| Sea cucumber, Apostichopus japonicus, has been becoming one of the most commercially important mariculture species in northern China in recent years. It is well known that sea cucumbers are deposit feeders, ingesting sediment to gain nutrients from organic matter, bacteria and protozoa, hence they are regarded as"environmental cleaners or scavengers". However, no quantitative studies about the impacts of sea cucumber aquaculture on the pond sediments and on the nearby coastal waters are available so far. The objective of the present study is to assess the effects of different polyculture systems on the ponds sediments and to evaluate the potential environmental effects of sea cucumber farming on nearby coast.Sediment samples were collected from three seawater aquaculture ponds, and soil characteristics, sediment oxygen consumption (SOC), dissolved organic carbon (DOC) and nutrient fluxes were measured using chamber incubations at laboratory. The results show that: Total organic carbon (TOC) and total nitrogen (TN) contents in the dry sediment of the ponds were low. TOC, total carbon (TC) contents and SOC of the sediment in the pond polycultured with jellyfish increased with culture time, indicating that jellyfish farming enhanced the accumulation of organic matter in the sediments to some extent. Sediment showed net nitrate and ammonium uptake in most ponds and months. Dissolved inorganic phosphate (DIP) was released from the sediments in all ponds with low flux rates. The results suggested that non-artificial-feeding sea cucumber culture ponds could not only yield valuable seafood products, but also effectively remove nutrients from the aquaculture systems and consequently alleviate nutrient loadings of the nearby coast.Sediments were sampled from sea cucumber-scallop polyculture"Large pond","Sea area"and"Common sea cucumber ponds"during October 2007 to June 2008. And sediment-water fluxes of nutrients, benthic nitrification and denitrification rates were measured in laboratory. The results showed that: Contents of total organic carbon (TOC) in the sediment of scallop culture area (SC-area) in"Large pond"were significantly higher than those in the area without scallop (Non-SC-area) during scallop culture period (p<0.05). Sediment oxygen consumption (SOC) in SC-area during scallop culture period were significantly higher than those in Non-SC-area (p<0.05). Ammonia was released from sediment in SC-area and Non-SC-area of"Large pond"in all months. Rates of nitrification in the sediments of SC-area were higher than that of Son-SC-aea in"Large pond". Rates of nitrification in"Sea area"and"Common sea cucumber pond"were lower. Rates of denitrification at all sampling sites were low. Denitrification rates in SC-area during scallop culture period and in April during"restoration period"were significantly higher than those in Non-SC-area (p<0.05). The results obtained from this study demonstrate that scallop aquaculture in"Large pond"may result in organic matter accumulation in the bottom, however, the sediments may be recovered from enrichment in short time (4-6 months); Common aquaculture model of sea cucumber would not lead to organic accumulation in the sediment both within the pond and nearby coast.Sediment samples were collected from in sea cucumber (Apostichopus japonicus) experimental enclosures with different cultural models from May to November in 2007, and sediment-water fluxes of oxygen, nitrogen and phosphorus were investigated using laboratory chamber incubations. Sediment oxygen cemand (SOC) in enclosures were not different significantly between feed model and unfed model (p>0.05), indicating that feeding did not lead to enriched sediments. Dissolved inorganic phosphate (DIP) was released from the sediments in most enclosures. The fluxes of DIP among months were significantly different (p<0.05). Fluxes of nitrate + nitrite (NO3-+ NO2-) in the enclosures with feeding models were two to three times higher than that with non-feed models. Fluxes of ammonium uptaken by sediments in the enclosures with feeding models were greater than that with non-feed models when sea cucumber density was high. The density of sea cucumber and feed model had signification effects on nitrification, denitrification and nitrate reduction rates of sediment. Rates of nitrification, denitrification and nitrate reduction of different models were much lower compared with other farming ponds and ranged from 0～106.20 mg·m-2·d-1, 0～3.03μmol·m-2·d-1Effects of temperature and dissolved oxygen on the sediment-water interface nutrient fluxes in sea cucumber aquaculture ponds were studied using laboratory cultivation methods. The results showed that: Water temperature impacted nutrient fluxes in the pond sediment significantly (p<0.05). High temperature is conducive to the release of ammonia nitrogen from the sediment, but disadvantageous to release of nitrate in the sediment; Dissolved oxygen is an important factor to control the pond sediment nutrient change. The release of sediment ammonia nitrogen was accelerated in anaerobic conditions and decreased in anaerobic conditions; The sediment oxygen consumption increases with increasing temperature and dissolved oxygen; Nitrification and denitrification were affected by temperature and dissolved oxygen significantly (p<0.05). Both nitrification and denitrification increased with increasing temperature and nitrification increased more with an increase of temperature at the high content of dissolved oxygen (8mg/L). Nitrification increased with increasing dissolved oxygen and denitrification decreased with an increase of DO.Effects of bioturbation of sea cucumber, Apostichopus japonicus Selenka, on the pond bottom soil were studied and compared with that of Phascolosoma esculenta using mesocosms established in the field and laboratory. The results showed that: Bioturbation of sea cucumber (size, 1.6-7.2g ind-1) and P. esculenta significantly affected the organic matter content and its stability in the surface layer of the bottom soil, and their effects varied with the contents of organic matter in the bottom soil. In the conditions with low organic matter contents in the bottom soil (field experiment), bioturbation of A. japonicus resulted in a significant increase of TON and decrease of stability of organic matter in the surface layer of the bottom soil (p<0.05). In the conditions with high organic matter contents in the bottom soil (laboratory experiment), bioturbation of A. japonicus and P. esculenta significantly reduced the contents of TOC and TON in the surface layer of the sediment. Effects of A. japonicus on the content of organic matter in the deep layer of the sediment were not visible, while effects of P. esculenta were larger. P. esculenta increased the content of organic matter in the deep layer and reduced the stability of sediment, which indicates P.esculenta serves as an"Downward-conveyors"in the experimental system. In the laboratory experiment, heterobacteria of the surface layer in the sediment in Treatment containing high density of A. japonicus were more than other Treatments and controls significantly, which demonstrated that bioturbaton of A. japonicus enhance the growth of bacteria.
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