Research On Carbon Sequestration Of Cultured Oyster Crassostrea Gigas And Its Fouling Organisms In Sungo Bay

Carbon cycling in coastal waters is an important part of ocean carbon cycle, andalso is the critical point which significantly effected by human activies. There aremass of aquaculture in coastal waters. Shellfish culture was regarded creating greatinfluence of material cycle, especially for carbon cycle of coastal waters. Aim at thelimit on fundamental researches of “carbon sink fishery”, this paper focused on themain farming shellfish-oyster. Taking Sungo Bay as a typical study area, we conduct-ed quantificat evaluation of carbon distribution in growth and metabolism of oysterand carbon sequestration of its flouing organisms; build the carbon budget modelamong a year; did correlational studies of biodeposit on its character, composition andcontribution of sediments; provide basic data and scientific proof to elucidate the roleof filter feeders shellfish aquaculture in ocean carbon cycle. Major research resultsincluding the following parts:1. Assessment of carbon sequestration by farming oyster harvest. Artificialbreeding oyster and natural seeding oyster were suited for their growth and marinefouling organisms during May2012and October2013. According to the elementanalysis and standardization of carbon sequestration, carbon removing from the sea byoyster harvest was assessed. The study results showed that: when harvest, shell heightand dry weight of soft tissue of artificial breeding oyster and natural seeding oysterwere91.5±12.3mm,1.07±0.37g after15moths culture and75.4±7.3mm,0.87±0.30gafter24months respective. Dominant species of fouling organisms were M. edulis, C.intestinalis and S. clava. Wet weight of the total artificial breeding oyster rope was14908.3±2023.8g and above60%were live oyster, in natural seeding oyster rope theywere15017.7±2528.1g and about45%. Dry weights of these two ropes were8025.1±1031.4g and8441.8±1548.2g. Calculated by the carbon content of eachsample, carbon harvest from artificial breeding oyster rope was938.1±121.1g, and theother was989.4±179.1g. As a result of standardization, the carbon sequestration rateof artificial breeding oyster was2.36tC/hm2·year, for natural seeding oyster it was 1.56tC/hm2·year. Carbon sequestration ability of both were at very high levels. Hugeamounts of carbon were removed off the sea by harvest.2. The diurnal rhythm of C. gigas. The diurnal rhythm of respiration, excretionand calcification in three size (Shell height：S:2.5cm; M:5.5cm; B:6.8cm) C. gigaswere researched in this paper. Indoor and experiment in the sea area for oyster wereall conducted under10℃,18℃and20℃. The result demonstrated that metabolism ofoyster changed as a rhythm, its oxygen consumption played as a diurnal rhythm,higher at night when water temperature was10℃and opposite at18℃in the sea area,the difference value was0.07-0.08mg·ind-1·h-1. Meanwhile, oxygen consumption at20℃was stable. Excretion of C. gigas did not change with the respiration. The trendline of excretion was same at day and night. It was considered that excretion of C.gigas may be affected by tidal rhythm. Calcification of oyster did not demonstrateobvious rhythm, but it was significantly different between hours and hours (P＜0.05).So it’s better to avoid calculate the level of metabolism by physiological indexgathered in a short interval, replicates in different time were needed.3. Respiratory quotient of cultured oyster C. gigas and its marine foulinganimal species and impact from calcification. In this paper, RQ and O/N of culturedoyster C. gigas and3marine fouling animal species (Mytilus edulis, Ciona intestinalis,and Styela clava) were measured in respiratory chamber, so as to discuss the effect ofcalcification in RQ determination. The results demonstrated that calcification rate of C.gigas and M. edulis were56.37±14.85and17.95±7.21μmol·g-1·h-1, respectively.3.72±0.80and1.48±0.14mg·L-1DIC in the water were correspondingly decreased,which occupied about60.9±7.6%and39.9±5.7%of respiration CO2, respectively. RQvalues of4animals were C. gigas1.38±0.19; M. edulis1.18±0.11; C. intestinalis1.11±0.05and S. clava1.32±0.19, which results agreed with the O/N values except C.intestinalis. Meanwhile, uncorrected RQ values of C. gigas and M. edulis were0.56±0.19and0.70±0.04, respectively, and contrary to the O/N values. Therefore, itwas obviously that Calcification could result in a significant influence on the respiratory quotient by affecting water DIC concentration and should be accuratelycalculated in RQ measurement.4. Organic content, sinking velocities and potential dispersion of biodepositsfrom long-line cultured C. gigas. Organic content, sinking velocities and potentialdispersion of biodeposits from the long-line cultured oyster C. gigas were studiedfrom April to December2012. Results show that the organic content of biodepositsvaried between11.7%and22.3%and differed significantly among all9months(p<0.01). The average sinking velocities of biodeposits were: Group B,1.42±0.72cm·s-1; Group M,1.16±0.54cm·s-1; and Group S,0.93±0.49cm·s-1. The potentialdispersion distance of biodeposits from C. gigas averaged from48.31m to203.97m.The maximum dispersion distance estimated in August was379.6m. With the impactof current, perturbation by wild organisms and resuspension, biodeposits may have amuch wider dispersion. Evidences from the stable isotope indicated that biodepositsfrom C. gigas contributed21.68±0.52%of the organic content in sediment of theoyster farm. The organic C and N values of sediment from the oyster farm wassignificantly higher than that from the uncultivated area.5. Contribution of organic matters in the sediment from biodeposits oflong-line cultured C. gigas. Shellfish has significant biodeposition which canaccelerate the transport of particulate matter from sea water to seabed. In Sungo Bay,long-line cultured oyster works in this way by its biodeposits including faeces andpseudofaeces. In this paper, we set up8sites (5of oyster cultural area,3as controlsites) to sample. Sediments from each site, biodeposits and suspended particulatematters from SG2and SG6were sampled for stable isotope analysis. The resultsshowed that: δ13C, δ15N values of sediments were δ13C‰-22.82to-21.62,15N‰4.73to6.21. In SPM of SG2site, biodeposits contributed about9.95%, and sedimentsfrom control site and SG2were54.19%and35.86%, respective. In typical sites,stable isotope method could be effective. Biodeposits from oyster contributed4.06%to28.64%in the sediments of each area, on average of13.96±8.62%. 6. Carbon budget of long-line cultured C. gigas and its fouling organisms.Carbon budget was very important for the carbon sequestration assessment of culturedoyster and its fouling organisms. In this paper, each physiological activity related tocarbon was analyzed including food intake, calcification, respiration andbiodeposition to build the carbon budget. Our results demonstrated that carbon infeces occupied42%-48%of the carbon in food intake and was the largest part ofoutlay.11%-22%of carbon was released by respiration. Carbon in excretion was thefewest part, about0.65%-0.1. Carbon was used to growth was33%-38%, calculatedby the carbon budget formula. In the cultural360d，one oyster utilized14968mg Cfrom the water and formed3parts of carbon sequestration:3600mg in the shell,430mg in the soft tissue and3322mg in its biodeposits. That in M. edulis was840mg inshell,216mg in soft tissue and3501mg in biodeposits. C. intestinalis created2000403.3mg C in these360d and S. clava8226.9mg. Carbon budget of culturedoyster and its fouling organisms was finished in standardization.