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Microplastics are a persistent and ubiquitous source of pollution in the marine environment, representing a severe threat to tropical coral reefs. The effects of microplastics on reef-building (hard) corals have been documented (interference with normal digestion process, polyp retraction, oxidative stress, impairment of the photosynthetic machinery, bleaching). However, the impact of microplastics on soft corals, the second most abundant benthos of tropical reefs, remains to be thoroughly studied. In this work, we analysed the effects of a short-term microplastic exposure on the cellular physiology of the soft coral Coelogorgia palmosa. We found that samples exposed to >50 mg l−1 of microplastic showed significant increase in the activities of the antioxidant enzymes glutathione reductase, catalase, and superoxide dismutase, suggesting a rise in oxidative stress. Furthermore, exposure to microplastics increased lipid peroxidation, indicating oxidative damage. Overall, our results show that similar to hard corals, microplastic ingestion causes oxidative stress and cellular damage in soft corals. Our study provides a first assessment of physiological effects of microplastic exposure on the soft coral, Coelogorgia palmosa, highlighting the need for further investigations about these contaminants and their influence on marine benthic fauna. Such information is crucial to understand how different reef organisms respond to microplastic pollution and who the ecological winners or losers will be in an increasingly polluted marine environment. Key policy highlights The effect of microplastic contamination at the cellular and molecular level has never been investigated before in alcyonacean corals. Concentrations of 50–70 mg l−1 of polyethylene caused significant rise in oxidative stress in Coelogorgia palmosa after 48 h. After 48 h exposure to 50 mg l−1 significant oxidative damage was recorded. No significant modulation in the expression of the cytoprotective protein Hsp60 was observed after exposure to microplastics.

Nudibranchs have a mostly carnivorous diet, and they prey on a wide variety of other animal taxa. Many species, mainly belonging to the Cladobranchia suborder, feed on cnidarians, including member of the class Hydrozoa. Several hydrozoan species display a symbiotic lifestyle, being associated with other benthic invertebrates, including for instance bryozoans, corals, octocorals, and sponges. In our knowledge, no record of nudibranch predation on symbiotic hydrozoans has been reported so far, possibly thanks to the protective action by the host towards its symbiotic hydrozoan. Here, we show the unexpected case of a nudibranch belonging to the recently described species Sakuraeolis marhe (Fernández-Simón and Moles, 2023) feeding on Zanclea sp. 2, a hydrozoan associated with the cheilostome bryozoan Celleporaria sp. This trophic association is confirmed by the presence and storage of the nematocysts into the nudibranch cnidosacs. Moreover, the nudibranch appears to selectively store mostly a single type of nematocyst, that is large size stenotele. The observation here reported represents the first well-documented record of a nudibranch feeding on a symbiotic hydrozoan and the first confirmed case of predation on Zanclea polyps. Moreover, we provide additional genetic information and the first description of the internal anatomy of S. marhe.

The red gorgonian Paramuricea clavata is a fundamental ecosystem engineer of coralligenous biocenosis in the Mediterranean Sea, where it plays crucial ecological functions and enhances the habitat biodiversity. However, this species is strongly endangered due to climate change-related stressors such as mucilage events, which have increased in recent decades causing extensive damage and mortality, but whose impacts at the molecular and cellular levels are still unexplored. In this study, different cellular stress biomarkers were analyzed in mucilage-colonized P. clavata specimens living in the Portofino Marine Protected Area (Ligurian Sea, Italy), in order to elucidate the cellular pathways affected by mucilage and the cellular defense mechanisms adopted. Within these colonies, portions of healthy tissue located at different distances from mucilage-induced necrosis were considered. Our results showed that mucilage affected the cellular oxidative status and impaired lipid cell membranes of the whole P. clavata colony. Indeed, an increase in the superoxide dismutase (SOD) and glutathione reductase (GR) enzymatic activity and in the level of lipid peroxidation (LPO) was detected in colonies showing mucilage-induced necrotic tissues compared to healthy ones. In particular, fragments sampled just next to the necrotic tissue displayed the highest levels of SOD and LPO, indicating that harmful oxidative damage was in progress, especially in portions neighboring the mucilage colonization. In this context, the up-regulation of the antioxidant mechanisms might represent a defense and a barrier from hypoxic or anoxic conditions created by mucilage overgrowth or by the invasion of toxic organisms embedded in the mucilaginous aggregates. On the contrary, the cellular protein homeostasis, analyzed by the expression of the 60-kDa Heat shock protein (Hsp60), was not altered by the mucilage. This analysis contributes to provide new insights into the cellular and molecular response of gorgonians to a stress source whose effects are likely to worsen in a climate change scenario.

Massive coral bleachingepisodes induced by thermal stress areone of the first causes of coral death worldwide. Overproduction ofreactive oxygen species (ROS) has been identified as one of the potentialcauses of symbiosis breakdown between polyps and algae in corals duringextreme heat wave events. Here, we propose a new strategy for mitigatingheat effects by delivering underwater an antioxidant to the corals.We fabricated zein/polyvinylpyrrolidone (PVP)-based biocomposite filmsladen with the strong and natural antioxidant curcumin as an advancedcoral bleaching remediation tool. Biocomposites' mechanical,water contact angle (WCA), swelling, and release properties can betuned thanks to different supramolecular rearrangements that occurby varying the zein/PVP weight ratio. Following immersion in seawater,the biocomposites became soft hydrogels that did not affect the coral'shealth in the short (24 h) and long periods (15 days). Laboratorybleaching experiments at 29 and 33 & DEG;C showed that coral coloniesof Stylophora pistillata coated withthe biocomposites had ameliorated conditions in terms of morphologicalaspects, chlorophyll content, and enzymatic activity compared to untreatedcolonies and did not bleach. Finally, biochemical oxygen demand (BOD)confirmed the full biodegradability of the biocomposites, showinga low potential environmental impact in the case of open-field application.These insights may pave the way for new frontiers in mitigating extremecoral bleaching events by combining natural antioxidants and biocomposites.

