The hidden biodiversity of tropical coral reefs

Contrasting effects of increasing dissolved iron on photosynthesis and O2 availability in the gastric cavity of two Mediterranean corals

Iron (Fe) plays a fundamental role in coral symbiosis, supporting photosynthesis, respiration, and many important enzymatic reactions. However, the extent to which corals are limited by Fe and their metabolic responses to inorganic Fe enrichment remains to be understood. We used respirometry, variable chlorophyll fluorescence, and O2 microsensors to investigate the impact of increasing Fe(III) concentrations (20, 50, and 100 nM) on the photosynthetic capacity of two Mediterranean coral species, Cladocora caespitosa and Oculina patagonica. While the bioavailability of inorganic Fe can rapidly decrease, we nevertheless observed significant physiological effects at all Fe concentrations. In C. caespitosa, exposure to 50 nM Fe(III) increased rates of respiration and photosynthesis, while the relative electron transport rate (rETR(II)) decreased at higher Fe(III) exposure (100 nM). In contrast, O. patagonica reduced respiration, photosynthesis rates, and maximum PSII quantum yield (Fv/Fm) across all iron enrichments. Both corals exhibited increased hypoxia (<50 µmol O2 L-1) within their gastric cavity at night when exposed to 50 and 100 nM Fe(III), leading to increased polyp contraction time and reduced O2 exchange with the surrounding water. Our results indicate that C. caespitosa, but not O. patagonica, might be limited in Fe for achieving maximal photosynthetic efficiency. Understanding the multifaceted role of iron in corals' health and their response to environmental change is crucial for effective coral conservation.

Systematics and character evolution of capitate hydrozoans

Capitate hydrozoans are a morphologically and ecologically diverse hydrozoan suborder, currently including about 200 species. Being grouped in two clades, Corynida and Zancleida, these hydrozoans still show a number of taxonomic uncertainties at the species, genus and family levels. Many Capitata species established symbiotic relationships with other benthic organisms, including bryozoans, other cnidarians, molluscs and poriferans, as well as with planktonic dinoflagellates for mixotrophic relationships and with bacteria for thiotrophic ectosymbioses. Our study aimed at providing an updated and comprehensive phylogeny reconstruction of the suborder, at modelling the evolution of selected morphological and ecological characters, and at testing evolutionary relationships between the symbiotic lifestyle and the other characters, by integrating taxonomic, ecological and evolutionary data. The phylogenetic hypotheses here presented shed light on the evolutionary relationships within Capitata, with most families and genera being recovered as monophyletic. The genus Zanclea and family Zancleidae, however, were divided into four divergent clades, requiring the establishment of the new genus Apatizanclea and the new combinations for species in Zanclea and Halocoryne genera. The ancestral state reconstructions revealed that symbiosis arose multiple times in the evolutionary history of the Capitata, and that homoplasy is a common phenomenon in the group. Correlations were found between the evolution of symbiosis and morphological characters, such as the perisarc. Overall, our results highlighted that the use of genetic data and a complete knowledge of the life cycles are strongly needed to disentangle taxonomic and systematic issues in capitate hydrozoans. Finally, the colonization of tropical habitat appears to have influenced the evolution of a symbiotic lifestyle, playing important roles in the evolution of the group.

Host specificity of coral-associated fauna and its relevance for coral reef biodiversity

Coral-associated fauna predominantly consists of invertebrates and constitutes an important component of coral reef biodiversity. The symbionts depend on their hosts for food, shelter and substrate. They may act as parasites by feeding on their hosts, by overgowing their polyps, or by excavating their skeletons. Because some of these species partly reside inside their hosts, they may be cryptic and can easily be overlooked in biodiversity surveys. Since no quantitative overview is available about these inter-specific relationships, this present study adresses variation in host ranges and specificity across four large coral-associated taxa and between the Atlantic and Indo-Pacific oceans. These taxa are: coral barnacles (Pyrgomatidae, n = 95), coral gall crabs (Cryptochiridae, n = 54), tubeworms (Serpulidae, n = 31), and date mussels (Lithophaginae, n = 23). A total of 335 host coral species was recorded. An index of host specificity (STD) was calculated per symbiont species, based on distinctness in taxonomic host range levels (species, genus, family, etc.). Mean indices were statistically compared among the four associated taxa and the two oceanic coral reef regions. Barnacles were the most host-specific, tubeworms the least. Indo-Pacific associates were approximately 10 times richer in species and two times more host-specific than their Atlantic counterparts. Coral families varied in the number of associates, with some hosting none. This variation could be linked to host traits (coral growth form, maximum host size) and is most probably also a result of the evolutionary history of the interspecific relationships.

