长江口中华绒螯蟹放流亲蟹的繁殖力评估

在长江口中华绒螯蟹亲蟹生殖洄游期间, 通过研究中华绒螯蟹放流群体和自然群体繁殖力随壳宽的变化规律, 比较放流群体和自然群体繁殖力的差异, 从而评估人工增殖放流亲蟹的繁殖力。结果显示, 随着壳宽的增大, 中华绒螯蟹放流群体和自然群体的繁殖力都显著增加(P<0.05)。在相同壳宽范围内, 放流群体和自然群体的繁殖力之间没有显著差异(P>0.05)。回归分析显示, 放流群体繁殖力(F)与壳宽(CW)呈幂函数关系: F=3.979CW6.208(R2=0.822);自然群体F与CW呈幂函数关系: F=1.696CW6.636(R2=0.673)。协方差分析显示, 放流群体与自然群体F与CW的两条曲线在显著性为0.05时拟合较好。研究结果表明, 放流群体与自然群体的繁殖力与壳宽之间无显著性差异, 推断放流亲蟹能够适应长江口天然水域环境, 并与自然群体的繁殖力水平相当。     

中华绒螯蟹MSTN基因SNPs多态性及与生长性状的关联分析

为研究中华绒螯蟹(Eriocheir sinensis)肌肉生长抑制素基因(myostatin, MSTN)的多态性及其与生长性状的相关性, 对中华绒螯蟹3个群体(育种群体、大赛群体、野生群体)共321个个体MSTN基因的多态性进行筛选, 发现该基因的第1外显子存在3个多态性SNP位点(S1: C714T; S2:G729A; S3:G753T), 均为处于Hardy-Weinberg平衡(P>0.05)的中、高度多态性位点。利用一般线性模型分析3个位点及其基因型组合与生长性状的相关性, 发现S1位点对中华绒螯蟹的体重和壳长等生长性状有显著影响(P≤0.05), 而其余2个位点与生长性状无显著关联性。结果表明S1位点的TT基因型对中华绒螯蟹的生长最为有利, 可作为分子标记辅助育种的候选标记。     

中华绒螯蟹一龄早熟和二龄成熟家系生长规律的比较研究

中华绒螯蟹(Eridcheir sinensis)1龄性早熟是扣蟹养殖过程中的一个重要问题,尚不清楚1龄性早熟和2龄正常性成熟后代的生长发育规律是否存在差异,本研究通过构建1龄性早熟和正常性成熟中华绒螯蟹家系,综合比较了单养条件下两种家系子一代(以下简称早熟F1和正常F1)在扣蟹和成蟹阶段的生长蜕壳规律、雌蟹腹脐覆盖腹甲宽度比例、成熟后的性腺指数(GSI)和肝胰腺指数(HSI)。结果显示:(1)早熟F1雄体在第1、2次和第7、8次蜕壳后的体重显著大于正常F1雄体(P0.05);而早熟F1雌体在第1~5次和第7次蜕壳后的体重显著大于正常F1雌体(P0.05);(2)第1和2次蜕壳后早熟F1的增重率较高,正常F1在第3~8次蜕壳后的增重率略高于早熟F1,两群体在扣蟹阶段的特定生长率均呈下降趋势,且正常F1高于早熟F1,其中雌雄个体在第3~4次蜕壳后的特定生长率均存在显著差异(P0.05);(3)早熟F1在第1~5次蜕壳间隔较长,而第6~8次蜕壳间隔较短;两种家系在扣蟹养殖阶段蜕壳4~6次,成蟹养殖阶段蜕壳2~4次,其中早熟F1在扣蟹阶段的平均蜕壳次数低于正常F1,而在成蟹阶段的平均蜕壳次数高于正常F1;(4)早熟F1腹脐覆盖腹甲宽度比例一直高于正常F1,但二者无显著差异(P0.05);(5)无论雌体还是雄体,早熟F1和正常F1的性腺指数和肝胰腺指数均无显著差异,单养条件下性腺均可发育成熟(P0.05)。综上,单养条件下,中华绒螯蟹早熟F1和正常F1的生长模式存在显著差异,两者都可以完成生殖蜕壳和性腺发育成熟,这为今后深入研究中华绒螯蟹个体生物学提供了理论依据和参考资料。     

