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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.

Scyllaeidae is a small group of nudibranchs comprising three genera ( Scyllaea , Notobryon , and Crosslandia ) with striking morphological similarities, making their identification challenging based on external features alone. Previous studies have highlighted the significance of central radular teeth in distinguishing Notobryon from Scyllaea and Crosslandia . The genus Scyllaea , commonly known as the sargassum nudibranch, currently consists of only two valid species, Scyllaea pelagica and Scyllaea fulva . These species inhabit seaweed Sargassum spp., feeding on hydroids. During a biodiversity survey conducted in April 2023, seven sargassum nudibranch individuals were collected from the seaweed Sargassum spp. at a depth of 2 meters in Tai She Wan through SCUBA diving. Initially, the specimens were misidentified based on their resemblance to Notobryon wardi and previous local records. However, thorough morphological and molecular examinations confirmed them to be Scyllaea fulva , representing the first record of this species in Hong Kong. Notably, our specimens lacked the blue spots observed in specimens from Thailand and the West Pacific Ocean, as reported in previous studies. Internally, a pineapple-like structure formed a honeycomb pattern on the surface of the masticatory edge of the jaw flap, with the presence of central radular teeth. A Maximum Likelihood tree analysis revealed Crosslandia to be the sister group of Scyllaea . Comparative analysis of intra-specific distances between individuals from the Philippines, French Polynesia, and Hong Kong indicated a close relationship between the Hong Kong specimens and those from the Philippines. Furthermore, we provide a detailed description of the external and internal morphology of Scyllaea fulva in this paper, integrating valuable morphological information for future species identification purposes.

Tubastraea is a genus of azooxanthellate scleractinian corals belonging to the family Dendrophylliidae, which are commonly called sun corals. This genus currently has only seven recognized species. In this paper, we report three new species of Tubastraea , including T. dendroida sp. nov., which has a tree-like colony, T. violacea sp. nov., which has violet polyps, and T. chloromura sp. nov., which has olive green polyps. These species are distinct in their septal structures, as well as their rDNA sequences including the entire ITS1 , 5.8S and ITS2 , and a segment of the 18S and 28S genes.

We studied the morphology, host specificity, feeding rate and larval settlement preference of the corallivorous nudibranch Phestilla subodiosa collected from the field. These specimens collected from the scleractinian coral Monipora peltiformis in Hong Kong waters are morphologically different from the holotype and paratypes collected from an aquarium culture of Montipora spp., as they have diamond-shaped swollen bulbs, and brown spots on cerata, as well as bulbs and the body immediately posterior to cerata. In experiments where P. subodiosa individuals were placed on the surface of several species of common scleractinian corals collected from Hong Kong waters, the nudibranchs were found to feed on M. peltformis at a rate of 0.05 cm 2 individual -1 d -1 ; however, they were killed and eaten by other tested coral species ( Pavnoa decussata , Porites lutea and Duncanopsammia peltata ). When cultured in seawater conditioned with M. peltiformis , the veliger larvae required six days to become competent for settlement, and at day 9 could reach a maximum metamorphic rate of 31.1%. At competence, the veliger larvae could be induced to settle, indicating the presence of a larval settlement cue released by the host coral. Other coral species or their conditioned seawater did not induce settlement of the P. subodiosa larvae. Overall, our study expands the distribution record of P. subodiosa , adds this species to the list of corallivorous nudibranchs in Hong Kong waters, provides morphological features that were not included in the original description of this species, reveals the host specificity, and provides the feeding rate of this species. These results contribute to a better understanding of the diversity and potential impact of corallivorous nudibranchs in coral ecosystems.

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.

