圈养林麝粪样类固醇激素水平与麝香分泌的关系

基于非损伤取样和放射免疫法（RIA）,于2018年9月1日-10月15日期间对四川马尔康林麝繁育场的36头雄性圈养林麝（Moschus berezovskii）的粪样类固醇激素水平进行了检测,结合麝香分泌数据采集,探究了林麝的粪样睾酮和皮质醇水平与其麝香分泌的关系,结果表明：四川马尔康圈养林麝的麝香分泌（12.53±0.76）g（n=36）与粪样睾酮水平（106.03±12.34）ng/g（n=36）呈显著正相关（r=0.436,P < 0.01）,泌香较多雄麝（16.50±0.61）g（n=17）的睾酮水平（141.51±21.86）ng/g（n=17）显著地高于泌香较少（8.98±0.59）g（n=19）雄麝（74.27±7.93）ng/g（n=19）（t=-3.252,df=34, P < 0.01）,方程y=0.021x+10.270（R²=0.120,P < 0.05）可较好地拟合二者间关系。麝香分泌与皮质醇浓度（47.49±1.53）ng/g（n=36）相关不显著（r=0.078,P > 0.05）,泌香较多雄麝的皮质醇浓度（48.98±2.28）ng/g（n=17）略高于泌香较少雄麝（46.17±2.14）ng/g（n=19）,差异不显著（P > 0.05）,方程y=0.038x+10.730（R²=0.023,P > 0.05）可近似拟合皮质醇与泌香量间的关系。此外,雄麝睾酮水平对泌香量有显著影响（P < 0.05）,睾酮水平较高林麝泌香量（14.97±1.17）g（n=12）显著高于睾酮水平较低个体的泌香量（11.32±0.90）g（n=24）（F=4.79,P < 0.05）,而睾酮、皮质醇和年龄对麝香分泌的综合效应及变量间的交互作用均不显著（P > 0.05）。研究确定了圈养林麝粪样睾酮和皮质醇水平与麝香分泌量间的关系,可用于麝类驯养实践的麝香产量预测及品系选育。     

盐度、温度和光照强度对针叶蕨藻的生长及光合活性的影响

为探究环境因子对针叶蕨藻（Caulerpa sertularioides）生长的影响,对不同盐度、温度和光照强度下针叶蕨藻的生长和叶绿素荧光参数进行了研究。结果表明：藻体日特定生长率（SGR）、最大光量子产量（F_v/F_m）、实际光合效率（Yield）、电子传递速率（ETR）和光化学淬灭（qP）随盐度升高呈先上升后下降的变化趋势,非光化学淬灭（qN）则呈相反的变化趋势,藻体光合活性和固碳效率在盐度27.5‰时达到最高,且与25‰和30‰盐度的差异显著（P<0.05,n=3）。藻体SGR、F_v/F_m、Yield、ETR和qP随温度升高而下降,qN则相反,藻体光合活性和固碳效率在26℃下达到最高,且与28℃和30℃的差异显著（P<0.05,n=3）。藻体的SGR、F_v/F_m、Yield、ETR和qP随光照强度升高呈先上升后下降的变化趋势,qN则相反,且在18.75 μmol/（m²·s）弱光照下出现轻微光抑制,藻体生长、光合活性及固碳效率在光照强度25.00 μmol/（m²·s）时达到最高,但与18.75和31.25 μmol/（m²·s）的差异不显著（P>0.05,n=3）。因此,针叶蕨藻在27.5‰盐度、26℃和25.00 μmol/（m²·s）光照强度下生长最快且光合作用能力最高。     