中华绒螯蟹对苦草生境的依赖与破坏

确定浅水草型湖泊水草资源对放养中华绒螯蟹的承载量是探明水草多元功能的途径之一。本研究通过构建中华绒螯蟹栖息与生长所需的小生境,观察和分析了蟹-草之间的相互关系。试验结果显示苦草对放养中华绒螯蟹的承载量为1.08ind/100g/m~2,中华绒螯蟹的生长比速SGR(％/day)与其对苦草的拥有量Vp(g/m~2/ind)呈正相关,即SGR=0.464 0.003Vp。中华绒螯蟹特别是雄蟹对苦草的影响主要表现为破坏性,破坏率VD(g/ind/m~2/d)与雌、雄蟹的放养密度(S_F,S_m,ind/m~2)有显著的线性关系,即V_D=2.08 0.11S_F 5.83S_M。实验结果为草型湖泊渔-蟹混养生态渔业管理提供了理论依据。     

长江口中华绒螯蟹放流亲蟹的繁殖力评估（英文）

在长江口中华绒螯蟹亲蟹生殖洄游期间,通过研究中华绒螯蟹放流群体和自然群体繁殖力随壳宽的变化规律,比较放流群体和自然群体繁殖力的差异,从而评估人工增殖放流亲蟹的繁殖力。结果显示,随着壳宽的增大,中华绒螯蟹放流群体和自然群体的繁殖力都显著增加(P0.05)。在相同壳宽范围内,放流群体和自然群体的繁殖力之间没有显著差异(P0.05)。回归分析显示,放流群体繁殖力(F)与壳宽(CW)呈幂函数关系:F=3.979CW6.208(R2=0.822);自然群体F与CW呈幂函数关系:F=1.696CW6.636(R2=0.673)。协方差分析显示,放流群体与自然群体F与CW的两条曲线在显著性为0.05时拟合较好。研究结果表明,放流群体与自然群体的繁殖力与壳宽之间无显著性差异,推断放流亲蟹能够适应长江口天然水域环境,并与自然群体的繁殖力水平相当。     

池塘养殖中华绒螯蟹扣蟹附肢自切规律的研究

对中华绒螯蟹扣蟹培育池塘中幼蟹的自切规律进行了调查研究,结果显示:1)池塘养殖幼蟹的自切率较高,达29.2%,但无性别差异;根据体重将幼蟹分成4种规格(大:6~8 g;中:4~6 g;小:2~4 g;极小:0~2 g),就不同规格扣蟹而言,中等规格扣蟹的自切率相对较高,但4者之间差异不显著(P>0.05)。2)大多数个体自切一条(50%~60%)或2条附肢(25%~35%),自切3个或3个附肢以上的比例较低,自切5条附肢比例仅为2%。3)附肢自切通常发生在幼蟹身体的其中一侧,身体两侧同时自切的概率较低(12%~15%)。4)各肢型受到自切的概率不同,后3对附肢的自切率显著高于第1第2对附肢(P<0.05),自切螯足的概率最低。5)整体上,扣蟹雌雄个体的自切规律基本一致,不存在显著的性别差异(P>0.05)。     

