Abstract. The western tropical Atlantic off Northeast Brazil is a dynamically complex region where major current systems contribute to interhemispheric exchanges, yet it remains one of the least observed ocean areas in terms of integrated, depth-resolved, and ecosystem-wide measurements. The two ABRACOS (Acoustics along the BRAzilian COaSt) surveys, conducted during austral spring 2015 (ABRACOS 1) and austral autumn 2017 (ABRACOS 2) aboard the R/V ANTEA, were designed to address this gap through coordinated multidisciplinary observations spanning the continental shelf, slope, seamounts, and open ocean along the Fernando de Noronha Ridge. Although each survey represents a synoptic seasonal snapshot, hydrographic and current observations from both campaigns have been shown to be representative of canonical spring and autumn conditions in the region. The dataset combines continuous underway measurements — thermosalinograph, ship-mounted ADCP, multifrequency active acoustics (38, 70, 120, and 200 kHz), and meteorological data — with station-based physical, biogeochemical, and biological sampling at 117 oceanographic stations. Station-based observations include 96 CTD-O₂ profiles, 881 discrete rosette bottle samples (salinity, dissolved oxygen, nutrients, pigments, cytometry, and phytoplankton abundance), 266 plankton net deployments, and 116 trawl operations targeting demersal and deep-pelagic communities from 10 to 1,100 m depth. Biological sampling yielded 172,241 taxonomically identified specimens representing 1,532 taxa across planktonic, nektonic, and demersal compartments. The dataset is further complemented by 3,466 stable isotope measurements (δ¹³C and δ¹⁵N) across particulate organic matter, zooplankton, and demersal and deep-pelagic organisms, as well as mercury concentrations and microplastic occurrence data for 194 and 381 individuals, respectively, collected during ABRACOS 2. All datasets are quality-controlled, harmonised across surveys using consistent station identifiers and taxonomic referencing against WoRMS and Eschmeyer's Catalog, and publicly archived in the SEANOE repository under dedicated DOIs. Having already supported more than 80 peer-reviewed publications across nine thematic domains — from physical oceanography and taxonomy to trophic ecology, anthropogenic contamination, and ecosystem connectivity — the ABRACOS dataset constitutes a unique multi-trophic, multi-compartment, and multi-contaminant baseline for the western tropical Atlantic, designed to support comparative analyses, ecosystem modelling, and synthesis efforts at regional to global scales. The datasets described in this paper are publicly available through SEANOE (https://www.seanoe.org).

Context Swordfish are among the most abundant top predators in the Indian Ocean, and play a key role in pelagic food webs. However, their feeding habits and ocean-wide trophic niche remain poorly known. Investigating swordfish foraging behaviour, diet variability and trophic position can provide important information on predator–prey dynamics and improve our understanding of open-ocean ecosystems functioning. Aims This study aims to evaluate the ecological role of swordfish in pelagic food webs across major biogeochemical provinces of the Indian Ocean and adjacent waters of the Atlantic. Methods We investigated the trophic ecology of swordfish using stomach content analysis and stable isotopic value (δ13C and δ15N) measurements from white muscle tissue. On the basis of 872 non-empty stomachs and 759 muscle samples collected between 1998 and 2011 across five biogeochemical provinces, we described swordfish prey composition, prey size structure and size-related prey biomass. We further analysed feeding patterns and swordfish’s relative trophic position within the pelagic ecosystem. Key results Epipelagic and vertically-migrating mesopelagic fishes, together with cephalopods, constituted the principal prey groups by number and reconstituted weight, alternating in dominance among provinces. Ommastrephid squids formed the primary component of the cephalopod prey group, a pattern consistently reported across ocean basins. Stomach content analysis showed an ontogenetic dietary shift, with dominance transitioning from fish to cephalopod prey. Although micronektonic prey dominated numerically, more than 70% of the total consumed prey biomass originated from large nektonic species, highlighting their crucial importance for swordfish populations. Muscle δ15N values increased with body size, indicating a rise in trophic position during growth, which was likely to be driven by the consumption of larger fish prey and an increasing contribution of cephalopods to the diet. Conclusions Swordfish exhibit a flexible and opportunistic feeding strategy, with their diet being largely composed of a limited number (5–7) of dominant prey species that vary across provinces and seasons. Muscle δ13C and δ15N values indicated a distinct isotopic niche within each Indian Ocean province, suggesting mid-term (months) residential behaviour at the provincial scale. Implications Residential behaviour may increase swordfish vulnerability to local depletion under excessive fishing pressure, potentially leading to mesopredator-release effects and broader trophic cascades. Continuous long-term monitoring of the Indian Ocean pelagic ecosystem is therefore essential to support sound management and sustainable exploitation of pelagic resources. This should include larger-expanded stomach-content sampling, improved δ13C and δ15N baseline and mid-trophic-level values and modelling of their pathways. In addition, estimates of tissue turnover rates, currently unavailable for swordfish, are needed to improve the evaluation of migratory and residential behaviour and refine interpretation of stable isotope data.

