Despite the global expansion of coral restoration initiatives that depend on volunteer divers in supporting these programs, research exploring their motivations, sentiments and knowledge remains scarce. This study employed a mixed-methods analysis of surveys (n = 83) and interviews (n = 15) of a heterogeneous population of coral restoration volunteers and a control group of divers in Roatan, Honduras to explore these aspects. Experienced coral restoration volunteers did not perceive their contributions to coral health protection as being greater than control group non-volunteer divers, despite displaying a deeper understanding of the threats to coral reefs. Notably, both new volunteers prior to training and experienced restoration volunteers were more than twice as likely as control divers to highlight reducing carbon emissions as critical for coral health. While volunteer divers exhibit a strong baseline awareness and concern for coral reef threats, they report that participation in restoration efforts leads to significant learning gains regarding coral conservation. The insights gained from the motivations and learning outcomes of volunteers in coral restoration in Roatan may inform similar initiatives globally, potentially impacting a wide range of volunteer-based ecosystem restoration programs and diver-involved projects, thereby enhancing volunteer engagement and educational outcomes in environmental conservation efforts.

Cryptic species in coral reefs, such as sea slugs, represent an important portion of their biodiversity, which is usually underestimated. Autonomous Reef Monitoring Structures (ARMS) have been implemented to estimate cryptic diversity in coral reefs. Therefore, this research aimed to contribute to the southern Gulf of Mexico (GM) and the Caribbean Sea (CAR) coral reefs’ sea slugs’ diversity and distribution using ARMS as a collection method. Fifty-eight ARMS were placed at three coral reefs in the GM and CAR, recovered after 1–2 years and then, disassembled at the laboratory. Plates were individually placed in trays with seawater, where we searched for sea slugs. A total of 242 organisms were found belonging to 31 species; 20 of them were identified to the species level, while 11 were determined up to genus or family. More than half of the species (19) were found in Bajo de 10 (GM), while 15 species were found in the CAR localities. Unlike previous studies, we assessed sea slugs’ diversity exclusively by an indirect sampling method. In this work, we found 9.4% of the sea slug diversity recorded in the Caribbean, and we report four determined species for the first time in the country. New records of species, and even one family for the GM stress the gap of information that we still need to fulfil in the area. We recognize ARMS as a useful tool to find juvenile, cryptic and rare species of sea slugs, as well as to standardize their quantification and record their diversity.

Tropical coastal ecosystems are in decline worldwide due to an increasing suite of human activities, which threaten the biodiversity and human wellbeing that these ecosystems support. One of the major drivers of decline is poor water quality from land-based activities. This review summarises the evidence of impacts to coastal ecosystems, particularly coral reefs, from sediments, nutrients, chemicals and pathogens entering coastal zones through surface and groundwater. We also assess how these pollutants affect the health of coastal human populations through: (1) enhanced transmission of infectious diseases; (2) reduced food availability and nutritional deficit from decline of fisheries associated with degraded habitat; and (3) food poisoning from consumption of contaminated seafood. We use this information to identify opportunities for holistic approaches to integrated watershed management (IWM) that target overlapping drivers of ill-health in downstream coastal ecosystems and people. We demonstrate that appropriate management requires taking a multi-sector, systems approach that accounts for socio-ecological feedbacks, with collaboration required across environmental, agricultural, public health, and water, sanitation and hygiene sectors, as well as across the land–sea interface. Finally, we provide recommendations of key actions for IWM that can help achieve multiple sustainable development goals for both nature and people on coasts.

Global climate change has aggravated the severity of space competition put up by marine sponges in the tropical coral reef ecosystems. We report here an outbreak of coral-killing sponge Clathria (Microciona) aceratoobtusa (Carter, 1887) over live coral colonies of the genus Turbinaria in an unprotected reef (mainland patch reef) in the Gulf of Mannar in India. An outbreak of this orange-reddish sponge was observed during an explorative dive in April 2020. Live coral cover in the reef was 62.06% (SD±3.36), which was dominated by the genus Turbinaria with 82.31%. Among the total of 549 Turbinaria colonies counted in five transects, 21.86% (n = 120) of colonies were found infested by the sponge. As the mainland patch reef lies outside the boundary of marine protected area, it is exposed to human-induced threats, apart from climate change implications. This report would serve as an evidence to indicate the intensity of the space competition waged by sponges in a disturbed reef ecosystem.

The coral reefs of the Pitcairn Islands are in one of the most remote areas of the Pacific Ocean, and yet they are exposed to the impacts of anthropogenic climate change. The Pitcairn Islands Marine Protected Area was designated in 2016 and is one of the largest in the world, but the marine environment around these highly isolated islands remains poorly documented. Evidence collated here indicates that while the Pitcairn Islands' reefs have thus far been relatively sheltered from the effect of warming sea temperatures, there is substantial risk of future coral decalcification due to ocean acidification. The projected acceleration in the rate of sea level rise, and the reefs' exposure to risks from distant ocean swells and cold-water intrusions, add further uncertainty as to whether these islands and their reefs will continue to adapt and persist into the future. Coordinated action within the context of the Pitcairn Islands Marine Protected Area can help enhance the resilience of the reefs in the Pitcairn Islands. Options include management of other human pressures, control of invasive species and active reef interventions. More research, however, is needed in order to better assess what are the most appropriate and feasible options to protect these reefs.

