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Previous studies of the coral communities in Hong Kong focused on the characterisation of benthic cover, with little attention given to colony size structure. We conducted transect surveys at 52 sites across a gradient of water quality, identified 6774 coral colonies to 23 genera and measured the size of each colony. The southern waters harboured less diverse (1-9 genera) and fewer corals (2-28 colonies) than the eastern waters (3-16 genera and 17-427 colonies) per site. The density of juveniles (< 5 cm diameter) was low (0.06-4.23 colonies 100 m -2 ), indicating recruitment limitation and/or post-recruitment mortality. Corals in the estuarine waters were typically more right-skewed in size structure compared to those in the oceanic waters, indicating recruitment failure and/or high juvenile mortality. Even in the oceanic waters, the size structure of several genera differed, indicating coral sizes can reflect the impact of not only water quality but also environmental disturbances such as bleaching and overgrazing by sea urchins., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This paper reports several new occurrences for Asteroidea and Echinoidea in Hong Kong. New records for asteroids include Anseropoda rosacea, Aquilonastra cepheus, Pentaceraster alveolatus, Pentaceraster sibogae, and Culcita novaeguineae. For echinoids, new records include Coelopleurus maculatus, Eucidaris metularia, Prionocidaris baculosa, Echinostrephus molaris, Pseudoboletia indiana, Salmacis bicolor, Stomopneustes variolaris, Toxopneustes pileolus, Clypeaster reticulatus, Metalia spatagus, and Nacospatangus altus. Several novel ecological observations on behavior, diet and morphological variation are also described. These additional occurrences and new observations are attributed to more comprehensive reporting from SCUBA diving as well as the advent of shared resources from social media platforms.

Tubastraea, commonly known as sun coral, is a genus of brightly coloured azooxanthellate corals in the family Dendrophylliidae. The diversity of this genus is low, with only seven recognized species. Herein, we describe Tubastraea megacorallita sp. nov. from Hong Kong based on morphological and molecular analyses. This new species exhibits several characteristics of the genus including being colonial, having a rough texture of corallum and no epitheca. It can be distinguished from its congenerics by bigger corallites, and the Pourtals plan arrangement of its septa. The rDNA gene sequences (consisting of ITS1, 5.8S, ITS2, 18S and 28S) showed 2.455.18% divergence from those of its closest relatives, T. coccinea and T. micranthus.

Coolia malayensis is one of the commonly found benthic dinoflagellates in Hong Kong which can produce biotoxins and threaten the early life stages of marine invertebrates. Seawater temperature has been recognized as one of the primary environmental factors that affect the formation of harmful algal blooms. The present study evaluated the responses of C. malayensis, including growth, toxicity and toxin content (putative analogues of okadaic acid and azaspiracids), after exposure to a range of seven different temperatures (i.e., 16°C, 18°C, 20°C, 22°C, 24°C, 26°C, and 28°C). The highest algal density and specific growth rate were recorded at 24°C. Significantly higher F v /F m (maximum quantum yield of PSII) and total phaeo-pigment values were observed in the exponential growth phase at 28°C. The toxicity of the algal extract, which was assessed by the lethality rate of Artemia larvae, increased with temperature. The highest toxin content was detected at the second highest temperature treatment, i.e., 26°C. Overall, temperature had significant effects on the physiological activities and toxicity of C. malayensis. This study has raised attention to the potentially increasing risks posed by toxic benthic dinoflagellates during heat waves in coastal waters., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier Ltd.)

Species of Fukuyoa, recently revised from the globular Gambierdiscus, are toxic benthic dinoflagellates associated with ciguatera. In this study, a total of ten strains of Fukuyoa collected from Hong Kong waters were characterized using morphological and phylogenetic analyses. Results from both analyses showed that one of the strains is a putative new species, namely Fukuyoa sp. HK Type 1 (plate formula Po, 3', 7″, 6c, 7s, 5‴, 1p and 2'‴ with a distinctive small and narrow cell shape, narrow Po plate, high Po pore density, large and broad Plate 1' but small and round Po pore size, small and narrow Plate 2', long and narrow Plates 2'‴ and 1p), and the others were F. ruetzleri. This is the first report of these two species of Fukuyoa in the South China Sea and Asia-Pacific region. Phylogenies on 18S, 28S D1/D3 and D8/D10 ribosomal DNA sequences strongly support that Fukuyoa sp. HK Type 1 is currently the most divergent species in the genus Fukuyoa. The diagrammatic plots on the p-distance matrices of 18S, 28S D1/D3 and D8/D10 and ITS regions resolved that the species of Fukuyoa were separated into three main groups, i.e., Fukuyoa sp. HK Type 1, F. paulensis and a group consisting of F. ruetzleri, F. yasumotoi and F. cf. yasumotoi, while Fukuyoa sp. HK Type 1 was always the most distant from the other two groups. Additionally, the pairwise p-distance values calculated based on the ITS region have always been the highest for pairs between Fukuyoa sp. HK Type 1 and other Fukuyoa species, ranging from 0.142 to 0.150. Our molecular results suggested that Fukuyoa sp. HK Type 1 is a putative new species. Both morphological and molecular data of more strains from different localities should be, however, collected to address its intraspecific variability and further evaluate its taxonomic status. A bioassay analysis demonstrated that algal lysates extracted from F. ruetzleri and Fukuyoa sp. HK Type 1 were lethal to brine shrimp larvae, indicating that both species were toxic. Bulk cultures were tested for Pacific ciguatoxins (P-CTXs) and maitotoxins (MTXs) by liquid chromatography-tandem mass spectrometry (LC-MS/MS). All isolates of Fukuyoa produced neither P-CTXs nor MTX-1, but isolates of F. ruetzleri produced a compound putatively assigned as MTX-3. This study has updated the current biodiversity and distribution of the toxic benthic dinoflagellates Fukuyoa, and thus contributes to the understanding of their emerging threats to the sub-tropical reef systems locally and regionally., (Copyright © 2018 Elsevier B.V. All rights reserved.)