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Hong Kong has a long historical record of harmful algal blooms (HABs). In the 1980s–1990s, HABs were mainly pollution-related and most of the events happened in estuaries and enclosed embayment such as Tolo Harbour and Port Shelter. The major cause of HABs in 1980s–1990s was closely related to nutrients enrichment; included but not limited to changes in the concentration and ratio of soluble N and P in seawater. The major causative organisms of HABs in Hong Kong by then were meso-plankton such as selected species of diatoms and dinoflagellates. Sometimes, zooplankton was also a cause of red tides (the common name of HABs). There has been gradual change after the 2000s. It is attributed to higher and higher influences from the region, namely the Zhujiang (Pearl) River delta. There are increasing influences from Chinese mainland due to extraordinary social and economic growths during the past 20 years. In the past 10 years, HABs in Hong Kong was mainly subject to regional impacts in the Zhujiang River delta. Both the duration period and covered areas have been enlarged which overwhelmed the localized influences of stream pollution and self-contamination of aquaculture zones. More flagellates of uncommon happening become dominant species in HAB now. Nevertheless, the seasonal impact of Noctiluca scintillans in late winter to mid spring remained. [ABSTRACT FROM AUTHOR]

Resting cysts play crucial roles in the ecology of dinoflagellates, especially in wintering or surviving unfavorable conditions, seeding harmful algal blooms (HABs), and facilitating the geographic expansion. Encystment of dinoflagellates is tightly coupled with sexual reproduction in most cases, which can occur either through homothallism (self-fertilization) or heterothallism (intercrossing of +/− strains). The types of sexual reproduction have important ecological implications. The toxic and HAB-forming dinoflagellate, Pheopolykrikoides hartmannii has been previously reported to be heterothallic. Here, we provide visual confirmation of homothally of P. hartmannii and the first detailed visual recording of cyst germination based on the observations of a clonal isolate from Jiaozhou Bay, China. To document the homothallism, we first observed cell pairs in sexual mating, planozygotes with two longitudinal flagella, and cysts with typical morphology as described previously from the clonal culture. We then germinated a single cyst, established a new clonal culture from one of the two daughter cells after the first cell division of the germling (i.e. from the diploid germling to two haploid cells), and produced cysts again from the newly established clonal culture. For the observation of the germination time-series, we took micrographs and videos to show all germination processes, particularly with an interesting observation of the short amoeboid stage of the germling releasing from the archeopyle (~15 s), which was a landmark of the germination process and has not been reported elsewhere. This definitive evidence of homothallic sexuality and cyst production in P. hartmannii provides a new insight into the biology and ecology of the species, particularly a mechanism that may partly account for the population dynamics and ubiquitous distribution of the species. [ABSTRACT FROM AUTHOR]

Carbonyl compounds, especially polyunsaturated aldehydes (PUAs), are increasingly reported as teratogenic to grazers and deleterious to phytoplankton. While PUAs have been considered to be mainly produced by diatoms after cell wounding, little is known about whether microalgae other than diatoms, particularly harmful algal bloom (HAB)-forming species, produce carbonyl compounds. In this study, we analyzed the carbonyl compounds from eight common HAB-forming species (Akashiwo sanguinea, Karenia mikimotoi, Karlodinium veneficum, Margalefidinium polykrikoides, Prorocentrum donghaiense, P. minimum, Scrippsiella trochoidea, and Heterosigma akashiwo) using gas chromatography-mass spectrometry in full scan and selected ion monitoring (SIM) modes. Our results show a ubiquitous presence of carbonyl compounds in both dissolved and particulate forms in all species we examined. In the full scan mode, 133 chromatographic peaks were detected from 51 samples altogether. Both the varieties of carbonyl compounds and their quantities were algal species dependent, although most of the carbonyl compounds could not be fully identified according to the mass spectral database only due to the unavailability of enough standards for all analytes. Aided with nine standards in SIM mode, we further identified and quantified all nine aldehydes (2-methyl-2-pentenal, trans-2-nonenal, cis-6-nonenal, 2,6-dimethyl-5-heptenal, trans-2-hexenal, trans-2-decenal, 2,4-heptadienal, trans-trans-2,4-octadienal, and trans-trans-2,4-decadienal). Four of these nine aldehydes were detected in particulate form, which confirmed that trans-2-nonenal could be produced by K. mikimotoi, Karl. veneficum, P. donghaiense, P. minimum, S. trochoidea, and H. akashiwo, 2,4-heptadienal and trans-trans-2,4-decadienal by A. sanguinea, M. polykrikoides, and S. trochoidea, and trans, trans-2,4-octadienal by S. trochoidea, respectively. We proved that some dinoflagellate and raphidophyte species could contribute to the pool of carbonyl compounds including PUAs in a marine ecosystem. Some carbonyl compounds, particularly those in high cell quota and/or dissolved concentration, may be related to fish-killing or allelopathy which needs further identification and quantification. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs), caused by the overgrowth of certain phytoplankton species, have negative effects on marine environments and coastal fisheries. In addition to cell-counting methods using phytoplankton nets, a hydroacoustic technique based on acoustic backscattering has been proposed for the detection of phytoplankton blooms. However, little is known of the acoustic properties of HAB species. In this study, as essential data to support this technique, we measured the acoustic properties of two HAB species, Akashiwo sanguinea and Alexandrium affine, which occur in the South Sea off the coast of Korea. Due to the small size of the target, we used ultrasound for the measurements. Experiments were conducted under laboratory and field conditions. In the laboratory experiment, the acoustic signal re]from each species was directly proportional to the cell abundance. We derived a relationship between the cell abundance and acoustic signal re]for each species. The measured signals were compared to predictions of a fluid sphere scattering model. When A. sanguinea blooms appeared at an abundance greater than 3 500 cells/mL, the acoustic signals varied with cell abundance, showing a good correlation. These results confirm that acoustic measurements can be used to detect HAB species. [ABSTRACT FROM AUTHOR]

The dinoflagellate genus Karenia is known for recurrent harmful blooms worldwide. However, species diversity of the genus is generally overlooked owing to the difficulty of identifying small unarmored dinoflagellates. We have established four clonal cultures of Karenia longicanalis isolated from the type locality, Hong Kong harbor (strain HK01) and other three locations along the Chinese coasts (strains YB01, DT01, and NJ01). The morphology of the strain was studied by light and scanning electron microscopy (LM and SEM) and the pigment composition analyzed by high-performance liquid chromatography. We provide the first molecular data of K. longicanalis based on the large subunit (LSU) rRNA gene sequence and internal transcribed spacer (ITS). The four strains showed identical LSU rDNA sequences with a similarity of 99.4% to the holotype of Karenia umbella (strain KUTN05) from Australia. In the ITS phylogeny, the sequence of K. umbella branched between the Chinese strains of K. longicanalis. A careful comparison of the morphology of K. longicanalis and K. umbella reveals the similarity in the diagnostic characters. Differences may appear due to the sample treatment for SEM. We conclude that K. umbella is a junior synonym of K. longicanalis. [ABSTRACT FROM AUTHOR]