川西平原小流域不同水体N2O排放特征及驱动因素

氧化亚氮（N₂O）是一种潜在的、强大的温室气体,应该根据京都议定书规定开展监测和削减。河流、水库、鱼塘和沟渠等受人类影响的小流域水生生态系统是氮素生物地球化学循环的活跃区域,更是N₂O重要的源和汇。然而,同一流域不同水体N₂O的排放特征差异及其驱动因素尚不清楚。因此,选择川西平原西河流域作为研究区,于2016年6月到2017年5月连续监测不同水体水气界面的N₂O排放强度,并结合聚类分析解析N₂O排放特征的驱动因素。结果显示,不同水体的N₂O年排放通量差异显著,沟渠的N₂O年排放通量最高（（52.68±36.09）μg m^-2 h^-1）,城市段河流和鱼塘次之（（34.16±23.97）μg m^-2 h^-1和（29.03±31.41）μg m^-2 h^-1）,乡镇段和农区段河流再次（（8.32±28.60）μg m^-2 h^-1和（8.52±9.43）μg m^-2 h^-1）,水库最低（（-16.45±29.76）μg m^-2 h^-1）。除水库表现为N₂O的汇,其他水体均表现为N₂O的排放源。另外,不同水体N₂O排放的季节特征差异显著,农区段河流和农业沟渠表现为夏天最高,冬春最低（P<0.05）,而其他水体均表现为冬春显著高于夏秋（P<0.05）。根据N₂O排放季节特征及其驱动因素可将西河流域水体分为四类：第一类农业类水体的N₂O排放季节特征受气象因素和农业活动的联合驱动;第二类城乡类河流和第三类鱼塘分别受控于人类活动和养殖活动,与降雨温度等气象指标关系较弱;第四类水库主要受控于气象因素。并且,第一类农业类水体已成为大气N₂O排放的重要源,农业氮素管控是区域控制N₂O排放的重点。     

广西扶绥白头叶猴对栖息地的选择与利用

为了解白头叶猴（Trachypithecus leucocephalus）的栖息地利用规律及其影响因素,2016年2月至2017年1月,采用瞬时扫描取样法对广西崇左白头叶猴国家级自然保护区一群白头叶猴的栖息地利用进行了研究。结果表明,白头叶猴对山体不同部位的利用存在显著性差异（χ² =39.467,df=3,P<0.001）,其中,对崖壁（56.75±9.55）%的利用比例最大,其次是对山坡（39.42±10.93）%和山顶（2.98±2.54）%的利用,而对山脚（0.84±1.47）%的利用频率最低。白头叶猴对不同微生境类型的利用存在差异（χ²=27.709,df=3,P<0.001）,其中对乔木（49.37±12.31）%的利用比例最大,其次是裸岩（24.05±13.61）%,随后依次为藤本（15.48±8.01）%和灌木（10.87±5.45）%。白头叶猴主要在山坡上觅食,利用崖壁移动、休息,进行社会活动;主要利用裸岩进行社会活动,觅食、移动、休息主要发生在乔木上。从整体来看,白头叶猴在雨季对乔木的利用频率显著大于旱季（Z=-2.680,n=12,P=0.007）;雨季在山坡觅食频率显著大于旱季（Z=-2.517,n=12,P=0.012）,而在崖壁觅食频率刚好相反（Z=-2.842,n=12,P=0.004）;白头叶猴雨季在乔木休息的频率显著大于旱季（Z=-2.355,n=12,P=0.019）。白头叶猴对栖息地的利用受到温度的影响。白头叶猴对乔木的总体利用频率随着平均温度的升高而增加（r=0.664,n=12,P=0.018）;觅食时,对崖壁、裸岩的利用频率均与平均温度成负相关关系（崖壁：r=-0.685,n=12,P=0.014;裸岩：r=-0.600,n=12,P=0.039）;休息时,对乔木的利用频率与平均温度呈正相关关系（r=0.650,n=12,P=0.022）。不同季节,白头叶猴对栖息地的利用方式不同。白头叶猴的栖息地利用模式可能是在觅食利益和捕食风险之间作出的权衡,并受到环境温度的影响。     

