Introduction The long-spined black sea urchin Diadema antillarum is a keystone herbivore on Caribbean reefs, yet population recovery following mass mortality events has been slow and spatially variable. Restocking programs increasingly rely on aquaculture, but rearing conditions may generate behavioral and morphological shifts that affect post-release survival.Objectives This study evaluated whether a short-term uncaged mid-water grow-out treatment could condition aquaculture-reared Diadema to express traits more similar to wild conspecifics.Methods Juveniles reared in an uncaged mid-water treatment were compared with individuals maintained in standard aquaculture nurseries and with wild individuals. We assessed retention, relative growth rate, diurnal sheltering behavior, and spine characteristics.Results The proportion of Diadema remaining in the uncaged mid-water treatment was low, with 19 of 64 Diadema present after 6 weeks. Remaining Diadema individuals were larger than aquaculture counterparts, although relative growth rates did not differ significantly among treatments. Mid-water conditioned individuals exhibited diurnal sheltering behavior and spine thickness comparable to wild Diadema, whereas aquaculture reared individuals sheltered less during the day and had thinner spines.Conclusion Exposure to natural environmental conditions for 6 weeks during grow-out partially restored wild-like behavioral and morphological traits in aquaculture reared Diadema, indicating that conditioning can improve survival chances of restocked individuals.

Maritime fuel spills resulting from bukering and transportation accidents pose an increasing risk to marine and coastal ecosystems. Post-spill, ammonia disperses via water currents, distributing its concentration spatially and extending ecotoxicological impacts beyond the release point. This study proposes a spatially explicit framework for delineating ecotoxicological hazard zones for ammonia spills, providing a transferable approach for environmental risk assessment across space and time. The framework integrates species sensitivity distributions with exposure dynamics, linking species sensitivity to ammonia and its transformation products with ecological responses and recovery. Hazard zone thresholds are derived from species sensitivity distributions. Total ammonia nitrogen (TAN) concentrations exceeding 140 mg/L (95% CI: 106–193 mg/L) defined critical zones, causing rapid, lethal effects across all taxa and worst-case ecosystem recovery. Concentrations between 27.6 and 143 mg/L TAN (95% CI: 24–194 mg/L) defined high hazard zones, with mixed lethal and sublethal effects at short- to intermediate-duration exposures. Elevated hazard zones corresponded to 0.4–4.3 mg/L TAN (95% CI: 0.12–7.8 mg/L), producing sublethal effects over intermediate to extended durations. Concentrations of approximately 0.23 mg/L TAN (95% CI: 0.05–0.7 mg/L) defined minimal hazard zones, affecting only the most sensitive taxa over long durations. Molluscs are highly vulnerable and should be incorporated into risk reduction measures in port areas. Together with dispersion modelling, the framework enables the estimation of hazard distances to support rapid response, environmental management planning and risk-based mitigation. The approach is transferable to other dispersive contaminants and emerging marine fuels, supporting broader environmental risk management.

Biogenic reefs, shaped by organisms like corals, tubeworms, and bivalves, have faced extensive degradation worldwide, resulting in a vast reduction in their extent. The remaining reefs are essential habitat for marine vertebrates, providing food, shelter, and nursery grounds. However, the role of natural shellfish reefs as essential fish habitats is poorly understood, particularly in temperate regions. We assessed the effect of reef presence on marine vertebrate diversity and composition and compared traits for habitat and feeding strategy at 2 shellfish reefs in the North Sea: a mixed shellfish reef and a horse mussel reef. We also assessed the complementarity of 2 non-invasive techniques: eDNA metabarcoding and baited camera analysis (baited remote underwater video systems [BRUVs]). Stations inside and outside reefs were compared. Vertebrate diversity was consistently higher within both reefs than in their surroundings, declining with increasing distance from the reefs up to 400-1500 m from the reef edge. Community composition varied, with several species, such as gobies, gunnels, clingfish, and sculpins, occurring more frequently within the reefs. Commercial species like cod, pollock, and mullet also occurred more often in reef areas, with reefs likely serving as juvenile habitats for species like ling. Functional diversity showed that reefs attracted mostly invertivores and pelagic species adapting their diet to food availability. eDNA identified more species overall, while BRUVs detected both adult and juvenile stages, highlighting the value of complementary methods in biodiversity assessments. These results emphasize the importance of temperate reefs as essential fish habitats and inform more effective conservation and fisheries management strategies.

