Baseline assessment of coral diseases in an environmentally extreme environment of the northern Persian Gulf

Management strategy influences coral oxidative stress responses in a marine protected area in the Southwestern Atlantic

Coral reefs are experiencing accelerated degradation due to global and local stressors. The understanding of how corals cope with these disturbances is urgent. We focused on elucidating antioxidant capacity responses of the Mussismilia harttii and Siderastrea sp. corals, in reefs with use management in a marine protected area. We tested whether the activity of antioxidant enzymes in healthy colonies is higher at multiple-use reefs than at no-take reef, and whether the activity of antioxidant enzymes is higher for bleached than for healthy Siderastrea sp. colonies. Lipid peroxidation and enzymatic activity found in bleached colonies evidence chronic stress and cellular damage not related to thermal anomalies. Chronic stress in healthy colonies was also found but responses differed among species, being higher at multiple use reefs, mainly for Siderastrea sp. We highlight the role of the local conservation actions in the integrity of coral physiology and reef resilience under global climate changes.

Reactions of juvenile coral to three years of consecutive thermal stress

As global temperatures continue to rise, corals are being exposed to increasing heat stress throughout their early life stages; however, the impact of this phenomenon is poorly understood. We exposed the reef-building coral Acropora tenuis juveniles to ∼26-28 °C (control) and ∼ 31 °C (heat stress) for one week per year over three consecutive years. In the first year of heat stress, >96 % of juveniles survived despite symbiotic algal densities in juvenile corals declining. In comparison, survival rates in the third year of heat stress declined to 50 %. Survival rates under natural conditions after stress also gradually decreased in the stressed groups. The rate in the reduction of survivorship was prominent in the consecutive thermally stressed groups (juveniles stressed twice in two years). Symbiotic algal density and photosynthetic activity (Fv/Fm) also declined in stressed juvenile groups. However, heat stress did not significantly affect the growth of juveniles. In the third year of heat stress, temperature negatively affected the physiology of juveniles in terms of survivorship, brightness (an indicator of bleaching), symbiotic algal density, and photosynthetic efficiency. Stress across consecutive years appeared to cause the survivorship of juvenile corals to decline, with three years of stress contributing to the severe decline of a reef. In conclusion, A. tenuis juveniles are not able to acclimatize to heat stress, with successive heat waves of <7 days in the summer potentially negatively affecting resilience.

Acclimation potential of Acropora to mesophotic environment

Mesophotic coral ecosystems may serve as a refuge for reef-building corals to survive the ongoing climate change. Distribution of coral species changes during larval dispersal. However, the acclimation potential in the early life stages of corals at different depths is unknown. This study investigated the acclimation potential of four shallow Acropora species at different depths via the transplantation of larvae and early polyps settled on tiles to 5, 10, 20, and 40 m depths. We then examined physiological parameters, such as size, survival, growth rate, and morphological characteristics. The survival and size of juveniles of A. tenuis and A. valida at 40 m depth were significantly higher than those at other depths. In contrast, A. digitifera and A. hyacinthus showed higher survival rates at shallow depths. The morphology (i.e., size of the corallites) also varied among the depths. Collectively, the shallow coral larvae and juveniles displayed substantial plasticity at depth.

Coral growth anomalies, neoplasms, and tumors in the Anthropocene

One of the most widespread coral diseases linked to anthropogenic activities and recorded on reefs worldwide is characterized by anomalous growth formations in stony corals, referred to as coral growth anomalies (GAs). The biological functions of GA tissue include limited reproduction, reduced access to resources, and weakened ability to defend against predators. Transcriptomic analyses have revealed that, in some cases, disease progression can involve host genes related to oncogenesis, suggesting that the GA tissues may be malignant neoplasms such as those developed by vertebrates. The number of studies reporting the presence of GAs in common reef-forming species highlights the urgency of a thorough understanding of the pathology and causative factors of this disease and its parallels to higher organism malignant tissue growth. Here, we review the current state of knowledge on the etiology and holobiont features of GAs in reef-building corals.