会仙岩溶湿地4种覆被下土壤酶活性和微生物生物量

研究湿地系统中的稻田被撂荒以后土壤酶活性和微生物生物量的变化可以为湿地的保护提供参考依据。以桂林会仙岩溶湿地为研究样地,采集芦苇湿地、华科拉莎草湿地、稻田撂荒地（以双穗雀稗和莲子草为优势植被）和稻田的耕层土壤样品,采用比色法和氯仿熏蒸法分别检测土壤酶活性和微生物生物量。结果表明,稻田撂荒地的土壤微生物生物量碳（MBC）为（345.20±30.06） mg/kg,显著低于其它三种覆被下的土壤;微生物生物量氮（MBN）、微生物DNA、蔗糖酶活性和碱性磷酸酶活性分别为（48.03±18.48） mg/kg、（5.65±1.48）μg/kg、（19.16±1.43） mg g^-1（24h）^-1和（2.20±0.94） mg g^-1（24h）^-1,均显著低于稻田,而与两种天然湿地没有显著差异。主成分分析表明,稻田撂荒地能与稻田明显分开,而与其它两种覆被土壤有所交叉。统计分析表明,MBC和碱性磷酸酶活性均与pH呈显著正相关关系（P<0.05）;MBN、蔗糖酶活性和碱性磷酸酶活性均与土壤总有机碳（SOC）呈显著的正相关关系（P<0.05）;土壤微生物DNA与SOC、总氮（TN）和碱解氮（AN）均呈显著正相关关系（P<0.01）,与Mg²⁺呈显著正相关关系（P<0.05）。以上研究结果表明,会仙湿地中的稻田在撂荒以后,土壤微生物生物量和两种土壤酶活性显著降低,影响微生物生物量和土壤酶活性变化的主要因素是pH、SOC、TN、AN和Mg²⁺。因此,建议在稻田撂荒地上重新种植水稻,以加快会仙岩溶湿地的恢复过程。     

不同恢复方式下大兴安岭重度火烧迹地林地土壤温室气体通量

为研究大兴安岭重度火烧迹地在不同恢复方式下林地土壤CO₂、CH₄和N₂O排放特征及其影响因素,采用静态箱/气相色谱法,在2017年生长季（6月-9月）对3种恢复方式（人工更新、天然更新和人工促进天然更新）林地土壤温室气体CO₂、CH₄、N₂O通量进行了原位观测。研究结果表明：（1）3种恢复方式林地土壤在生长季均为大气CO₂、N₂O的源,CH₄的汇;生长季林地土壤CO₂排放通量大小关系为人工促进天然更新（（634.40±246.52）mg m^-2 h^-1） > 人工更新（（603.63±213.22）mg m^-2 h^-1） > 天然更新（（575.81±244.12）mg m^-2 h^-1）,3种恢复方式间无显著差异;人工更新林地土壤CH₄吸收通量显著高于人工促进天然更新;天然更新林地土壤N₂O排放通量显著高于其他两种恢复方式。（2）土壤温度是影响3种恢复方式林地土壤温室气体通量的关键因素;土壤水分仅对人工更新林地土壤N₂O通量有极显著影响（P < 0.01）;3种恢复方式林地土壤CO₂通量与大气湿度具有极显著的响应（P < 0.01）;土壤pH仅与天然更新林地土壤CO₂通量显著相关（P < 0.05）;土壤全氮含量仅与人工促进天然更新林地土壤CH₄通量显著相关（P < 0.05）。（3）基于100年尺度,由3种温室气体计算全球增温潜势得出,人工促进天然更新（1.83×10⁴ kg CO₂/hm²） > 人工更新（1.74×10⁴ kg CO₂/hm²） > 天然更新（1.67×10⁴ kg CO₂/hm²）。（4）阿木尔地区林地土壤年生长季CO₂和N₂O排放量为8.85×10⁶ t和1.88×10² t,CH₄吸收量为1.05×10³ t。     