Reef habitats, both natural and humanmade, play a vital role in marine ecosystems by providing structure, shelter and resources for a range of different species. New anthropogenic marine structures function as new substrate and can be seen as an artificial reef. Implementing nature-based solutions enhances the ecological value of the structure and this approach is increasingly adopted. Artificial reefs are widely studied, yet predicting their community composition compared to natural reefs remains challenging. This case-study assesses how comparable the community compositions, including number and type of non-indigenous species (NIS), on an artificial and natural oyster reef are after 13 years of succession. Additionally, we examine the impact of morphology- and genomics-based identification methods on alpha and beta diversity using eDNA metabarcoding of water samples and morphological identifications of hand-collected animals from tidal pools collected at three timepoints. Finally, we compared the species and biological traits detected by the two methods. Both reefs showed similar community composition and prevalence of NIS. The artificial reef did not appear to facilitate the spread of NIS more than the natural reef at this stage of development. In addition, eDNA outperformed hand-collection in the detection of highly mobile, sessile and filter feeding species, while hand-collection of animals better identified burrowing and tube-dwelling organisms. We conclude that the artificial reef closely resembled the natural one, demonstrating successful ecological integration. These findings can inform nature-based construction and emphasize the need for tailored long-term monitoring based on target taxa and associated traits.

To monitor the effect of nature restoration projects in North Sea ecosystems, accurate and intensive biodiversity assessments are vital. DNA-based techniques and especially environmental (e)DNA metabarcoding is becoming a powerful monitoring tool. However, current approaches rely on genetic target regions under 500 bp, offering limited taxonomic resolution. We developed a method for long-read eDNA metabarcoding, using Nanopore sequencing of a longer amplicon and present DECONA, a read processing pipeline to enable improved identification of marine vertebrate species. We designed a universal primer pair targeting a 2 kb region of fish mitochondrial DNA and compared it to the commonly used MiFish primer pair targeting a ~ 170 bp region. In silico testing showed that 2 kb fragments improved accurate identification of closely related species. Analysing eDNA from a North Sea aquarium showed that sequences from both primer pairs could be assigned to most species, and additional species level assignments could be made through the 2 kb primer pair. Interestingly, this difference was opposite in eDNA from the North Sea, where not the 2 kb but the MiFish primer pair detected more species. This study demonstrates the feasibility of using long-read metabarcoding for eDNA vertebrate biodiversity assessments. However, our findings suggests that longer fragments are less abundant in environmental settings, but not in aquarium settings, suggesting that longer fragments may provide a more recent snapshot of the community. Thus, long-read metabarcoding can expand the molecular toolbox for biodiversity assessments by improving species-level identification and may be especially useful when the temporal origin of the eDNA signal is better understood.

DNA-based methods and developments of sequencing technologies are integral to macrobenthos biodiversity studies, and their implementation as standardized monitoring methods is approaching. Evaluating the efficacy and reliability of these technological developments is crucial for macrobenthos biodiversity assessments. In this study, we compared three DNA-based techniques for assessing the diversity of bulk macrobenthos samples from the Belgian North Sea. Specifically, we compared amplicon sequencing using Illumina MiSeq and portable real-time sequencing of Oxford Nanopore versus shotgun sequencing using Illumina NovaSeq sequencing. The 313 bp mitochondrial cytochrome c oxidase subunit I (COI) metabarcoding fragment served as the target region for the metabarcoding analysis. Our results indicate that Oxford Nanopore and MiSeq metabarcoding had similar performances in terms of alpha and beta diversity, revealing highly similar location-specific community compositions. The NovaSeq metagenomics method also resulted in similar alpha diversity, but slightly different community compositions compared to the metabarcoding approach. Despite these differences, location-specific community compositions were maintained across all platforms. Notably, read counts from the NovaSeq metagenomic analysis showed the weakest correlation to size corrected morphological abundance and there were mismatches between morphological identification and all DNA based findings which are likely caused by a combination of factors such as primer efficiency and an incomplete reference database. Our findings underscore the critical importance of database completeness prior to implementing DNA-based techniques as standardized monitoring method, especially for metagenomics. Nevertheless, our findings emphasize that Oxford Nanopore metabarcoding proves to be a viable alternative to the conventional Illumina MiSeq metabarcoding platform for macrobenthos biodiversity monitoring.