The authors thank all the people involved in collecting/providing material or organising sampling campaigns: Peter Schuchert (MHNG, Switzerland), Tullia Isotta Terraneo (KAUST, Saudi Arabia), Malek Amr Gusti (KAUST, Saudi Arabia), Timothy Ravasi (OIST, Japan), the captain and crew of the MV Dream-Master (Saudi Arabia), the KAUST Coastal and Marine Resources Core Lab, Inga Dehnert (UNIMIB, Italy), Nicholas WL Yap (NUS, Singapore), Sudhanshi S Jain (NUS, Singapore), Stephen Keable (Australian Museum), Penny Berents (Australian Museum), Anne Hoggett (Australian Museum), Lyle Vail (Australian Museum). Additionally, we wish to thank Leen P. van Ofwegen (Naturalis, The Netherlands) for his valuable help in identifying the octocoral Paralemnalia sp., Peter Schuchert for his comments on an earlier version of the manuscript, and two anonymous referees for their thorough revision of this work. Permissions relevant to undertake the research have been obtained from the applicable governmental agencies. Fieldwork at St. Eustatius was funded through a Martin Fellowship from Naturalis Biodiversity Center to SM, while logistic support was supplied by St. Eustatius Marine Parks (STENAPA), the Caribbean Netherlands Science Institute (CNSI) and Scubaqua Dive Centre. Samples from Eilat (Israel) were collected during the HyDRa Project funded by the EU FP7 Research Infrastructure Initiative ‘ASSEMBLE’ (Grant #227799) to DP. Financial support to DP for collecting samples at Lizard Island (Australia) was provided by the 2018 John and Laurine Proud Fellowship and the Australian Museum’s Lizard Island Research Station. Fieldwork in Mozambique was conducted during the Green Bubbles financed by EU’s H2020 research and innovation programme to DP, under the Marie Sklodowska-Curie grant agreement no 643712 (Permit n° 09/2018 ANAC). Fieldwork in Singapore was partially funded by the National Research Foundation, Prime Minister’s Office, Singapore under its Marine Science R&D Programme (MSRDP-P03) to DH.

Microplastics pollution differentially impacts coral reef systems, by threatening corals physically, through physiological distress and by increasing diseases. However, most of the studies to date have focused on scleractinian corals. The present work reports for the first time the patterns of microplastic ingestion and adhesion by the alcyonacean Coelogorgia palmosa. Feeding and adhesion tests were carried out with various concentrations of polyethylene microbeads. Results showed a wide range of surface adhesion, ranging from 3 to 1573 microbeads per coral fragment, suggesting that adhesion driven by mucus is the main mechanism of microplastic trapping. Polyethylene was ingested by 60% of coral fragments, and the average number of ingested microbeads was much lower compared to scleractinian corals. Considering the ecological importance of soft corals in coral reef ecosystems, specific attention regarding microplastic pollution effects on this taxon is recommended.

An integrated approach using morphological and genetic data is needed to disentangle taxonomic uncertainties affecting the hydrozoan families Sphaerocorynidae and Zancleopsidae. Here we used this approach to accurately characterise species in these families, identify the previously unknown polyp stages of the genera Euphysilla and Zancleopsis, which were originally described exclusively based on the medusa stages, describe a new sphaerocorynid genus and species, and assess the phylogenetic position of the two families within the Capitata. The monotypic genus Astrocoryne was found to be a synonym of Zancleopsis. Astrocoryne cabela was therefore transferred to the genus Zancleopsis as Zancleopsis cabela comb. nov. The new polyp-based genus and species Kudacoryne diaphana gen. nov. sp. nov. was erected within the Sphaerocorynidae. Both taxa are primarily based on genetic data, but the introduction of this new genus was made necessary by the fact that it clustered with the genera Heterocoryne and Euphysilla, despite showing Sphaerocoryne-like polyps. Interestingly, the species analysed in this work showed contrasting biogeographical patterns. Based on our data and literature records, some species appear to have a wide circumtropical range, whereas others are limited to few localities. Overall, these results lay the ground for future investigations aimed at resolving the taxonomy and systematics of these two enigmatic families.

Scleractinian corals provide habitats for a broad variety of cryptofauna, which in turn may contribute to the overall functioning of coral symbiomes. Among these invertebrates, hydrozoans belonging to the genus Zanclea represent an increasingly known and ecologically important group of coral symbionts. In this study, we analysed 321 Zanclea colonies associated with 31 coral genera collected from 11 localities across the Indo-Pacific and Caribbean regions, and used a multi-disciplinary approach to shed light on the evolution and biogeography of the group. Overall, we found high genetic diversity of hydrozoans that spans nine clades corresponding to cryptic or pseudo-cryptic species. All but two clades are associated with one or two coral genera belonging to the Complex clade, whereas the remaining ones are generalists associated with both Complex and Robust corals. Despite the observed specificity patterns, no congruence between Zanclea and coral phylogenies was observed, suggesting a lack of coevolutionary events. Most Zanclea clades have a wide distribution across the Indo-Pacific, including a generalist group extending also into the Caribbean, while two host-specific clades are possibly found exclusively in the Red Sea, confirming the importance of this peripheral region as an endemicity hotspot. Ancestral state reconstruction suggests that the most recent common ancestor of all extant coral-associated Zanclea was a specialist species with a perisarc, occurring in what is now known as the Indo-Pacific. Ultimately, a mixture of geography- and host-related diversification processes is likely responsible for the observed enigmatic phylogenetic structure of coral-associated Zanclea.