重庆市近郊大气无机氮、硫沉降特征及其来源分析

以重庆市近郊中梁山槽谷为研究区,利用气象站和沉降仪获取2017年5月-2018年4月的大气无机氮、硫沉降数据和降水δ¹⁵N-NO₃^-、δ¹⁸O-NO₃^-和δ³⁴S-SO₄^2-、δ¹⁸O-SO₄^2-数据,通过离子浓度比值、同位素值和气团后向轨迹探讨了研究区大气中氮、硫沉降变化特征及其来源。结果表明：（1）大气DIN总沉降量为19.99 kg/hm²,干、湿沉降量分别占11%和89%;大气S总沉降量为32.62 kg/hm²,干、湿沉降量分别占13%和87%。大气氮、硫湿沉降量与降水量均呈正相关（n=12,P < 0.01）,氮、硫干湿沉降量具有明显的季节差异。（2）降水NH₄⁺-N/NO₃^--N比值介于0.45-2.2之间,雨季（5-10月）NH₄⁺-N/NO₃^--N>1,旱季（11-次年4月）NH₄⁺-N/NO₃^--N<1,表明雨季氮主要来源于农业源,旱季来源于工业和交通源;降水NO₃^-/SO₄^2-比值介于0.1-1.25之间,平均值为0.63,表明硫来源以固定污染源（燃煤）为主。（3）大气降水δ¹⁵N-NO₃^-、δ¹⁸O-NO₃^-值分别为-3.8‰-3.9‰（平均值为0.4‰±2.6‰）和58.7‰-98.7‰（平均值为76.1‰±14.3‰）,夏季偏负,冬季偏正;降水δ³⁴S-SO₄^2-和δ¹⁸O-SO₄^2-变化范围分别为1.3‰-3.2‰（平均值为2.3‰±1‰）和5.3‰-8.5‰（平均值为7.1‰±1.6‰）,大气降水中NO₃^-和SO₄^2-主要来源于当地的化石燃料燃烧,同时受到周边污染物的远距离传输影响。（4）气团后向轨迹表明影响研究区氮、硫干湿沉降来源的主要因素是东亚季风,北东-南西走向的川东平行岭谷大地貌格局加剧了季风的影响。     

初夏渤海湾初级生产力分布特征及影响因素

根据2016年初夏在渤海湾周边重要经济开发区外海域所进行的调查和研究数据进行分析,利用稳定同位素¹³C示踪技术估算海域内初级生产力（Primary Productivity,PP）等,同时结合叶绿素a（Chlorophyll-a,Chl a）,营养盐以及透明度等水文环境参数,深入分析和探讨初夏渤海湾环境特征对浮游植物生物量（Chl a）和初级生产力的影响。结果表明：受陆地径流和渤海中部冷流输入等因素的影响,调查海域呈现3个温盐特征差异显著的海区,即近岸高温低盐海区、中部高温高盐海区和湾口低温高盐海区。Chl a受温度和营养盐等因素影响整体呈现近岸高湾口低、表层高底层低的分布特征,含量变化范围为1.27-20.82 mg/m³;在近岸营养盐含量充足,温度适宜,浮游植物生产旺盛,Chl a平均含量达（8.37±2.90）mg/m³,其中表层近27.5%水样中含量超10 mg/m³,存在发生赤潮的风险。而在中部和湾口区域受营养盐限制和温度的影响,Chl a含量远低于近岸。PP整体水平在44.79-792.73 mg C m^-3 d^-1之间,平均为（144.13±137.79）mg C m^-3 d^-1。其中近岸营养盐含量充足浮游植物生长旺盛,初级生产力水平较高,而中部和湾口海域受营养盐和温度的限制,初级生产力水平较低。初级生产力指数I（同化系数）变化范围在0.79-5.90 mg C/（mg Chl a·h）之间,平均为（3.40±1.33）mg C/（mg Chl a·h）。利用标准深度积分模型对水柱初级生产力（Depth-integrated primary productivity,∑PP）进行估算,结果表明其范围在56.88-772.31 mg C m^-2 d^-1之间,平均为（232.26±126.47）mg C m^-2 d^-1,近岸受陆源输入影响Chl a较高,在天津海河口和黄骅市排污河外出现高值点,受透明度的影响,中部和湾口部分站点出现高生产力区。     