饥饿胁迫对中华绒螯蟹(Eriocheir sinensis)仔蟹的影响

在26.2 ～28.4℃水温条件下,研究了饥饿对中华绒螯蟹(Eriocheir sinensis)仔蟹的形态、行为、存活及体重损失的影响,同时确定了仔Ⅱ的营养饱和储存点(PRS)和不可恢复点(PNR).结果表明:饥饿胁迫下中华绒螯蟹仔Ⅰ、仔Ⅱ、仔Ⅲ的初次死亡时间(T1)分别为8.0、14.0和20.3 d,50％死亡时间(Ts0)分别为11.4、16.0和25.5 d,100％死亡时间(T100)分别为15.0、22.0和32.3 d,耐饥饿能力为仔Ⅲ＞仔Ⅱ＞仔Ⅰ;饥饿期间中华绒螯蟹体内水分含量持续升高,干重量降低显著,干重损失速率也随时间延长逐渐减小;先饱食后饥饿的给饵模式中仔Ⅱ蜕皮率随初始饱食时间延长而升高,50％个体完成蜕皮所需饱食时间(PRS50)为2.10d,各处理组仔Ⅱ的蜕皮周期与持续饱食组均无显著差异(P＞0.05),但只有饱食3d以上才能达到持续饱食饲养蟹的增重率;先饥饿后饱食的给饵模式中,仔Ⅱ的蜕皮率随着初始饥饿时间的延长而下降,其中仔Ⅱ50％不能蜕皮的初始饥饿时间(PNR50)和100％不能蜕皮的初始饥饿时间(PNR100)分别为10 d和14 d,并且蜕皮周期相对延长,延长时间约等于初始饥饿时间,不存在额外的摄食时间来弥补饥饿期间损失的能量,各处理组蜕皮后仔蟹与对照组体重无显著差异(P＞0.05).     

超声波遥测在中华绒螯蟹产卵场研究中的应用

利用一种超声波标志的体外固定方法,采用超声波遥测法,分析了抱卵中华绒螯蟹(Eriocheir sinensis)在产卵场附近水域的水平和垂直活动规律。结果表明:超声波标志的体外固定对中华绒螯蟹死亡率无显著影响(P0.05);移动追踪系统对超声波标志的最大追踪距离为532±16 m;2014年12月共放流14只超声波标志的抱卵中华绒螯蟹,12月下旬至翌年5月上旬10次追踪分别追踪到10、12、13、9、9、9、9、6、4、2只标志蟹;标志蟹主要分布在深水航道的南北两侧的堤坝附近水域,1月标志蟹出现在中游区域的频次显著大于下游区域(P0.05),随后呈逐步东移的趋势,4月出现在下游区域的频次显著大于中游区域(P0.05);标志蟹的栖息水深在不同时间之间差异极显著(P0.01),1月上旬至2月上旬标志蟹逐步由水深8.25±3.35 m的水域移至水深11.10±2.64 m的水域栖息,2月下旬至4月上旬标志蟹偏好水深6.35 m左右的水域,4月下旬标志蟹的栖息水深为9.89±2.59 m。本文成果将为水生动物的生态习性、栖息地定位等研究提供技术支持。     

中华绒螯蟹蜕壳生长及其与相关基因表达的关联分析

蜕壳是甲壳动物常见的生长发育现象,但对调控蜕壳与生长的内在机制尚缺乏足够了解。本研究在室内条件下,对中华绒螯蟹(Eriocheir sinensis)一个蜕壳周期内的个体蜕壳与生长现象进行了连续观察,分析了2个蜕壳相关基因,即蜕皮激素受体基因(Ec R)和维甲类X受体基因(RXR),以及1个生长相关基因肌肉生长抑制素基因(MSTN)的表达及其与生长性状的相关性。结果发现,中华绒螯蟹在蜕壳后会出现一个跳跃式生长期,之后进入了一个缓慢持续上升过程,当营养物质积累到一定程度(肥满度达60%左右时)时启动下一次蜕壳;MSTN基因的表达与壳长(r=﹣0.450,P0.05)、壳宽(r=﹣0.410,P0.05)增长率呈显著负相关,而与肥满度呈显著正相关(r=0.450,P0.05),Ec R和RXR基因的表达与体重、壳长和壳宽的增长率均没有显著相关性;相对来说,MSTN在蜕壳后的表达量越高,则增重率越小;而Ec R和RXR在蜕壳后表达量越高,其增重率越大。本研究结果表明,中华绒螯蟹在蜕壳后其生长具有一定的规律性,肥满度可以作为衡量中华绒螯蟹体内营养积累启动蜕壳的指标,Ec R、RXR及MSTN基因表达与生长表型具有一定的相关性。     