Unveiling the hidden threat of microplastics to coral reefs in remote South Atlantic islands

The widespread presence of marine microplastics (< 5 mm) is a significant concern, as it may harm marine biodiversity and ocean ecosystems. Corals' capacity to ingest microplastics has emerged as a significant threat to reef ecosystems, owing to the detrimental physiological and ecological effects it can trigger. The extent of the impact of microplastics on Brazilian corals remains unclear and this study aimed to investigate its distribution and characteristics in four coral species: Favia gravida, Mussismilia hispida, Montastrea cavernosa, and Siderastrea stellata, found in the Trindade and Martim Vaz Islands - the most isolated archipelago of Brazil, located about 1200 km (680 miles) east of the coast. This study aims to reveal the extent of microplastic distribution in the coral reef environment, assess the amount of microplastics in different coral species, and compare each species' capacity to adhere and accumulate microplastics. A high concentration of ingested and adhered microplastics was detected in all coral species evaluated in the present study. No significant differences were observed in the sampling points which indicates that although the sampling points are located at different distances from the coast, the microplastic pollution is equally distributed in the region. Polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), poly(methyl methacrylate) (PMMA), Rayon, and Nylon particles were detected, with a predominance of PE (45.5 %). No significant differences in microplastic concentration were detected among the various species and locations studied. Our research presents findings that demonstrate the extensive occurrence of microplastic contamination in coral colonies located on remote islands.

Black Mantle Tissue of Endolithic Mussels (Leiosolenus spp.) Is Cloaking Borehole Orifices in Caribbean Reef Corals

Bioerosion caused by boring mussels (Mytilidae: Lithophaginae) can negatively impact coral reef health. During biodiversity surveys of coral-associated fauna in Curaçao (southern Caribbean), morphological variation in mussel boreholes was studied. Borings were found in 22 coral species, 12 of which represented new host records. Dead corals usually showed twin siphon openings, for each mussel shaped like a figure of eight, which were lined with a calcareous sheath and protruded as tubes from the substrate surface. Most openings surrounded by live coral tissue were deeper and funnel-shaped, with outlines resembling dumbbells, keyholes, ovals or irregular ink blotches. The boreholes appeared to contain black siphon and mantle tissue of the mussel. Because of the black color and the hidden borehole opening in live host corals, the mantle tissue appeared to mimic dark, empty holes, while they were actually cloaking live coral tissue around the hole, which is a new discovery. By illustrating the morphological range of borehole orifices, we aim to facilitate the easy detection of boring mussels for future research.

Diversity of Seahorse Species (Hippocampus spp.) in the International Aquarium Trade

Seahorses (Hippocampus spp.) are threatened as a result of habitat degradation and overfishing. They have commercial value as traditional medicine, curio objects, and pets in the aquarium industry. There are 48 valid species, 27 of which are represented in the international aquarium trade. Most species in the aquarium industry are relatively large and were described early in the history of seahorse taxonomy. In 2002, seahorses became the first marine fishes for which the international trade became regulated by CITES (Convention for the International Trade in Endangered Species of Wild Fauna and Flora), with implementation in 2004. Since then, aquaculture has been developed to improve the sustainability of the seahorse trade. This review provides analyses of the roles of wild-caught and cultured individuals in the international aquarium trade of various Hippocampus species for the period 1997–2018. For all species, trade numbers declined after 2011. The proportion of cultured seahorses in the aquarium trade increased rapidly after their listing in CITES, although the industry is still struggling to produce large numbers of young in a cost-effective way, and its economic viability is technically challenging in terms of diet and disease. Whether seahorse aquaculture can benefit wild populations will largely depend on its capacity to provide an alternative livelihood for subsistence fishers in the source countries. For most species, CITES trade records of live animals in the aquarium industry started a few years earlier than those of dead bodies in the traditional medicine trade, despite the latter being 15 times higher in number. The use of DNA analysis in the species identification of seahorses has predominantly been applied to animals in the traditional medicine market, but not to the aquarium trade. Genetic tools have already been used in the description of new species and will also help to discover new species and in various other kinds of applications.

The Extraordinary Importance of Coral-Associated Fauna

Coral reefs are one of the most diverse marine ecosystems on Earth and one of the richest in terms of species interactions. Scleractinian corals are usually the most likely to provide numerous different habitats and to support many symbiotic relationships. However, many other invertebrate groups, such as sponges, bryozoans, and other cnidarians, establish strict symbiotic relationships with other marine organisms. Despite the nature of these relationships—as well as the factors that drive their establishment—being unclear in most cases, a few studies have already shown that some associations may increase the resistance of their hosts to external disturbances. Thus, the potential ability of each member of these diverse symbiotic assemblages to influence the fitness and long-term survival of their hosts bring the coral-associated fauna to the top of the list of coral reef studies. Unfortunately, the widespread degradation of coral reef ecosystems may threaten the existence of the intimate relationships that may go unrecognized complicating our understanding of the intricate networks connecting the fates of reef species. Therefore, this unprecedented loss of biodiversity calls for synergic conservation and monitoring actions aimed at significantly increasing our efforts to search for and describe as much of the diversity of coral-associated organisms as possible, shedding new light on the complex, elusive mechanisms controlling coral reef functioning.