林下植被和凋落物对寒温带森林生长季土壤CH4通量的影响

为进一步探究林下植被和凋落物管理对我国寒温带森林生长季土壤CH₄通量的影响,采用静态箱-气相色谱法对大兴安岭北部4种林型（白桦林、山杨林、樟子松林和兴安落叶松林）4种处理（自然状态、去除凋落物、去除林下植被以及去除林下植被和凋落物）的土壤CH₄通量排放特征进行观测研究。结果表明：该地区森林生长季土壤均表现为CH₄的汇,4种林型不同处理后土壤CH₄通量表现为单峰变化趋势,吸收峰值出现在7月或8月。自然状态4种林型土壤CH₄平均吸收通量表现为白桦林（-79.23±14.92）μg m^-2 h^-1>山杨林（-64.27±9.60）μg m^-2 h^-1>樟子松林（-62.54±15.48）μg m^-2 h^-1>兴安落叶松林（-48.73±12.26）μg m^-2 h^-1,兴安落叶松土壤CH₄平均吸收通量显著小于其他三种林型（P<0.05）。相比于自然状态,4种林型在去除凋落物后土壤CH₄吸收通量提高了2.12%-12.15%,但变化幅度均没有达到显著水平（P>0.05）。去除林下植被后4种林型CH₄吸收通量提高了0.84%-20.55%,且只有山杨林吸收增加达到显著水平（P<0.05）。同时去除林下植被和凋落物后,对白桦林和樟子松土壤CH₄通量影响不显著（P>0.05）,但对山杨林和兴安落叶松林影响显著（P<0.05）。总之,去除凋落物或林下植被均会提高土壤对CH₄吸收,去除林下植被对土壤CH₄通量的影响要大于去除凋落物的影响,但不同林型不同处理之间还存在差异。     

浙江南部近海前肛鳗营养生态位变化研究——基于稳定同位素技术

基于2016年和2020年浙江南部近海收集的71尾前肛鳗样品,通过测定碳氮稳定同位素比值计算其营养生态位指标,对比分析前肛鳗不同发育过程、不同季节及不同年份营养生态位的差异,探究营养生态位的变动规律及对资源的利用情况。结果表明：（1）2016年和2020年前肛鳗平均δ¹³C值分别为（-15.19±0.31）‰、（-15.90±0.45）‰;平均δ¹⁵N值分别为（12.42±0.45）‰、（12.92±0.25）‰;（2）单因素方差分析表明,2016年前肛鳗不同发育过程δ¹³C值差异不显著（P>0.05）,δ¹⁵N值差异显著（P<0.05）,不同季节间δ¹³C值和δ¹⁵N值均存在显著差异（P<0.05）,而2020年前肛鳗不同发育过程δ¹³C值和δ¹⁵N值差异均不显著（P>0.05）,不同季节间δ¹³C值存在显著差异（P<0.05）,δ¹⁵N值差异不显著（P>0.05）;（3）从个体发育来看,2016年前肛鳗有向高营养级饵料生物摄食的趋势,而2020年前肛鳗摄食特化现象不明显,但均随个体发育过程生态位宽幅逐渐减小,表明个体发育过程营养生态位会出现资源竞争共存分化现象;（4）种群营养多样性指标结果显示前肛鳗在秋、冬两季食物来源较春、夏两季更广泛,春季营养多元化程度与秋季相似,夏季营养多元化程度与冬季相似,各季节间营养生态位重叠较小,存在明显的时间分化现象;（5）2020年前肛鳗种群营养结构多样性指标相比2016年均出现不同程度的降低,两年的SEAc未发生重叠现象。由于种内种间的竞争压力,研究发现前肛鳗在个体发育过程及不同时间段都出现了营养生态位分化现象,从而达到维持物种共存、保持食物网结构稳态的目的。     

Alien molluscs affect the composition and diversity of native macroinvertebrates in a sandy flat of Lake Neuchâtel,Switzerland