The Con Dao archipelago hosts the oldest MPA in Vietnam and is recognized as a regional marine biodiversity hotspot. Here, we applied environmental DNA (eDNA) metabarcoding to assess coastal fish diversity across four major habitat types: coral reefs, seagrass beds, mangroves, and a harbour in the Con Dao archipelago. Using MiFish-U 12S primers at eight stations, we detected 282 operational taxonomic units, corresponding to 144 fish taxa. Fish assemblages exhibited strong habitat structuring: community composition differed markedly among habitats, with minimal overlap. Only three species were shared across all habitats. Multivariate analyses confirmed that habitat type, rather than spatial distance among sites, was the primary driver of community differentiation. Mangrove and seagrass supported distinct assemblages that were underrepresented in existing species checklists and MPA management frameworks. Notably, eDNA detected cryptic and non-commercial species overlooked by conventional survey methods. These results substantially expand the known fish diversity of the Con Dao Archipelago and highlight the need to incorporate habitat heterogeneity, particularly non-reef ecosystems, into MPA design and monitoring. Although eDNA metabarcoding is subject to amplification biases and limited taxonomic resolution in reference databases, it offers a powerful complement to traditional surveys for characterizing under-sampled habitats.

The environmental DNA (eDNA) technique characterizes spatio-temporal fish diversity patterns along estuarine habitats, such as hard-to-reach mangroves, yet it has rarely been applied in West Africa. In this study conducted over two seasons (dry and rainy) in coastal Guinea Bissau, fish eDNA was extracted from water samples collected in three habitats with distinct human uses. These habitats included site-specific mangroves, rice fields, and transition zones sampled in three sites: Elalab in Cacheu, Malafo in Oio, and Cafine in Tombali regions. As a reference, DNA barcoding of 181 fishes resulted in 243 DNA sequences for two mitochondrial markers (139 for COI and 104 for 12S), corresponding to 76 species (69 for COI and 56 for 12S), after morpho-genetic confirmation. The metabarcoding analysis detected 49 environmental DNA-Operational Taxonomic Units (eOTUs), attributed to 15 fish orders, 29 families, 38 genera, and 32 species. Fish abundance varied between sites and seasons but not between habitats. The southern Cafine site had a significantly lower abundance during the dry season, whereas the northern Elalab site hosted relatively fewer species during the rainy season. The transition from rice fields to mangrove habitat showed a positive trend in Shannon diversity with no fish being present in the rice fields during the dry season except for Malafo. Remarkably, Coptodon cf. guineensis, Sarotherodon melanotheron and Pseudotolithus elongatus dominated the fish assemblages. This pioneering eDNA study efficiently surveyed seasonal fish diversity within Bissau-Guinean mangroves, demonstrating its potential as a novel fish monitoring tool toward effective conservation in West Africa. The coupling of these results with the human uses of mangroves should be a target in future biomonitoring initiatives in the country and the broader region.

