Isolation of a novel antibacterial phenyl thioketone from the seagrass, Cymodocea serrulata.

A total of 40 extract types of varying polarities from commonly occurring seagrasses were tested for their antibacterial efficiency against 14 clinically isolated human pathogens using agar well diffusion technique. The extracts from acetone of Cymodocea serrulata expressed moderate broad span of activity against a range of gram-positive and gram-negative isolates that were at least resistant to five of the commercially available antibiotics at a minimal concentration of 10 µg. The active extracts of C. serrulata that showed maximal inhibitions were purified using column chromatography that afforded six compounds (a-f). Compound f elicited pronounced inhibitions against Escherichia coli with minimal inhibitory concentration values of 1-3 µg concentration using micro-dilution method. The active compound was identified as phenyl thioketone using various spectral analyses. This is the first investigation that reveals thioketone functionality from this seagrass species possessing antibacterial actions. This study indicates that there are thiocarbonyl groups from marine floral sources too, which could be possibly used for therapeutic purposes.

Variation in black and white band disease progression in corals of the Gulf of Mannar and Palk Bay, Southeastern India.

Information on the progression of coral diseases and transmission to live corals is scarce despite the fact that coral disease poses one of the most lethal threats to the survival of coral reefs. In this study, in situ progression rates of lesions similar to black band disease (BBD) and white band disease (WBD) were measured in different species of corals from the Gulf of Mannar (GoM) and Palk Bay, southeastern India, during the period between January and December of 2009. Maximum progression rates of 3 and 1.6 cm mo-1 for BBD and WBD, respectively, were observed during May, when the temperature exceeded 30°C. The annual progression rate was 10.9 and 4.9 cm yr-1 for BBD at GoM and Palk Bay, respectively. Significant variation in the progression rate (p < 0.001) was observed between months in all the examined species. Significant correlation between temperature and disease progression rates for BBD (R2 = 0.875, p ≤ 0.001) and WBD (R2 = 0.776, p ≤ 0.001) was recorded. Rates of disease progression were higher in Palk Bay than in GoM. This could be attributed to the higher temperature coupled with higher anthropogenic activities in Palk Bay. Severe mortality was observed due to both BBD and WBD. No sign of recovery was noticed in the disease-affected colonies at either study site. Anthropogenic activities should be checked, and further research on both the transmission and progression rate and role of the diseases in reef dynamics should be carried out to understand the causal factors in reef degradation and generate a plan to manage the reef properly.

Coral diseases are major contributors to coral mortality in Shingle Island, Gulf of Mannar, southeastern India.

The present study reports coral mortality, driven primarily by coral diseases, around Shingle Island, Gulf of Mannar (GOM), Indian Ocean. In total, 2910 colonies were permanently monitored to assess the incidence of coral diseases and consequent mortality for 2 yr. Four types of lesions consistent with white band disease (WBD), black disease (BD), white plaque disease (WPD), and pink spot disease (PSD) were recorded from 4 coral genera: Montipora, Pocillopora, Acropora, and Porites. Porites were affected by 2 disease types, while the other 3 genera were affected by only 1 disease type. Overall disease prevalence increased from 8% (n = 233 colonies) to 41.9% (n = 1219) over the 2 yr study period. BD caused an unprecedented 100% mortality in Pocillopora, followed by 20.4 and 13.1% mortality from WBD in Montipora and Acropora, respectively. Mean disease progression rates of 0.8 ± 1.0 and 0.6 ± 0.5 cm mo-1 over live coral colonies were observed for BD and WBD. Significant correlations between temperature and disease progression were observed for BD (r = 0.86, R2 = 0.75, p < 0.001) and WBD (R2 = 0.76, p < 0.001). This study revealed the increasing trend of disease prevalence and progression of disease over live coral in a relatively limited study area; further study should investigate the status of the entire coral reef in the GOM and the role of diseases in reef dynamics.

COVID-19 lockdown improved the health of coastal environment and enhanced the population of reef-fish.

Reduction in the impact of human-induced factors is capable of enhancing the environmental health. In view of COVID-19 pandemic, lockdowns were imposed in India. Travel, fishing, tourism and religious activities were halted, while domestic and industrial activities were restricted. Comparison of the pre- and post-lockdown data shows that water parameters such as turbidity, nutrient concentration and microbial levels have come down from pre- to post-lockdown period, and parameters such as dissolved oxygen levels, phytoplankton and fish densities have improved. The concentration of macroplastics has also dropped from the range of 138 ± 4.12 and 616 ± 12.48 items/100 m2 to 63 ± 3.92 and 347 ± 8.06 items/100 m2. Fish density in the reef areas has increased from 406 no. 250 m-2 to 510 no. 250 m-2. The study allows an insight into the benefits of effective enforcement of various eco-protection regulations and proper management of the marine ecosystems to revive their health for biodiversity conservation and sustainable utilization.

Marine debris - An emerging threat to the reef areas of Gulf of Mannar, India.

Underwater survey was conducted to assess the accumulation and impact of marine debris in the reef areas of Gulf of Mannar in southeast India. A combination of roving diver technique and belt transect method was applied for the assessment, which was conducted during the period between February 2018 and March 2019. An estimated total reef area of 1152 m2 has been affected by marine debris. Abandoned fishing nets were found to constitute the major portion of 43.17 ± 5.48% of the marine debris. Live corals were found to be dominant substrates for marine debris with 39.11%. The average prevalence of coral colonies in contact with marine debris was 3.28 ± 0.27%. Prevalence of corals in contact with debris was very high in genus Acropora with 8.23 ± 1.29% followed by Montipora with 4.63 ± 1.29% due to their complex growth form. Of the corals in contact with debris, 47.56% were fragmented and 34% were found with tissue loss.