The spread of alien molluscs is a serious threat to native biodiversity in fresh waters. Alien freshwater molluscs may deplete the resources of native species and alter the physical structure of the habitat through their shell mass. These changes might have both positive and negative effects on native community members. We investigated the native macroinvertebrate community in relation to the densities of four alien mollusc species (Corbicula fluminea, Dreissena polymorpha, Potamopyrgus antipodarum and Lithoglyphus naticoides) in a sandy flat of Lake Neuchatel, Switzerland. The habitat examined was dominated by these alien mollusc species. The abundance of the alien molluscs did not directly impact the native community assembly. However, C. fluminea and D. polymorpha influenced the composition and diversity of native macroinvertebrates by transforming the sandy substratum into a partly hard substratum habitat. Substantial differences in community composition between shallow (<3.5 m) and (≥5 m) deep sites were recorded. At shallow sites, the abundance of D. polymorpha was significantly reduced as a result of depth-selective feeding of ducks. A controlled shell decay study revealed that shells of alien molluscs (C. fluminea, D. polymorpha) persist for a longer period in the sediment than those of native molluscs. Consequently, shells of alien molluscs have a long-lasting impact by modifying the sandy habitat. This form of ecosystem engineering favours the occurrence of several native taxa, but is disadvantageous for other taxa with specific habitat requirements, and thus can be regarded as an indirect impact of competition.     

Factors affecting the distribution and abundance of the commensal <Emphasis Type="Italic">Temnocephala iheringi</Emphasis> (Platyhelminthes: Temnocephalidae) among the southernmost populations of the apple snail <Emphasis Type="Italic">Pomacea canaliculata </Emphasis>(Mollusca: Ampullariidae)

Temnocephala iheringi is the most common temnocephalan inhabiting the mantle cavity of the apple snail Pomacea canaliculata, a freshwater neotropical gastropod that has become a serious rice pest in Southeastern Asia. T. iheringi has been recorded from Mato Grosso (Brazil) to water bodies associated with the Río de la Plata river (Argentina). During an extensive survey in the southern limit of the native area of P.␣canaliculata the presence of T. iheringi eggs was recorded in several apple snail populations, extending the known distribution of the commensal more than 400 km southwards. The aim of this study was to understand the factors affecting the distribution and abundance of T. iheringi among populations of P.␣canaliculata. Only 23% of the apple snail populations inhabiting streams harboured temnocephalans while the occurrence among lentic ones was 71%. T. iheringi was found mostly in populations of apple snails living in non-alkaline sites and where snails attaining sizes larger than 4 cm were very common. The prevalence of the temnocephalans in lentic populations was higher than 90%. The number of eggs on the shell (not including the umbilicus) ranged between 0 and 470 and was different among populations of P.␣canaliculata. The prevalence and number of eggs were lower in the lotic populations, except for a stream population immediately downstream of a lake with commensals. There was no difference between males and females of P. canaliculata neither in the prevalence nor in the number of eggs on the shell. The southernmost population of the world of P. canaliculata harbours commensals that tolerate cold winter water temperatures (4–5 °C) as well as its host. On the other hand, T. iheringi was found only in sites with bicarbonate concentrations lower than 6.6 meq l⁻¹, suggesting that the tolerance of the commensal is very much lower than that of the apple snail (up to 9.95 meq l⁻¹). The number of worms inside each snail or the life history variation of P. canaliculata could explain the influence of the size of the snails on the occurrence of T. iheringi. In the big-sized snails, where the number of commensals is higher, the probability of survival of at least one worm is also higher, specially during the hibernation period, when crawling and feeding are null and snails remain buried. On the other hand, P. canaliculata snails from lentic populations are generally bigger and mostly iteroparous, while those inhabiting streams are smaller and semelparous. In these populations the snails have access to mate only with snails of their same cohort, while in iteroparous populations they can copulate with individuals of other cohorts, allowing the inter-generation transmission of worms and the long term persistence of the population of commensals.     

The effect of season and location on phosphoadenylate concentrations and adenylate energy charge in two species of freshwater clams

Summary Concentrations of phosphoadenylate nucleotides and the adenylate energy charge ((ATP+1/2ADP)/(ATP+ADP+AMP)) have been suggested as sensitive integrating measures of the energy state of organisms. This synoptic study investigated the seasonal and spatial variation of phosphoadenylate concentrations and AEC in two freshwater bivalve molluscs, the paper-shell clam, Anodonta imbecillis and the asian clam, Corbicula fluminea. Concentrations of all three adenylates, as well as the total adenylate concentration and adenylate energy charge of both species varied seasonally. These fluctuations were closely related to reproductive periods in both species. Total adenylate concentrations and ATP concentrations were slightly negatively correlated with shell length in A. imbecillis but the ADP and AMP concentrations and AEC were not significantly correlated with shell length. In C. fluminea the AEC was negatively correlated were positively correlated with shell length. Neither species exhibited significant differences in AEC between two collection locations. When C. fluminea collected from the Savannah River were acclimated and fed in the laboratory their AEC increased significantly.     