Waminoa spp. are acoel flatworms mainly found as ectosymbionts on scleractinian corals. Although Waminoa could potentially represent a threat to their hosts, not enough information is available yet regarding their ecology and effect on the coral. Here, the Waminoa sp.–coral association was analyzed in Singapore reefs to determine the prevalence, host range, and preference, as well as the flatworm abundance on the coral surface. Moreover, the impact of Waminoa sp. on the expression of putative immune- and stress-response genes (C-type lectin, C3, Hsp70 and Actin) was examined in the coral Lobophyllia radians. The association prevalence was high (10.4%), especially in sites with lower sedimentation and turbidity. Waminoa sp. showed a wide host range, being found on 17 coral genera, many of which are new association records. However, only few coral genera, mostly characterized by massive or laminar morphologies appeared to be preferred hosts. Waminoa sp. individuals displayed variable patterns of coral surface coverage and an unequal distribution among different host taxa, possibly related to the different coral growth forms. A down-regulation of the expression of all the analyzed genes was recorded in L. radians portions colonized by Waminoa individuals compared to those without. This indicated that Waminoa sp. could affect components of the immune system and the cellular homeostasis of the coral, also inhibiting its growth. Therefore, Waminoa sp. could represent a potential further threat for coral communities already subjected to multiple stressors.

Interspecific associations are common in coral reefs, but those involving hydrozoans and octocorals have not been widely investigated. The hydroid Pteroclava krempfi (Hydrozoa, Cladocorynidae) lives in association with different soft coral taxa (Alcyonacea), showing a widespread distribution. However, very little information is available on the ecology of these relationships. Here, we tested for differences in the taxon-specific prevalence and habitat preference of the symbiosis and determined ecological traits of the P. krempfi-host associations in central Red Sea reefs. P. krempfi was found associated with the alcyonacean genera Lobophytum, Rhytisma, Sarcophyton and Sinularia, updating its host range and geographic distribution. The symbiosis prevalence was high in the area and especially at inshore sites compared to midshore and offshore sites. Rhytisma was the most common host, while the association with Lobophytum showed the lowest taxon-specific prevalence. P. krempfi did not show a clear preference for a specific alcyonacean size, and an increase in host size automatically led to an increase in the surface occupied by hydrozoans, although they rarely colonized more than 50% of the upper surface of the host. The spatial distribution of the hydroids on the host surface appeared related to the host genus and size as well as to the coverage of the hydroids. Despite the nature of this symbiosis requiring further investigation, P. krempfi did not seem to play a role in affecting the bleaching susceptibilities of the host colonies. The study shows that the Red Sea coral reef symbioses are more widespread than previously known and therefore deserve more attention.

Corals show spatial acclimatisation to local environment conditions. However, the various cellular mechanisms involved in local acclimatisation and variable bleaching patterns in corals remain to be thoroughly understood. In this study, the modulation of a protein implicated in cellular heat stress tolerance, the heat shock protein 70, was compared at both gene (hsp70) and protein (Hsp70) expression level in bleaching tolerant near-coast Acropora muricata colonies and bleaching susceptible reef colonies, in the lagoon of Belle Mare (Mauritius). The relative Hsp70 levels varied significantly between colonies from the two different locations, colonies having different health conditions and the year of collection. Before the bleaching event of 2016, near-coast colonies had higher basal levels of both Hsp70 gene and protein compared to reef colonies. During the bleaching event, the near-coast colonies did not bleach and had significantly higher relative levels of both Hsp70 gene and protein compared to bleached reef colonies. No significant genetic differentiation between the two studied coral populations was observed and all the colonies analysed were associated with Symbiodiniaceae of the genus Symbiodinium (Clade A) irrespective of location and sampling period. These findings provide further evidence of the involvement of Hsp70 in conferring bleaching tolerance to corals. Moreover, the consistent expression differences of Hsp70 gene and protein between the near-coast and reef coral populations in a natural setting indicate that the modulation of this Hsp is involved in local acclimatisation of corals to their environments.

Plastic pollution threatens the marine environment, especially due to the adverse effects caused by micro and nano particles interacting with the marine biota. In order to provide reliable data regarding micro and nanoplastic contamination and the related impacts, efficient analytical solutions are needed. We developed a new analysis workflow that uses marine sponges to monitor plastic pollution by characterizing the plastic particles accumulated in their tissue. Specimens of cf. Haliclona (Haplosclerida) were sampled in the Maldivian archipelago. The aim was to optimize the method and to carry out a pilot study of the contamination of the related reef habitat. Particles were isolated, size fractioned, counted and submitted to morphological and chemical characterization. The constituting polymer was identified by infrared microspectroscopy for particles >25 μm, and by pyrolysis coupled with gas chromatography mass spectrometry for those

Coral reefs are known to be among the most biodiverse marine ecosystems and one of the richest in terms of associations and species interactions, especially those involving invertebrates such as corals and sponges. Despite that, our knowledge about cryptic fauna and their ecological role remains remarkably scarce. This study aimed to address this gap by defining for the first time the spatial ecology of the association between the epibiont hydrozoan Nemalecium lighti and the Porifera community of shallow coral reef systems at Bonaire. In particular, the host range, prevalence, and distribution of the association were examined in relation to different sites, depths, and dimensions of the sponge hosts. We report Nemalecium lighti to be in association with 9 out of 16 genera of sponges encountered and 15 out of 16 of the dive sites examined. The prevalence of the hydroid–sponge association in Bonaire reef was 6.55%, with a maximum value of over 30%. This hydrozoan has been found to be a generalist symbiont, displaying a strong preference for sponges of the genus Aplysina, with no significant preference in relation to depth. On the contrary, the size of the host appeared to influence the prevalence of association, with large tubular sponges found to be the preferred host. Although further studies are needed to better understand the biological and ecological reason for these results, this study improved our knowledge of Bonaire’s coral reef cryptofauna diversity and its interspecific associations.