The development of tuna fisheries in the Indian Ocean is closely linked to the use of Fish Aggregating Devices (FADs). While FADs increase fishing efficiency, their sustainability raises concerns. Information on FAD utilization, particularly in Indonesia, remains limited. This study investigates Indonesia's anchored FADs (aFADs) tuna fisheries through a semi-structured survey of 293 tuna fishers using FADs in eight major Indonesian fishing ports in the Indian Ocean. With the exception of one group of handline vessels that use lights to attract tuna and operate at night, all other groups (purse seiners, troll-line, and handline vessels) utilize aFADs in over 90 % of their tuna-targeted fishing operations. All aFADs were reported to be privately owned, either by vessel captains, vessel owners, fishing associations, or companies, with aFAD sharing primarily occurring within the same aFAD ownership group. On average, vessels or groups of vessels owned between 1 aFAD (hook and line vessels) to 8 aFADs (purse seiners). aFAD arrays reported by respondents showed an average of 4-5 aFADs within 10 nm of the aFADs they utilize. Long aFAD lifetimes (2-4 years on average) indicated the skilled knowledge of fishers in using and maintaining these devices. Interestingly, the number of aFADs visited by fishing vessels was not correlated with the trip duration and remained relatively low (< 16 aFADs visited for all vessels). This suggests that vessels tend to exploit the same aFAD array throughout their trip, even when it lasts several months. Landing data supported these findings and revealed seasonal patterns in aFAD use, including partial shifts in target species for hook and line vessels. The findings of this study are expected to provide quantitative insights and contribute to the sustainable management of tuna FAD fisheries in Indonesia and the Indian Ocean.

The oceanic zone of Northeast Brazil in the southwestern tropical Atlantic Ocean is characterised by the presence of a variety of current systems. Thus, it has the potential to host a large diversity of phytoplankton species. In this context, we propose a comprehensive checklist of documented marine phytoplankton species in this region. To this end, we have compiled all the published material and supplemented it with original data from two comprehensive surveys, the ABRA & Ccedil;OS surveys, covering the shelf, slope, and offshore areas of Northeast Brazil. Even if few articles were atrieved from our review research, a total of 719 phytoplankton taxa are reported, including 98 new records plus 45 potential new records from the ABRACOS data. Most taxa are accompanied by a comprehensive library of illustrations. The two major phytoplankton groups, dinoflagellates and diatoms, contributed similarly to the total checklist richness, which is consistent with the global phytoplankton diversity. The contribution of nano- and microphytoplankton varies between areas. The shelf displays a greater diversity of pennate and small/medium-sized diatoms. This may be attributed to the inputs from estuarine rivers as well as the resuspension of benthic diatoms. Conversely, dinoflagellates are more prevalent offshore, demonstrating their adaptability to changing nutritional conditions, by employing numerous metabolic and growth strategies to survive. This checklist, which reveals an remarkable diversity of nano- and microphytoplankton in Northeast Brazil, provides a valuable reference for scientists and managers to monitor community evolution under global change.

Coastal lagoons are transitional ecosystems that host a unique diversity of species and support many ecosystem services. Owing to their position at the interface between land and sea, they are also subject to increasing human impacts, which alter their ecological functioning. Because coastal lagoons are naturally highly variable in their environmental conditions, disentangling the effects of anthropogenic disturbances like eutrophication from those of natural variability is a challenging, yet necessary issue to address. Here, we analyze a dataset composed of macrobenthic invertebrate abundances and environmental variables (hydro-morphology, water, sediment and macrophytes) gathered across 29 Mediterranean coastal lagoons located in France, to characterize the main drivers of community composition and structure. Using correlograms, linear models and variance partitioning, we found that lagoon hydro-morphology (connection to the sea and lagoon surface), which affects the level of environmental variability (salinity and temperature), as well as lagoon-scale benthic habitat diversity (using macrophyte morphotypes) seemed to regulate macrofauna distribution, while eutrophication and associated stressors like low dissolved oxygen, acted upon the existing communities, mainly by reducing species richness and diversity. Furthermore, M-AMBI, a multivariate index composed of species richness, Shannon diversity and AMBI (AZTI’s Marine Biotic Index) and currently used to evaluate the ecological state of French coastal lagoons, was more sensitive to eutrophication (18%) than to natural variability (9%), with nonetheless 49% of its variability explained jointly by both. To improve the robustness of benthic indicators like M-AMBI and increase the effectiveness of lagoon benthic habitat management, we call for a revision of the ecological groups at the base of the AMBI index and of the current lagoon typology which could be inspired by the lagoon-sea connection levels used in this study.