The present study enhances knowledge of the biodiversity of diatoms in Chuuk, Micronesia following our 2018 study on the seaweed-associated diatoms. We collected planktonic samples of diatoms from five sites of reef flats using a 20 μm mesh net, and two samples of seaweeds with epiphytes by hand from an islet on the barrier reef. In addition, the seaweed-associated diatoms from our 2018 study were analysed using scanning electron microscopy. A total of 109 diatom taxa are documented in the present study. Of these, 70 species were from net samples, and 39 species from the seaweed-associated diatoms. Thirty-one species are newly recorded from Micronesian waters. Most taxa are benthic or tychoplanktonic; euplanktonic diatoms were rare. The occurrence of benthic diatoms from the water column might be related to the Chuuk environmental conditions which include shallow water, strong light intensity and high grazing pressure, to which benthic diatoms seem to be able to better adapt than planktonic diatoms.

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

Poor connectivity between diverse resource users and complex wider governance networks is a challenge in environmental governance. Organizations that ‘broker’ interactions among these relationships are expected to improve governance outcomes. Here, we used semi-structured interviews and social network analysis to identify actors in positions to broker coral reef-related information to and from resource users and to assess the performance of these brokers. Representatives (n = 262) of actor groups were interviewed, including local and national government, non-governmental organizations (NGOs), community organizations and resource user groups from 12 communities across four Caribbean countries, to map information-sharing networks and to identify brokers. Broker performance was assessed through separate interviews with coral reef resource users (n = 545). The findings show that marine NGOs were the highest-functioning brokers. Where such local-level organizations were absent, government agencies in reef management roles acted as brokers, but their performance was lower. Actors in brokerage positions did not always effectively share information, with broker performance being positively correlated with network brokerage scores. The results further our understanding of the roles of brokers in different governance contexts. Identifying those in brokerage positions and supporting their roles in connecting local resource users to wider governance networks could encourage functional brokerage and enhance reef management outcomes.

The Abrolhos bank, in southern Bahia State (BA), is the largest coral reef system in the southwestern Atlantic. It is highly influenced by the Brazil Current (BC), since it is located in the continental shelf. By contrast, Todos os Santos Bay (TSB), in Salvador, capital of Bahia State (BA) has an important coral biodiversity, located in a bay inlet with restricted water circulation. Coral cores were collected in those sites and were analyzed for density band counting and by Th/U dating to estimate growth rates and age. In this work, we present 14C ages of some of these bands in order to evaluate the marine reservoir effect (MRE) to which the colonies were subjected during growth. It is the first study making use of coral skeleton samples for MRE determination for the Brazilian coast. ΔR was calculated to be –151±23 14C yr, while that for the TSB was –107±51 14C yr.

The Vulnerable bumphead parrotfish Bolbometopon muricatum, a highly prized fishery resource worldwide, has experienced population declines throughout its geographical range. There is limited knowledge of the distribution and abundance of, and threats to, this fish in Indian waters, particularly for the Andaman and Nicobar Islands. To assess the species’ distribution and conservation status we conducted underwater surveys across 75 sites around 51 islands and interviewed 99 fishers across the Andaman and Nicobar archipelago. We recorded a total of 59 individual B. muricatum across nine sites from the northernmost island in the Andamans (Landfall Island) to the southernmost island in the Nicobars (Great Nicobar Island). Interviews revealed that most fishers (100% in Nicobar, 94% in Middle Andaman, 62% in South Andaman) had seen B. muricatum, and knowledge of the species is highest amongst spearfishers. Generalized linear models indicated that presence of marine protected areas and high live coral cover influenced the abundance and distribution of B. muricatum. The species' density seems to be naturally low in the archipelago. We discuss our findings in the light of protecting rare and threatened species, and recommend strengthening the existing marine protected areas in these islands.

Boring sponges are an important component of bioeroder assemblages in tropical coral reefs. They are considered as a potential threat for coral reef health, and the increase of dead corals is expected to promote their abundance. The relationship between the availability of dead coral substrata and the development of boring sponge assemblages was evaluated during El Niño 2015–16 at five reefs from Zihuatanejo, Guerrero, Mexico. Environment and substrate quality were assessed. Overall, environment conditions remained normal in relation to previous studies in the area. Only water temperature showed unusually high records at all sites and coincided with bleaching and mortality of corals, possibly caused by the effects of the El Niño event. Abundance of boring sponges in dead corals and coral rubble was lower than during previous studies. Although sponge abundance was not directly related to cover of both dead corals and coral rubble, cover of dead corals showed a high correlation with the variation in the structure of sponge assemblages across sites. Cliona vermifera dominated sponge assemblages at all sites, and its abundance was high under conditions of high cover of live corals and low cover of bleached corals. Since overall sponge abundance responded in a similar way, these results suggest that boring sponge assemblages dominated by C. vermifera are enhanced by conditions favourable for corals. Our results imply that El Niño events in the Mexican Pacific are not likely to cause immediate population outbreaks of boring sponges.