The cushion seastar Culcita schmideliana has gained major attention in the last few years because of its selective predation on juvenile corals, as well as its ability to generate large demographic assemblages, causing delays in coral recovery after large mortality events in the Republic of Maldives. However, a lack of data regarding the factors affecting its distribution and habitat selection still persists in this area. Here, we adopted a novel approach in the study of corallivorous seastar habitat selection that combined ecological and digital photogrammetry data. In this regard, we tested 3 different parameters as factors influencing seastar habitat choice in the South-East region of Faafu Atoll, Republic of Maldives, namely prey abundance, Linear Rugosity Index (LRI), and Average Slope (AS). The analysis of selectivity coefficient (Ei) of seastars for different habitat types showed a preference for reefs characterized by medium AS values (Ei = 0.268), a LRI included between 2 and 2.5 (Ei = 0.180), and a juvenile coral density ranging between 10 and 20 colonies m−2 (Ei = 0.154). A multiple linear regression analysis showed that different AS and LRI values explained the 43.1% (R2 = 0.431, P = 0.007) and the 48.1% (R2 = 0.481, P = 0.024) of variance in seastars abundance, respectively, while juvenile coral densities did not significantly affect this (R2 = 0.132, P = 0.202). These results provide new information on the distribution and behaviour of an important corallivore of Maldivian reefs, such as C. schmideliana.

Coral diseases are emerging as a major threat to coral reefs worldwide, and although many of them have been described, knowledge on their epizootiology is still limited. This is the case of the Halofolliculina ciliate infections, recognized as the skeletal eroding band (SEB) and Caribbean ciliate infection (CCI), two diseases caused by ciliates belonging to the genus Halofolliculina (Class Heterotrichea). Despite their similar macroscopic appearance, the two diseases are considered different and their pathogens have been hypothesized to belong to different Halofolliculina species. In this work, we analysed the morphology and genetic diversity of Halofolliculina ciliates collected in the Caribbean Sea, Red Sea and Indo-Pacific Ocean. Our analyses showed a strong macroscopic similarity of the lesions and similar settlement patterns of the halofolliculinids from the collection localities. In particular, the unique erosion patterns typical of the SEB were observed also in the Caribbean corals. Fine-scale morphological and morphometric examinations revealed a common phenotype in all analysed ciliates, unequivocally identified as Halofolliculina corallasia. Phylogenetic analyses based on nuclear and mitochondrial (COI) molecular markers consistently found all samples as monophyletic. However, although the nuclear marker displayed an extremely low intra-specific diversity, consistent with the morphological recognition of a single species, the analyses based on COI showed a certain level of divergence between samples from different localities. Genetic distances between localities fall within the intra-specific range found in other heterotrich ciliates, but they may also suggest the presence of a H. corallasia species complex. In conclusion, the presented morpho-molecular characterization of Halofolliculina reveals strong similarities between the pathogens causing SEB and CCI and call for further detailed studies about the distinction of these two coral diseases.

Coral bleaching represents the most serious threat to contemporary coral reefs. In response, focus is being laid on understanding the cellular processes involved in the response of corals to the environmental stresses and the molecular mechanisms that determine the bleaching patterns. In the present study, a component of the cellular stress response such as the expression of the heat shock proteins (Hsps) was analyzed following the coral bleaching event which occurred in the central Red Sea (Saudi Arabia) in 2015. During this event, corals of different species, growth forms and sites showed variable bleaching susceptibility. In particular, we investigated the expression of Hsp70, Hsp60 and Hsp32 in both healthy and bleached colonies belonging to four different coral species (Goniopora lobata, Porites lobata, Seriatopora hystrix and Stylophora pistillata), in order to explore the intra- and inter-specific modulation of these biomarkers as well as the existence of spatial patterns of Hsp expression. In healthy colonies, the level of all the biomarkers was significantly different among the different species, although within each species it remained similar regardless of the distance from the shore. All the coral species showed a significant modulation of the Hsp expression in response to bleaching, whose typology and amplitude were species-specific. In all the species, Hsp70 and Hsp60 showed a coordinated dual expression, which, in response to bleaching resulted in an up-regulation in G. lobata and P. lobata and in a down-regulation in S. hystrix and S. pistillata. Hsp32 was up-regulated in all four species following bleaching, indicative of elevated oxidative stress. Overall, the protein expression profiles of each species contribute to assess the role of Hsps in regulating the susceptibility to thermal stresses of the various coral taxa of the Red Sea.

Small island nations like the Maldives are highly dependent on healthy coral reefs and the ecosystem services they provide. Lately, Maldivian reefs have experienced considerable degradation as a result of severe mass bleaching events and accumulating threats posed by pollution, human development, coral diseases, and outbreaks of corallivores. Coral restoration can be a useful mitigation tool in assisting natural recovery, especially when economically important reef areas such as resort reefs are in poor health with slow natural recovery. This study assesses the performance efficiency of lagoon mid-water rope nurseries for coral gardening in two different atolls in the Maldives for the first time. Three different coral genera, namely Acropora, Pocillopora, and Porites, were assessed applying a common monitoring protocol. Fragment survival was generally very high, exceeding 90% survivorship for the genus Acropora and Pocillopora, while nursing success for Porites was significantly lower (66%). We further report benchmark growth rates for these genera in mid-water rope nurseries in the Maldives. The study also identifies potential threats to coral nursing success, namely disease occurrence and predation, as we report the corallivorous nudibranch Phestilla on in situ nursing stock for the first time. Overall, our results suggest that the use of mid-water rope nurseries in lagoons is an efficient and widely applicable technique for rearing corals in the Maldives. We aim to provide useful insight into best practices for applying this coral gardening technique on a wider scale in the archipelago and highlight future research requirements.

