‘Tropicalization’, the phenomenon of species shifting their ranges, has become increasingly prevalent as a response to environmental modifications induced by global change. This study points to an accelerated tropicalization process of marine fish species in the Gulf of Cadiz, a bioinvasion hotspot adjacent to the Strait of Gibraltar. We report accelerated, unusual, and rare occurrences of 15 fish species expanding and potentially establishing their ranges in the Gulf of Cadiz, driven by ocean warming over the past decade. These new insights are the combined consequence of a range expansion of some species, likely facilitated by temperature increases, an intensification of maritime traffic (with a consequent rise in propagule pressure), and a possible increase in sampling efforts and citizen science.

Many marine invertebrates are intermediate hosts to parasites. As some of these parasites may influence host behaviour and act as cryptic agents involved in mass mortality, knowledge of their presence, dynamics, and life cycles is important. Our aim with the present study is to provide a survey of parasites in subtidal cockles in the Limfjorden (Denmark), to examine their influence on cockles, and to assess their possible role in the surfacing of cockles, as this phenomenon is considered a prelude to mortality. The trematode fauna of the studied subtidal population was poor in species, but about 19% of the examined cockles in late summer and autumn were infected by Monorchis parvus – a species not previously reported from cockles in Danish waters. Heavily infected cockles were filled with small, undulating, worm-like sporocysts, each filled with metacercariae. From August to November, the number of metacercariae in sporocysts increased, and at a certain point, the growing stock of sporocysts is supposed to reach a level where the cockle is unable to perform vital life functions. Our data show that infected individuals exhibit less annual shell growth than uninfected ones. There was no significant difference in the prevalence of M. parvus between unburied and buried cockles. Cockle-eating fish from the family Sparidae are known as final hosts to M. parvus, but these fish do not occur in Danish waters. Therefore, the record-high presence of M. parvus in cockles from the Limfjorden is surprising, and we consider alternative life cycle options for this trematode.

A considerable knowledge gap exists in relation to the presence and even existence of seagrass within Northern Ireland’s waters. Peer-reviewed publications on the historical ecology of seagrass are scarce and a collated timeline of references directly focusing on Northern Irish seagrasses does not exist. Recognising abiotic and biotic induced environmental change within key marine features such as seagrass is vital when attempting to measure the biodiversity and carbon sequestration services they provide. The research undertaken during this study identified three distinct periods within the archival records, which could be matched to the ecological history of seagrass in Northern Ireland. The first period (extensive and dense seagrass meadows from 1790 to 1880) was characterised by extensive seagrass meadows which were dense and healthy. The second period (degradation from 1880 to 1940) saw the beginnings of decline in seagrass from the 1790s, initially from anthropogenic influences and later from the seagrass wasting disease) and the final period (signs of recovery from 1940 to present day) showed small amounts of local regrowth of seagrass but at far reduced densities compared to the historical baseline described. These three defined periods all delivered varying degrees of anthropogenic stressors which determined the conservational health of seagrass in Northern Ireland. Seagrass habitats have become integral components in future-proofing the coastal marine environment against the effects of climate change and its associated impacts. Therefore, it is envisaged that the historical baseline that this manuscript provides will greatly benefit habitat managers in protecting, repairing, and restoring lost seagrass meadows.

A poorly understood and partially described planktonic copepod, Labidocera gangetica Sewell, 1934, is fully described herein from the Hooghly River, a century after its initial collection from the Rangoon (now Yangon) River estuary by Sewell (1912). The complete description of L. gangetica suggests possible uncertainty regarding the validity of the species Labidocera jaafari Othman, 1986, due to the morphological similarity in their overall body plan. In particular, the features of the leg 5 of both sexes are identical, suggesting that L. jaafari is probably a synonym of L. gangetica. Additionally, the taxonomic features of the mouthparts and swimming legs are illustrated for the first time.

In the present study, species of the genus Talorchestia (Dana, 1852), found in India are discussed. Previously, six species of the genus were recorded from India including Talorchestia affinis (Maccagno, 1936); Talorchestia buensis (Bhoi, Patro & Myers, 2023); Talorchestia gracilis (Dana, 1852); Talorchestia lakshadweepensis (Trivedi, Lowry & Myers, 2020b); Talorchestia martensii (Weber, 1892); and Talorchestia spinipalma (Dana, 1852). The taxonomy and distribution of these six species are discussed. Additionally, a new species, Talorchestia dandi sp. nov., is described on the basis of specimens collected from Gujarat State, India. This new species can be differentiated from its closely related species, Talorchestia morinoi (Othman & Azman, 2007), by the comparatively longer antenna 2, the telson with higher length to width ratio, the epimeron 3 with marginal setae, and the subequal carpus and propodus of pereopod 3.