Vietnam's oldest marine protected area, the Con Dao Archipelago, hosts a high diversity of fishes, but they are not taken into account in its management. Knowledge of the spatial and temporal diversity of fishes is critical to identify the ecological functions of protected habitats, including as nurseries and feeding grounds. One way to assess diversity is using light traps that target young fish stages.Fish were collected monthly from June 2016 to May 2017 using light traps in three main habitats: seagrass beds, coral reefs and the harbour. Morphometry and DNA barcoding were used to identify the species caught.A total of 11,293 fish were collected, of which 1,248 were barcoded and assigned to 158 species belonging to 81 genera and 34 families, evidence that coral reefs and seagrass beds in Con Dao marine protected area (MPA) are home to a highly diverse and abundant community of fish species. Species richness and Shannon diversity indices did not differ significantly among sampling sites, but both species composition and diversity indices differed in the wet and dry seasons. The abundance of fish was related to sea water temperatures, which varied significantly depending on the month. During the dry season, fish diversity peaked in April, when the water temperature was highest.Conserving fish in Con Dao MPA is important not only for the characterization of the trophic network in coral reefs and seagrass beds but also for preservation of coral reef ecosystems and endangered species. Ensuring connectivity between coral reefs and seagrass beds in Con Dao MPA would facilitate fish conservation but, at present, the MPA only focuses on protecting fragmented habitats that are home to a number of endangered mammal species. Local authorities should establish a continuum of protected areas along coastal habitats and seasonal controls on fishing as part of sustainable management of MPAs.

Scientific fishing programmes were carried out between 1979 and 2013 in several West African estuarine, coastal and lagoon ecosystems. Batrachoides liberiensis represented only 5.2% of the occurrences, of which the majority were recorded in the Sine Saloum estuary. This originality makes it possible to use this population to characterise certain features of the biology and ecology of this little described species. B. liberiensis was recorded in waters with a salinity of 25-46, transparency of 1-3.5 m, at depths of 2-10 m. It was particularly abundant in areas at a distance of 15-35 km from the mouth. The water temperature did not appear to be a determining factor for this species. The sex ratio of the population, whose total length ranged from 10 to 371 mm, was in favour of females (87%) with an estimated size at first maturity of 189 mm (total length). The parameters of the length-weight relationship were estimated at K = 1.0009*10(-5) and b = 3.097. The diet of B. liberiensis consisted mainly of molluscs and crabs, present in respectively, 53.6% and 50.7% of the stomach contents analysed.

This is a complete database of metabarcodes for fish diversity in the mangroves of Guinea-Bissau.It includes the sequences generated specifically from 49 eOTUs. Each taxa has been sequenced with a 12S marker: a 106 bp fragment using EcoPrimers by (Kelly et al., 2014; Riaz et al., 2011).The Excel file consists of three tabs:- BOLD tab: the taxonomic assignment of the obtained eOTUs- Reads tab: the reads of each eOTU per sample- Replicate tab: the characterization of each water sample

Small island developing states (SIDS) are highly dependent on coastal marine resources. Artisanal fishers in SIDS currently face multiple stressors related to global environmental change. Considering Mauritius (South Western Indian Ocean) as a case study, this paper characterizes artisanal fishers in SIDS and assesses their perception of global change using the Local Ecological Knowledge (LEK) approach. A semi-structured survey method was used to interview 247 fishers from all around the country. Artisanal fishers used multiple fishing areas and gears, with half of the fishers using Fish Aggregating Devices (FADs). Six main groups of fishers were identified according to their fishing strategies, which reflected different target species in their reported catches. The majority of fishers reported lower fish abundances and fewer species now compared to 10 to 15 years ago. All groups of fishers observed environmental change over the same period. Such ecological knowledge highlights the exposure of fishers to stressors induced by environmental change. The characterization of the groups of fishers and their fishing strategies will be useful to better evaluate adaptation strategies and support management measures to face global environmental change.