Species delimitation of corals is one of the most challenging issues in coral reef ecology and conservation. Morphology can obscure evolutionary relationships, and molecular datasets are consistently revealing greater within-species diversity than currently understood. Most phylogenetic studies, however, have examined narrow geographic areas and phylogeographic expansion is required to obtain more robust interpretations of within- and among- species relationships. In the case of the blue coral Heliopora, there are currently two valid species (H. coerulea and H. hiberniana) as evidenced by integrated genetic and morphological analyses in northwestern Australia. There are also two distinct genetic lineages of H. coerulea in the Kuroshio Current region that are morphologically and reproductively different from each other. Sampling from all Heliopora spp. across the Indo-Pacific is essential to obtain a more complete picture of phylogeographic patterns. To examine phylogenetic relationships within the genus Heliopora, we applied Multiplexed inter simple sequence repeat (ISSR) Genotyping by sequencing (MIG-seq) on > 1287 colonies across the Indo-West Pacific. Maximum likelihood phylogenetic trees indicated the examined Heliopora samples comprise three genetically distinct groups: H. coerulea group, H. hiberniana group, and a new undescribed Heliopora sp. group with further subdivisions within each group. Geographic structuring is evident among the three species with H. hiberniana group found in the Indo-Malay Archipelago and biased toward the Indian Ocean whilst Heliopora sp. was only found in the Kuroshio Current region and Singapore, indicating that this taxon is distributed in the western Pacific and the Indo-Malay Archipelago. Heliopora coerulea has a wider distribution, being across the Indian Ocean and western Pacific. This study highlights the effectiveness of phylogenetic analysis using genome-wide markers and the importance of examining populations across their distribution range to understand localized genetic structure and speciation patterns of corals.

The crown-of-thorns starfish (COTS) is a coral predator that is widely distributed in Indo-Pacific Oceans. A previous phylogenetic study using partial mitochondrial sequences suggested that COTS had diverged into four distinct species, but a nuclear genome-based analysis to confirm this was not conducted. To address this, COTS species nuclear genome sequences were analysed here, sequencing Northern Indian Ocean (NIO) and Red Sea (RS) species genomes for the first time, followed by a comparative analysis with the Pacific Ocean (PO) species. Phylogenetic analysis and ADMIXTURE analysis revealed clear divergences between the three COTS species. Furthermore, within the PO species, the phylogenetic position of the Hawaiian sample was further away from the other Pacific-derived samples than expected based on the mitochondrial data, suggesting that it may be a PO subspecies. The pairwise sequentially Markovian coalescent model showed that the trajectories of the population size diverged by region during the Mid-Pleistocene transition when the sea-level was dramatically decreased, strongly suggesting that the three COTS species experienced allopatric speciation. Analysis of the orthologues indicated that there were remarkable genes with species-specific positive selection in the genomes of the PO and RS species, which suggested that there may be local adaptations in the COTS species.

The intensity and frequency of coral bleaching events have increased worldwide especially due to thermal stress and seawater pollution. Although it has been observed that metal concentration in seawater can affect the coral’s ability to adopt cellular defensive mechanisms to counteract bleaching, more investigations are needed to better understand the role of metals in coral physiology. In this study, we analyzed the individual and combined effects of prolonged heat stress and manganese (Mn) and iron (Fe) enrichments at the cellular level on the coralStylophora pistillata. Thermal stress caused an up-regulation in the expression of the host Heat shock proteins (Hsps) 60 and 70, which showed a parallel pattern of modulation in all treatments, as well as an increase of lipid peroxidation (LPO) in the holobiont. Fe enrichment did not induce any change in Hsp expression or in the oxidative status of the corals both at the ambient temperature of 26°C or at increased temperature, suggesting that Fe didn’t seem to play a role in mitigating the cellular damages and the coral bleaching. Mn or MnFe enrichment at 26°C seemed to increase the oxidative stress in zooxanthellae, since high LPO and glutathione reductase (GR) levels were recorded, but it did not cause any effect on polyp Hsp expression, probably due to the antioxidant action of GR. With the temperature increase, Mn enrichments prevented any increase in Hsp levels and caused a significant decrease of LPO and GR activity, strengthening a previous hypothesis suggesting that Mn could mitigate the negative cellular effects produced by the thermal stress.

Hydrozoans of the genus Zanclea have been acknowledged only recently as a fundamental component of the highly diverse fauna associated with reef-building scleractinian corals. Although widely distributed in coral reefs and demonstrated to be important in protecting corals from predation and diseases, the biodiversity of these hydrozoans remains enigmatic due to the paucity of available morphological characters, incomplete morphological characterisations and the possible existence of cryptic species. Recently, molecular techniques have revealed the existence of multiple hidden genetic lineages not yet supported by diagnostic morphological characters. In this work, we further explore the morpho-diversity of three genetic lineages, namely Zanclea associated with the coral genera Goniastrea (clade I), Porites (clade II) and Pavona (clade VI). Aside from providing a complete classical characterisation of the polyp and medusa stage of each clade, we searched for new potential taxonomic indicators either on symbiotic hydroids or on host corals. On the hydroids, statistical analyses on almost 7,000 nematocyst capsules revealed a significant difference in terms of nematocyst size among the three Zanclea clades investigated. On each host coral genus, we identified peculiar skeletal modifications related to the presence of Zanclea symbionts. Lastly, we discussed the potential diagnostic value of these footprints in the characterisation of Zanclea–scleractinian associations.

