stock. Sexually dimorphic characteristics are clearly present, as females are larger than males within age classes and males tend to dominate the oldest age classes. A male represented the maximum age of 261 years and is older than the maximum age previously documented for this region. Sex-specific ALKs were robust and reliable but not interchangeable. This population had higher estimated natural mortality rates than presumed for other regions in the Mid-Atlantic, and females have the highest mortality rate. However, recruitment expansion was also occurring which would affect the age-frequency data used to derive mortality estimates and result in higher mortality. Age frequencies at GB suggest effective recruitment to the population each year since 1867 CE. Reduced recruitment periods are documented and likely attributed to fluctuating environmental conditions. Sex-based demographics are clearly divergent in regard to growth rate, maximum size, longevity and mortality rates.

This study analysed and compared the shell shape, morphometrics and relative growth of four sympatric limpet species (Patella depressa, Patella ulyssiponensis, Patella vulgata and Siphonaria pectinata) collected at Praia da Luz in Lagos (Algarve coast – southern Portugal). Morphometric relationships were established through regression analysis between linear (shell length, width and height), ponderal (total weight), area (shell base and surface areas) and volume variables (shell internal and total volumes). Relative growth (isometry vs allometry) was analysed to assess variation in the growth rate of morphometric variables throughout the species ontogeny. In addition, morphometric indices (ellipticity, conicity, density, surface area and volumetry) were calculated to further characterize shell shape. Overall, 1482 individuals with broad size and weight ranges were analysed (P. depressa = 354; P. ulyssiponensis = 306; P. vulgata = 408; S. pectinata = 414). All regressions were highly significant (P < 0.001) and the morphometric variables were strongly correlated (r = 0.761 to 0.994). Among 28 morphometric relationships, there were 14 isometries, 13 positive allometries and only one negative allometry. The morphometric indices revealed clear morphological differences between species and were mostly size-dependent, reflecting gradual changes in shell shape during growth. The main results are compared with a compilation of analogous data reported for these limpet species throughout their distributional range. Overall, the general trends in relative growth are discussed in terms of the species life habits, main traits and functional morphology.

Lichens are a well-known symbiosis between a host mycobiont and eukaryote algal or cyanobacterial photobiont partner(s). Recent studies have indicated that terrestrial lichens can also contain other cryptic photobionts that increase the lichens’ ecological fitness in response to varying environmental conditions. Marine lichens live in distinct ecosystems compared with their terrestrial counterparts because of regular submersion in seawater and are much less studied. We performed bacteria 16S and eukaryote 18S rRNA gene metabarcoding surveys to assess total photobiont diversity within the marine lichen Lichina pygmaea (Lightf.) C. Agardh, which is widespread throughout the intertidal zone of Atlantic coastlines. We found that in addition to the established cyanobacterial photobiont Rivularia, L. pygmaea is also apparently host to a range of other marine and freshwater cyanobacteria, as well as marine eukaryote algae in the family Ulvophyceae (Chlorophyta). We propose that symbiosis with multiple freshwater and marine cyanobacteria and eukaryote photobionts may contribute to the ability of L. pygmaea to survive the harsh fluctuating environmental conditions of the intertidal zone.

The dynamics of phytoplankton biomass in the vertically mixed south-eastern part of the Bisan Strait, in the Seto Inland Sea of Japan, may be considered to be strongly dependent not only on nutrients but also on light status. This was investigated by examining variations in chlorophyll-a (Chl-a), nutrients, and Secchi-disc depth through high-frequency sampling (a mean of once every 1.7 days) at the same station from April to October 2019. Precipitation during the Japanese rainy season (East Asian monsoon rains) was associated with a decrease in salinity from 32 to 31 in late July. The highest concentration of dissolved inorganic nitrogen (DIN), the most deficient nutrient, also was recorded in late July in association with seasonal precipitation. However, the measured Chl-a peak (max. 4 μg l−1) in early August was not as high as expected, possibly due to low water clarity. A relatively small but substantial peak of DIN (max. 4 μM) was recorded in mid-August, which coincided with the passing of a typhoon. The small peak of DIN coupled with higher water clarity thereafter was followed by a phytoplankton bloom from mid-August to early September, at which the highest Chl-a (7 μg l−1) occurred. It is suggested that increased light penetration enhanced the efficiency of nutrient assimilation and thereby triggered the late-summer phytoplankton bloom. In contrast to the adjacent stratified areas, light rather than nutrient status appears to be the key determinant for the onset of phytoplankton blooms in the Bisan Strait.

