庄河海域菲律宾蛤仔底播增殖区自身污染

采用生物沉积物捕集器和封闭式代谢瓶,周年现场研究了庄河海域菲律宾蛤仔的生物沉积速率、排氨率和排磷率.结果表明:菲律宾蛤仔的生物沉积速率、排氨率和排磷率均具有明显的季节变化.生物沉积速率为0.15～1.47 g·ind-1·d-1(年均0.61 g·ind-1·d-1);其排氨率及排磷率分别为0.02～0.40 mg·ind-1·d-1(年均0.17 mg·ind-1·d-1)和0.01～0.39 mg·ind-1·d-1(年均0.13 mg·ind-1·d-1).根据以上结果,估算庄河海域底播增殖菲律宾蛤仔每年产生的生物沉积物达到5.46×107t(干质量),折合有机物9.07×106t、有机碳1.00x106t和有机氮1.18xlO5t;而氨氮和磷酸盐分别为1.49x104t和1.15x104t.表明浅海高密度、规模化菲律宾蛤仔增养殖区自身污染严重,其对环境的影响不可忽视.     

温度、盐度及交互作用对僧帽牡蛎(Saccostrea cucullata)呼吸排泄的影响

采用实验生态学方法研究了温度(13、18、23、28、31、34℃)和盐度(18、23、28、33)对僧帽牡蛎(Saccostrea cueullata)耗氧率和排氨率的影响,并分析了二者交互作用对呼吸排泄的影响。结果表明,不同温度条件下,僧帽牡蛎的耗氧率变化范围为0.43-3.15mg g~(-1)h~(-1),排氨率的变化范围为72.62-1245.77μg g~(-1)h~(-1),方差分析显示,温度和盐度对僧帽牡蛎耗氧率(F=60.440,P0.01)和排氨率(F=61.083,P0.01)的影响均极显著;二者的交互作用对僧帽牡蛎耗氧率(F=4.907,P0.01)和排氨率(F=11.412,P0.01)影响也极显著,耗氧率(Y)、排氨率(Y)与温度(T)和盐度(S)之间的二元线性回归方程为y=a+bT+cS+dT×S。在一定温度范围内(13-31℃)僧帽牡蛎单位体重耗氧率(Y)与温度(T)呈正相关符合指数方程Y=ae~(bT),其中a的取值范围为0.1378-0.2117,b的取值范围为0.0757-0.0912;单位体重排氨率也与温度呈正相关,符合上述指数方程,其中a的取值范围为20.364-30.634,b的取值范围为0.1004-0.1341。不同温度和盐度条件下,僧帽牡蛎呼吸排泄的氧氮比在2.20-7.78之间,平均值为3.81。     

杭州西湖北里湖沉积物氮磷内源静态释放的季节变化及通量估算

通过采集北里湖不同季节的柱状芯样,在实验室静态模拟沉积物氨氮(NH+4-N)和可溶解性磷酸盐(PO3-4-P)的释放,同时研究了沉积物间隙水中NH+4-N及PO3-4-P的垂直分布特征.结果表明,沉积物间隙水NH+4-N随深度的增加有上升的趋势,PO3-4-P随深度的增加呈先升后降的趋势.氮、磷营养盐在沉积物—水界面均存在浓度梯度,表明存在自间隙水向上覆水扩散的趋势.沉积物NH+4-N在春季、夏季、秋季、冬季的释放速率分别为0.074 mg·m-2· d-1、0.340mg· m-2· d-1、0.087 mg· m-2· d-1、0.0004 mg·m-2·d-1,pO3-4-P的释放速率则分别为0.340 mg·m-2·d-1、0.518 mg·m-2·d-1、0.094 mg·m-2·d-1、-0.037 mg· m-2·d-1.不同采样点表现出明显的季节和空间差异性,释放速率表现为夏季＞春季、秋季＞冬季.根据静态模拟出的不同季节下内源氮、磷释放速率计算,全湖内源氮、磷营养盐的贡献分别为0.0037、0.0057t/a.该研究可为北里湖富营养化及内源污染的治理提供基础数据.     

