A Study On Ecophysiological Characteristics Of Bivalves In Seagrass Meadow And Ecological Restoration Of The Eelgrass Zostera Marina L.

Based on the status of degradation of seagrass meadows in northern China, theecophysiological parameters of typical bivalves were in situ measured in a seagrass（Zostera marina L.） meadow, and ecological characteristics of the eelgrasspopulations were investigated in Swan Lake, Shandong province, and the conditionsand methods were studied preliminarily for ecological restoration of Z. marina. Ourstudies included measurement methods and seasonal variations of the biodepositionby two typical bivalves （Ruditapes philippinarum and Crassostrea gigas） in aseagrass meadow, variations in the respiration and excretion of the two bivalves,ecological survey of the seagrass meadow in Swan Lake, and optimal conditions andevaluation for the transplantation of Z. marina. The main results are as followed:1. Biodeposition rates by the infaunal bivalve R. philippinarum and theepifaunal bivalve C. gigas were in situ measured using biodeposit traps in Swan Lake.Results showed that the biodeposit traps designed in this study could be used toaccurately measure biodeposition rates by infaunal bivalves and epifaunal bivalves inshallow waters （intertidal areas）.2. From November2011to January2013, biodeposition rates of the Manilaclam R. philippinarum with shell length of22.6-28.0mm ranged from2.19to91.25mg/ind d, and the biodeposition rates of clams with shell length of28.0-32.8mmranged from5.79to129.00mg/ind d. Biodeposition rates of the Pacific oyster C.gigas with shell height of82.8-123.5mm ranged from133.62to2099.01mg/ind d.Natural deposition rate in the intertidal eelgrass meadow ranged from16.68to104.91g/m²d. The biodeposition rate and natural deposition rate varied significantly withseasons, lower in winter and spring and higher in summer and autumn. It is estimatedthat in September R. philippinarum and C. gigas in Swan Lake could remove respectively281.310³kg and142.210³kg seston via intense filtering andbiodeposition, which could induce strong pelagic-benthic coupling.3. From May2012to January2013, oxygen consumption rates （RO） of R.philippinarum with shell length of23.6-28.5mm,28.4-32.9mm and33.4-36.3mmranged respectively from0.053to0.510mg/ind h,0.079to0.720mg/ind h, and0.106to0.932mg/ind h. ROof C. gigas with shell height of83.1-110.8mm ranged from0.106to3.659mg/ind h. From May to September2013, ammonia excretion rates （RN）of R. philippinarum ranged respectively from0.325to1.469μmol/ind h,0.496to1.693μmol/ind h, and0.476to2.459μmol/ind h. RNof C. gigas ranged from0.357to12.590μmol/ind h. From May to September2013, the O:N ratio of R. philippinarumranged respectively from16.1to45.2,18.0to57.8, and18.2to44.2; and the O:Nratio of C. gigas ranged from16.8to283.6. ROand RNincreased with the increase oftemperature, and the O:N ratio decreased during reproduction. It is estimated that inSeptember clams in Swan Lake could consume43.3×10³kg dissolved oxygen andexcrete1.7×10³kg ammonia nitrogen; and oysters in Swan Lake could consume5.6×10³kg dissolved oxygen and excrete0.3×10³kg ammonia nitrogen.4. From September2011to January2013, the shoot density of Z. marina inintertidal zone of Swan Lake ranged from337to889ind/m². δ¹³C（‰） of leaf rangedfrom-10.24to-7.06, and δ¹⁵N（‰） from4.95to8.32. The ranges of moisture contentsof underground stem, sheath and leaf were84.1-91.6%,86.4-91.4%,81.3-88.6%respectively. Eelgrass （Zostera marina） was transplanted with a new simple method,i.e several rooted shoots tied on a small elongate stone with cotton thread wereplanted. We summarise the optimal conditions for transplantation in coastal zone:illumination intensity is more than2360lx （water depth was less than6m in coastalwaters of Weihai）, and the buried depth was less than10cm in Swan Lake. Thetransplanted eelgrass grew in good condition in Huiquan Bay, Qingdao, which couldtestify that the new method was effective and practical.