Seven oceanographic expeditions were conducted between the years 2013 and 2018 to determine the horizontal and vertical distribution schemes in the epipelagic and mesopelagic copepod community structure of the Caribbean Oceanic ecoregion (CAO) and the oceanographic variables that regulate it. Four indicator species are suggested for the North Equatorial Current and the Caribbean Surface Water (CSW) mass (Clausocalanus furcatus, Oncaea venusta, Temora stylifera and T. turbinate) and two indicator species for deep-water masses such as the Western North Atlantic Central Water (NACW) and the Antarctic Intermediate Water (AAIW) (Mormonilla phasma and Conaea rapax). The copepod assemblage responds to local oceanographic patterns that are regulated (24%) by the variability of dissolved oxygen and temperature in the water column. The horizontal structure of the copepod assemblage in offshore waters presented a spatial sectorization. Three zones were differentiated: (1) oceanic Colombian zone; (2) influence of the Magdalena River zone; and (3) offshore north-east zone. Water mass mixing processes and migration mechanisms favour the homogeneity of the vertical assemblage of copepods in the CAO ecoregion. This study provides relevant information on the structure and density of copepod species, providing key information to describe the ecological processes and the different responses to the oceanographic factors that modulate them.

Bioluminescence is widespread in the marine environment. The bioluminescence of some species of the fireworm Odontosyllis (Annelida: Syllidae: Eusyllinae) has been well studied, although the presence or absence of bioluminescence in most species of this genus is yet to be revealed. The bioluminescent worms were observed after sunset around the new moon day in July and October 2020 and in July to October 2021 in Nagasaki Prefecture, Japan. Molecular phylogenetic analysis based on two mitochondrial and one nuclear gene sequence showed that the worms were closely related to Odontosyllis australiensis, but the partial 16S rRNA gene sequences differed by 2% between those of the Japanese and Australian material. Because only epitokes, i.e. morphologically modified sexually mature worms, were collected, further studies on morphological characters of atokes would be required in the future. We therefore tentatively refer to them as Odontosyllis cf. australiensis. Molecular phylogenetic analysis also showed that known bioluminescent Odontosyllis species belong to various lineages.

We record for the first time a nominal species of the genus Microscleroderma in the Western Atlantic, and the first record of the genus Amphibleptula in Mexico. Two new species of ‘lithistid’ Tetractinellida are described: Microscleroderma mexica sp. nov. from crevices of two reefs in Veracruz, Mexico, and Amphibleptula aaktun sp. nov. from the anchialine cave El Aerolito, Cozumel Island, Mexico. Microscleroderma mexica sp. nov. is characterized by its tubular and cup-shaped to wavy laminar habitus, hirsute surface and two size categories of oxea diactines. Amphibleptula aaktun sp. nov. is characterized by its ficiform or lobular habitus with an exhalant area at the flat top of the body, divided into numerous vertical septa-like structures; its desmas have thinner epirhabds, and thinner oxea than those of Amphibleptula madrepora. This is the second species of Amphibleptula that has been described; hence, we propose the redefinition of the genus. Both species described have a shallow distribution (≤21 m depth); they are differentiated from each other by the disjunction between their habitats as well as by their morphology.

The aim of this work was to describe and compare the main fatty acids and biodiesel indices of some green and brown macroalgae (seaweeds) collected from the Persian Gulf, as an alternative raw material for renewable biodiesel production. The macroalgae showed low lipid content (< 10% DW) but marine macroalgae with total lipid content > 5% DW are a good source for biodiesel production. The total lipid content and saturated fatty acids (SFAs) of green algae were higher than that of brown algae, while higher accumulation of unsaturated fatty acids (USFAs) was observed in brown seaweeds. Further, the main fatty acid in all studied seaweeds was palmitic acid (C16:0), which was followed by oleic acid (C18:1). The results of this work showed that three of the green algae, especially C. sertularioides, could be a potential source of fatty acids for biodiesel production owing to their high total lipid content, high cold flow indices (long chain saturated factor, cold filter plugging point and cloud point) and a fatty acid profile rich in SFAs with a high amount of C18:1, which is suitable for oil-based bio products. In contrast, the brown seaweeds Sargassum boveanum and Sirophysalis trinodis lipid content had a high proportion of polyunsaturated fatty acids (PUFAs), which makes them suitable for replacing fish oil.

