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Aim: Effective control of invasive species and conservation of native biodiversity requires accurate species identification. Several species of apple snails (Ampullariidae: Pomacea) from South America have become widespread pests in Asia since their introduction in the early 1980s, but their taxonomic uncertainty has hindered our understanding of the invasive processes. We aim to determine the identity and distribution of Pomacea species in Hong Kong, which has been known as a stepping stone of species invasion. Location: Hong Kong. Methods: We collected 162 apple snails from five freshwater wetlands of Hong Kong, sequenced the mitochondrial COI, genotyped the nuclear EF1α and built a COI dataset of 1378 sequences of apple snails from mainland China, Malaysia, Argentina and Brazil. We identified the species, determine the introgression pattern and analysed their population structures. Results: We found the co‐occurrence of P. canaliculata, P. maculata and P. occulta in Hong Kong for the first time. Pomacea canaliculata represented the dominant species (85% of collected specimens). The three Pomacea species from Hong Kong had low genetic diversity. High genetic similarity existed between P. canaliculata populations of Hong Kong and Malaysia, P. occulta populations of Hong Kong and mainland China and P. maculata populations of mainland China and Malaysia. Our samples contained a high proportion of hybrids. Main conclusions: Apple snails may have been introduced into Hong Kong multiple times: both P. canaliculata and P. occulta likely came from Argentina; P. maculata came from both Argentina and Brazil. Genetic drift largely explains the differentiation of Pomacea spp. among regions. Introgressive hybridization may have contributed to population fitness by increasing genetic variation to neutralize the founder effect. The knowledge on species identity, distribution and genetic diversity of apple snails from this study will contribute to better understanding their invasive mechanisms and prevention of their continued spread in Asia. [ABSTRACT FROM AUTHOR]

Bacteria play important roles in coral health, yet little is known about the dynamics of coral-associated bacterial communities during coral bleaching. Here, we reported the dynamic changes of bacterial communities in three scleractinian corals (Montipora peltiformis , Pavona decussata and Platygyra carnosa) during and after bleaching through amplicon sequencing. Our results revealed that the bacterial composition and dominant bacteria varied among the three coral species. The higher susceptibility of M. peltiformis to bleaching corresponded to a lower bacterial community diversity, and the dominant Synechococcus shifted in abundance during the bleaching and coral recovery phases. The resilient P. decussata and P. carnosa had higher bacterial diversity and a more similar bacterial composition between the healthy and bleached conditions. Overall, our study reveals the dynamic changes in coral-associated microbial diversity under different conditions, contributing to explaining the differential susceptibility of corals to extreme climate conditions. • Bacterial composition of coral is host-specific. • Lower bacterial α diversity may be related to host susceptibility to stress. • More dynamic bacterial community changes for tolerant corals indicated a more flexible response to stress. • Dominant Synechococcus in M. peltiformis is an important indicator species for healthy status. [ABSTRACT FROM AUTHOR]

This study has explored perceived crowding of an underwater environment. Two dimensions were assessed: the number of divers seen and the proximity of divers to each other. Data were obtained from a survey of 216 divers who undertook diving in Hong Kong during 2013–14. Photographs depicting four levels of crowding (number of divers) and four levels of diver proximity in different combinations were shown to the respondents for assessing acceptability. Between the two variables, the “number of divers” was the most influential factor to divers' perceived crowding. Divers' begin to feel unacceptably crowded if 7∼8 divers are visible to them at one time. Based on this, it is likely that the usage of Hong Kong diving sites has already exceeded its social carrying capacity. Implications for future research and diving tourism management for Hong Kong diving sites are also discussed in the paper. [ABSTRACT FROM AUTHOR]