Subsea power cables, required for offshore generated wind power transport, emit electromagnetic fields (EMFs) into the marine environment. EMFs also occur naturally, resulting from biotic (animals) and abiotic (geomagnetic field) sources. Skate and oviparous shark embryos in the egg can sense EMF from predators and respond by reducing their normal movement ('freezing response') to prevent detection and subsequent predation. When nursery areas overlap with power cables, embryos will be exposed to varying levels of anthropogenic EMFs and effects thereof on embryonic development is currently understudied. Here, we present behavioral responses of thornback ray (Raja clavata) embryos to varying field-related EMF levels (1.8-4.6 μT) generated by alternating current throughout embryogenesis (∼20 weeks). Chronically exposed individuals were overall more active, including 33 % more tail undulations and 150 % increased body movements, compared to non-exposed individuals. This increased activity suggests that eggs exposed to EMFs generated by subsea power cables might be at risk of increased predation. We found no indications of reduced health or survival after hatching, or changes in development time or biometry. Effects on subsequent life stages cannot be excluded, follow-up studies should observe hatchling development. We did not observe an increase in freezing response resulting from EMF change as described by other researchers who used different types and intensities of EMF cues. We recommend that different species, along with DC exposure, should be studied to gain a more complete insight into the potential effects of EMF exposure during embryogenesis of these EMF-sensitive species.

The aim of this paper is to identify an optimised strategy for the reintroduction of two anadromous sturgeon species to Europe: the critically endangered European sturgeon (Acipenser sturio) and the vulnerable Atlantic sturgeon (A. oxyrinchus). Restoration efforts began in the 1970s, followed by artificial rearing and release of A. sturio in rivers of the French Atlantic coast and North Sea since 1991, and artificial rearing and release of A. oxyrinchus in Baltic Sea rivers in 2006. This approach was based on the most recent geographical occurrences of both species but may no longer be a viable strategy. We deliver evidence that both species spawned in North Sea rivers into the twentieth century by analysing acipenserid remains and argue that additional factors need to be considered to determine which species has to be reintroduced at which locality. Factors include the increased international interest in sturgeon restoration, the scarcity of A. sturio that limits stocking possibilities and monitoring population developments, the risk of hybridisation and outbreeding of the genetically eroded A. sturio, the limited availability of suitable rivers due to habitat degradation, and the possible poleward (northward) shifts in suitable habitats due to climate change. This paper analyses the various factors and re-evaluates three alternative, theoretical strategies to determine their advantages and disadvantages: (1) prioritising the restoration of only the critically endangered A. sturio, (2) maintaining a strict north–south division of reintroductions for the two species, and (3) restoring a ‘mixed zone’ of sympatric occurrences in Northwest Europe, particularly in North Sea rivers. This re-evaluation emphasizes the need for scientific communities in Europe to closely collaborate in reintroducing sturgeon species.

BACKGROUND:European flat oysters (Ostrea edulis) are sequential hermaphrodites that alternate sex in response to environmental change. Epigenetics, including DNA methylation, are often involved in sex reversal through influencing gene transcription. Knowledge on the epigenetic mechanisms underlying sex reversal in hermaphrodite bivalves is limited to gonadal tissue and previous studies have only compared DNA methylomes of males and females. Therefore, the aim of this study is to assess whether sex-specific DNA methylation can be identified in somatic gill tissue of the flat oyster. RESULTS:By comparing whole-genome methylomes of 35 oysters of different sex phenotypes using nanopore sequencing, we demonstrate the presence of sex-specific DNA methylation patterns in somatic gill tissue. A total of 9,654 regions and 2,576 genes were differentially methylated between male, female, and hermaphrodite oysters. Functional analysis of differentially methylated genes indicated an association with energy homeostasis and metabolic processes, implying a remodeling of the energy balance. CONCLUSIONS:This study is the first to characterize DNA methylomes of hermaphrodite oysters, providing new insights into the epigenetic mechanisms underlying sex reversal in a sequential hermaphrodite invertebrate. Additionally, this study characterizes sex-specific DNA methylation in somatic gill tissue, paving the way for non-lethal sex identification using epigenetic biomarkers.