Impact of invasive apple snails in Hong Kong on wetland macrophytes,nutrients, phytoplankton and filamentous algae

1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g⁻¹ snail DW d⁻¹. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m⁻², forming a spongy pond scum in the no‐apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out‐competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out‐competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co‐dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re‐introduce native snails which can control the development of filamentous algae.     

Molluscan cellulolytic activity responses to zinc exposure in laboratory and field stream comparisons

Changes in cellulolytic activity of Asiatic clams (Corbicula fluminea) and snails (Mudalia dilatata) were monitored throughout 30-d exposures to constant additions (0.0, 0.025, 0.05, 0.50, and 1.0 mg l⁻¹) of zinc (Zn). All exposures of 0.05 mg Zn 1⁻¹ or greater significantly reduced enzyme activity (exo- and endocellulase) in both molluscs as early as 10 d following exposures in outdoor laboratory streams incorporating New River water as diluent. More sterile laboratory stream exposures were less consistent in yielding quantifiable differences that could be attributed to metal induced stress apart from effects of nutritional stress. Tests conducted under natural field conditions during all seasons did not differ significantly with respect to changes in annual energetics of either clams or snails. However, evidence of differing uptake routes, with respect to two ecologically and physiologically distinct molluscs, was apparent in bioaccumulation, growth, and enzyme activity throughout exposure and following 60-d recovery.     

Feeding of the leech <Emphasis Type="Italic">Glossiphonia weberi</Emphasis> on the introduced snail <Emphasis Type="Italic">Pomacea bridgesii</Emphasis> in India

The predation potential of the indigenous leech Glossiphonia weberi on the snail Pomacea bridgesii, introduced in India, was evaluated in the laboratory. Snails used belonged to the size-classes ≤‰3.0, 3.1–5.0, 5.1–7.0 and 7.1–9.0 mm in shell height, using them both separately and together (mixed) in combinations. In each experiment lasting 24 h a single leech belonging to the size-classes 2.0–3.9, 4.0–5.9, 6.0–7.9, 8.0–9.9 and 10.0–11.9 mm in length was used. Except the 4.0–5.9 mm size-class, leeches were able to capture and kill P. bridgesii irrespective of latter’s size; the predation, however, was confined to snails ≤3.0 mm. The rate of predation varied with the size of the predator and the prey, and a leech was able to kill a maximum of three snails per day. In India, in nature G. weberi feeds mostly on the pulmonate snail, Lymnaea (Radix) luteola. Experimental studies, however, revealed that G. weberi prefers the snails P. bridgesii and L. (R) luteola at the same rate from amongst the many other either less or not-preferred native operculate and non-operculate snails.     

A preliminary investigation into the use of the invasive golden apple snail,Pomacea canaliculata (Lamarck, 1822), as a water purifier and food source in the breeding ponds of the oriental weatherloach Misgurnus anguillicaudatus (Cantor, 1842)

This study investigated the feasibility of using an invasive snail, Pomacea canaliculata, as a food source and water purifier for the commercial breeding of the loach Misgurnus anguillicaudatus. The predatory potential of M. anguillicaudatus (3.5–5.5?g) against hatchling snails was evaluated in aquaria and simulated paddy fields. Some hatchling snails left the water to avoid being preyed upon by the loaches, and approximately 10 hatchlings died per day in the presence of five loaches in aquaria, whereas a weaker snail control effect was observed in the simulated paddy fields. The growth of rice seedlings (Oryza sativa) was not reduced by the presence of hatchling snails alone, but the shoot biomass of seedlings coexisting with snails was promoted after introducing the loaches. Additionally, the presence of P. canaliculata adults improved the aquatic environment in the short term for loach breeding by decreasing the turbidity of the water. Importantly, M. anguillicaudatus (12–18?g) mortality decreased and its weight increased in the presence of adult snails.     