体质量和水温对太湖秀丽白虾人工驯养子代耗氧率和排氨率的影响

以太湖秀丽白虾(Exopalaemon modestus)人工驯养子代为实验样本,实验共设置6个体质量梯度及7个温度梯度,样本体质量范围为(0.12±0.01)～(1.93±0.05)g,实验温度范围为12℃～30℃,研究了体质量及水温对耗氧率和排氨率的影响。结果表明:秀丽白虾耗氧率变幅为0.1497～0.9053mg·g-1·h-1,均值为0.3901mg·g-1·h-1;排氨率变幅为0.0165～0.0866mg·g-1·h-1,均值为0.0379mg·g-1·h-1。体质量、水温及两者的交互效应均对耗氧率和排氨率具有极显著的影响(P0.01)。体质量与耗氧率和排氨率之间的回归关系分别符合幂函数方程Ro=0.3114W-0.2414(r=-0.436)和Rn=0.0307W-0.3007(r=-0.653);水温与耗氧率和排氨率之间的回归关系分别符合指数方程Ro=0.0711e0.0749t(r=0.877)和Rn=0.0113e0.0530t(r=0.747);体质量、水温与耗氧率及排氨率的二元回归方程分别为Ro=0.028T-0.147W-0.053(r=0.948)和Rn=0.002T-0.017W+0.013(r=0.922)。耗氧率和排氨率Q10变幅分别为1.17～4.20和1.15～2.29,均值分别为2.10和1.64。在实验温度范围内,氧氮比均随着水温的上升而增大,变幅为7.42～13.62,均值为10.04。秀丽白虾在低温阶段(12℃～18℃)主要以蛋白质为供能物质,在高温阶段(21℃～30℃)对脂肪的利用有所增加,中等规格个体的脂肪代谢率最高。     

卵形鲳鲹幼鱼耗氧率和排氨率的初步研究

运用封闭流水式实验方法对不同体重和放养密度的卵形鲳鲹(Trachinoms ovatus)幼鱼耗氧率和排氨率进行了初步的研究。结果表明,卵形鲳鲹幼鱼的耗氧率随着鱼体重的增加而逐渐下降,排氨率总体上也呈降低的趋势,体重对卵形鲳鲹耗氧率、排氨率的影响均达到显著水平(P0.05);光照对卵形鲳鲹幼鱼的耗氧率和排氨率影响非常显著(P0.01),幼鱼在遮光条件下的耗氧率和排氨率分别比在自然光照条件下要低25.18%～40.76%和16.28%～40.28%;随着放养密度的增加,卵形鲳鲹幼鱼的耗氧率逐渐降低,排氨率随着密度的增加呈先上升后下降的趋势,放养密度对卵形鲳鲹耗氧率、排氨率的影响均达到显著水平(P0.05)。卵形鲳鲹的耗氧率和排氨率具有明显的昼夜变化,白天的耗氧率和排氨率均高于夜间值,耗氧率的低谷值为高峰值的69.68%,排氨率的低谷值为高峰值的30.91%。卵形鲳鲹幼鱼的窒息点溶解氧含量为(0.991±0.058)mg/L。     

温度和个体大小对单齿螺耗氧率和排氨率的影响

采用静水法测定了不同温度、不同个体大小的单齿螺耗氧率和排氨率。结果表明:在16-33℃的实验温度范围内单齿螺的耗氧率(R_O)和排氨率(R_N)与软体部干重(W)都呈负相关,它们之间关系可以分别用幂函数R_O=aW^-b和R_N=a₁W^-b1表示。16～29℃温度范围内单齿螺的耗氧率和排氨率均随温度的升高而增加,29℃时耗氧率和排氨率达到最大值,当温度继续升高超过29℃后,耗氧率和排氨率则随温度的升高而下降,耗氧率、排氨率与温度之间呈显著的指数函数关系R_O=ce^dT和R_N=c₁e^d1T;不同个体大小单齿螺的O:N比在16～20℃时较大,Q₁₀取值范围0.56-3.74,平均值为1.64。方差分析表明,温度、软体部干重对单齿螺的耗氧率和排氨率均有极显著的影响(P<0.01)。     

