Search Results (33)

Bivalves possess a diverse array of photoreceptive organs that are significant for their evolutionary success and systematic classification. Giant clams are the largest bivalve mollusks, with mantle tissue permanently extended in nature to maintain symbiosis with zooxanthellae and perceive environmental cues. Eyes serve as critical sensory organs for these organisms, yet the structural and functional characteristics of tridacnine eyes remain inadequately understood. This study systematically investigated the ocular traits and visual resolution of three ecologically distinct giant clam species (Tridacna crocea, T. squamosa, T. maxima) using morphometric analysis, hematoxylin-eosin (HE) staining, transmission electron microscopy (TEM), and grating stimulation assays. Significant interspecific differences were observed in eye count, diameter, and pupil-to-eye ratio (PER): T. maxima exhibited the highest mean eye count (221 ± 8), T. squamosa the largest mean eye diameter (0.490 ± 0.082 mm), and T. crocea the highest mean PER (0.363 ± 0.041). Eyes were numerically symmetric on the left and right mantles but positionally asymmetric, showing random distribution patterns along the mantle margin without fixed corresponding locations across species. All three species possessed typical pinhole eyes lacking lenses and retinas, primarily composed of filler cells, receptor cells, and sparse neurons, with symbiotic zooxanthellae distributed in the surrounding mantle tissue. Grating stimulation assays revealed resolvable stripe periods of 5.82–11.64° (T. crocea), 8.62–13.16° (T. squamosa), and 10.15–12.26° (T. maxima), confirming T. crocea as the species with the highest visual resolution. These ocular variations are inferred to reflect adaptive evolution driven by ecological niches and habitat-specific factors (water depth or light intensity), while the simplified pinhole morphology is consistent with their sedentary lifestyle and metabolic dependence on symbiotic zooxanthellae. These ocular variations provide potential morphological markers for the systematic classification of Tridacninae and offer valuable insights for researchers studying the evolutionary plasticity of bivalve visual systems. Full article

Coral reef ecosystems represent one of the most biodiverse and productive marine habitats, yet they are increasingly threatened by a range of anthropogenic stressors. Among these, emerging contaminants including pharmaceutical and personal care products (PPCPs) have started to feature as contaminants of concern due to their persistence, bioaccumulation potential, and complex interactions within reef environments. This review synthesizes current research on the occurrence, transport pathways, and ecological impacts of emerging contaminants, specifically focusing on PPCPs on coral reef systems. Evidence indicates that compounds such as UV filters, antibiotics, and endocrine-disrupting chemicals can impair coral physiology, disrupt symbiotic relationships with zooxanthellae, and contribute to bleaching events. The review further highlights the variability in coral species’ sensitivity to these contaminants, with documented effects ranging from oxidative stress to reduced growth and reproductive capacity. Despite advances in detection and risk assessment, significant knowledge gaps remain regarding long-term exposure, mixture effects, and the influence of local environmental conditions on contaminant toxicity. By consolidating recent findings, this review underscores the urgent need for targeted research and policy action to mitigate the threat of emerging contaminants to coral reef ecosystems. Full article

The coral Acropora aff. tenuis selectively acquired various zooxanthella (Symbiodiniaceae) strains, and one of the selective factors was lectins. The A. aff. tenuis lectin AtTL-2 was identified as a factor for Symbiodiniaceae acquisition by the coral, but the mechanism is not fully known. The acquisition process involves three steps: chemotaxis, entry into the coral, and phagocytosis. In this study, we examined the function of AtTL-2 in more detail. Immunohistochemistry analysis was performed to examine the distribution of AtTL-2. The effect of AtTL-2 on the number of Symbiodiniaceae acquired was measured in A. aff. tenuis juvenile polyps with and without AtTL-2 siRNA treatment. The effect of AtTL-2 fixation was examined by monitoring the acquisition of AtTL-2–fixed beads by A. aff. tenuis. AtTL-2 was distributed in nematocysts, spirocysts, and around Symbiodiniaceae. AtTL-2 siRNA inhibited the acquisition of Symbiodiniaceae by juvenile polyps. Fixation of AtTL-2 promoted bead acquisition by juvenile polyps more than fixation of bovine serum albumin (BSA). Moreover, more AtTL-2–fixed beads were bound to the Symbiodiniaceae-enclosed cells than BSA-fixed beads. AtTL-2 is released from spirocysts and binds to Symbiodiniaceae. AtTL-2 then promotes the phagocytosis of Symbiodiniaceae by gastrodermal cells of A. aff. tenuis. Full article