Microplastics are recognized as a growing threat for the marine environment that may even affect areas generally considered pristine. In this work we surveyed the microplastic contamination in the Faafu Atoll (Maldives, Indian Ocean) across twelve sampling station, located either inside or outside the reef rim. Sediments and seawater samples were collected. Despite the remoteness of the atoll, the scarce local population and low touristic annual afflux, the detected average abundance were 0.32 ± 0.15 particles/m3 in the surface water and 22.8 ± 10.5 particles/m2 in the beach sediments. Polymers identified through Fourier-Transform Infrared spectroscopy were mostly polyethylene, polypropylene, polystyrene, polyvinylchloride, polyethyleneterephtalate, and polyamide. Elastomeric residues and charred microparticles were also found. In particular, the charred microparticles were prevalently located nearby the inhabited island and they might be considered a peculiarity of the area, related to local practice of burning plastic waste at the shoreline.

Fire corals of the hydrocoral genus Millepora provide an important ecological role as framework builders of coral reefs in the Indo-Pacific and the Atlantic. Recent works have demonstrated the incongruence between molecular data and the traditional taxonomy of Millepora spp. based on overall skeleton growth form and pores. In an attempt to establish a reliable and standardized approach for defining species boundaries in Millepora, we focused on those from the Red Sea. In this region, three species are currently recognized: the fan-shaped branching M. dichotoma, the blade-like M. platyphylla, and the massive/encrusting M. exaesa. A total of 412 colonies were collected from six localities. Two mitochondrial marker genes (COI and 16S rDNA) were sequenced to obtain phylogeny reconstructions and haplotype networks. Eight morphological traits of pores and the nematocysts of both polyp and eumedusoid stages were measured to determine whether significant morphological differences occur among the three species. Both markers clearly resolved M. dichotoma, M. platyphylla, and M. exaesa as distinct, monophyletic lineages in the Red Sea. Nevertheless, they also revealed deep genetic breaks with Southwestern Indian Ocean populations of the three species. In the Red Sea, the three species were further distinguished based on their pore and nematocyst features. A discriminant analysis revealed dactylopore density, number of dactylopores per gastropore, dactylopore distance, and gastropore diameter as the most informative discriminative characters. The heteronemes, the large and small stenoteles of polyps, and the distribution of mastigophores of eumedusoids also showed significant interspecific differences. An integrated morpho-molecular approach proved to be decisive in defining species boundaries of Millepora supported by a combination of pore and nematocyst characters, which may be phylogenetically informative.

Although corallivory is recognized as a threat affecting the structure and integrity of coral reef habitats, ecological data on most species of coral consumers remain limited, slowing down the development of conservation and restoration strategies of the reef ecosystems. In this study, the population distribution and corallivorous behaviour of the cushion sea star Culcita sp. were investigated in the south region of Faafu Atoll, Maldives. Most sea stars were found on reef slopes within 0–10m depth and in areas characterized by low live coral cover. Several coral genera were preyed on by the sea star. Although most of the consumed corals belong to the genus Acropora, a feeding preference for the genera Pocillopora and Pavona and a consistent avoidance of the genus Porites were observed. Furthermore, the majority of the prey corals were small colonies (< 10cm diameter), even though Culcita sp. appeared to be capable of partially consuming larger colonies. Dietary preferences for specific coral colonies or genera have the potential to generate local shifts in coral community composition and structure and may affect reef recovery following natural and anthropogenic disturbance in an already impacted environment such as the Maldivian reefs.

In light of the recent marine oil spill that occurred off the coast of Mauritius (Indian Ocean), we comment here the incident, the containment method used by the local population, the biological impact of oil spill on two sensitive tropical marine ecosystems (coral reefs and mangrove forests), and we suggest monitoring and restoration techniques of the impacted ecosystems based on recent research advancements.

The octocoral family Alcyoniidae represents a rich source of bioactive substances with intriguing and unique structural features. This review aims to provide an updated overview of the compounds isolated from Alcyoniidae and displaying potential cytotoxic activity. In order to allow a better comparison among the bioactive compounds, we focused on molecules evaluated in vitro by using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide (MTT) assay, by far the most widely used method to analyze cell proliferation and viability. Specifically, we surveyed the last thirty years of research, finding 153 papers reporting on 344 compounds with proven cytotoxicity. The data were organized in tables to provide a ranking of the most active compounds, to be exploited for the selection of the most promising candidates for further screening and pre‐clinical evaluation as anti‐cancer agents. Specifically, we found that (22S,24S)‐24‐methyl‐22,25‐epoxyfurost‐5‐ene‐3β,20β‐diol (16), 3β,11‐dihydroxy‐24‐methylene‐9,11‐secocholestan‐5‐en‐9‐one (23), (24S)‐ergostane‐3β,5α,6β,25 tetraol (146), sinulerectadione (227), sinulerectol C (229), and cladieunicellin I (277) exhibited stronger cytotoxicity than their respective positive control and that their mechanism of action has not yet been further investigated

In the Maldivian islands, the lack of sewage wastewater treatment and an improper landfill enhance the potential hazard of emerging contaminants, including pharmaceuticals and personal care products. In order to analyze the occurrence of emerging contaminants in the marine biota, sponges were collected in two coral reef areas of Magoodhoo island (Faafu), one near the landfill and the other furthest from the island. Caffeine, fluoxetine and norfluoxetine were detected only in the proximity of the landfill, with caffeine showing the highest concentration (28.4 ng/g d.w.), followed by fluoxetine (6.00 ng/g d.w.). Norfluoxetine was below the limit of quantification of 10 ng/g d.w. Nitro xylene, N,N-Diethyl-meta-toluamide and galaxolide were found in both areas, with concentrations of 3.51/6.11/8.54 and