The gastrointestinal microbiota of mammals plays a crucial role in host health, influencing nutrient absorption, lipid metabolism, and immune system regulation. This study examines the current state of research on gut microbiota in pinnipeds and cetaceans, significant indicators of ocean health. To this end, a bibliometric and an in-depth analysis was conducted using the Scopus database. A total of 83 articles published between 1994 and 2023 were found on this topic. In this period, publications showed a 6.9% annual increase, reflecting a growing interest in this field. The USA and China lead in research output, reflecting their high investment in research funding. Study topics were classified in characterization, characterization and comparison, bacterial isolation, and others. Regarding the origin of the samples, faecal samples predominated over gastrointestinal tissues and oral swabs. The most abundant bacterial phyla were Firmicutes, Proteobacteria, Fusobacteria, and Bacterioidetes. The research also highlights the presence of pathogenic bacteria underscoring the need to better understand the health implications for these species. The analysis also reveals that studies focus on a few species, such as Phoca vitulina (Harbor seal) and Tursiops truncatus (Bottlenose dolphin), reflecting a bias towards more accessible and studied species. To advance in this area, it is recommended to broaden the range of species and countries studied, improve sampling methodologies, and foster international collaborations. Research on marine mammal gut microbiota remains an expanding field, offering significant insights into the biology and ecology of these animals.

The two-spined deepwater cardinalfish, Epigonus bispinosus Okamoto & Gon 2018 is documented for the first time from the Arabian Sea (n= 2) (137.4–151.1 mm SL). The specimens were caught by a demersal shrimp trawl operated along the Kerala coast at a depth of 250–420 m. This species was previously recorded in South Africa and northern Madagascar regions. The present study also provides the first molecular information on E. bispinosus based on mitochondrial cytochrome oxidase subunit I and 16S ribosomal RNA genes. Detailed taxonomic identification, and molecular and phylogenetic analysis are described.

This study is the first to investigate the intra- and interspecific differences in otolith’s length (Lo), width (Wo), perimeter (Po), area (Ao), and mass asymmetry (OMA) in the pelagic Ethmalosa fimbriata, demersal Galeoides decadactylus, and benthic Cynoglossus monodi collected from the Lebe fishing site located along the Komo Estuary, central-western Gabon. The objectives were to (1) verify whether or not otolith morphometry differs in relation to living depth levels of the three species, (2) examine fluctuating asymmetry (FA) in the otolith morphometry, and (3) assess the relationship between OMA and total length (TL). A significant asymmetry was found in Lo, Wo, Po, and Ao between the left and right otoliths within and among males and females at the intraspecific level and only in Wo and Ao at the interspecific level due to FA. At the intraspecies level, a significant OMA was only observed within females of G. decadactylus and C. monodi and males and females of E. fimbriata and C. monodi. Moreover, a significant relationship between OMA and TL was detected only among males and females within the pelagic E. fimbriata and the demersal G. decadactylus, and no significant relationship was found at the interspecific level. As a result, significant differences in Wo and Ao and non-significant differences in OMA were recorded between the three species based on variations in living depth levels. These results highlight the importance of using otolith morphometry and OMA analyses to address the relationship between fish species and their living depth levels.

The aim of this study was to evaluate the antifungal spectrum of activity, synergy, and mode of action of carboxy-terminally amidated antimicrobial peptides (AMPs) derived from tachyplesin-I (T-I) from the horseshoe crab Tachypleus tridentatus and a lysine-rich analogue of magainin-2 (MSI-94) from the clawed frog Xenopus laevis. In vitro antimicrobial tests against 17 fungal strains demonstrated that the modified AMPs exhibited broad antifungal activity, particularly against filamentous fungi and yeasts relevant to aquaculture and agriculture. Additive antimicrobial activity was observed with the combination of T-I and MSI-94 against Candida albicans and Rhodotorula mucilaginosa, indicating an enhancement of their antiyeast properties. Furthermore, we found that both peptides target the fungal cell surface, increasing membrane permeability and leading to cell death. Overall, our findings highlight the biotechnological potential of aquatic AMPs in developing novel antifungal therapeutics applicable across various fields.

