The Effect of Bioturbation Activity of the Ark Clam Scapharca subcrenata on the Fluxes of Nutrient Exchange at the Sediment–Water Interface

Filter-feeding shellfish are common benthos and significantly affect the biogeochemical cycle in the shallow coastal ecosystems.Ark clam Scapharca subcrenata is one of the widely cultured bivalve species in many coastal areas owing to its tremendous economic value.However,there is little information regarding the effects of the bioturbation of S.subcrenata on the fluxes of nutrient exchange in the sediment-water interface(SWI).In this regard,S.subcrenata was sampled during October 2016 to determine the effects of its bioturbation activity on the nutrient exchange flux of the SWI.The results showed that the biological activity of S.subcrenata could increase the diffusion depth and the rate of the nutrients exchange in the sediments.The bioturbation of S.subcrenata could allow the nutrients to permeate into the surface sediments at 6-10cm and increase the release rate of nutrients at the SWI.The releasing fluxes of DIN and PO43−-P in the culture area were found to be around three times higher than that in the non-cultured region.The culture of S.subcrenata has been proved to be an important contributor to nutrient exchange across the SWI in the farming area of Haizhou Bay.Nutrients exchange in the SWI contributes a part of 86%DIN,71%PO43−-P and 18%SiO32−-Si for the aquaculture farm.

Improvement on the Effectiveness of Marine Stock Enhancement in the Artificial Reef Area by a New Cage-Based Release Technique

The release technique,affecting the survival rate of fish species released for stock enhancement,plays a vital role in the effectiveness of the enhancement.In order to improve the probability of released fish settling down to bottom,a new cage-based release technique was designed and tested via a water tank with artificial reef models.Two coral reef fish species,Sebastes schlegelii and Paralichthys olivaceus were assessed using this technique.Fish behavior and distribution in water tank were recorded and compared with the traditional release release techniques.Results showed that in the case of cage-based release technique:1)when the release process is just finished,the distribution index(DI)of juveniles S.schlegelii and P.olivaceus were 97.8%and 98.9%at reef area,40%and 71.1%at release point,respectively,which was higher than those using two alternative techniques;2)its impact duration was less than that in the other two conditions,where the DI within 4 hours was higher after releasing,especially for S.schiegelii.These findings indicated that the new cage-based technique could release the fish into the specified location,and has a potential to mitigate the stress reaction of fish caused by releasing process.