Corals can be considered holobiont organisms, since they have an important symbiotic relationship with microbial communities such as zooxanthellae, bacteria, Archaea, fungi and viruses. It is important to understand how those microbial communities influence the health of the corals and how environmental conditions could affect them. The present study aimed to describe the bacterial communities associated with three Brazilian coral species, Millepora alcicornis, Mussismilia harttii and Phyllogorgia dilatata, by a culture-independent method, using 16S rRNA gene sequencing. The corals were collected from two distinct coral reefs: Recife de Fora, in Bahia (BA) and Búzios, in Rio de Janeiro (RJ). The phylum Proteobacteria showed the highest relative abundance in most corals and sites. The bacterial compositions of these three corals from the two sample sites were very distinct from each other, not presenting similarities in coral species or related to sampling site. In M. alcicornes/RJ, the most abundant class was Gammaproteobacteria, order Piscirickettsiales, while the same species collected in BA showed unassigned Gammaproteobacteria, and Vibrionaceae was the second most abundant family. M. harttii/BA presented the most distinct bacterial phylum composition with 16 phyla (26% Proteobacteria, 16% Chloroflexi, 12% Acidobacteriota). Full article

The phylum Cnidaria comprises five main classes—Hydrozoa, Scyphozoa, Hexacorallia, Octocorallia and Cubozoa—that include such widely distributed and well-known animals as hard and soft corals, sea anemones, sea pens, gorgonians, hydroids, and jellyfish. Cnidarians play a very important role in marine ecosystems. The composition of their fatty acids (FAs) depends on food (plankton and particulate organic matter), symbiotic photosynthetic dinoflagellates and bacteria, and de novo biosynthesis in host tissues. In cnidarian lipids, besides the common FA characteristics of marine organisms, numerous new and rare FAs are also found. All Octocorallia species and some Scyphozoa jellyfish contain polyunsaturated FAs (PUFAs) with 24 and 26 carbon atoms. The coral families can be distinguished by specific FA profiles: the presence of uncommon FAs or high/low levels of common fatty acids. Many of the families have characteristic FAs: Acroporidae are characterized by 18:3n6, eicosapentaenoic acid (EPA) 20:5n3, 22:4n6, and 22:5n3; Pocilloporidae by 20:3n6, 20:4n3, and docosahexaenoic acid 22:6n3 (DHA); and Poritidae by arachidonic acid (AA) and DHA. The species of Faviidae show elevated concentrations of 18:3n6 and 22:5n3 acids. Dendrophylliidae, being azooxanthellate corals, have such dominant acids as EPA and 22:5n3 and a low content of DHA, which is the major PUFA in hermatypic corals. The major and characteristic PUFAs for Milleporidae (class Hydrozoa) are DHA and 22:5n6, though in scleractinian corals, the latter acid is found only in trace amounts. Full article

The zooxanthellate jellyfish Cassiopea andromeda (Forsskål, 1775), a Lessepsian species increasingly common in the western and central Mediterranean Sea, was investigated here to assess its potential as a source of bioactive compounds from medusa specimens both collected in the wild (the harbor of Palermo, NW Sicily) and reared under laboratory-controlled conditions. A standardized extraction protocol was used to analyze the biochemical composition of the two sampled populations in terms of protein, lipid, and pigment contents, as well as for their relative concentrations of dinoflagellate symbionts. The total extracts and their fractions were also biochemically characterized and analyzed for their in vitro antioxidant activity to quantify differences in functional compounds between wild and reared jellyfish. The two populations were similar in terms of extract yield, but with substantial differences in biomass, the number of zooxanthellae, protein and lipid contents, and fatty acid composition. The hydroalcoholic extracts obtained from jellyfish grown under controlled conditions showed greater antioxidant activity due to the presence of a higher content of bioactive compounds compared to wild jellyfish. This study could be the basis for considering the sustainable breeding of this holobiont or other similar organisms as a source of valuable compounds that can be used in the food, nutraceutical, or pharmaceutical sectors. Full article