不同盐度条件下中华绒螯蟹亲蟹行为及血淋巴生理变化

设定淡水对照组、盐度18适应组、盐度30骤变组(18→30)和盐度0骤变组(18→0),采用视频记录分析法研究了不同盐度条件下中华绒螯蟹雌性亲蟹的8项行为学指标变化,并测定了血淋巴渗透压及离子、血蓝蛋白含量。结果表明:中华绒螯蟹亲蟹封闭反应行为仅发生于盐度组(盐度18组和盐度30骤变组),且盐度30骤变组封闭反应时间显著高于盐度18组(P<0.05);腹部开合行为仅见于盐度0骤变组;盐度组第一触角回缩时间显著高于对照组(P<0.05);其他5项行为学指标活动频率均于盐度0骤变组最高。各实验组亲蟹血淋巴渗透压及离子浓度均高于外界实验水体,且均随盐度升高而增大。血蓝蛋白含量随盐度的降低而升高,盐度0骤变组血蓝蛋白含量显著高于盐度30骤变组(P<0.05)。分析认为,中华绒螯蟹亲蟹在0～30盐度范围内进行高渗透压调节,腹部开合行为是其在低盐度环境下暴露尾肠吸收水中离子的一种行为策略,封闭反应有助于机体减少高盐度坏境下水的吸收及扩散失盐。     

Selection and preference of benthic habitat by small and large ammocoetes of the least brook lamprey (<Emphasis Type="Italic">Lampetra aepyptera</Emphasis>)

In this laboratory study, we quantified substrate selection by small (<50 mm) and large (100–150 mm) ammocoetes of the least brook lamprey (Lampetra aepyptera). In aquaria, ammocoetes were given a choice to burrow into six equally-available substrate types: small gravel (2.360–4.750 mm), coarse sand (0.500–1.400 mm), fine sand (0.125–0.500 mm), organic substrate (approximately 70% decomposing leaves/stems and organic sediment particles, and 30% silt and fine sand), an even mixture of silt, clay, and fine sand, and silt/clay (<0.063 mm). Fine sand was selected with a significantly higher probability than any other substrate. Fine sand habitat is limited in many streams, in part owing to geology, but also as a result of channelization and excessive silt/clay sedimentation, which is a conservation concern. Our results indicate that ammocoetes of least brook lampreys are habitat specialists that prefer fine sand habitat. Hence, availability of fine sand habitat may limit distributions and population sizes.     

Habitat partitioning between prey soldier crab Mictyris brevidactylus and predator fiddler crab Uca perplexa

Interaction and habitat partition between the soldier crab Mictyris brevidactylus (prey) and the fiddler crab Uca perplexa (predator) were examined at a sandy tidal flat on Okinawa Island, Japan, where they co-occur. Both live in dense colonies. When the soldier crabs were released in the densely populated habitat of the fiddler crab, male fiddler crabs, which maintain permanent burrows in hard sediment, preyed on small soldier crabs and repelled large ones. Thus, the fiddler crabs prevented the soldier crabs from trespassing. It was also observed whether soldier crabs burrowed successfully when they were released 1) where soldier crab burrows just under the sand were abundant, 2) in a transition area between the two species, 3) an area without either species, and 4) where artificial tunnels simulated soldier crabs' feeding tunnels were made by piling up sand in the area lacking either species. In contrast to the non-habitat area, many soldier crabs burrowed in the sediment near the release point in the tunnel, transition and artificial tunnel areas. This indicates that the feeding tunnels on the surface attracted other crabs after emergence. When the large male fiddler crabs were transplanted into the artificial burrows made in soft sediment of the soldier crab habitat, all left their artificial burrows by 2 days. In the fiddler crab habitat, however, about one-third of the transplanted male fiddler crabs remained in the artificial burrows after 3 days. The soldier crabs regularly disturb the sediment by the up and down movement of their burrow (small air chamber) between tides. This disturbance probably prevents the fiddler crab from making and occupying permanent burrows. Thus, it appears that these crabs divide the sandy intertidal zone by sediment hardness and exclude each other by different means.     