This study assessed the effects of TCDD, two PCB mixtures (Clophen A50 and Aroclor 1254), and field extracts from marine sediments and swimming crab tissues on early-life development in Caenorhabditis elegans. Gravid nematodes were exposed on agar, and isolated eggs and larvae were tested in solution. Larval development was evaluated after 72 hours. Reporter gene assays (DR-CALUX) were also used to quantify dioxin-equivalent toxicity (TEQ). Exposure to 10 pM Clophen A50 and TCDD on agar inhibited L3-L4 transition by 60 % and 50 %, respectively. Liquid exposure to 5 µM Aroclor 1254 or TCDD (10 nM and 10 µM) delayed development by 20-40 %. Field extracts contained TEQ values of 0.67-4.91 ng/kg (0.2-1.47 pM TCDD), reducing L3-L4 development by 40-60 %. Both bioassays effectively assessed the toxicity of persistent organic pollutants in environmental samples. Agar exposure mimics realistic uptake, while liquid assays offer faster, high-throughput screening.

The development of offshore wind farms (OWFs) in coastal seas presents both risks and opportunities for threatened elasmobranch populations, but their actual influence on elasmobranch presence and habitat use remains unclear. As more OWFs are planned, the lack of available space puts pressure on stakeholders to create multi-use areas as demands from fisheries, conservation and the energy sector become increasingly overlapping. Insight into interactions between these demands is needed to support policymakers in marine spatial planning and management decisions. One of the important questions is to what extent OWFs influence elasmobranch presence and habitat use. Here, we (i) ascertain elasmobranch occurrence in OWFs, (ii) determine whether elasmobranch presence varies between sampling locations, and (iii) investigate the influence of seasonality on elasmobranch presence. We collected 436 seawater samples within four OWFs and the presence of 5 different elasmobranch species (2 sharks, 3 skates) was confirmed. The overall detection probability of elasmobranchs in the four OWFs was 8.5 %. A quarterly sampling campaign over 2 years demonstrated the seasonality of Mustelus asterias on the subsea power cables, which corresponded with known migratory movements of this species. Our findings confirm that sharks and skates are present in OWFs. We advise caution when introducing multi-use activities that could counteract the benefits of bottom trawling fisheries exclusion. Investigating how these threatened species use OWFs would aid policymakers in determining the (multi-use) function of OWFs in terms of EU legislative acts including the Habitat Directive, MSFD, Biodiversity Strategy 2030 and the Nature Restoration Law.

Subsea power cables are expanding in number and capacity due to increasing demand to transport offshore generated energy. Energy transported through a cable creates an electromagnetic field (EMF). Elasmobranchs are dependent on their perception of the earth's magnetic field and biologically induced electric fields, for orientation, navigation, locating conspecifics and detecting prey. EMF levels from subsea power cables will add to natural signals potentially disrupting elasmobranch perception, but the effects are not fully understood. Reported behavioural responses include attraction, disturbance, and indifference, varying with exposure type, level and experimental set-up. In this study, the effects of EMF on swimming behaviour of 14 individual small-spotted catshark Scyliorhinus canicula were studied. All sharks were exposed to field-relevant EMF gradients cables in three trials: 15.0 μT AC, 19.6 μT DC, and a control treatment. Sharks showed no startle response to EMF onset, did not alter movement towards or away from the cable, and crossed it as frequently as in control trials. Hidden Markov Models showed that behavioural states were best explained by EMF treatment, trial order and sex. Sharks showed 25 % less time transiting during DC trials when compared to AC and control trials. These findings indicate reason for further refined studies to better determine behavioural effects from direct current subsea power cables with S. canicula, for example using tagging studies. In addition, exploring effects on other species will help obtain a broader understanding of the potential impacts of EMF on benthic elasmobranchs.

Tropical coastal ecosystems are increasingly threatened by rising seawater temperatures and terrestrial nutrient input, yet the combined impact of these stressors on food web complexity remains poorly understood. Using marine lakes in Raja Ampat, Indonesia, as natural analogs for varying environmental conditions, we investigated how temperature and terrestrial influence shape food web structure and carbon source utilization. We applied an approach at 2 scales, combining whole food web stable isotope analysis in 2 contrasting lakes-one with elevated temperature and high terrestrial input, the other with ocean-like conditions-with a broader survey of 16 additional lakes using the filter-feeding mussel Brachidontes as a proxy for baseline carbon sources. Biodiversity, food web complexity, and functional redundancy were reduced in the marine lake with higher temperatures and greater terrestrial input. Bulk stable carbon and nitrogen isotope values from Brachidontes from 16 different marine lakes revealed a shift in the main food source underlying the food web from marine to terrestrial organic matter, with a shift from particulate organic matter to the use of sponge-derived material (reworked/recycled organic material) in environments with high temperatures and high terrestrial inputs. The use of Brachidontes as an integrative indicator of basal carbon sources offers a valuable tool for monitoring and managing the ecological impacts of environmental change in tropical coastal systems. Extrapolating our findings to coastal marine systems, our results suggest a potential shift toward simplified, less resilient trophic structures in ecosystems with combined thermal and terrestrial stressors.