Mantis shrimps are commercially important crustaceans in many areas of the world. In contrast to the relatively common studies of adults, limited studies have been attempted of larvae because of a lack of identification keys. The objectives of this study were two-fold: (1) to link wild-caught larval specimens from the Seto Inland Sea to a certain species and (2) to present a detailed morphological description of the last larval stage. The resulting molecular phylogenetic tree based on 16S rRNA gene sequences strongly implies that our larval specimens were linked to Levisquilla inermis, which was barcoded from a newly collected adult specimen with a morphological identification. K2P genetic divergence was found to be 0% among the larval and adult specimens. The congeneric species L. jurichi was the sister group of the L. inermis cluster, but the K2P distance between them was 3.4%, and it was considered a distinct species. Morphological observations provided five major distinguishing characteristics of the last-stage larva of L. inermis: (1) propodus of second maxilliped with three basal spines, (2) all five pleopods possessing an appendix interna with cincinnuli, (3) exopod of uropod longer than the endopod, (4) distal margin of the exopod of the uropod reaching the lateral tooth of telson, and (5) telson with nine intermediate denticles. Overall, our results reveal the importance of combining molecular and morphological analyses for solving stomatopod larval identification. This finding can be used to support and facilitate future research on the taxonomy and biodiversity of stomatopod larvae.

The introduction of Pacific oysters to the sedimentary south-eastern North Sea coast and their establishment on intertidal native blue mussel beds has caused the development of mixed reefs of mussels and oysters with extensive tidepools. Tidepools have been intensively studied at rocky shores where they show community structures, which usually differ from that of the surrounding emerging substrates. Tidepools at sedimentary coasts, however, have received less attention. We compared the community structure and species interactions inside and outside tidepools in oyster reefs by determining densities of snails, barnacles and amphipods. Snail densities were similar in and outside tidepools. Barnacle coverage on bivalve shells, however, was lower inside tidepools, which may be caused by higher predation pressure and increased snail grazing under permanently submerged conditions, as was revealed by field and laboratory experiments. Additionally, we studied the occurrence of copepod and trematode parasites in blue mussels inside and outside tidepools. Prevalence and intensity of parasitic copepods was higher in mussels inside tidepools. Trematode parasites, by contrast, showed a lower intensity in mussels inside tidepools. This can be explained by high amphipod densities found inside tidepools because trematode larvae represent a food source of amphipods. Our study suggests that the community structure of oyster reefs within tidepools is not a submerged equivalent to that of intertidal reefs. As their counterparts at rocky shores, they show their own species distribution patterns with particular species interactions and only provide refuge for specific species such as parasitic copepods.

Responses of corals to seawater acidification have been extensively studied. Sensitivity varies widely between species, highlighting the need to avoid extrapolation from one to another to get an accurate understanding of coral community responses. We tested the responses of seven coral species (Acropora cytherea, Acropora hyacinthus, Acropora pulchra, Leptastrea pruinosa, Montipora grisea, Pavona cactus, Pocillopora verrucosa) from the Mo'orea lagoon to a 48-day exposure to three pH scenarios (pH 7.95, 7.7 and 7.3). Tissue necrosis, mortality, growth rates, photophysiological performances and colour index were recorded. Few significant differences were noted between pH 7.95 and 7.7, but species-specific responses were observed at pH 7.3. While our data do not allow identification of the mechanisms behind this diversity in response between species inhabiting the same environment, it can exclude several hypotheses such as local adaptation, skeletal type, corallum morphology or calcification rate as sole factors determining coral sensitivity to pH.

