Impacts of Integrated Multi-Trophic Aquaculture on Phytoplankton in Sanggou Bay

Integrated multi-trophic aquaculture(IMTA)has been considered as an ecofriendly culture system providing a potential solution to environmental risks caused by intensive monoculture system.However,the impact of IMTA on phytoplankton remains unclear.In this study,the spatial and temporal variations of phytoplankton in Sanggou Bay were investigated seasonally based on 21 sampling sites covering three cultivation zones(bivalve zone,IMTA zone,and kelp zone)and one control zone(without aquatic cultivation).In total,128 phytoplankton species,with diatoms and dinoflagellates as the dominant groups,were obtained across the whole year,and the mean Shannon diversity index(H')and species richness(SR)were determined as 1.39 and 9.39,respectively.The maximum chlorophyll a(Chl-a)(6.32μg L^(-1))and plankton diversity(H'of 1.97)occurred in summer and autumn,respectively.Compared to other zones,the bivalve zone displayed significantly higher Chl-a and lower H'in majority of time.Pairwise PERMANOVA analysis indicated that the phytoplankton assemblage in the bivalve zone was significantly different with the control and kelp zones,while the IMTA zone maintained close to other three zones.Based on generalized additive models,temperature,NO_(2)^(-)-N,N/P ratio,SiO_(3)^(2-)-Si,and salinity were determined as the key factors underlying Chl-a and phytoplankton diversity.Addi-tionally,the results of redundancy analysis further indicated that the phytoplankton assemblage in the bivalve zone is positively re-lated with nutrients such as NO_(3)^(-)-N and NH_(4)^(+)-N as well as water depth,while the phytoplankton assemblages in the kelp,control,and IMTA zones are associated with NO_(2)^(-)-N,SiO_(3)^(2-)-Si,and salinity.Taken all observations into consideration together,it can be inferred that IMTA can effectively reduce Chl-a level compared to bivalve monoculture by reducing the nutrients.However,the SR,H’,and species composition of phytoplankton are primarily determined by local environment factors such as temperature,water depth,salinity and SiO_(3)^(2-)-Si.

Carbon and nitrogen isotopes analysis and sources of organic matter in surface sediments from the Sanggou Bay and its adjacent areas, China

Naturally existing stable carbon and nitrogen isotopes are important in the study of sedimentary organic matter sources. To identify the sources of sedimentary organic matter in Sanggou Bay and its adjacent areas, which is characterized by high-density shellfish and seaweed aquaculture, the grain size, organic carbon （OC）, total nitrogen （TN）, carbon and nitrogen isotopic composition （δ13C andδ15N） of organic matter in the surface sediment were determined. The results showed that, in August, sedimentary OC and TN ranged from 0.17% to 0.76% and 0.04% to 0.14%, respectively. In November, OC and TN ranged from 0.23% to 0.87% and 0.05% to 0.14%, respectively. There was a significant positive correlation between OC and TN （R=0.98, P＆lt;0.0001）, indicating that OC and TN were homologous. In August, theδ13C andδ15N of organic matter varied from -23.06‰ to -21.59‰ and 5.10‰ to 6.31‰, respectively. In November,δ13C andδ15N ranged from -22.87‰ to -21.34‰ and 5.13‰ to 7.31‰, respectively. This study found that the major sources of sedimentary organic matter were marine shellfish biodeposition, seaweed farming, and soil organic matter. Using a three-end-member mixed model, we estimated that the dominant source of sedimentary organic matter was shellfish biodeposition, with an average contribution rate of 65.53% in August and 43.00% in November. Thus, shellfish farming had a significant influence on the coastal carbon cycle.

Burial fluxes and source apportionment of carbon in culture areas of Sanggou Bay over the past 200 years

In this study, we assessed the burial fluxes and source appointment of different forms of carbon in core sediments collected from culture areas in the Sanggou Bay, and preliminarily analyzed the reasons for the greater proportion of inorganic carbon burial fluxes （BFTIc）. The average content of total carbon （TC） in the Sanggou Bay was 2.14%. Total organic carbon （TOC） accounted for a small proportion in TC, more than 65% of which derived from terrigenous organic carbon （Ct）, and while the proportion of marine-derived organic carbon （Ca） increased significantly since the beginning of large-scale aquaculture. Total inorganic carbon （TIC） accounted for 60%-75% of TC, an average of which was 60%, with a maximum up to 90% during flourishing periods （1880-1948） of small natural shellfish derived from seashells inorganic carbon （SheU-IC）. The TC burial fluxes ranged from 31 g/（m2.a） to 895 g/（m2.a） with an average of 227 g/（m2.a）, which was dominated by TIC （about 70%）. Shell-IC was the main source of TIC and even TC. As the main food of natural shellfish, biogenic silica （BSi） negatively correlated with BFTIc through affecting shellfish breeding. BFTIc of Sta. S1, influenced greatly by the Yellow Sea Coastal Current, had a certain response to Pacific Decadal Oscillation （PDO） in some specific periods.