Abundant mineral resources in the deep sea are prospected for mining for the global metal market. Seafloor massive sulphide (SMS) deposits along the Mid-Atlantic Ridge are one of the potential sources for these metals. The extraction of SMS deposits will expose adjacent marine ecosystems to suspended particle plumes charged with elevated concentrations of heavy metals and other potentially toxic compounds. Up to date there is no information about the impact of mining activities on deep-sea benthic ecosystems such as abundant deep-sea sponge grounds in the North Atlantic Ocean. Sponge grounds play a major role in benthic-pelagic coupling and represent an important habitat for a diversity of vertebrates, invertebrates and microorganisms. To simulate the effects of mining plumes on benthic life in the deep sea, we exposed Geodia barretti, a dominant sponge species in the North Atlantic Ocean, and an associated brittle star species from the genus Ophiura spp. to a field-relevant concentration of 30 mg L-1 suspended particles of crushed SMS deposits. Three weeks of exposure to suspended particles of crushed SMS resulted in a tenfold higher rate of tissue necrosis in sponges. All brittle stars in the experiment perished within ten days of exposure. SMS particles were evidently accumulated in the sponge’s mesohyl and concentrations of iron and copper were 10 times elevated in SMS exposed individuals. Oxygen consumption and clearance rates were significantly retarded after the exposure to SMS particles, hampering the physiological performance of G. barretti. These adverse effects of crushed SMS deposits on G. barretti and its associated brittle star species potentially cascade in disruptions of benthic-pelagic coupling processes in the deep sea. More elaborate studies are advisable to identify threshold levels, management concepts and mitigation measures to minimize the impact of deep-sea mining plumes on benthic life.

Information on the distribution of marine migratory species is lacking, and for a long time, these species have been overlooked in the designation of Marine Protected Areas (MPAs). This study analysed the home range of pygmy blue whales (PBWs) from western Australia to eastern Indonesia to be able to assess the overlap with current MPAs. In this study, data from 11 individual PBWs tagged in the Perth Canyon were used. Two home range methods, adaptive Local Convex Hull (a-LoCoH) and Brownian Bridge Movement Model (BBMM), were performed and compared to identify core use areas and connections between these areas (i.e., migration corridors). By assessing the relative properties and visually inspecting the home ranges, 90% BBMM (home range and migration corridor) and 50% BBMM (core use area) are chosen as the best results, because they cover the connected core-use areas to a large extent. The home ranges that were covered by current MPAs were only 2% in Indonesia and 16% in Australia. Important migration corridors without current protection are in the east Savu Sea, south of Timor Island, and wider Banda Sea. It is noteworthy that comparing methods is relevant to be able to choose the most suitable method for the data used and the goal of this study. The limited overlap between the calculated home ranges and the MPAs of the Indonesian waters articulates the importance of in-depth scientific studies to be able to evaluate, implement and develop marine conservation planning.

The die‐off of the long‐spined sea urchin Diadema antillarum in the 1980s highlighted its crucial role as a primary grazer in tropical western Atlantic coral reefs. However, natural recovery has been slow, exacerbated by a new die‐off in 2022. Interest in actively restoring D. antillarum populations has grown with the emergence of culture and rearing techniques. Restocking reefs with laboratory‐reared urchins shows potential for enhancing coral reef resilience by reducing algal cover and promoting coral settlement, but success rates vary. Predation and migration contribute to low retention rates, with distinguishing between them is challenging. In this study near Saba, Caribbean Netherlands, we released 200 laboratory‐reared D. antillarum on a reef and monitored for D. antillarum retention and potential D. antillarum predator presence and interaction for 35 days. Only 40% of the urchins were still present on the reef after day one. The Spanish hogfish Bodianus rufus was identified as the primary daytime predator, responsible for nine direct predation events. No nighttime predation was observed, but interaction with a batwing coral crab Carpilius corallinus was noted. These insights can help optimize future restocking attempts and emphasize the importance of assessing predator presence beforehand. Reefs with high abundances of predators such as Spanish hogfish should be avoided for D antillarum restocking. In addition, before being released, lab‐reared animals should be given time to acclimate to conditions in the wild by being placed in protected in situ cages. Here, they could also grow to larger sizes that are less vulnerable to predation.