The sea bivalve clam Tridacna crocea inhabiting the shallow sea of tropical and subtropical zones lives with the symbiotic alga zooxanthella in its mantle. Zooxanthellae algae perform photosynthesis and supply nutrients to T. crocea. Recently, the abundance of T. crocea has decreased rapidly due to overfishing in coastal areas in Okinawa, Japan. T. crocea culture systems for mass production will contribute to the conservation of T. crocea and thus marine ecosystems. Environmental control methods for T. crocea culture have not been established because of a lack of knowledge about the appropriate environmental conditions for T. crocea growth. The present study was initiated to obtain basic data for developing environmental control methods for T. crocea land-based aquaculture. The effects of water temperature, dissolved oxygen concentration, and photosynthetic photon flux density (PPFD) on the O₂ exchange rates of the symbiotic system of T. crocea and zooxanthella, which are indicators of photosynthesis and respiration in the system, and the effect of daily integrated PPFD on T. crocea growth were investigated. Basic knowledge was obtained for the development of optimal environmental control technology for T. crocea clam culture. The optimum water temperature and dissolved oxygen concentration for photosynthesis in this symbiotic system were 28 °C, 5–6 mgO₂ L⁻¹ and 500 μmol m⁻² d⁻¹, respectively. The optimum daily integrated PPFD for clam growth was 20 mol m⁻² d⁻¹. Full article

As an important mollusk in reef ecosystems, Tridacna squamosa forms pro-survival symbiotic relationships that hinge on an exquisite redox equilibrium between the host and the photosynthetic symbiont, zooxanthellae. The exact regulatory mechanisms thereof remain poorly understood. In this study, a novel Nfe2-like transcription factor in T. squamosa was identified and characterized with respect to its antioxidant and cytoprotective roles. Gene structure and phylogenetic analysis reveal that T. squamosa possesses a single transcription factor TsNfe2l in contrast to mammalian Nfe2l1 (Nrf1) and Nfe2l2 (Nrf2), belonging to protein members of the bZIP-NFE2 subfamily and functionally resembling the mammalian Nfe2l1. A conserved bZIP domain permits its binding to the antioxidant response element (ARE) in vitro and in HEK293T cells. Further analyses such as promoter prediction suggest that TsNfe2l target genes engage mainly in the regulation of multiple enzymes involved in antioxidation and allied pathways. Notably, TsNfe2l transcriptionally upregulates carnosine synthase (TsATPGD), which subsequently produces L-carnosine abundantly to shield cells from oxidative damage. Moreover, the blockage of TsNfe2l nucleic acid binding reduced the expression of TsATPGD and L-carnosine content in the gill, resulting in elevated lipid peroxidation. Collectively, our findings establish novel molecular insight into TsNfe2l as a critical regulator of redox homeostasis in T. squamosa through carnosine synthesis. Full article

Symbiotic microorganisms in reef-building corals, including algae, bacteria, archaea, fungi, and viruses, play critical roles in the adaptation of coral hosts to adverse environmental conditions. However, their adaptation and functional relationships in nutrient-rich environments have yet to be fully explored. This study investigated Duncanopsammia peltata and the surrounding seawater and sediments from protected and non-protected areas in the summer and winter in Dongshan Bay. High-throughput sequencing was used to characterize community changes, co-occurrence patterns, and factors influencing symbiotic coral microorganisms (zooxanthellae, bacteria, and archaea) in different environments. The results showed that nutrient enrichment in the protected and non-protected areas was the greatest in December, followed by the non-protected area in August. In contrast, the August protected area had the lowest nutrient enrichment. Significant differences were found in the composition of the bacterial and archaeal communities in seawater and sediments from different regions. Among the coral symbiotic microorganisms, the main dominant species of zooxanthellae is the C1 subspecies (42.22–56.35%). The dominant phyla of bacteria were Proteobacteria, Cyanobacteria, Firmicutes, and Bacteroidota. Only in the August protected area did a large number (41.98%) of SAR324_cladeMarine_group_B exist. The August protected and non-protected areas and December protected and non-protected areas contained beneficial bacteria as biomarkers. They were Nisaea, Spiroplasma, Endozoicomonas, and Bacillus. No pathogenic bacteria appeared in the protected area in August. The dominant phylum in Archaea was Crenarchaeota. These symbiotic coral microorganisms’ relative abundances and compositions vary with environmental changes. The enrichment of dissolved inorganic nitrogen in environmental media is a key factor affecting the composition of coral microbial communities. Co-occurrence analysis showed that nutrient enrichment under anthropogenic disturbances enhanced the interactions between coral symbiotic microorganisms. These findings improve our understanding of the adaptations of coral holobionts to various nutritional environments. Full article