Tributyltin (TBT) and triphenyltin (TPT) concentrations in water samples from Tanabe Bay were found to range from 4–28 ng l−1 and 3–7 ng l−1, respectively. In fishing ports, the concentrations of TBT in surface water were similar to those in bottom water. However, in aquafarming areas with poor flushing, the concentrations of TBT in bottom water were higher than those in surface water. This suggested that the TBT in water samples is re-eluted from sediment. No difference in the concentration of TPT was observed between the surface and bottom waters. The concentrations of TBT and TPT in sediment samples ranged from 3–23 μg kg−1 dry weight and 2–37 μg kg−1 dry weight. TBT and TPT concentrations ranged from 3.1–100 μg kg−1 and 3.1–7.2 μg kg−1 in oysters and gastropods, and from 1.1–4.9 μg kg−1 and ＜0.2–3.9 μg kg−1 in fish, respectively. Organotin concentrations in biota were lower than the tolerable average residue levels (TARLs). Alternative biocides – i.e. diuron, chlorothalonil, dichlofluanid, irgarol 1051 and Sea-Nine 211 – were also detected in surface water, and chlorothalonil and irgarol 1051 were detected in sediment. The concentrations of these compounds in surface water and sediment were lower than those reported previously. Dichlofluanid, chlorotharonil and irgarol 1051 were also found at low levels in oysters and gastropods, and at ranges of 325–339 μg kg−1, 268–291 μg kg−1 and 43–49 μg kg−1, respectively, in fish; the concentrations in fish were close to the TARL levels.

The Lakshadweep archipelago constitutes a major coral region of India but still lacks sufficient biodiversity data owing to its remoteness and a low number of faunal studies in the past. The present paper describes two new Pseudoceros species collected from Agatti Island, Lakshadweep, India. Pseudoceros bipurpurea sp. nov. and Pseudoceros galaxea sp. nov. are described based on external and internal characters, supported with histological studies and photographs. Pseudoceros bipurpurea sp. nov. is characterized by a cream background colour and an orange median line surrounded by dense patches of purple spots, which tend to disperse and broaden towards the posterior end. Pseudoceros galaxea sp. nov. displays a brown background colour with numerous white to cream dots covering almost the entire dorsal surface and a thin black margin. This study adds two new species to the polyclad fauna in Indian waters, raising the count to 68 species. An updated checklist of polyclads from Indian coast is also provided.

Invasive predators can have wide-ranging effects on invaded ecosystems and identifying the prey spectra and preferences of invaders are important steps in assessing their potential impacts on native biota. In this study, we investigated prey preferences of two invasive crab species (Hemigrapsus sanguineus and Hemigrapsus takanoi) that recently invaded Europe's shores and compared them with preferences of native shore crabs (Carcinus maenas) of similar size. In laboratory experiments, all three crab species preferred animal over algal prey. In general, sessile mussels (Mytilus edulis) were preferred over motile amphipods (Gammarus locusta) by all three crab species but amphipod predation was lower in the invasive compared with the native crabs. For the two invasive crab species, this pattern was the same in treatments where prey was offered separately (no-choice treatments) or simultaneously (choice treatments), while for the native crabs, mussel preference disappeared in choice treatments. The general preference of mussels by all three crab species suggests that local invasions of crabs most likely lead to increased competition among crabs. In addition, given that local densities of invasive crabs are often much higher than those of native crabs, predation pressure on native mussels can be expected to strongly increase at invaded sites. In contrast, local predation pressure on amphipods may be less affected by the crab invasions. Further field studies are needed to establish the magnitude of competition and predation pressure exerted by the invaders under natural conditions.

Haliactis arctica is a poorly known species of sea anemone of the family Halcampactinidae known only from the Arctic. So far, there have been no reports of it after the original description, based on a few specimens from Greenland, Spitsbergen, the Barents Sea, Novaya Zemlya and the Chukchi Sea. The rich collection of the Zoological Institute RAS, which includes more than 100 specimens, has allowed a detailed morpho-anatomical study of this sea anemone. Examination of the external and internal morphology of H. arctica indicates a noticeable variability of structural features, especially the retractor muscles, parietal muscles and acontia. Comparison of characters between H. arctica with the other representatives of Halcampactinidae shows significant differences in the organization of these anemones. Their morphological differences and also significant geographic remoteness suggest that they should be attributed to different families, however, at present it is impossible to conduct thorough molecular genetic studies that can confirm or refute this assumption.