Genetic species identification and population structure of grouper Epinephelus coioides (Hamilton, 1822) collected from fish markets along the Persian Gulf and the Oman Sea

Many ecologically important and valuable fisheries marine species have been misidentified in terms of both the statistical data and market demand. Correct identification at the species level and the population genetic structure of the orange-spotted grouper (Epinephelus coioides), a precious fish in the Persian Gulf and the Oman Sea, was tested using mitochondrial cytochrome oxidase subunit I (DNA barcoding) and D-loop sequencing. The results revealed that the Epinephelus species found in the region, including E. coioides, E. bleekeri, E. polylepis, and E. chlorostigma were all mistakenly grouped together and identified as only E. coioides. Moreover, the analysis of molecular variance (AMOVA) of E. coioides samples using the D-loop showed a significantly unique genetic structure (Φ_ST = 0.068, p < 0.001) within the E. coioides population throughout the Persian Gulf and the Oman Sea, with the pairwise genetic difference between sampling locations in UAE and the Iranian coast. Moreover, D-loop sequences analysis showed two distinct haplotype groups scattered among the sampling locations, which did not correlate with the geographic distance between the sampling locations. These findings indicate that the issue of misidentification should be highlighted in the management and conservation of E. coioides. As this type of misidentification is likely to happen to other threatened marine species as well, the efficacy of using genetic markers for the correct identification, both at the species and the population level, is vital.

Recurrent disease outbreak in a warm temperate marginal coral community

Coral diseases contribute to the rapid degradation of coral reefs on a global scale. Although widespread in tropical and subtropical reefs, disease outbreaks have not been described in warm temperate areas. Here, we report the outbreak of a new coral disease in a warm temperate marginal coral community in Japan. Outbreaks of the disease have been observed during the summer and autumn months since 2014. It affects the coral species Porites heronensis and was tentatively named "White Mat Syndrome" (WMS) as it consists of a white microbial mat dominated by Thiothrix sp., a sulfide oxidizing bacteria. Outbreaks followed high seasonal temperatures and were associated with the macroalga Gelidium elegans, which acts as a pathogen reservoir. With ocean warming and the anticipated increase in novel coral-algae interactions as some coral species shift poleward, WMS and emerging diseases could hinder the role of temperate areas as a future coral refuge.

Four-Year Field Survey of Black Band Disease and Skeletal Growth Anomalies in Encrusting Montipora spp. Corals around Sesoko Island, Okinawa

The Indo-Pacific zooxanthellate scleractinian coral genus Montipora is the host of many coral diseases. Among these are cyanobacterial Black Band Disease (BBD) and Skeletal Growth Anomalies (GAs), but in general data on both diseases are lacking from many regions of the Indo-Pacific, including from Okinawa, southern Japan. In this study, we collected annual prevalence data of Black Band Disease (BBD) and Skeletal Growth Anomalies (GAs) affecting the encrusting form of genus Montipora within the shallow reefs of the subtropical Sesoko Island (off the central west coast of Okinawajima Island) from summer to autumn for four years (2017 to 2020). In 2020 Montipora percent coverage and colony count were also assessed. Generalized Linear Models (GLM) were used to understand the spatial and temporal variation of both BBD and GAs in the nearshore (NE) and reef edge (RE) sites, which revealed higher probability of BBD occurrence in RE sites. BBD prevalence was significantly higher in 2017 in some sites than all other years with site S12 having significant higher probability during all four surveyed years. In terms of GAs, certain sites in 2020 had higher probability of occurrence than during the other years. While the general trend of GAs increased from 2017 to 2020, it was observed to be non-fatal to colonies. In both diseases, the interaction between sites and years was significant. We also observed certain BBD-infected colonies escaping complete mortality. BBD progression rates were monitored in 2020 at site S4, and progression was related to seawater temperatures and was suppressed during periods of heavy rain and large strong typhoons. Our results suggest that higher BBD progression rates are linked with high sea water temperatures (SST > bleaching threshold SST) and higher light levels (>1400 µmol m−2 s−1), indicating the need for further controlled laboratory experiments. The current research will help form the basis for continued future research into these diseases and their causes in Okinawa and the Indo-Pacific Ocean.