Although coral species exhibit differential susceptibility to stressors, little is known about the underlying molecular mechanisms. Here we compared scleractinian corals Montipora peltiformis and Platygyra carnosa collected during the 2017 El Niño heat wave. Zooxanthellae density and chlorophyll a content declined and increased substantially during and after heat stress event, respective. However, the magnitude of change was larger in M. peltiformis. Transcriptome analysis showed that heat-stressed corals corresponded to metabolic depression and catabolism of amino acids in both hosts which might promote their survival. However, only M. peltiformis has developed the bleached coral phenotype with corresponding strong stress- and immune-related responses in the host and symbiont, and strong suppression of photosynthesis-related genes in the symbiont. Overall, our study reveals differences among species in the homeostatic capacity to prevent the development of the bleached phenotype under environmental stressors, eventually determining their likelihood of survival in the warming ocean. [Display omitted] • Two coral species were sampled during the 2017 El Niño heat wave in Hong Kong. • Montipora peltiformis was more susceptible than Platygyra carnosa. • M. peltiformis and P. carnosa lost 90.2 % and 42.2 % of zooxanthellae, respectively. • In both species, hosts responded more strongly to stresses than zooxanthellae. • Stress and immune responses were stronger in M. peltiformis. [ABSTRACT FROM AUTHOR]

Erosion of coral substrate plays a crucial role in reef calcium carbonate budget, but little is known about erosion in subtropical corals. In a 2-year study of coral substrate erosion, we deployed Porites skeletal blocks at nine sites across subtropical Hong Kong waters. External erosion varied from 0.05 to 3.07 kg m−2 yr−1 and accounted for 23.4–99.2% of the total erosion. More than half of the study sites had substantial external erosion (> 1 kg m−2 yr−1), and the values were positively correlated with density of the sea urchin Diadema setosum. Excluding urchins from access to the skeletal blocks using cages reduced external erosion by more than 90%. Overall, our study revealed that external erosion caused by urchin grazing contributed predominantly to the total coral skeletal loss in Hong Kong waters. Control of sea urchin population is needed to reduce coral erosion in places with high urchin density. (149 words). • Coral substrate erosion was studied by deploying coral blocks in the field • Erosion and accretion were quantified using microCT • High erosion was found in more than half of the study sites • External erosion was the main contributor to the overall erosion • Sea urchin grazing was likely the cause of the high external erosion [ABSTRACT FROM AUTHOR]

We surveyed 41 sites to provide an updated baseline of Hong Kong coral communities. Five community types were identified, among them the most common one inhabited oceanic waters and dominated by both massive and upward-plating corals. The 41 sites had 2.1–⁠79% coral cover; among them 21 in the eastern waters had >40% coral cover. Corals in several sites showed signs of external bioerosion or bleaching-induced damage. Sites in the southern waters had low coral cover. Both coral cover and generic richness correlated negatively with several water quality parameters including total inorganic nitrogen concentration and turbidity, indicating the development of Hong Kong's coral communities is constrained by water quality parameters. Management actions are proposed to reduce bioerosion, and to monitor sites affected by bleaching. [ABSTRACT FROM AUTHOR]

During the summer of 2017 we visited 33 sites with substantial coral cover across Hong Kong waters. At six sites where coral bleaching was observed, video-transect surveys were conducted, which revealed 18.7% to 56.1% bleached colonies and 5.9% to 57.6% bleached coral covered area per site. Mainly affected were three plate-like and three massive coral species. Water quality parameters were analyzed, which indicated that hyposalinity might have triggered the bleaching event. Tagging and follow-up field observation revealed a pattern of recovery depending on coral growth form, with high recovery rates (>93%) at five sites dominated by massive and submassive corals, but moderate (70%) at a site dominated by plate-like corals. Our study shows that the corals of Hong Kong exhibit differential susceptibility to bleaching and ability to recover, therefore it is imperative to establish a long-term monitoring programme to detect the changes in community structure over time. • We surveyed 33 sites during the 2017 coral bleaching event in subtropical Hong Kong. • In six sites there were 18.7–56.1% bleached colonies and 5.9–57.6% bleached coral covered area per site. • High recovery rates at five sites dominated by massive and submassive corals. • Moderate at a site dominated by plate-like corals. • Hyposalinity might have triggered the bleaching event. [ABSTRACT FROM AUTHOR]