三种流速对卵形鲳鲹幼鱼耗氧率和排氨率的影响

【摘要】采用实验生态学方法, 研究了饥饿态下平均体重分别为(2.54±1.09) g、(24.35±7.19) g、(233.79±26.00) g、(508.98±126.61) g的卵形鲳鲹幼鱼(Trachinotus ovatus)在静水、0.1 m·s -1、0.2 m·s -1三种流速下的耗氧率和排氨率的变化。结果表明, 卵形鲳鲹体重对耗氧率和排氨率影响显著(P < 0.05)。在同一流速下, 耗氧率和排氨率分别随体重的增加而下降, 体重与两者间的回归关系符合异速方程Y=aWb。卵形鲳鲹的耗氧率和排氨率随着流速的升高均出现升高的趋势, 流速对均重为24.35 g和233.79 g卵形鲳鲹的耗氧率和排氨率影响显著(P < 0.05)。在静水条件下, 卵形鲳鲹代谢氧氮比的范围为31.36-46.32, 表明卵形鲳鲹主要以脂肪和碳水化合物为能源, 蛋白质其次。在试验流速范围内, 均重为24.35 g卵形鲳鲹幼鱼的氧氮比随着流速的升高而升高, 其他两组的氧氮比则随着流速的升高而降低。     

铜锈环棱螺对藻华水体沉积物-水界面营养盐通量的影响

于2008年在室内小型试验模拟生态系统中进行了为期1个月的铜锈环棱螺生物干扰对底泥耗氧率和上覆水营养盐通量的影响试验,根据铜锈环棱螺放养密度设置了3个处理组和1个对照组。与试验前相比,培养1个月后,所有处理组和对照组的底泥耗氧率均显著下降;各处理组的底泥耗氧率初期高于对照组,后期低于对照组,且密度高的处理组其底泥耗氧率高于密度低的处理组。除12月7日外,对照组沉积物始终向上覆水释放铵氮,且释放量逐渐减小,而各处理组中,除试验初期沉积物向上覆水释放铵氮外,试验中后期均表现为吸收铵氮。除试验初期外,处理组和对照组中亚硝酸盐+硝酸盐通量主要表现为向上覆水中释放,且处理组1与对照组间存在显著差异(P<0.05)。磷酸盐通量主要表现为,试验初期沉积物向上覆水中释放,后期被沉积物吸收。本试验结果表明,短期内铜锈环棱螺的生物干扰增加了底泥耗氧率,但其长期效应可使底泥耗氧率下降,铜锈环棱螺的存在促进了沉积物中的总体硝化速率,加快了沉积物中的N循环。     

鲻幼鱼耗氧率、排氨率和窒息点的研究

为探讨鲻幼鱼的耗氧率、排氨率和窒息点,采用封闭流水式实验方法,在不同体质量、光照、放养密度、水流速度以及昼夜更替的条件下,测定鲻幼鱼的耗氧率和排氨率,并且观测体质量对幼鱼窒息点和窒息时间的影响。实验期间水温为19℃±1℃,盐度30,pH7.7。研究结果显示:鲻幼鱼的耗氧率随体质量增加而上升,其变化趋势可用幂函数方程表达:Y=0.4759X0.1878(R2=0.9454);光照对耗氧率的影响较大,对排氨率无明显影响;放养密度对耗氧率的影响差异显著(P0.05),对排氨率的影响差异极显著(P0.01);幼鱼的呼吸代谢旺盛时段在中午11∶00至夜间23∶00;流速对耗氧率和排氨率的影响差异均极显著(P0.01);不同体质量幼鱼窒息点和窒息时间的差异极显著(P0.01)。     

摄食对南方鲇耗氧和氨氮排泄的影响

采用流水式呼吸仪,在水温27.0±0.5℃条件下同时测定了南方鲇(Silurus meridionalisChen)摄食前后的耗氧率和排氨率。实验结果表明:摄食前标准耗氧率和标准排氨率分别为116.4±6.4mgO2/kg/h和6.9±1.4mgNH4 /kg/h。摄食后耗氧率和排氨率均呈现迅速上升,到达最大值后再缓慢下降,然后恢复到静止水平的变化趋势:最大值分别为358.8±11.4mgO2/kg/h和76.1±2.5mgNH4 /kg/h;最大值出现时间分别为10.8±1.4h和10.1±0.9h;摄食后耗氧率和排氨率发生改变的持续时间分别为36.0±2.3h和37.2±2.8h;耗氧总增量和排氨总增量分别为88.3±2.7mgO2和23.1±1.7mgNH4 。实验结果显示,鱼类排氨率在摄食后的变化过程与其耗氧率的特殊动力作用(SDA)具有类似的特征,表明二者在能量代谢机制上相互关联;南方鲇的SDA总耗能的79.4%由蛋白质分解代谢所提供。     

Identification and characterization of the pathogenic effect of a Vibrio parahaemolyticus-related bacterium isolated from clam Meretrix meretrix with mass mortality