Lacydonia Marion & Bobretsky, 1875 is the sole genus in the family Lacydoniidae Bergström, 1914. We herein describe the new species of Lacydonia shohoensis sp. nov. from 2042-m deep bottoms at Shoho Seamount of the Nishi-Shichito Ridge, the Northwest Pacific Ocean. It is most similar to L. anapaulae Rizzo et al., 2016 in having a depression on the median anterior region and lacking lateral lobes on the posterior margin of prostomium whereas it is distinguished by possessing pygidium dorsally pigmented with three reddish spots and non-pigmented pygidial lateral cirri equally elongated.

Studies concerning octocoral species from the Persian Gulf coral reefs are few. This study documents the diversity and abundance of octocoral communities from three islands in the north Persian Gulf, namely, Larak Island, Hengam Island and Qeshm Island. Belt transects were used to survey the octocoral communities at these islands. We used a rapid ecological assessment technique (REA) to assess the status and abundance of octocorals. Also, K Independent sample analysis was conducted on abundance and Shannon Diversity index data to determine if octocoral abundance and species diversity varied between islands. A total of 22 morphospecies, belonging to seven alcyonacean families, including Plexauridae, Ellisellidae, Alcyoniidae, Nephtheidae, Briareidae, Acanthogorgiidae and Subergorgiidae, were identified in this study. Statistical analysis indicated octocoral abundance and diversity at Larak Island reefs were higher than those around Hengam and Qeshm islands. The primary data presented in this study could serve as the baseline data for long-term biomonitoring programmes to estimate the status of octocorals in the Persian Gulf.

Habitat structure increases richness and abundance of species in many environments by providing easy access to resources and refuge from predators. In coral reefs, corals are habitat for many organisms and differences in their morphologies may act as variation in habitat structure for associated fauna. In the present study, we investigate whether there are differences in the richness and abundance of molluscs associated with three species of Mussismilia corals exhibiting different growth morphologies, in two different reef areas of the Bahia state. Mussismilia harttii has a meandroid pattern, M. hispida is a massive coral, M. braziliensis also has a massive growth pattern with crevices at the corallum base. Coral characteristics were measured in the laboratory. Significant differences were identified for richness among coral species – higher values were reported in colonies of M. harttii and no significant statistical differences were observed between M. braziliensis and M. hispida. Considering the density of associated molluscs, the same pattern was found. The results are in accordance with previous studies and indicate the importance of M. harttii as a key habitat to maintain a richer and more abundant associated fauna. The internal volume of interpolypal space is an important factor influencing the richness and density of associated species.

The caridean shrimp family Chlorotocellidae has so far not been reported from Korean waters. One of the four genera in the family is herein reported, based on the species Anachlorocurtis commensalis. Specimens were collected from antipatharian black corals by scuba diving at depths ranging from 20–60 m from three localities: Jejudo Island (33°13′N) between the South Sea of Korea and the north-eastern East China Sea, Namhyeongjedo Islet (34°53′N) in the Korea Strait, and Dokdo Island (37°15′N) in the East Sea. The species had previously been reported in tropical to subtropical latitudes in the western Pacific, with known records from southern Taiwan (up to 21°55′N) to central Japan (down to 34°50′N). The species is thus recorded for the first time from a temperate region in the western Pacific Ocean, postulated to be influenced by a branch of the Kuroshio Warm Current.

Two new genera and six new species of benthic amphipods from the soft sediments of the Perdido Fold Belt region, western Gulf of Mexico, are described. Morphological comparisons of the new species with description of their congeners resulted in the determination of one new genus and one new species of the family Melitidae as Dentimelita lecroyae gen. nov., sp. nov., one new genus and four new species of the family Pardaliscidae as Pardaliscella perdido sp. nov., Paraeperopeus longirostris gen. nov., sp. nov., Pardaliscoides ecosur sp. nov. and Tosilus cigomensis sp. nov., and one new species of the family Unciolidae as Neohela winfieldi sp. nov. The occurrence of the newly described amphipods in the Perdido Fold Belt region represented new geographic range extensions for the genera, including new records of Neohela in the Gulf of Mexico, Pardaliscella and Pardaliscoides in the western Atlantic and Tosilus in the Atlantic.