The Pearl River Delta (PRD) region on the southeast coast of China has long been known as a highly productive fishing ground. Since the late 1980s, fishing pressure in the PRD has been intense, which warrants concerns of potential fishery-related impacts on the food resources and foraging ecology of apex marine predators in this region, such as the Indo-Pacific humpback dolphin (Sousa chinensis). In this study, we examined 54 stomachs with food remains, collected from beached carcasses of humpback dolphins recovered during fifteen years between 2003 and 2017. The 6043 identified prey items represent 62 teleost taxa, primarily small estuarine fish, but also larger reef fish. The dolphins appear to be opportunistic foragers, hunting across the water-column, with preference for shoaling and meaty fishes (e.g. Collichthys lucidus IRI% = 38.6%, Johnius belangerii IRI% = 23.1%, Mugil cephalus IRI% = 14.0%). Our findings suggest a dietary shift in recent years, from primarily demersal (as previously reported) to greater intake of neritic and pelagic fish. Dolphin foraging group size has decreased in recent years, which corresponds with declining size and numbers of prey items retrieved from dolphin stomachs. We suggest that these are indicators of declining food resources. Faced with a shortage of preferred prey, humpback dolphins may have broadened their dietary spectrum to maintain their daily energy intake, while their foraging group size decreased in response to the altered tradeoff between the costs and benefits of group foraging., (© 2021 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)

Members of the nudibranch genus Phestilla are common predators of scleractinian corals, but currently this genus has 10 described species only. Here we describe Phestilla goniophaga sp. nov., the first formally named predatory nudibranch species of the stony corals from the genus Goniopora . The new species can be distinguished from its congeneric species by the large number of long cerata (up to 16 rows and 23 cerata per row), and white rounded hump on the notum. The hump resembles the mouth of the coral poly, while the cerata resemble the coral tentacles. The egg masses of P. goniophaga sp. nov. are unique among Phestilla spp. egg masses in being bright orange in color, and forming a coiled ribbon. Analysis of the COI , 16S rRNA and H3 genes of P. goniophaga sp. nov. also showed that this species is distinct from other congeneric species.

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.)

Corals are exposed to organic ultraviolet (UV) filters and other personal care product (PCP) ingredients in the environment, but the toxicities of organic UV filters and their related PCP to corals are not well understood. In this study, 7-day exposures were conducted to evaluate the toxicities and bioaccumulation of two organic UV filters, ethylhexylmethoxy-cinnamate (EHMC; octinoxate) and octocrylene (OC) (single- and combined-chemical tests), and diluted sunscreen wash-off water containing both active ingredients to the adult life stage of two hard coral species, Seriatopora caliendrum and Pocillopora damicornis. In the single-chemical tests, death (33.3%) and bleaching (83.3%) were only observed in the 1000 μg/L EHMC treatment of S. caliendrum. In the sunscreen product exposures, 5% sunscreen water (containing 422.34 ± 37.34 μg/L of EHMC and 33.50 ± 7.60 μg/L of OC at Day 0) caused high mortality in S. caliendrum (66.7-83.3%) and P. damicornis (33.3-50%), and tissue concentrations were up to 10 times greater than in the single-chemical exposures; co-exposure to EHMC and OC at similar levels to those in the sunscreen product resulted in bioaccumulation similar to the single-chemical tests. These results confirm the bioaccumulation potential of EHMC and OC and show that other ingredients in sunscreen products may increase the bioavailability of active ingredients to corals and exacerbate the toxicity of sunscreen products. Future studies on the toxicities of PCPs to aquatic organisms should not only focus on the toxicities of active ingredients., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

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.)

Coolia are marine benthic dinoflagellates which are globally distributed and potentially toxic. This study provides the first investigation of species diversity and toxicity assessment of Coolia in Hong Kong waters. Fifty-one strains of four Coolia species, including C. malayensis, C. canariensis, C. tropicalis, and C. palmyrensis, were isolated from twelve sub-tidal habitats, and identified phylogenetically using 28S rDNA sequences. Exposure experiments (48-hour) demonstrated that the algal lysates extracted from the four Coolia species exhibited different toxic effects on the lethality and abnormality of two invertebrate larvae, i.e., brine shrimp Artemia franciscana and sea urchin Heliocidaris crassispina. Heliocidaris crassispina was more sensitive to the toxic effects of Coolia species than A. franciscana. Toxicity tests from both larvae revealed that C. malayensis was generally more toxic, and caused higher mortality rates when compared with the other three species. The emerging threat of harmful benthic dinoflagellates to marine environments and sensitive biota is discussed., (Copyright © 2017 Elsevier Ltd. All rights reserved.)