A mass mortality of clam, Meretrix meretrix, occurred in Jiangsu Province of China in the late September of 2007. Of the isolates obtained from the diseased clams, MM21 had the strongest virulence to the clam in the virulence test, with a LD50 value of ∼6 × 10⁶ CFU ml⁻¹. MM21 was identified as Vibrio parahaemolyticus by the VITEK 2 Compact system and 16S rDNA sequencing. Detection of virulence-associated genes by PCR indicated that MM21 was positive for toxR and tlh, and negative for tdh. Compared with control group, histiocytes from MM21-infected clams displayed a variety of cytopathological changes by transmission electron microscopy examination, which included increased lipid droplets in hepatocytes, deposition of granules in the mantle, excessive secretion in the gill. The results of our study suggested that MM21 may have been an etiological element in the mass mortalities of hard clam (M. meretrix) in Jiangsu Province of China in 2007.     

亚热带养殖海湾皱瘤海鞘生物沉积的现场研究

皱瘤海鞘是亚热带海域分布最广和数量最多的附着生物种类之一.2012年1月-7月在典型的亚热带养殖海湾-大亚湾大鹏澳海域,利用沉积物捕集器现场测定了皱瘤海鞘(Styela plicata)的生物沉积速率,并测定了生物沉积物中有机物(OM)、总碳(TC)、总氮(TN)、有机碳(OC)和有机氮(ON)含量.结果显示:皱瘤海鞘的生物沉积速率变化范围为每天145.5-1011.8m/个,平均每天516.0mg/个,海鞘的生物沉积速率变化范围为每天154.8-1065.8 mg/g干重,平均每大463.3 mg/g干重.海鞘生物沉积物中OM、TC、OC、TN和ON含量分别为14.38％、10.80％、2.87％、3.06％和0.86％,高于自然沉积物中的含量,分别为13.39％、7.36％、2.32％、2.29％和0.67％.其中TC和ON含量要显著高于自然沉积物(P＜0.05).皱瘤海鞘的OM、TC、OC、TN和ON的生物沉积速率分别为每天74.20,55.73,14.80,15.79和4.43 mg/个.实验期间附着在浮筏养殖设施和养殖牡蛎壳上的海鞘密度变化范围为54.9-222.1个/m2,平均147.5个/m2,养殖海域单位面积的海鞘生物沉积速率平均为每天76.1 g/m2,是自然沉积速率(平均每天62.7 g/m2)的1.21倍,其中OM、TC、OC、TN和ON的平均沉积速率分别为每天10.94,8.21,2.18,2.32和0.65 g/m2.据此可推算,大鹏澳筏式牡蛎养殖海区(约103 hm2)皱瘤海鞘的年生物沉积物负荷为29000 t,其中OM,TC,OC,TN和ON分别4100,3100,820,870和240 t.研究结果说明,海鞘等附着生物在大规模浅海贝类养殖中对养殖生态环境的影响也不容忽视.     

Pathology survey of the short-neck clam Ruditapes philippinarum occurring on sandy tidal flats along the coast of Ariake Bay, Kyushu, Japan

The pathological condition of the short-neck clam Ruditapes philippinarum was surveyed along the coast of Kumamoto, Japan, in June 2004. DNA sequences of the non-transcribed spacer region and internal transcribed spacer region flanking 5.8S rRNA identified Perkinsus olseni among the clams. Ray’s fluid thioglycollate medium assay indicated that 96.7% of the clams surveyed from the Kiguchi River tidal flat (native clams, Stn KR-N) and 96.7% of the clams surveyed from the Midori River tidal flat (Stn MR) were infected with P. olseni with an infection intensity of 464,278 and 199,937 Perkinsus cells/gram tissue wet weight (gWW), respectively. In contrast, 66.7% of the clams imported from China and stored along the Kiguchi River tidal flat (Stn KR-I) and 20.2% of clams from the Arao tidal flat (Stn AT) were infected with P. olseni with an infection intensity of 37,547 and 3382 Perkinsus cells/gWW, respectively. Brown ring disease was detected in the clam population from Stn KR-I at a prevalence of 90.0%. Polymerase chain reaction and the 16S rRNA sequence suggested that the agents of brown ring disease observed at Stn KR-I were Vibrio tapetis-like bacteria. Sporocysts and metacercariae of unidentified trematodes were also observed in the gonads and mantle of the clams from Stn KR-I, Stn MR, and Stn AT, at prevalences of 7.1-42.9%. Metacestodes (larval tapeworms) were found in the foot and digestive gland at a prevalence of 52.5%, 30.0%, and 14.3% in clams from Stns MR, AT, and KR-N, respectively. Histology also showed massive hemocyte infiltration and inflammation among clams heavily infected with P. olseni. Castration of the follicle was typical among clams infected with the trematode. The data indicate that most of the clams along the coast of Kumamoto are infected with various pathogens at various rates of infection, and these pathogens could have negative effects on the clam population in the long term.     