The spatial competition in the White Sea’s Halichondria panicea sponge was studied through a field experiment assessing growth in isogeneic and allogeneic sponge fragments of equal or different sizes. After 3 months and 1 year in seawater, growth was evaluated using ImageJ software on photographs. Intraspecific competition among allogeneic H. panicea individuals led to a decrease in relative growth, with the size of interacting individuals influencing competitive strategy. Optimal growth occurred when competitors were larger, minimal when sizes were equal, suggesting an alternative competitive strategy in the latter case. Competition between isogeneic individuals of H. panicea was weak or even absent; fusion of isogeneic fragments increased the growth intensity and substrate coverage by the sponge. Analysing the growth directions of sponges, we have found a phenomenon that may be interpreted as an attempt to ‘avoid’ physical contact with a competitor. In the neighbourhood with an allogeneic individual of larger or smaller size, the growth towards the competitor was lower than in other directions, regardless of whether the neighbouring individuals reached contact with each other or not. This may indicate that growth was redirected due to some distant communication mechanisms. The growth of allogeneic and isogeneic explants before contact occurred in a similar manner. Apparently, H. panicea cannot recognize the genetic nature of a competitor at a certain distance.

Jellyfish are widely distributed throughout the world’s oceans. However, understanding jellyfish species’ distributions remains poor. Here, we addressed this knowledge gap by applying an approach that uses citizen science observations to inform collection of samples which then undergo molecular analysis. Doing so allowed us to confirm the presence of the jellyfish Cyanea purpurea in the waters of Hong Kong SAR for the first time. Due to morphological overlap in Cyanea species, DNA analysis confirmed specimen identification. Samples were taken from 19 jellyfish individuals for subsequent DNA analysis. Ten samples (53%) were confirmed as C. purpurea, two samples (10%) were identified as Cyanea nozakii, and seven samples (37%) were not able to be identified. The combined application of citizen science and DNA analysis has proven effective in confirming the presence of C. purpurea in Hong Kong waters. This approach of using citizen science observations to inform the collection of samples for subsequent molecular analysis could be transferrable to other similar situations in which identification based solely on morphology is insufficient, potentially enhancing our ability to recognise species occurrence.

From December 2023 to November 2024, regular surveys were conducted to document finfish bycatch in the trawl fishery landing at Veraval Fishing Harbour, northeastern coast of the Arabian Sea. As an outcome of this exploration, three male specimens of Callionymus gardineri and five (four males and one female) specimens of C. omanensis were collected. Both species were recorded for the first time from the north-western Arabian Sea, coastal waters of India, accompanied by a new maximum length record for C. omanensis (Lmax = 122.1 mm standard length). Callionymus omanensis was originally described based on a single male specimen, whereas the description of female C. omanensis was interpreted. While the exact justification for their distribution in this new locality remains unknown, both dragonet species likely moved eastwards from their native habitats along the western Arabian Sea coast. This strongly suggests a significant research gap in our understanding of low-value deep-sea trawl bycatch, necessitating further exploration to improve biodiversity assessments. Herein, the detailed meristic counts and morphometric measurements are compared, and updated distributional information is collated.

In Iceland, sheltered rocky intertidal zones like Breiðafjörður bay are dominated by monospecific stands of Ascophyllum nodosum, providing key habitats for marine organisms. Increasing demand for A. nodosum has led to its commercial exploitation, yet impacts on fish assemblages remain poorly known. Using a novel multi-mesh netting approach, we characterised seasonal patterns in fish composition, abundance, size structure, age, and diet. Additionally, to assess the local effects of seaweed harvesting, commercial harvesting was conducted, with comparisons being made between treatment and control unharvested areas during different seasons. Nine fish species were identified, with Pollachius virens, Myoxocephalus scorpius, and Gadus morhua being the most common. Fish abundance peaked in summer, and declined the following spring, suggesting cohort turnover with juvenile gadoids relying on these habitats as nurseries. P. virens showed increased length through seasons, whereas no trends in length or abundance were observed for M. scorpius. Effects of seaweed harvesting were minimal, although fish diversity was slightly higher and G. morhua significantly larger in control plots. Stomach contents exhibited a greater diversity of prey types in harvested sites, suggesting potential impacts on trophic dynamics. These findings underscore the importance of A. nodosum-dominated habitats as nursery grounds for commercially valuable gadoids and highlight the need for a precautionary approach to seaweed harvesting to maintain ecosystem health.