Despite alterations caused by anthropogenic activities in Singaporean coral reefs, the sponge communities are quite diverse and Xestospongia testudinaria is one of the most common sponge species. In the present study, we used 16S rRNA gene barcoded pyrosequencing to characterize and compare bacterial communities from different biotopes (sponge, seawater and sediment) and to identify dominant bacterial symbionts of X. testudinaria in a Singaporean coral reef ecosystem. Our results showed that biotope appears to affect the richness, composition and abundance of bacterial communities. Proteobacteria was the most abundant phylum in sediment and seawater whilst Chloroflexi was more abundant in X. testudinaria. Members of the order Caldilineales (fermentation of organic substrates), Chromatiales (purple sulphur bacteria), Rhodospirillales (purple non-sulphur bacteria) and Syntrophobacterales (sulphate-reducing bacteria) were relatively more abundant in X. testudinaria samples.

Small-island coral reef ecosystems are usually closely coupled to the activities of human inhabitants. Ahus Island (Papua New Guinea) is an isolated Pacific island with a rapidly growing population, heavy reliance on marine resources and limited infrastructure. We hypothesized that untreated sewage was driving distinct benthic assemblages around Ahus and neighbouring uninhabited Onetah. At sites with varying proximities to beach toilets, fore-reef herbivorous fish biomass and benthic composition were measured alongside reef-flat sedimentary oxygen consumption (SOC); a high SOC rate reflects high organic input into coastal waters, thus serving as a potential indicator of sewage input. Fish biomass was low (17.1–20.1 g m–2), but consistent between sites. However, cyanobacteria dominated the fore-reef closest to toilets (62 ± 3%) with highest reef-flat SOC, whereas hard corals dominated furthest away (63 ± 1%), where SOC was lowest. To our knowledge, this is the first study that used SOC to detect local differences in sewage pollution. The results indicate that whilst corals can maintain their dominance on overfished reefs, additional sewage stress may drive pronounced benthic shifts, highlighting the urgency to improve small-island waste management.

The bearded fireworm, Hermodice carunculata, is a common species in the marine annelid taxon Amphinomidae. It has a widespread distribution throughout the Atlantic, Gulf of Mexico, the Caribbean, Mediterranean and Red Seas. We review its environmental tolerances, defence mechanisms and feeding habits to evaluate its potential to survive in changing ocean conditions, to increasingly emerge as a nuisance species and to invade new geographic areas. Hermodice carunculata tolerates a wide range of environmental conditions, including temperature, salinity, oxygen saturation and various types of pollution. It has few natural predators because it is protected by its sharp chaetae and probably by toxins. Hermodice carunculata is best known for consuming live cnidarians, and has been implicated in transmitting coral pathogens, but it also feeds non-selectively on detritus. In the short term, we predict that H. carunculata will be able to withstand many future ecological challenges and possibly contribute to coral reef decline. In the long term, ocean acidification may negatively impact its defence mechanisms and survival. Its invasive potential may be significant. We highlight the gaps in our knowledge about the reproduction and development of this species, the nature and origin of its toxins and role of microbes in their feeding behaviour and defensive strategies.

Diplosoma gumavirens specimens were collected from the Penghu Islands, Taiwan. This is the first record of photosymbiotic ascidians in the Taiwan Strait, where the minimum water temperature in the winter is <16°C because of intrusion of the China Coastal Current.

The species Homostichanthus duerdeni and Anemonia sargassensis are recorded for the first time in the Mexican Caribbean. Homostichanthus duerdeni is taxonomically diagnosed, and images from living specimens, including external and internal features and cnidae, are provided. The extension of the geographical distribution range of A. sargassensis is discussed, as well as the taxonomic status of the previous records of actiniarians in the Mexican Caribbean. An updated list of sea anemones in the region is provided, comprising 15 species in 11 localities along the Mexican Caribbean.

One species of Microtabella, Microtabella interrupta, is widespread and has been known since the 19th Century but it has a convoluted taxonomic history leaving it presently the only species in the genus. The name interrupta derives from the chain-forming habit and the plastids being confined to a portion of the cell by a set of distinctively distended septa. This character makes it very easy to identify and very easy to overlook similar species, especially because the tabulate frustules are most often seen in girdle view. I found specimens of a new taxon that had these characters and was distinguished with difficulty in girdle view by the coarser striae on the copulae and the recurved edges of the septa. However, in valve view Microtabella rhombica n. sp. has a much broader, rhombic outline. Ultrastructural differences include a more elongated apical pore field with a prominent spine, biseriate striae on the copulae and a different form of the ligule (a raised bar on the last copula). Like Microtabella interrupta, the mature epitheca of Microtabella rhombica comprises numerous copulae with nearly flat septa, two copulae with distended septa and four hyaline pleurae that lack septa. This species could well be widespread but, as with other monospecific genera in which there is a strong distinguishing character, care must be taken to look beyond the outstanding feature.