Restoration and artificial reefs can assist the recovery of degraded reefs but are limited in scalability and climate resilience. The Mineral Accretion Technique (MAT) subjects metal artificial reefs to a low-voltage electrical current, thereby creating a calcium-carbonate coating. It has been suggested that corals on MAT structures experience enhanced health and growth. However, prior studies report conflicting results potentially due to different conditions, species and approaches used. We investigated how MAT influences the bleaching resilience, condition and growth of four coral species and natural coral recruitment in Kenya. Coral fragments were outplanted on charged iron tables using commonly-applied settings (6 V; 0.84 A m-2). After one month, when all tables had acquired a calcium-carbonate coating, half of the tables were taken off electricity to serve as controls. Both treatments (MAT and Control) were monitored on coral brightness, condition (live tissue cover), growth and natural recruitment for one year, during which a marine heatwave occurred. Coral bleaching was significantly more severe on MAT for all studied species. For three species, coral condition dropped sharply during the heatwave and this decline was faster and more severe on MAT. Coral growth was reduced during the heatwave for all corals and remained low for one species on MAT. After one year, the Control harboured 34 coral recruits, whereas none were found on MAT. Thus, while MAT can be useful to prevent corrosion of metal artificial reefs, we do not recommend MAT as reported here to improve coral growth, condition, heat resilience or recruitment.

Information about reproductive habitat and migration pathways is of paramount importance to restore migratory fish species. This study assesses the availability of spawning and nursery habitats for the European sturgeon (Acipenser sturio) in the delta and lower Rhine (covering over 350 river kilometres) as part of a larger feasibility assessment for a future restoration of this critically endangered species. The general approach has three steps: (1) the identification of the species' specific habitat requirements, based on a systematic literature review; (2) the collection and preprocessing of data from two countries, including the 1D and 2D modelling of water depths and flow velocities; and (3) GIS-based mapping of spawning and nursery habitat. Based on a HSI score of 1, we identify a total of 0.75 km2 as minimal spawning habitat, potentially suitable for approximately 2500 female European sturgeons (one spawning site would use ~300 m2). This is sufficient, as currently, only an estimated maximum number of 750 adults exist. Suitable spawning habitat is mainly located in the German state of North Rhine-Westphalia, whereas suitable nursery habitat is mainly located in the Netherlands. The availability is, however, significantly reduced by coastal infrastructure (damming) and inland navigation. The insights gained can be used to assess the current suitability of the river Rhine for the species' reintroduction and to identify opportunities for habitat restoration and protection for various life stages. The outcomes thus play an essential role in the conservation of the species. In addition, the modelling approach developed could be applied to other northwestern European rivers. This broader application would allow intercomparison and support decisions about which rivers are best suited for future reintroduction of the critically endangered European sturgeon.

Tropical western Atlantic reefs have gradually shifted from being dominated by corals to being mainly covered by macroalgae. The mass-mortality of the sea urchin Diadema antillarum in the 80s and the slow to non-existent recovery exacerbated this shift. Chemical cues associated with these reefs are expected to have shifted too with potential negative effects on larval recruitment, possibly limiting recovery of important species like D. antillarum . In this study, we tested the effects of naturally derived biofilm and macroalgae species native to Caribbean coral reefs on the settlement rate of cultured D. antillarum larvae in two separate experiments. Crustose coralline algae (CCA) were included in both experiments, making it possible to compare settlement rates from both experiments. A biofilm of one week old yielded significantly lower settlement rates compared to two, four, and six weeks old biofilm and the highest settlement rate was found for CCA with over 62% of total larvae. All six tested macroalgae species resulted in settled larvae, with little significant difference between algal species, partly due to a high variation in settlement rates within treatments. Sargassum fluitans induced the highest settlement rate with 33%, which was not significantly different from CCA with 29%. We conclude that dominant macroalgae species likely to be encountered by D. antillarum on shifted reefs are no major constraint to settlement. Our findings increase the understanding of alternative stable state settlement dynamics for a keystone coral reef herbivore.