The Mekong River is one of the largest rivers in the world and hosts the second greatest fish diversity in the world after the Amazon. However, despite the importance of this diversity and its associated biomass for human food security and the economy, different anthropogenic pressures threaten the sustainability of the Mekong River and fish diversity, including the intense damming of the main river. Both the increase in salt-water penetration into the Mekong Delta and the disrupted connectivity of the river may have serious impacts on the numerous freshwater and migratory species. To evaluate the potential of an eDNA approach for monitoring fish diversity, water was sampled at 15 sites along the salinity gradient in the Mekong Delta and along 1500 km of the main stream, from Vietnam to Thailand and Laos. A total of 287 OTUs were recovered, of which 158 were identified to the species level using both reference sequences available in GenBank and references obtained locally. Agglomerative hierarchical clustering and PCA identified up to three main species assemblages in our samples. If the transition from brackish to freshwater conditions represents the main barrier between two of these assemblages, more surprisingly, the two other assemblages were observed in the freshwater Mekong, with a spatial disjunction that did not match any biogeographic ecoregion or the Khone falls, the latter thought to be an important fish dispersion barrier. Between 60% and 95% of the freshwater species were potamodromous. This pioneer eDNA study in the Mekong River at this geographical and ecological scale clearly confirmed the potential of this approach for ecological and diversity monitoring. It also demonstrated the need to rapidly build an exhaustive Mekong fish barcode library to enable more accurate species' assignment. More eDNA surveys can now be expected to better describe the ecological niche of different species, which is crucial for any models aimed at predicting the impact of future damming of the Mekong.

This study provides length-weight relationships (LWR) that had not yet been reported for four fish species belonging to four different families: Chrysichthys johnelsi Daget, 1959, Cynoglossus senegalensis (Kaup, 1858), Citharichthys stampflii (Steindachner, 1894) and Pseudotolithus typus, Bleeker, 1863. Data were collected in the Fatala estuary, republic of Guinea, each month between January 1993 and March 1994, using alternately a purse seine net (length 250 m, height 20 m, 14 mm side mesh) and gillnets (side mesh sizes of 10, 12.5, 15, 15.5, 20, 22.5, 25, 30, 35 and 40 mm). For each fish specimen, fork or total length and total weight were measured with precision to 0.1 cm and 0.1 g respectively. A wider size range, compared to the size range available in FishBase, was obtained for Pseudotolithus typus. The present study also provides a new maximum total length for Citharichthys stampflii. The determination coefficient (r(2)) between length and total body weight ranged between 0.958 in Citharichthys stampflii and 0.989 in Cynoglossus senegalensis. The allometric coefficient b varied from 2.9552 (Chrysichthys johnelsi) to 3.7288 (Citharichthys stampflii). The value of LWRs for the four fish species should assist fisheries scientists and managers to complement their further studies of population parameters to improve management decisions in Fatala estuary and, more widely, in West Africa.

Tropical marine ecosystems are highly biodiverse and provide resources for small-scale fisheries and tourism. However, precise information on fish spatial distribution is lacking, which limits our ability to reconcile exploitation and conservation. We combined acoustics to video observations to provide a comprehensive description of fish distribution in a typical tropical environment, the Fernando de Noronha Archipelago (FNA) off Northeast Brazil. We identified and classified all acoustic echoes into ten fish assemblage and two triggerfish species. This opened up the possibility to relate the different spatial patterns to a series of environmental factors and the level of protection. We provide the first biomass estimation of the black triggerfish Melichthys niger, a key tropical player. By comparing the effects of euphotic and mesophotic reefs we show that more than the depth, the most important feature is the topography with the shelf-break as the most important hotspot. We also complete the portrait of the island mass effect revealing a clear spatial dissymmetry regarding fish distribution. Indeed, while primary productivity is higher downstream, fish concentrate upstream. The comprehensive fish distribution provided by our approach is directly usable to implement scientific-grounded Marine Spatial Planning.

