Allelopathic eff ects of macroalga Corallina pilulifera on the red-tide forming alga Heterosigma akashiwo under laboratory conditions

Over the past few years, harmful algal blooms （HABs）, such as red tides, have been frequently observed in coastal zones worldwide. The natural allelopathic interactions among macroalgae and red tide microalgae can alter the structure and succession of aquatic ecosystems. We investigated the influence of four environmental factors （temperature, salinity, light, and pH） on the allelopathic effects of the macroalgae Corallina pilulifera on red-tide forming Heterosigma akashiwo under laboratory conditions. Each of the factors had four levels： temperature （15, 20, 25, and 30℃）, salinity （10, 20, 30, and 40）, light （20, 100, 200 and 400 gmol/（m2.s））, and pH （5.5, 7, 8.5, and 10. Two-factor experiments were designed for each two environmental factors, with six combination treatments （temperature-salinity, temperature-light, temperature-pH, salinity-light, salinity-pH, and light-pH）. Results showed that the allelopathic effect was significantly influenced by temperature, salinity, light, and pH. As single factors, the low temperature （15 ℃）, low salinity （10）, high-intensity light （400umol/（m2.s））, and high pH （10） treatments substantially enhanced the allelopathic effect. The strongest allelopathic effect of C. pilulifera on H. akashiwo was observed under the following treatments： 15℃ and salinity of 40, 25℃ and pH 10, 25℃ with medium- to high-intensity light at 200-400 umol/（m2.s）, 400umol/（m2.s） and salinity of 10, 400 gmol/（m2·s） and pH 10, and pH 10 with a salinity of 40.

Newly recorded bloom-forming dinoflagellate Gymnodinium impudicum in Haizhou Bay,Yellow Sea,China

With the development of industrialization and aquaculture in Jiangsu and Shandong Provinces along the South Yellow Sea coast,China,eutrophication has greatly intensified in the region,resulting in frequent occurrence of diverse harmful algal blooms.An algal bloom formed by a chain-forming dinofl agellate species was recorded in the Haizhou Bay,South Yellow Sea,in September 2020.The causative species was isolated and studied in morphology,molecular phylogeny,pigment profile,presence of paralytic shellfish toxins,and acute toxicity.The loop-shaped apical groove running anticlockwise around the apex,the presence of peridinin as characteristic pigment,as well as a single phylogenic clade of 28S ribosomal DNA(100%posterior probability),defined this species as Gymnodinium impudicum,a non-toxic species that exhibited no obvious biotoxicity to the rotifer Brachionus plicatilis,the copepod Artemia salina,and the shrimp Neomysis awatschensis.Gymnodinium impudicum is typically distributed in coastal waters with high nitrate concentrations,where it reaches a maximum density of 2.6×10~5 cells/L.This is the first report of a G.impudicum bloom in the Yellow Sea;however,G.impudicum blooms may have been misidentified or underreported in Haizhou Bay due to the species morphological similarity with G.catenatum.A combination of multiple methods is recommended to accurately identify new algal bloom species.