A first phylogenetic study on stoloniferous octocorals off the coast of Kota Kinabalu, Sabah, Malaysia, with the description of two new genera and five new species

Sabah, Malaysia, is well known for its extensive and diverse coral reefs. It is located on the northwestern edge of the Coral Triangle, the region with the highest marine biodiversity. Much of the marine fauna here is still unknown, especially inconspicuous animals, such as small stoloniferous octocorals, which are common on coral reefs. Here, we describe two new monospecific genera of the family Arulidae found off the coast of Kota Kinabalu, Sabah, East Malaysia; Bunga payung gen. nov. et sp. nov. and Laeta waheedae gen. nov. et sp. nov. As well, the stoloniferan genus Phenganax Alderslade & McFadden, 2011 belonging to the family Clavulariidae is expanded with three new species, P. marumi sp. nov., P. subtilis sp. nov., and P. stokvisi sp. nov., which are all sclerite-free. Additionally, we report a possibly undescribed species, closely related to the clavulariid genera Azoriella Lopez-Gonzalez & Gili, 2001 and Cervera Lopez-Gonzalez et al., 1995. As this and other recent studies have shown, discoveries of small stoloniferous octocorals are helping to fill gaps in our knowledge of the overall systematics of Octocorallia.

Pollution and coral damage caused by derelict fishing gear on coral reefs around Koh Tao, Gulf of Thailand

Most lost fishing gear is made of non-biodegradable plastics that may sink to the sea floor or drift around in currents. It may remain unnoticed until it shows up on coral reefs, beaches and in other coastal habitats. Stony corals have fragile skeletons and soft tissues that can easily become damaged when they get in contact with lost fishing gear. During a dive survey around Koh Tao, a small island in the Gulf of Thailand, the impact of lost fishing gear (nets, ropes, cages, lines) was studied on corals representing six different growth forms: branching, encrusting, foliaceous, free-living, laminar, and massive. Most gear (>95%) contained plastic. Besides absence of damage (ND), three categories of coral damage were assessed: fresh tissue loss (FTL), tissue loss with algal growth (TLAG), and fragmentation (FR). The position of the corals in relation to the fishing gear was recorded as either growing underneath (Un) or on top (On), whereas corals adjacent to the gear (Ad) were used as controls. Nets formed the dominant type of lost gear, followed by ropes, lines and cages, respectively. Branching corals were most commonly found in contact with the gear and also around it. Tubastraea micranthus was the most commonly encountered coral species, either Un, On, or Ad. Corals underneath gear showed most damage, which predominantly consisted of tissue loss. Fragmentation was less common than expected, which may be related to the low fragility of T. micranthus as dominant branching species. Even if nets serve as substrate for corals, it is recommended to remove them from reefs, where they form a major component of the plastic pollution and cause damage to corals and other reef organisms.

Lack of host specificity of copepod crustaceans associated with mushroom corals in the Red Sea

The radiation of symbiotic copepods (Crustacea: Copepoda) living in association with stony corals (Cnidaria: Scleractinia) is considered host-specific and linked to the phylogenetic diversification of their hosts. However, symbiotic copepods are poorly investigated, occurrence records are mostly anecdotal, and no explicit analysis exists regarding their relationship with the hosts. Here, we analysed the occurrence of symbiotic copepods on different co-occurring and phylogenetically closely related scleractinian corals. We used an innovative approach of DNA extraction from single microscopic specimens that preserves the shape of the organisms for integrative morphological studies. The rationale of the study involved: (i) sampling of mushroom corals (Fungiidae) belonging to 13 species and eight genera on different reefs along the Saudi coastline in the Red Sea, (ii) extraction of all the associated copepods, (iii) morphological screening and identification of copepod species, (iv) use of DNA taxonomy on mitochondrial and nuclear markers to determine species boundaries for morphologically unknown copepod species, (v) reconstruction of phylogenies to understand their evolutionary relationships, and (vi) analysis of the ecological drivers of the occurrence, diversity and host specificity of the copepods. The seven species of coral-associated copepods, all new to science, did not show any statistically significant evidence of host-specificity or other pattern of ecological association. We thus suggest that, contrary to most assumptions and previous anecdotal evidence on this coral-copepod host-symbiont system, the association between copepods and their host corals is rather labile, not strict, and not phylogenetically constrained, changing our perception on evolutionary patterns and processes in symbiotic copepods.