Reef-building corals, recognized as cornerstone species in marine ecosystems, captivate with their unique duality as both symbiotic partners and autotrophic entities. Beyond their ecological prominence, these corals produce a diverse array of secondary metabolites, many of which are poised to revolutionize the domains of pharmacology and medicine. This exhaustive review delves deeply into the multifaceted world of coral-derived lipids, highlighting both ubiquitous and rare forms. Within this spectrum, we navigate through a myriad of fatty acids and their acyl derivatives, encompassing waxes, sterol esters, triacylglycerols, mono-akyl-diacylglycerols, and an array of polar lipids such as betaine lipids, glycolipids, sphingolipids, phospholipids, and phosphonolipids. We offer a comprehensive exploration of the intricate biochemical variety of these lipids, related fatty acids, prostaglandins, and both cyclic and acyclic oxilipins. Additionally, the review provides insights into the chemotaxonomy of these compounds, illuminating the fatty acid synthesis routes inherent in corals. Of particular interest is the symbiotic bond many coral species nurture with dinoflagellates from the Symbiodinium group; their lipid and fatty acid profiles are also detailed in this discourse. This exploration accentuates the vast potential and intricacy of coral lipids and underscores their profound relevance in scientific endeavors. Full article

Coral reefs in Sanya Bay have been degrading in recent decades under climate change and human activities. To identify physiological changes of scleractinian corals and corresponding influencing factors, aquatic environmental factors and physiological parameters of Pocillopora damicornis, Porites pukoensis and their symbiotic zooxanthellae were examined in four Sanya Bay coral reef areas in December 2020 (winter) and July 2021 (summer). The density and chlorophyll a+c₂ content of the symbiotic zooxanthellae were significantly high in winter and low in summer. Superoxide dismutase and caspase3 activities of corals and zooxanthellae were high in summer and low in winter, whereas catalase activity showed the opposite pattern. The variations were consistent for both coral symbionts. Water temperature and salinity were the main factors affecting the physiological variations of corals. Compared with winter, the high temperature/low salinity aquatic environment in summer reduced the density and chlorophyll a+c₂ content of zooxanthellae, resulting in high superoxide dismutase and caspase3 activities in the corals and zooxanthellae. In addition, turbidity was an important factor affecting the physiological characteristics of coral–zooxanthellae symbionts among the four coral reef areas. Our results have important implications for understanding the changes in coral reef communities in Sanya Bay and coral reef protection. Full article

Cassiopea andromeda (Forsskål, 1775), commonly found across the Indo-Pacific Ocean, the Red Sea, and now also in the warmest areas of the Mediterranean Sea, is a scyphozoan jellyfish that hosts autotrophic dinoflagellate symbionts (family Symbiodiniaceae). Besides supplying photosynthates to their host, these microalgae are known to produce bioactive compounds as long-chain unsaturated fatty acids, polyphenols, and pigments, including carotenoids, with antioxidant properties and other beneficial biological activities. By the present study, a fractionation method was applied on the hydroalcoholic extract from two main body parts (oral arms and umbrella) of the jellyfish holobiont to obtain an improved biochemical characterization of the obtained fractions from the two body parts. The composition of each fraction (i.e., proteins, phenols, fatty acids, and pigments) as well as the associated antioxidant activity were analyzed. The oral arms proved richer in zooxanthellae and pigments than the umbrella. The applied fractionation method was effective in separating pigments and fatty acids into a lipophilic fraction from proteins and pigment–protein complexes. Therefore, the C. andromeda–dinoflagellate holobiont might be considered as a promising natural source of multiple bioactive compounds produced through mixotrophic metabolism, which are of interest for a wide range of biotechnological applications. Full article