Personality interacts with habitat quality to govern individual mortality and dispersal patterns

Individual phenotypic differences are increasingly recognized as key drivers of ecological processes. However, studies examining the relative importance of these differences in comparison with environmental factors or how individual phenotype interacts across different environmental contexts remain lacking. We performed two field experiments to assess the concurrent roles of personality differences and habitat quality in mediating individual mortality and dispersal. We quantified the predator avoidance response of mud crabs, Panopeus herbstii, collected from low‐ and high‐quality oyster reefs and measured crab loss in a caging experiment. We simultaneously measured the distance crabs traveled as well as the stability of personalities across reef quality in a separate reciprocal transplant experiment. Habitat quality was the primary determinant of crab loss, although the distance crabs traveled was governed by personality which interacted with habitat quality to control the fate of crabs. Here, crabs on low‐quality reefs rapidly emigrated, starting with the boldest individuals, and experienced modest levels of predation regardless of personality. In contrast, both bold and shy crabs would remain on high‐quality reefs for months where bolder individuals experienced higher predation risk. These findings suggest that personalities could produce vastly different population dynamics across habitat quality and govern community responses to habitat degradation.     

Burrowing abilities and swash behavior of three crabs, Emerita analoga Stimpson, Blepharipoda occidentalis Randall, and Lepidopa californica Efford (Anomura, Hippoidea), of exposed sandy beaches

To investigate factors related to the distribution of intertidal species, and specific predictions of the swash exclusion hypothesis for exposed sandy beaches, we compared the burrowing abilities and swash behavior of three species of anomuran crabs in the superfamily Hippoidea (Emerita analoga, Blepharipoda occidentalis and Lepidopa californica) which commonly inhabit the intertidal and shallow subtidal zones of beaches along the California coast. Burrowing times in the laboratory increased significantly with crab size for all species in five sediment grain sizes ranging from fine sand to gravel (0.15 to 3.24 mm). For each species, burrowing times differed significantly among sand grain sizes, ranging from 0.3 to 21.5 s. Burrowing times for the hippid crab, E. analoga, were relatively constant across sediment types, while those of the albuneid crabs, B. occidentalis and L. californica, were rapid in fine to medium sands, and much slower in coarser sediments. Our results indicate that E. analoga is a substrate generalist while L. californica and B. occidentalis are substrate sensitive. Pre-burrowing times and behavior, distance moved, and burrowing times differed among the species in the swash zone. Combined times of preburrowing and burrowing were shorter than the swash period (6 s) for most E. analoga individuals. Fifty percent of the individuals of L. californica reached the substrate and burrowed in the swash period, while no individuals of B. occidentalis burrowed in that time. Pre-burrowing behavior and time may be valuable in explaining spatial and temporal patterns in the distribution of hippoid crabs on California beaches. Our results support predictions of the swash exclusion hypothesis concerning the burrowing and locomotory abilities of sandy beach macrofauna. The substrate generalist characteristics, and unique orientation and swimming abilities of the hippid crab, E. analoga, in intertidal swash may help explain the success of this species and its congeners, and have important implications for understanding patterns of macrofauna community structure on exposed sandy beaches in California and other regions.     

The relative importance of habitat-specific settlement, predation and juvenile dispersal for distribution and abundance of young juvenile shore crabs Carcinus maenas L.