Preferences elicitation can be a challenging exercise for citizens participating in assessment surveys. It is even more challenging when it comes to complex and unfamiliar ecosystems and the threatened ecosystem services they provide. Making people aware of the characteristics of the ecosystem services being valued is determinant for the assessment process. We investigated the impact of familiarity and academic information supply on people's preferences for twenty selected ecosystem services of French Mediterranean coastal lagoons. The results show that regardless of familiarity and information supply, there is a strong consensus about the highest importance of regulation and maintenance ecosystem services as well as environmental education and research opportunity ecosystem services. By contrast, nine of the cultural ecosystem services, together with two provisioning ecosystem services showed heterogeneous preferences among the different citizen groups. Using a combination of descriptive and inferential statistics these eleven ecosystem services split up into three clusters characterized as (i) contemplative leisure, (ii) heritage, and (iii) consumptive activities. Familiarity and academic information supply had a strong impact on the preferences for these three clusters of ecosystem services.

Length-weight relationships (W = aL(b)) were estimated for 5 fish species, the pearl stingray Fontitrygon margaritella (Compagno & Roberts, 1984), the West African spadefish Chaetodipterus lippei (Steindachner, 1895), the East Atlantic African spadefish Ephippus goreensis (Cuvier, 1831), the law croaker Pseudotolithus senegallus (Cuvier, 1830) and the Guinean sole Dagetichthys cadenati (Chabanaud, 1948). Fishes were collected during several scientific fishing surveys using purse seine (length 250 m, height 20 m, 14 mm mesh size) and beach seine (180 m length, 9 m height and 25 mm mesh net) conducted from April 1990 to October 2012 in the Sine Saloum estuary, Senegal. They were weighed to the nearest g and measured to the nearest mm (disc width for Fontitrygon margaritella and total length for the 4 other species). The values of parameter b in the LWR equations varied from 3.048 (Chaetodipterus lippei) to 3.274 (Dagetichthys cadenati) and the coefficient of determination (r(2)) varied between 0.969 (Fontitrygon margaritella) and 0.998 (Chaetodipterus lippei). In addition, new maximum lengths are proposed for Fontitrygon margaritella, Chaetodipterus lippei and Dagetichthys cadenati.

Knowledge about spatial and temporal variability in the distribution and abundance of predators is necessary to adapt measures to mitigate human-wildlife interactions. Acoustic telemetry and network analyses were used to investigate the spatial ecology of bull sharks, the species responsible for most shark bites in Reunion Island, one of the world's shark bite hotspots. The west coast of the island was not used uniformly by every individual, with size predicting the movements of sharks along the coast. Node-based metrics - closeness, node strength, and cumulated continuous residency times - derived from up to 181 monthly movement networks from 20 individuals, revealed that smaller sharks (<250 cm total length) primarily used the south-west coast while larger individuals spent most of their time in the northern region with regular visits to multiple areas along the coast. This study provides essential knowledge on bull shark behaviour and central areas used at different periods of the year, which correlates well with the dynamics of observed shark bites. Our approach provides a non-invasive alternative to help predicting and anticipating human-shark conflicts and avoid shark culling programmes detrimental to the conservation of large predators such as sharks.

The Maldives tuna fishery landings in 2018 were 148, 000 t and accounted for nearly a quarter of the global pole-and-line tuna catch. This fishery partially relies on a network of 55 anchored fish aggregating devices (AFADs) deployed around the archipelago. About one-third of the total pole-and-line tuna catch is harvested at AFADs. Although the AFAD fishery has existed for 35 years, knowledge on the behaviour of tuna in the AFAD array is still limited, precluding the development of science-based fishery management. In this study, local ecological knowledge (LEK) of fishers was used to improve our understanding of tuna behaviour, through personal interviews of 54 pole-and-line fishers from different parts of the archipelago. Interview results suggest that during the northeast monsoon tuna are more abundant on the eastern side of the Maldives, while during the southwest monsoon they are more abundant on the western side of the Maldives. Most fishers believed that tuna tend to stay at the AFADs for 3 to 6 days and remain within 2 miles from the AFADs when they are associated. Fishers believe that strong currents is the main factor for tuna departure from AFADs, though high sea surface temperatures and stormy conditions were also thought to contribute to departures. Moderate currents are believed to be a favourable condition to form aggregations at the AFADs while other factors such as suitable temperature, prey and attractants enhance this aggregation. Fishers also believe that there are multiple schools segregated according to size and species at AFADs and that catchability is higher at dawn and in the late afternoon when the tuna occur shallower in the water column. This study is an important step towards engaging the Maldivian tuna fishers into a science-based fishery management.