| Dinoflagellate cysts were identified and counted in surface sediments from Zhelin Bay and Guishan Island area of Guangdong province, in order to understand the distribution of dinoflagellate cyst in typical Guangdong coastal waters. Surface sediments from these two sea areas together with samples in sediment trap deposited in Daya Bay were incubated at 25℃under laboratory conditions to study the germination of cyst and other phytoplankton spores, and to discuss the contribution of resting spores to the vegetative population. Meanwhile, the dominant germinated species was identified by the morphological and molecular biology methods. The purpose of this study was to reveal the potential of the occurrence of harmful algal blooms (HAB) in Guangdong coastal waters, and to provide basic data and reference from HAB controlling and prevention.Results showed that cyst species diversities were lower in Zhelin Bay and Guishan Island area, with a total of 16 and 22 type identified respectively. Cyst types were of the common species in the two areas and the dominant species were those of heterotrophic species. Protoperidinium was the most abundant group in both species richness and quantitative number indicating the high eutrophic level in both sites. The cyst concentrations in Zhelin Bay were generally low due to the coarse sediment partials, which are not benefit for cyst deposition. Cyst concentrations in Zhelin Bay ranged from16.59 to 83.37 cysts/g D Wt with an average of 39.52 cysts/g D Wt. In addition, the predominance of cyst of heterotrophic dinoflagellates also contributed to the low cyst production in Zhelin Bay. The brown organic rich fine clay sediments in Guishan Island area favorite for the deposition and accumulation of cyst, and the embankment acts as a barrier to prevent the transference of cyst to the out area, which resulted in the high cyst concentrations. Cyst concentrations ranged from10.33 to 315.08 cysts/g D Wt with an average of 202.37 cysts/g D Wt in Guishan Island area. Cysts of the toxic species were observed in the survey, e.g. Polysphaeridinium zoharyi in Zhelin Bay, and cysts of Alexandrium spp. widely distributed in Guishan Island area with the highest proportion of 56.88%, indicating rich seed bed for Alexandrium blooms.Results from the germination experiments showed that the germinated phytoplankton species richness was lower than phytoplankton survey in all the three study areas. The species number was 33 in 26 genus in Zhelin Bay,22 in 19 genus in Guishan Island area and 37 in 27 genus in Daya Bay. The dominant diatom species included Nitzschia spp., Navicula spp., Coscinodiscus spp., Paralia sulcata, Skeletonema spp., Chaetoceros spp., Thalassiosira spp., and dominant dinoflagellate were Alexandrium spp., Scrippsiella spp., Gymnodinium spp. etc. Gymnodinium corii Schiller was the dominant dinoflagellate species in all of the three sites, with an average accounting for 73.1% of the proliferating dinoflagellate cells and the highest proportion up to 100%. Species in other phytoplankton groups such as haptophyta species Chrysochromulima spp. and Phaeocystis globosa, cyanobacteria species Anabaenopsis spp. and Chroococcus spp., chlorophyta specie Palmella mucosa, occurred abundantly in some samples. Species, which were not reported in study areas in previous surveys, were observed as well, which enriched phytoplankton information. The species composition of geminated phytoplankton was different after 20d and 40d incubation, and differed in samples collected from different months. Results from germination experiments suggested that the germination of resting spore better mirrored the phytoplankton composition in the water column to some extent. However, some nannophytoplankton species occurred abundantly in germinated phytoplankton, were seldom reported in water column in previous phytoplankton surveys, which might be ignored due to their small sizes.The dominant geminated species Gymnodinium sp. was observed under scanning electron microscope (SEM), and the sequences of ITS and LSU rDNA were analyzed. This species was identified as Gymnodinium corii based on morphological characteristics on SEM and rDNA sequences. This species has not been recorded in Chinese coastal water yes to the best of our knowledge. However, it is not meant that this species should be a new record in China and do not exist in the water column, due to the small cell size and naked cell wall. In our study, Gymnodinium corii occurred frequently and abundantly. Therefore, this species and other nanno harmful species should be put into regular monitoring to prevent the occurrence of its blooms.
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