Coral reefs have been rapidly deteriorating, worldwide, due to global warming, ocean acidification, bleaching, diseases, and various local anthropogenic stressors, such as coastal development, habitat destruction, overfishing and eutrophication, all of which have significantly impacted the metabolic functions of corals and other marine organisms. Global warming has been identified as the main culprit in the decline of coral reefs. In response, we assessed the metabolic responses of one of the most iconic Caribbean corals to elevated temperatures. Accordingly, the proteomic profile of Acropora palmata was investigated during the cool dry and hot wet seasons of 2014 and 2015 in Puerto Rico using a combination of two-dimensional gel electrophoresis (2D-GE) and mass spectrometry. The study revealed that the average number of differentially abundant proteoforms between seasons was 527 in the inner-shelf reef at Enrique and 1,115 in the mid-shelf reef at San Cristobal, both located on the insular shelf of southwestern Puerto Rico. Our results show significant changes in A. palmata’s proteome, inducing alterations in key metabolic, enzymatic, translational, and apoptotic processes, between the cool dry and hot wet seasons. Quantitative real-time reverse transcription PCR (qRT-PCR) was used to validate the variation in the expression of five candidate stress-related genes under different seasonal temperatures. The findings highlight key proteoforms whose abundance varied with temperature, offering insight into A. palmata’s metabolic capacity to acclimate and respond to seasonal temperature fluctuations.

The endosymbiotic association between the diatom Hemiaulus and the cyanobacterium Richelia was first observed in the Sea of Marmara in July 2021. The spatial distribution of the host diatom Hemiaulus spp. and the endosymbiont cyanobacterium Richelia intracellularis was investigated along with available physicochemical parameters. Three species of the Hemiaulus genus (H. hauckii, H. membranaceus, and H. sinensis) were morphologically identified in the study area. Hemiaulus hauckii and H. sinensis reached up to 128 × 103 cells L−1 and 38 × 103 cells L−1, respectively, while H. membranaceus was rarely observed. Each Hemiaulus cell contained one Richelia trichome, which had heterocysts at both ends. The surface water temperatures and salinity varied between 23.2°C and 28.5°C, 21.4 and 23.5, respectively. Dissolved oxygen levels ranged from 6.2 to 7.6 mg L−1, while chlorophyll-a concentrations were between 0.3 and 6.8 µg L−1. Nutrient concentrations varied between 0.05 and 0.18 μM for NO3 + NO2–N, 0.04–0.24 μM for NH4–N, 0.02–0.39 μM for PO4–P, and 0.18–1.42 μM for SiO2–Si. This study reveals that the Hemiaulus–Richelia symbiosis may promote the proliferation of diatom populations and may play an important role in nutrient dynamics in nitrogen-limiting environments and in the overall functioning of the marine ecosystem.

Five specimens of the rare alpheid shrimp Betaeus levifrons Vinogradov, 1950 were collected from the burrows of the mud-shrimp Upogebia major (De Haan, 1841) in Akkeshi and Usu Bays, along the Pacific coast of Hokkaido, Japan. As B. levifrons has been previously only reported from the Russian coast of the Sea of Japan, the Hokkaido specimens represent the first record of this species from the western Pacific coast as well as a new to the Japanese fauna. Ovigerous females of B. levifrons were recorded for the first time based on specimens. This study provides additional data on this species, including its distribution, colour variation, and DNA sequences of the mitochondrial 16S rRNA and cytochrome c oxidase subunit I barcoding regions. Lastly, we revised the available data on the symbiotic fauna of U. major.

Marine organisms account for more than half of the global biodiversity and have proven to be a rich source of pharmacologically active compounds. Turkey has an extensive coastline hosting a diverse marine ecosystem. This paper describes the phytochemical prospection based on chromatographic profiles of extracts, fractions, and sub-fractions from Turkish organisms. In addition, the samples were evaluated for their antioxidant, anticholinesterasic, and antibacterial activities. According to the chromatographic profiles, terpenes were identified in most samples, with the exception of Dictyonella incisa. Alkaloids were detected in Ascidiella aspersa, Eunicella cavolini, Halocynthia papillosa, Limaria hians, Microcosmus polymorphus, and D. incisa. The phenolic carboxylic acids were detected in all the samples, and the results for polyphenols were similar. The extract of P. clavata showed antioxidant activity in both models evaluated, whereas the remaining samples were positive only in the bioautographic assay. With regard to AChE inhibition, D. incisa fraction showed potent activity (%I ˃ 90%), while the sub- fractions were moderate (%I ˃ 45%). In the antibacterial assay, the same samples from D. incisa have shown activity against both Gram-negative and Gram-positive bacteria. On the other hand, the present study opens up avenues for future research on D. incisa by aligning alkaloids and neuroprotective effects, taking into account that inhibition of AChE is a therapeutic strategy in the treatment of Alzheimer’s disease.