Dinoflagellates are a major aquatic protist group with amphiesma, multiple cortical membranous “cell wall” layers that contain large circum-cortical alveolar sacs (AVs). AVs undergo extensive remodeling during cell- and life-cycle transitions, including ecdysal cysts (ECs) and resting cysts that are important in some harmful algal bloom initiation–termination. AVs are large cortical vesicular compartments, within which are elaborate cellulosic thecal plates (CTPs), in thecate species, and the pellicular layer (PL). AV-CTPs provide cellular mechanical protection and are targets of vesicular transport that are replaced during EC-swarmer cell transition, or with increased deposition during the cellular growth cycle. AV-PL exhibits dynamical-replacement with vesicular trafficking that are orchestrated with amphiesmal chlortetracycline-labeled Ca²⁺ stores signaling, integrating cellular growth with different modes of cell division cycle/progression. We reviewed the dynamics of amphiesma during different cell division cycle modes and life cycle stages, and its multifaceted regulations, focusing on the regulatory and functional readouts, including the coral–zooxanthellae interactions. Full article

An increasing ecological phase shift from coral-dominated reefs to macroalgae-dominated reefs as a result of anthropogenic impacts, such as eutrophication, sedimentation, and overfishing, has been observed in many reef systems around the world. Ocean warming is a universal threat to both corals and macroalgae, which may alter the outcome of competition between them. Therefore, in order to explore the effects of indirect and direct exposure to macroalgae on the physiological, biochemical, and genetic expression of corals at elevated temperature, the coral Acropora hyacinthus and highly invasive green algae Caulerpa taxifolia were chosen. Physiologically, the results exhibited that, between the control and direct contact treatments, the density and chlorophyll a content of zooxanthella decreased by 53.1% and 71.2%, respectively, when the coral indirectly contacted with the algae at an ambient temperature (27 °C). Moreover, the enzyme activities of superoxide dismutase (SOD) and catalase (CAT) in coral tissue were enhanced by interacting with algae. After an increase of 3 °C, the density and chlorophyll a content of the zooxanthella reduced by 84.4% and 93.8%, respectively, whereas the enzyme activities of SOD and CAT increased 2.3- and 3.1-fold. However, only the zooxanthellae density and pigment content decreased when Caulerpa taxifolia was co-cultured with Acropora hyacinthus at 30 °C. Molecularly, different from the control group, the differentially expressed genes (DEGs) such as Rab family, ATG family, and Casp7 genes were significantly enriched in the endocytosis, autophagy, and apoptosis pathways, regardless of whether Acropora hyacinthus was directly or indirectly exposed to Caulerpa taxifolia at 27 °C. Under thermal stress without algae interaction, the DEGs were significantly enriched in the microbial immune signal transduction pathways, such as the Toll-like receptor signaling pathway and TNF signaling pathway, while multiple cellular immunity (IFI47, TRAF family) and oxidative stress (CAT, SODC, HSP70) genes were upregulated. Inversely, compared with corals without interaction with algae at 30 °C, the DEGs of the corals that interacted with Caulerpa taxifolia at 30 °C were remarkably enriched in apoptosis and the NOD-like receptor signaling pathway, including the transcription factors such as the Casp family and TRAF family. In conclusion, the density and chlorophyll a content of zooxanthella maintained a fading tendency induced by the macroalgae at ambient temperatures. The oxidative stress and immune response levels of the coral was elevated at 30 °C, but the macroalgae alleviated the negative effects triggered by thermal stress. Full article

In recent years, ciliate infections have caused serious casualties to corals in the ocean. Infected corals die within a short period of time, which not only poses a threat to wild coral reefs, but also has a major impact on large scale aquaculture of coral. Clove is a kind of Chinese medicine with antifungal, antibacterial, antiviral, insecticidal, and other functions. Clove is a natural product. If it can be used in the treatment of coral ciliates, it will reduce this threat to the environment. The clove extract was diluted with sterile seawater to 500 ppm, 1500 ppm, 2500 ppm, 5000 ppm, 7500 ppm, and 10,000 ppm to carry out virulence test on ciliates. The results show that the LC₅₀ value is 1500 ppm, which can cause the death of ciliates in 10 min without causing significant changes in G. columna SOD, CAT, chlorophyll a, and zooxanthellae. In addition, observation of tissue slices revealed that no ciliates and vacuum were found in the G. columna tissue after 10 min of medicated bathing. In summary, 1500 ppm of clove extract can be used for the treatment of coral ciliates. Full article