Rapid spread of an invasive snail in South America: the giant African snail, <Emphasis Type="Italic">Achatina fulica</Emphasis>, in Brasil

Beginning around 1800, but primarily since the early and mid-twentieth century, the giant African snail, Achatina (Lissachatina) fulica Bowdich, 1822, has been introduced throughout the tropics and subtropics and has been considered the most important snail pest in these regions. In Brasil, specimens probably brought from Indonesia were introduced into the state of Paraná in the 1980s for commercial purposes (“escargot” farming) that were not successful. Achatina fulica is now widespread in at least 23 out of 26 Brasilian states and the Federal District, including the Amazonian region and natural reserves. Among the reasons for the species’ rapid invasion are its high reproductive capacity and the tendency for people to release the snails into the wild. Achatina fulica occurs in dense populations in urban areas where it is a pest in ornamental gardens, vegetable gardens, and small-scale agriculture. Also of concern is the damage caused to the environment, and potential competition with native terrestrial mollusks. It can also act as an intermediate host of Angiostrongylus cantonensis, a nematode that can cause meningoencephalitis in people, and it may be a potential host of A. costaricensis, which causes abdominal angiostrongylosis, a zoonosis that occurs from the southern United States to northern Argentina. Management and control measures for A. fulica are under way in Brasil through a national plan implemented by the Brasilian government.     

Changes in chemical components in the freshwater apple snail, Pomacea canaliculata (Gastropoda: Ampullariidae), in relation to the development of its cold hardiness

The apple snail, Pomacea canaliculata, is an invasive freshwater snail. It increases its cold hardiness before winter. However, the physiological mechanism of cold hardiness in molluscs is poorly understood, especially in freshwater molluscs. In this study, we examined the changes in low molecular weight compounds, glycogen and lipids, in the body of P. canaliculata in association with the development of cold hardiness. When snails without cold hardiness were experimentally cold-acclimated, the amount of glycerol, glutamine, and carnosine increased, while glycogen and phenylalanine decreased. Overwintering cold-tolerant snails collected from a drained paddy field in November also showed increased glycerol in their bodies with decreasing glycogen concentration, compared to summer snails collected from a submerged field. Water content also decreased during the cold acclimation, although the water loss was minimal. These results indicate that the freshwater snail, P. canaliculata enhances cold hardiness by accumulation of some kinds of low molecular weight compounds in its body as some insects do. However, the actual function of each low molecular compound is still unknown.     

Density-dependent growth and reproduction of the apple snail, Pomacea canaliculata: a density manipulation experiment in a paddy field

To examine density dependence in the survival, growth, and reproduction of Pomacea canaliculata, we conducted an experiment in which snail densities were manipulated in a paddy field. We released paint-marked snails of 15–20 mm shell height into 12 enclosures (pens) of 16 m² at one of five densities – 8, 16, 32, 64, or 128 snails per pen. The survival rate of released snails was 95% and was independent of snail density. The snail density had a significant effect on the growth and egg production of individual snails. This density dependence may have been caused by reduced food availability. The females at high density deposited fewer and smaller egg masses than those at low density, and consequently produced fewer eggs. The females at densities 8 and 16 deposited more than 3000 eggs per female, while the females at density 128 oviposited only 414 eggs. The total egg production per pen was, however, higher at higher snail density. The survival rates of juvenile snails were 21%–37% and were independent of adult density. The juvenile density was positively correlated with the total egg production per pen and hence was higher at higher adult density. However, the density of juveniles larger than 5 mm in shell height, i.e., juveniles that can survive an overwintering period, was not significantly different among density treatments. These results suggest that snail density after the overwintering period is independent of the density in the previous year. Thus, density dependence in growth and reproduction might regulate the population of P. canaliculata in paddies. Received: October 23, 1998 / Accepted: July 16, 1999