Green fluorescence is a common phenomenon in marine invertebrates and is caused by green fluorescent proteins. Many hydrozoan species display fluorescence in their polyps and/or medusa stages, and in a few cases patterns of green fluorescence have been demonstrated to differ between closely related species. Hydrozoans are often characterized by the presence of cryptic species, due to the paucity of available morphological diagnostic characters. Zanclea species are not an exception, showing high genetic divergence compared to a uniform morphology. In this work, the presence of green fluorescence and the morpho-molecular diversity of six coral- and bryozoan-associated Zanclea species from the Maldivian coral reefs were investigated. Specifically, the presence of green fluorescence in polyps and newly released medusae was explored, the general morphology, as well as the cnidome and the interaction with the hosts, were characterized, and the 16S rRNA region was sequenced and analyzed. Overall, Zanclea species showed a similar morphology, with little differences in the general morphological features and in the cnidome. Three of the analyzed species did not show any fluorescence in both life stages. Three other Zanclea species, including two coral-associated cryptic species, were distinguished by species-specific fluorescence patterns in the medusae. Altogether, the results confirmed the morphological similarity despite high genetic divergence in Zanclea species and indicated that fluorescence patterns may be a promising tool in further discriminating closely related and cryptic species. Therefore, the assessment of fluorescence at a large scale in the whole Zancleidae family may be useful to shed light on the diversity of this enigmatic taxon.

Microplastic pollution represents a serious hazard for the marine environment, including coral reefs. Scleractinian corals can easily mistake microplastics with their natural preys, and ingest them and all the annexed plasticizer additives. Here we selectively searched on field for five phthalates esters (PAEs) namely dibutyl-phthalate (DBP), benzylbutyl-phthalate (BBzP), diethyl-phthalate (DEP), Bis(2-ethylhexyl)-phthalate (DEHP), and dimethyl-phthalate (DMP) in the coral species Pocillopora verrucosa, Porites lutea and Pavona varians. Our data reveal that >95% of corals sampled were contaminated, with a maximum of 172.4 ng/g, a value 7 time-fold higher than those found in a previous study. The Σ5 PAEs showed an average of about 30 ng/g per coral, but no differences in PAEs contamination was detected between species, depth or reef exposure. Despite their effects on coral physiology are not yet known, PAEs should be now considered as a novel, and ubiquitous, form of contamination in corals.

The microbial communities associated with plant's compartments and the expression of the chloroplast chaperonin Hsp60 have been simultaneously analyzed during the diel cycle in the marine seagrass Thalassia hemprichii from the lagoon of Magoodhoo island (Maldives), characterized by remarkable daily shifts in temperature and light. Plants showed a significant up-regulation of Hsp60 expression from 8.00 a.m. to 2.00 p.m., in correspondence with the increase in temperature and light, confirming their role as defense mechanism against photoinhibition and oxidative damage. However, a further significant increase of the Hsp60 level was also observed when irradiance and temperature dropped, suggesting that the cellular stress was still in progress. The plant-associated microbial communities showed differences by plant compartment and sampling time, with the aboveground compartment (leaves) being much more dynamic than the belowground one (roots/rhizomes). In the phyllosphere, a progressive shift during the day from the absolute dominance of the Gammaproteobacteria class, mainly constituted of Enterobacteraceae family, to the increase of the biodiversity due to the rise of Alphaproteobacteria was observed. Belowground, the microbial diversity was much lower than aboveground, being Gammaproteobacteria the most represented class throughout all sampling times. Vibrionaceae family was the most abundant at 8:00 a.m. and 6.00 p.m. decreasing slightly at 2.00 p.m., partially replaced by Halomonadaceae. The combined biochemical and microbial markers allows to assess the plant stress response and to deepen the knowledge on the seagrasses adaptation to harsh and changing environmental conditions, resulting useful to detect early signs of change in an organism's physiological state. Furthermore, the variation of Hsp60 expression and associated bacterial communities in response to light and temperature fluctuations support the ‘holobiont’ theory, which considers the plant/microorganisms association as a functional unit, as suggested for corals.

Zanclea divergens is a tropical hydrozoan living in symbiotic association with bryozoans and currently reported from Papua New Guinea, Indonesia, and Maldives. Here, we used an integrative approach to assess the morpho-molecular diversity of the species across the Indo-Pacific. Phylogenetic and species delimitation analyses based on seven mitochondrial and nuclear loci revealed four well-supported molecular lineages corresponding to cryptic species, and representing a Pacific clade, an Indian clade, and two Red Sea clades. Since the general polyp morphology was almost identical in all samples, the nematocyst capsules were measured and analysed to search for possible fine-scale differences, and their statistical treatment revealed a significant difference in terms of length and width among the clades investigated. All Zanclea divergens specimens were specifically associated with cheilostome bryozoans belonging to the genus Celleporaria. The Pacific and Indian clades were associated with Celleporaria sp. and C. vermiformis, respectively, whereas both Red Sea lineages were associated with C. pigmentaria. Nevertheless, the sequencing of host bryozoans revealed that one of the Red Sea hydrozoan clades is associated with two morphologically undistinguishable, but genetically divergent, bryozoan species. Overall, our results show that Z. divergens is a species complex composed of morphologically cryptic lineages showing partially disjunct distributions and host specificity. The presence of two sympatric lineages living on the same host species reveal complex dynamics of diversification, and future research aimed at understanding their diversification process will likely improve our knowledge on the mechanisms of speciation among currently sympatric cryptic species.

