Hailong Wu

The origin of the Ulva macroalgal blooms in the Yellow Sea in 2013

Green algal blooms have occurred in the Yellow Sea for seven consecutive years from 2007 to 2013. In this study, satellite image analysis and field shipboard observations indicated that the Ulva blooms in 2013 originated in the Rudong coast. The spatial distribution of Ulva microscopic propagules in the Southern Yellow Sea also supported that the blooms originated in the Rudong coast. In addition, multi-source satellite data were used to evaluate the biomass of green algae on the Pyropia aquaculture rafts. The results showed that approximately 2784 tons of Ulva prolifera were attached to the rafts and possessed the same internal transcribed spacer and 5S rDNA sequence as the dominant species in the 2013 blooms. We conclude that the significant biomass of Ulva species on the Pyropia rafts during the harvesting season in radial tidal sand ridges played an important role in the rapid development of blooms in the Yellow Sea.

Changes to the biomass and species composition of Ulva sp. on Porphyra aquaculture rafts, along the coastal radial sandbank of the Southern Yellow Sea

Compositions, changes and biomass of attached Ulva species on Porphyra rafts along the radial sandbank in the Yellow Sea were investigated, and potential contributions to green tides was analyzed. Ulva prolifera, Ulva flexuosa and Ulva linza were all appeared throughout the investigated period. U. prolifera and U. flexuosa dominated attached Ulva population on Porphyra rafts. Attached Ulva species biomass showed obviously spatial and temporal variations. Temperature, Ulva microscopic propagules and human activities were main factors to influence attached Ulva species biomass. The total attached Ulva species biomass was more than 20,000 fresh weight tons in April, and the green tide causative species U. prolifera accounted 51.03% in April 2013 before green tides occurred. The high biomass of attached Ulva species would contribute most to green tides in the Yellow Sea. But how attached Ulva species on Porphyra rafts contributing to green tides in the Yellow Sea should be further studied.

Eutrophication assessment and bioremediation strategy using seaweeds co-cultured with aquatic animals in an enclosed bay in China

Intensive mariculture results in a rise in nutrient concentrations, then leads to serious eutrophication in coastal waters. Based on the sampling data obtained between August 2012 and July 2013, the eutrophication status in Yantian Bay was assessed, and the proportion of marine animals co-cultured with seaweeds was evaluated. The nutritional quality index (NQI) ranged from 4.37 to 13.20, indicating serious eutrophication conditions. The annual average ratio of nitrogen/phosphorus (N/P) was 25.19, indicating a nitrogen surplus in this system. DIN was selected as the best parameter to balance seaweed absorption and marine animal DIN production. Gracilaria lemaneiformis and Laminaria japonica were selected as co-cultured seaweeds. The optimal proportion of G. lemaneiformis production was assessed as 20074.14 tonnes. The optimal proportion of L. japonica production was evaluated as 15890.68 tonnes. High-temperature adapted seaweeds should be introduced for removing nutrients releasing by farmed aquatic animals in the summer in Yantian Bay.

Bioremediation efficiency of the largest scale artificial Porphyra yezoensis cultivation in the open sea in China

The bioremediation efficiency of Chinas largest scale Porphyra yezoensis cultivation for removing dissolved nutrients and controlling harmful algae was studied in the radial sandbanks waters of Jiangsu Province in the year 2012-2013. Mean nutrient concentration values in the P. yezoensis cultivation area were significantly lower than those in the non-cultivation area, especially during the cultivation season (p<0.05). Tissue nitrogen and phosphorus contents of seaweeds were 5.99-0.80% (dry weight (DW)) and 0.16-0.19% (DW), respectively. Production of P. yezoensis was 58950.87tons DW. Based on these values, 3688.15tons of tissue nitrogen and 105.61tons of tissue phosphorus were removed by harvesting P. yezoensis. The richness index of the red tide species Skeleton emacostatum declined from 0.32 to 0.05 during the P. yezoensis cultivation season. These results indicate that large-scale cultivation of P. yezoensis can be used to efficiently alleviate eutrophication and control harmful algae blooms in open sea.