Three EST-SSR Markers Associated with QTL for the Growth of the Clam Meretrix meretrix Revealed by Selective Genotyping

The clam Meretrix meretrix is a member of widely cultured, commercially important clams. A marker–trait association analysis was performed using expressed sequence tag (EST) simple sequence repeat (SSR) markers for marker-assisted selection in M. meretrix. Three markers, MM1272, MM2034, and MM7721, were found to be significantly associated with quantitative trait loci (QTLs) controlling shell length (P?<?0.0001) in clams of a fast-growing population (JSF) and a control population (JSC). The 144-bp allele of MM1272, the 154-bp allele of MM2034, and the 152- and 165-bp alleles of MM7721 showed a significantly higher frequency in the JSF population (17.65, 36.41, 28.67, and 29.33 %) than in the JSC population (4.65, 8.33, 3.47, and 5.56 %). The three markers showed lower values for the number of alleles and observed heterozygosity as well as a higher proportion of homozygotes in JSF than in JSC population. The three markers have been further confirmed in the high and low tails of another population (09G₃SPSB); similarly, lower values for the number of alleles and observed heterozygosity as well as a higher proportion of homozygotes were found in 09G₃SPSB_H. The putative functions of the three gene fragments containing MM1272, MM2034, and MM7721 also suggested that the three SSR-containing genes might be involved in growth of M. meretrix. All the results suggest that the three EST-SSR markers associated with growth QTLs would be useful for marker-assisted selection in M. meretrix breeding.     

Isolation and characterization of a virulent Vibrio sp. bacterium from clams (Meretrix meretrix) with mass mortality

MM5 was a bacterial strain isolated from moribund clam (Meretrix meretrix) collected from a farm with mass mortality outbreak. Primary genotypic and phenotypic identification including 16S rDNA sequence analysis, multilocus sequence analysis (MLSA) of four housekeeping genes (gapA, ftsZ, mreB and topA) and biochemical tests suggested that strain MM5 was a Vibrio species closest to but different from Vibrio furnissii. Our previous study indicated that MM5 could induce a high mortality of M. meretrix (Yue et al., 2010). Quantitative challenge test was performed in this study to further evaluate the pathogenic potential of MM5, which showed that at 84 h post-inoculation, the cumulative mortalities of the MM5-injected group were significantly higher than those of control groups (P < 0.05). Cytopathological and histopathological features of the clam infected by MM5 were carried out by transmission electron microscopy (TEM) and Hematoxylin and Eosin (H&E) staining, respectively. Cytopathologically, foci of MM5 were found in hepatocytes of the clam infected by MM5. In addition, cytopathological lesion was detected in foot of infected clam. Histopathologically, MM5 was detected in different tissues of infected clam, including hepatopancreas, mantle and gill. Challenge test combined with pathological features indicated that MM5 was virulent to M. meretrix.     

Effects of particle concentration and season on the filtration rates of the freshwater clam,Sphaerium striatinum Lamarck (Bivalvia: Pisidiidae)

The effects of particle concentration and season on the filtration rates of the freshwater clamSphaerium striatinum Lamarck were assessed by measuring clearance rates of small (2.02 μm) latex beads from dilute suspensions. Filtration rates decreased as particle concentration increased over a range of 2–64 mg 1⁻¹, with rates decreasing in similar proportion for clams of all sizes. For a 1-mg clam, rates decreased from approximately 8.4 to 0.57 ml clam⁻¹ h⁻¹. Seasonal filtration rates for adult clams peaked during periods of greatest reproduction. The patterns for smaller clams are similar, though proportional changes in filtration rates differ for various sizes of clams. It is estimated that clams occupying 1 m² of stream substrate removed about 3.67 gCa⁻¹. This is equivalent to 0.0004% of the carbon that flows past them annually. Filter-feeding provided only 24% of the calculated energy needs of the population, suggesting that another mode of feeding (e.g. deposit-feeding) may provide an important energy source for these forms. Funded in part by a grant-in-aid to D. J. Hornbach from Sigma-Xi, The Research Society. Funded in part by a grant-in-aid to D. J. Hornbach from Sigma-Xi, The Research Society.     