The phosphorus cycle in the Sanggou Bay

The phosphorus cycle is studied during 2013–2014 in the Sanggou Bay（SGB）, which is a typical aquaculture area in northern China. The forms of measured phosphorus include dissolved inorganic phosphorus（DIP）, dissolved organic phosphorus（DOP）, particulate inorganic phosphorus（PIP）, and particulate organic phosphorus（POP）.DIP and PIP are the major forms of total dissolved phosphorus（TDP） and total particulate phosphorus（TPP）,representing 51%–75% and 53%–80%, respectively. The concentrations and distributions of phosphorus forms vary among seasons relative to aquaculture cycles, fluvial input, and hydrodynamic conditions. In autumn the concentration of DIP is significantly higher than in other seasons（P〈0.01）, and higher concentrations are found in the west of the bay. In winter and spring the phosphorus concentrations are higher in the east of the bay than in the west. In summer, the distributions of phosphorus forms are uniform. A preliminary phosphorus budget is developed, and shows that SGB is a net sink of phosphorus. A total of 1.80×10^7 mol/a phosphorus is transported into the bay. The Yellow Sea is the major source of net input of phosphorus（61%）, followed by submarine groundwater discharge（SGD）（27%）, river input（11%）, and atmospheric deposition（1%）. The main phosphorus sink is the harvest of seaweeds（Saccharina japonica and Gracilaria lemaneiformis）, bivalves（Chlamys farreri）,and oysters（Crassostrea gigas）, accounting for a total of 1.12×10^7 mol/a. Burial of phosphorus in sediment is another important sink, accounting for 7.00×10^6 mol/a. Biodeposition by bivalves is the major source of phosphorus in sediment, accounting for 54% of the total.

Sediment Resuspension Mechanisms in Aquaculture Area, Sanggou Bay

The sediment resuspension mechanisms in Sungo Bay, a large-scale aquaculture area in north China, were investigated by analysing data collected during several periods from 2005 to 2006. Nortek 6M ADV current meter and YSI6600 were used to collect the field data on current speed, current direction and water turbidities 1 m above the bottom. Based on the collected field data, it could be found that wind-waves and currents were the main driving force for sediment resuspension. The correlation between suspended sediment concentration （SSC） and turbidity （NTU） is SSC = 15.908 x In （NTU） ＋ 7.0888 （n = 33, R2 = 0.7209）. Taking the key factor （angle 0） into account, the combination effect between wave and current were expressed. Results showed that the combined shear stress （row） of wave stress （re） and current stress （rw） could be calculated by row = rc ＋ 2√ rcrw sin θ ＋ rw sin^2 θ. The critical shear stress for sediment resuspension was about 0.059 N/m^2. The correlation between suspended sediment concentration and critical shear stress could be expressed by rcw = 238.06 SSC ＋ 25.215 （n = 25, R^2 = 0.7298）.

Seasonal Variations in Phytoplankton Community Structure in the Sanggou,Ailian,and Lidao Bays

The seasonal variations in phytoplankton community structure were investigated for the Sanggou Bay （SGB） and the adjacent Ailian Bay （ALB） and Lidao Bay （LDB） in Shandong Peninsula,eastern China.The species composition and cell abundance of phytoplankton in the bay waters in spring （April 2011）,summer （August 2011）,autumn （October 2011）,and winter （January 2012） were examined using the Uterm6hl method.A total of 80 taxa of phytoplankton that belong to 39 genera of 3 phyla were identified.These included 64 species of 30 genera in the Phylum Bacillariophyta,13 species of 8 genera in the Phylum Dinophyta,and 3 species of 1 genus in the Phylum Chrysophyta.During the four seasons,the number of phytoplankton species （43） was the highest in spring,followed by summer and autumn （40）,and the lowest number ofphytoplankton species （35） was found in winter.Diatoms,especially Paralia sulcata （Ehrenberg） Cleve and Coscinodiscus oculus-iridis Ehrenberg,were predominant in the phytoplankton community throughout the study period,whereas the dominance of dinoflagellate appeared in summer only.The maximum cell abundance of phytoplankton was detected in summer （average 8.08 × 103 cells L-1） whereas their minimum abundance was found in autumn （average 2.60 x 103 cellsL-1）.The phytoplankton abundance was generally higher in the outer bay than in the inner bay in spring and autumn.In summer,the phytoplankton cells were mainly concentrated in the south of inner SGB,with peak abundance observed along the western coast.In winter,the distribution of phytoplankton cells showed 3 patches,with peak abundance along the western coast as well.On seasonal average,the Shannon-Wiener diversity indices of phytoplankton community ranged from 1.17 to 1.78 （autumn 〉 summer 〉 spring 〉 winter）,and the Pielou＇s evenness indices of phytoplankton ranged from 0.45 to 0.65 （autumn 〉 spring 〉 summer〉 winter）.According to the results of canonical correspondence analysis,phosphate level was the major factor that limited the occurrence of P.sulcata and C.oculus-iridis,whereas optimal temperature and low salinity were responsible for Prorocentrum blooms in summer.The detailed description of seasonal variations in phytoplankton community structure in the three bays provide reference data for future studies on marine ecosystems and mariculture in adjacent areas.

Standing crop and primary production of benthic microalgae on tidal flats in the Sanggou and Jiaozhou Bays, China

The standing crop and primary production of benthic microalgae on tidal flats have seasonally been observed in the Sanggou and Jiaozhou Bays of the northern China coast during 1999 - 2000. The results show that the annual primary productions of benthic microalgae on tidal flats in the two bays are 2 532 and 7 542 tons carbon, which would be able to support 3.1 x 103 and 9.2 x 103 tons shellfish meat, respectively. The nature of sediment is essential for governing the biomass and primary production of benthic microalgae on tidal flats. The biomass and primary production of benthic microalgae on tidal flats with muddy sediments are higher than those with sandy sediments, which resulted from higher nutrient concentration and lower grazing pressure. That is the reason why in comparison with Xiangshan Bay the standing crop and production of benthic microalgae on tidal flats of the Sanggou and Jiaozhou Bays are low. Light was a key factor controlling vertical distribution of biomass and production of benthic microalgae on tidal flats of the two bays, resulted in appearance of maximum chlorophyll a and primary production at the surface layer and sharply decreased with depth of sediment.