Bioremediation using Gracilaria chouae co-cultured with Sparus macrocephalus to manage the nitrogen and phosphorous balance in an IMTA system in Xiangshan Bay, China

A cage experiment using the red alga Gracilaria chouae co-cultured with the black seabream Sparus macrocephalus in Xiangshan Bay, China was conducted to measure the nutrient flux of the integrated multi-trophic aquaculture (IMTA) system. Results showed that trash fish were the main nutrient input contributor and adult fish were the main nutrient output contributor in the system. Contents of N and P in adult fish accounted for 54.45% and 59.48% of N and P in trash fish and fry, which suggests that 45.55% of N and 40.52% of P generated by fish farming were released into to the water. G. chouae proved to be an efficient bioremediation species in this IMTA system. To balance the excess nutrients generated by the system, 231.09 kg of seedlings should be cultured and 5315.07 kg of adult seaweed should be harvested.

Effects of nitrogen and phosphorus enrichment on growth and photosynthetic assimilation of carbon in a green tide-forming species (Ulva prolifera) in the Yellow Sea

The hypothesis that nitrogen and phosphorus can have a positive effect on the bloom formation of Ulva prolifera along the southern coast of the Yellow Sea was examined. The nutrient enrichment on the growth and photosynthetic carbon assimilation of U. prolifera were investigated in laboratory. Four nitrogen and phosphorus treatments were established: high nitrogen and high phosphorus (HNHP), high nitrogen and low phosphorus, low nitrogen and high phosphorus, and low nitrogen and low phosphorus (LNLP). Fresh weights, relative growth rate (RGR), chlorophyll fluorescence parameters, photosynthetic rate, and the uptake of dissolved inorganic carbon (DIC) in U. prolifera were measured. The results showed that nitrogen and phosphorus enrichment significantly increased RGR of U. prolifera. The chlorophyll fluorescence parameters all reached maximum values under the HNHP treatment. The photosynthetic rate under the HNHP treatment also was the highest, which was 1.52 times that of the LNLP treatment. The DIC uptake under the HNHP treatment was 1.63 times greater than under the LNLP treatment. The photosynthesis and carbon fixation were significantly promoted by N and P enrichment. This work may further clarify the mechanisms of U. prolifera bloom formation and decline in the Yellow Sea.

Bioremediation using Gracilaria lemaneiformis to manage the nitrogen and phosphorous balance in an integrated multi-trophic aquaculture system in Yantian Bay, China

To reduce negative environmental impacts from human aquaculture activities, the red alga Gracilaria lemaneiformis was co-cultured with the fish Pseudosciaena crocea in an integrated multi-trophic aquaculture (IMTA) system for 35d in Yantian Bay. The eutrophication index value decreased from 14.5 to 8.4 after seaweeds were co-cultured in cage farming areas, which indicated that the eutrophic water column in Yantian Bay could be mediated by IMTA. Total DIN and DIP of the tidal input and output were 9.23kg, 0.19kg and 11.08kg, and 0.27kg, respectively. Total 5.24kg of dissolved N and 0.81kg of dissolved P were released from IMTA system. These results indicate that G. lemaneiformis co-cultured in IMTA system could not completely remove all excess nutrients. In theory, at least 324.48kg of seaweed seedlings would be required to balance excess nutrients generated from fish cages.

Bioremediation and nutrient migration during blooms of Ulva in the Yellow Sea, China

Abstract: Blooms of Ulva have been recorded for 10 consecutive years since 2007 in the Yellow Sea, China. There have been many studies estimating economic, environmental and social costs of these blooms. The present study evaluated potential environmental benefits of the removal of blooms. During the blooms of Ulva in 2013, the fresh biomass of Ulva increased from 1.01 × 104 metric tons to 4.1 × 106 tons in about 50 days, with the average growth rate of 12.80% d−1. The potential maximum nitrogen, phosphorus and carbon removal by the green tide was about 7.46 × 103, 1.05 × 103 and 1.73 × 105 tons, respectively. These results suggest that the harvest of Ulva from the Yellow Sea may provide invaluable ecosystem services by removing nutrients from these eutrophic waters prior to the onset of the death phase of Ulva.