Behavioral plasticity of the soft-shell clam, Mya arenaria (L.), in the presence of predators increases survival in the field

Soft-shell clams, Mya arenaria, are sessile, suspension-feeding bivalves that are preyed upon by the exotic green crab, Carcinus maenas. Clams evade crab consumers by burrowing deeper into the sediment after perceiving a threat from a nearby predator. The purpose of this study was to determine the types of signals that M. arenaria use to detect predators and the types of behaviors clams use to avoid being eaten. In a field study, clams increased their burial depth in the presence of green crab predators consuming conspecifics that were caged nearby, and also increased burial depth after artificial tactile stimulation in the laboratory assay. These results indicate that clams can use chemical and mechanical cues to detect potential predatory threats. We performed a field study to examine the difference in survivability of clams that had burrowed deeper into the sediment in response to predators vs. control clams that were burrowed less deeply. Significantly higher survival rates were observed in clams that had initially burrowed more deeply, suggesting that increasing burial depth is a valid predator avoidance strategy. Some bivalves also alter their pumping rates in the presence of predators, making them less apparent and providing more structural defense by covering soft tissue, and we measured pumping time of soft-shell clams in the presence and absence of predators, when burrowing was not an option for escape. Soft-shell clams did not alter their pumping time in the presence of green crab predators, possibly because they employ a burrowing method called “hydraulic” or “jet-propelled” burrowing, where it is necessary for the clam to pump in order to burrow. Chemical signals and tactile cues instigated behavioral changes in M. arenaria, and this change in behavior (increasing burial depth) increased clam survival in the field.     

Patterns of p53, p73 and mortalin gene expression associated with haemocyte polyploidy in the soft-shell clam, Mya arenaria

The molecular mechanisms by which haemocytes of clams are transformed in the course of haemic neoplasia remain by far unknown. The aim of this study was to quantify the expression of p53/p73 and mortalin genes, in relation with the ploidy status of clam haemocytes and to correlate the p53 expression with mortalin expression. For this purpose, soft-shell clams, Mya arenaria, were collected from an endemic zone for neoplasia. The ploidy of haemocytes was assessed for each individual clam by flow cytometry using a propidium iodide protocol, while p53/p73 and mortalin gene expressions were quantified by real-time RT-PCR. Results show that haemocytes of some clams with a moderate percentage (15-50%) of tetraploid cells have a significantly high level of p53 and p73 in comparison with clams belonging to categories with low (<15%) or high levels (>50%) of tetraploid cells, where low levels of expression of these genes were observed. Furthermore, mortalin gene expression is strongly correlated (r² = 0.68, p < 0.01) with p53 gene expression level. This reinforces the hypothesis of a cytoplasmic p53 sequestration mechanism in clam haemic neoplasia. Further studies are needed to confirm these preliminary results and further unravel the molecular pathways involved in this process. Our results are believed to provide phenotypic foundation for such studies to be undertaken.     

Phosphorus cycling by mussels (Unionidae : Bivalvia) in Lake St. Clair

The role of mussels in cycling phosphorus in Lake St. Clair during the May–October period was examined by measuring concentrations in the water column and in mussel tissue, and by measuring rates of biodeposition and excretion. Mean rates of biodeposition and excretion for Lampsilis radiata siliquoidea, the most abundant species, were 6.3 µg P (g shell-free dry wt)^-1 h^-1 and 1.3 µg P (g shell-free dry wt)^-1 h^-1, respectively; body tissue phosphorus content was 2.7 percent of dry wt. Seasonal changes in excretion rates appeared to be related to the gametogenic cycle of the organism, but seasonal changes in biodeposition rates were not apparent. Phosphorus assimilation efficiency for this species was about 40 percent. Overall, the mussel population in Lake St. Clair filtered about 210 MT of phosphorus, or about 13.5 percent of the total phosphorus load for the May–October study period. Of this amount, about 134 MT was sedimented to the bottom via biodeposition. Mussel biodeposition may be an important source of nutrients to other biotic components in the lake such as macrophytes and invertebrate deposit-feeders.