Formation Of Green Tides Research Articles

Tempo-spatial distribution and species composition of green algae micro-propagules in the coastal waters of Qinhuangdao after green tides bloom in 2020

Since 2015, the coastal waters of Qinhuangdao have been experiencing bloomed of green tides from April to September, with Jinmenghaiwan bath being the main affected area. Previous studies have shown that micro-propagules play an important role in the formation of green tides. In this study, we aimed to assess the temporal and spatial distribution of green algae micro-propagules in the coastal waters of Qinhuangdao after the green tides bloom in 2020. We found that the number of green algae micro-propagules in Jinmenghaiwan bath was significantly higher than that of the other surveyed areas. In addition, these micro-propagules of green algae presented a distribution trend of “high near the shore and low away from the shore” pattern. Compared to the period from October 2016 to April 2017, both the number of green algae micro-propagules and the proportion of Ulva prolifera micro-propagules in the coastal waters of Jinmenghaiwan bath decreased considerably in the period from October 2020 to April 2021. This may also be the reason why the green tides scale in 2021 was significantly lower than that in 2017. The results of this study will provide a theoretical basis for early warning and control of green tides in Qinhuangdao.

Factors influencing the spatial and temporal distributions of green algae micro-propagules in the coastal waters of Jinmenghaiwan, Qinhuangdao, China

Since 2015, green tides have impacted the coastal waters of Qinhuangdao, particularly at Jinmenghaiwan bath. Micro-propagules are considered the “seed bank” of algal blooms and play an important role in the formation of green tides. To investigate the spatial and temporal distributions of micro-propagules of green algae and associated environmental factors, a field survey was carried out in the coastal waters of Jinmenghaiwan, Qinhuangdao, China. The results showed that the NO3-N concentration was the most important impact factor of the abundance of micro-propagules and explained 42.9% of the total variance. Furthermore, the number of micro-propagules was significantly and positively correlated with the biomass of attached and floating macroalgae. Therefore, reducing the NO3-N concentration by controlling the NO3-N input from Tang River is expected to be an effective measure to prevent and control green tides in the coastal waters of Qinhuangdao.

Characterization and transcriptional analysis of one carbonic anhydrase gene in the green‐tide‐forming alga Ulva prolifera (Ulvophyceae, Chlorophyta)

SUMMARYUlva prolifera is a green‐tide‐forming macroalga dominating the green tides in the Yellow Sea from 2007 to 2019. The exponential growth of U. prolifera, and the correlating accumulation of biomass, rely heavily on its carbon fixation capability. Despite the importance of carbon fixation in algal growth, to date none of the genes involved in carbon fixation have undergone molecular characterization in U. prolifera. This study used Rapid Amplification of cDNA Ends (RACE) to characterize one full‐length carbonic anhydrase (CA) gene of U. prolifera (UpαCA1). An activity assay showed that UpαCA1 was an active CA. Real‐time quantitative PCR results showed that temperature, irradiance, salinity and pH could influence the transcriptional level of UpαCA1, indicating that UpαCA1 was sensitive to varying environmental factors. The results of this study provided further insights into our understanding of the influence of environmental factors on carbon fixation in U. prolifera and its subsequent role in the formation of green tides.

Distribution of green algae micro-propagules and their function in the formation of the green tides in the coast of Qinhuangdao, the Bohai Sea, China

Since 2015, a novel green tide has been recurring in the coastal areas of Qinhuangdao at the western coast of the Bohai Sea in China, threatening the environment and ecosystem of the Beidaihe seaside holiday resort along the coast. Micro-propagules of the green algae including gametes, spores, micro-germlings and micro-vegetative fragments play an important role in the formation of green tides. They serve as a “seed source” of green macroalgae, and their distributions could reflect and influence the “algae source” of green tides. In this study, monthly surveys in the inshore and offshore areas of the Qinhuangdao coast were conducted from April to September 2016 and in January 2017 to investigate the tempo-spatial distribution patterns and the biomass variations of the green algae micro-propagules. The obtained results show that micro-propagules were mainly distributed in the inshore areas with a significantly decreasing abundance towards offshore areas. Their biomass was highest in July and August, and lowest in winter. The areas that were affected by the green tides showed a remarkably higher abundance of micro-propagules compared to other areas. These micro-propagules could serve as the “seed” source of green tides. Their distribution patterns indicate that the green tide in the coastal areas of Qinhuangdao originated locally.

Tracing nitrogen sources fueling coastal green tides off a volcanic island using radon and nitrogen isotopic tracers

The main sources of nutrients fueling coastal green tides off a volcanic island surrounded by an oligotrophic ocean are obscure, although they result in many societal and ecosystem problems. In this study, we attempted to trace the source inputs of nutrients in coastal waters off a volcanic island, Jeju, Korea, where the formation of green tides is perennial, using a radioisotope (222Rn) and stable isotopes (δ15N and δ18O) as tracers. Sampling of groundwater, seawater, fish-farm water, and Ulva spp. was performed during April and July 2015. The contribution of submarine fresh groundwater discharge (SFGD) to the dissolved inorganic nitrogen input was >70%, with additional inputs from aqua-cultural activities and bottom sediments. The δ15N-NO3 and δ18O-NO3 values in the coastal seawater and groundwater indicate that the main source of NO3− is fertilizer, rather than other potential sources, such as aquacultural wastewater, sewage/manure contamination, or precipitation, in this region. The δ15N value (+7.3–+7.7‰) in Ulva spp. also indicates the same source. Thus, our results suggest that the rapid infiltration of land N-fertilizer and subsequent leakage into the coastal ocean through submarine groundwater discharge (SGD) results in green tide massive occurrence in coastal waters off a high-permeability volcanic island.

Tempo-spatial distribution and species diversity of green algae micro-propagules in the Yellow Sea during the large-scale green tide development

From 2008 to 2013, vast green tides mainly composed of Ulva prolifera consecutively invaded the coast of Qingdao (36°06′N, 120°25′E, PR China) in June and July. Previous studies have shown that the early green tides initially formed in the Porphyra yezoensis aquaculture area of the Subei Shoal, southern Yellow Sea. To date, multiple studies have demonstrated that green algae micro-propagules play an important role in the formation of green tides. In this study, we aimed to assess the temporal and spatial distribution of green algae micro-propagules in an extensive area of the Yellow Sea and to determine the species diversity of propagules during the development of the large-scale green tide. We found that the quantity of micro-propagules increased with the free-floating biomass from the initial generation to the development phase of the green tide in mid May. From late May to mid June, the micro-propagule density decreased sharply despite a continuous increase of the floating macroalgae biomass. In addition, our data indicate that the coastal area of the Subei Shoal has always been the distribution center of the micro-propagules, even prior to the large-scale green tide formation. Furthermore, diverse green algae species, including Ulva prolifera, Ulva linza, Ulva flexuosa, Ulva compressa, Ulva pertusa and Blidingia sp., were identified among the micro-propagules in the survey sea area. Finally, we determined that the distribution of U. prolifera micro-propagules is closely related to the floating algal mats and attached macroalgae on Porphyra aquaculture rafts.