The Zancleidae is a hydrozoan family that currently comprises three genera and 42 nominal species. The validity of numerous taxa in this family still needs to be assessed with integrative analyses and complete life cycle descriptions. The vast majority of its species live symbiotically with other organisms, among which cheilostomate bryozoans are the most common hosts. These bryozoan-associated zancleids are host-specific and encompass all species of the genera Halocoryne and Zanclella, as well as several species in the genus Zanclea. Zancleids show variable morphologies, including highly reduced polyps and medusae. Their phylogenetic history is uncertain due to the often intergrading morphologies and the shortage of molecular data. In the present study, two species of Zanclea from the Indian Ocean and the Red Sea are analysed, using morphological and DNA-based approaches. Morphological analyses of the polyp and medusa stages show that, despite a general resemblance with each other and with Zanclella diabolica, the two species differ in some characters, and this is supported also by molecular investigations. The DNA analyses show that the two species are monophyletic and closely related, but divergent from other Zanclea lineages. This newly recovered clade may correspond with the genus Zanclella or with a cryptic genus. The lack of both morphological and molecular data for several zancleid species did not allow to address this issue. Additionally, the single-and multi-locus phylogeny reconstructions reveal that both the family Zancleidae and the genus Zanclea are polyphyletic taxa, since they are composed of at least three divergent lineages. Most zancleid species have polyps and medusae similar to other closely related taxa, and this conserved general morphology poses a challenge in the delimitation of species, genera and even families in this group. Consequently, further conjunct morphological and molecular efforts are strongly needed to clarify the diversity and evolution of the family Zancleida as a whole.

Coral reefs are among the most diverse ecosystems in the world. The diversity of life found in the habitats created by corals is so large that the reefs are known as the “rainforests of the sea.” Unfortunately, severe natural and anthropogenic changes such as ocean warming, acidification, coral diseases, and plastic pollution are extremely detrimental to this ecosystem. To enrich the ambient conditions of the corals and boost their growth, the potential of two biocomposites is evaluated based on biodegradable polyurethane and silicone matrices as scaffolds for the growth of oceanic organisms. Furthermore, their degradation is investigated within the coral reefs of Faafu Atoll, Republic of Maldives. The observations indicate that there are a significant number of organisms that settle and grow on these biocomposites in the Maldivian lagoon, both of an animal and photosynthetic nature. The biocomposites have the potential to become suitable scaffolds for diverse hard bottom fouling organisms. Moreover, the presence of coral larvae on the biocomposites suggests that during their biodegradation, these biocomposites can support the growth of organisms, generating a suitable environment for triggering the birth of new corals.

WOS:000669987000010; Reef fishes are a treasured part of marine biodiversity, and also provide needed protein for many millions of people. Although most reef fishes might survive projected increases in ocean temperatures, corals are less tolerant. A few fish species strictly depend on corals for food and shelter, suggesting that coral extinctions could lead to some secondary fish extinctions. However, secondary extinctions could extend far beyond those few coral-dependent species. Furthermore, it is yet unknown how such fish declines might vary around the world. Current coral mass mortalities led us to ask how fish communities would respond to coral loss within and across oceans. We mapped 6964 coral-reef-fish species and 119 coral genera, and then regressed reef-fish species richness against coral generic richness at the 1 degrees scale (after controlling for biogeographic factors that drive species diversification). Consistent with small-scale studies, statistical extrapolations suggested that local fish richness across the globe would be around half its current value in a hypothetical world without coral, leading to more areas with low or intermediate fish species richness and fewer fish diversity hotspots.

Herein, we provide observation on the ecological relationships between the hydrozoan species Pteroclava krempfi and three alcyonacean genera: Lobophytum, Sarcophyton and Sinularia from protected and exposed reef habitats in the Maldives. The associations were found to be widespread in the investigated area with both an overall and taxon-specific symbiosis prevalence higher in the exposed reef sites. Pteroclava krempfi most frequently occurred with Lobophytum, followed by Sinularia and Sarcophyton. The prevalence of P. krempfi with soft corals was also positively correlated to percent host cover, which was higher in the outer reef sites, suggesting a host-reliant relationship for the hydrozoan. However, the nature of these relationships, as as well as the factors that drive their establishment, requires further investigation. The widespread degradation of coral reef ecosystems endangers the existence of many poorly understood, but intimate relationships that often go unrecognized.

Climate changes have increased the intensity/frequency of extreme thermal events, which represent serious threats to the health of reef-building corals. Since the vulnerability of corals exposed to thermal stresses are related to their ability to regulate Heat shock proteins (Hsps), we have analyzed together the time related expression profiles of the mitochondrial Hsp60 and the associated changes in tissue pigmentation in Seriatopora caliendrum subjected to 48 h of heat and cold treatments characterized by moderate (±2 °C) and severe (±6 °C) shocks. For the first time, an Hsp60 response was observed in a scleractinian coral exposed to cold stresses. Furthermore, the Hsp60 modulations and the changes in the tissue coloration were found to be specific for each treatment. A strong down-regulation at the end of the treatments was observed following both the severe shocks, but only the severe heat stress led to bleaching in concert with the lowest levels of Hsp60, suggesting that a severe heat shock can be more deleterious than an exposure to a severe cold temperature. On the contrary, a moderate cold stress seems to be more harmful than a moderate temperature increase, which could allow coral acclimation. Our results can provide a potential framework for understanding the physiological tolerance of corals under possible future climate changes.

Outbreaks of the corallivorous crown-of-thorns seastars have received increasing attention due to their negative impacts on coral reefs in the Indo-Pacific Ocean. However, outbreaks in remote and dislocated islands are still poorly understood. This study aims to begin filling informational gaps regarding outbreaks of Acanthaster planci in the remote islands of the central Ari Atoll, Republic of Maldives. The population of A. planci was monitored during three periods over 2 years (2015-2016) to evaluate variations in abundance and to characterise size structure and feeding behaviour. The outbreak appeared to be severe and active throughout the entire study period. The size structure analysis revealed a multimodal distribution dominated by individuals between 20 and 30 cm, suggesting that the outbreak may have resulted from a few nearby mass spawning events. Additionally, the most abundant live coral was Porites, which was also the most consumed genus; however, the electivity index showed a preference for corals of the genera Favites and Pavona. Finally, we also highlighted the need for more geographically extended surveys to better understand local patterns regarding outbreaks of A. planci in the Republic of Maldives.