Young juveniles of many motile benthic species are concentrated in structurally complex habitats, but the proximate causes of this distribution are usually not clear. In the present study, I assessed three potentially important processes affecting distribution and abundance of early benthic stages in the shore crab (Carcinus maenas): (1) selection of habitat by megalopae (postlarvae); (2) habitat-specific predation; and (3) post-settlement movements by juveniles. These processes were assessed concurrently over 3-9 days at two spatial scales: at the scale of square meters using cage techniques within nursery areas, and at the scale of hectares using isolated populations of juvenile shore crabs in small nursery areas as mesocosms. The results were compared to habitat-specific distribution in the field.Shore crab megalopae and first instar juveniles (settlers) were distributed non-randomly among micro-habitats in the assessed nursery areas, with great densities in both mussel beds, eelgrass and filamentous algal patches (on average 114-232 settlers m⁻²), and significantly smaller densities on open sand habitats at all times (on average 4 settlers m⁻²). The same habitat-specific settlement pattern was found in cages where predators were excluded, suggesting that active habitat selection at settlement was responsible for the initial distribution. Older juveniles (second to ninth instar crabs) were also sparse on sand, but in contrast to settlers, were concentrated in mussel beds, which showed significantly greater densities than eelgrass and algal habitats. The cage experiment demonstrated a dynamic distribution of juvenile crabs. Young juveniles constantly migrated over open sand habitats (20 m or further) and colonized the experimental plots in a habitat-specific pattern that reflected the distribution in the field. This pattern was also found for very small crabs colonizing predator-exclusion cages, suggesting that selection of habitat by migrating juveniles caused the ontogenetic change in habitat use. Although post-settlement movements were great within nursery areas, juvenile dispersal at a regional scale appeared to be small, and the recruitment of juvenile shore crabs to the shallow bays occurred mainly through pelagic megalopae.Conservative estimates at the scale of whole nursery areas, based on migration trap data and field samples, indicated great mortality of settlers and early benthic stages of shore crabs. Results from the cage experiment suggest that predation by crabs and shrimp were responsible for the high settlement mortality. Both enclosed cannibalistic juvenile crabs and local predators on uncaged habitat plots caused significant losses of settlers in all habitats (on average 22% and 64% 3 day⁻¹, respectively). The effect of predators was highly variable between trials, but differed little between habitat types, and predation had no detectable proximate effect on juvenile distribution, despite the great losses. Small settlement densities on sand habitats in combination with a refuge at low prey numbers, and an aggregation of cannibalistic juvenile crabs in nursery habitats appear to decrease the effect of habitat-specific predation rates on the distribution of juvenile shore crabs. This study demonstrates that active habitat selection at settlement followed by a dynamic redistribution of young juveniles can be the proximate processes responsible for habitat-specific distribution of epibenthic juveniles, and indicate that predation represents a major evolutionary process reinforcing this behavior.     

七种捕食性鱼类对中华绒螯蟹幼蟹捕食风险的评估

分别以鲤、鳜、斑点叉尾、黄颡鱼、瓦氏黄颡鱼、大口鲇和乌鳢作为捕食者,以中华绒螯蟹幼蟹作为猎物,在室内水泥池(2.4 m3)进行捕食试验。以日捕获率和日摄食率为指标,评估这些鱼类对幼蟹的捕食作用和危害程度,为提高湖泊幼蟹放流效果、建立蟹—鱼复合的优质高效养殖模式提供科学依据。在幼蟹完全暴露的条件下,经过多次(至少9次)重复的试验(短期1d和长期7d),鳜对不同大小的硬壳和软壳(刚蜕壳的)幼蟹没有任何捕食作用;黄颡鱼对硬壳和软壳幼蟹也没有捕食作用,但还需做进一步观察;虽然鲤、瓦氏黄颡鱼对硬壳蟹的捕获率低,但对软壳的幼蟹有较大的危害性,对幼蟹的日摄食率分别为0.070%、0.012%;大口鲇、斑点叉尾、乌鳢对幼蟹具有较强的捕食能力,对幼蟹的日摄食率分别为0.122%、0.188%和0.284%。根据这些研究结果,可以建议:(1)在池塘和湖泊河蟹养殖中,完全可以将鳜作为套养或混养对象,以期提高养殖效益;(2)在河蟹放养的湖泊,需要抑制乌鳢和大口鲇种群,适当减少鲤和瓦氏黄颡鱼丰度,以期减少这些鱼类的捕食作用,提高幼蟹存活率;(3)在河蟹养殖池塘,不能放养乌鳢、大口鲇、斑点叉尾、瓦氏黄颡鱼和鲤。     

The competitive and predatory impacts of the nonindigenous crab Carcinus maenas (L.) on early benthic phase Dungeness crab Cancer magister Dana

We evaluate the potential competitive and predatory impacts of nonindigenous European green crab Carcinus maenas on native Dungeness crab Cancer magister in the northeast Pacific. The coastal estuaries of Washington State, USA, provide appropriate habitat for recently introduced green crab, yet these areas are important nursery grounds for Dungeness crab and contribute greatly to the coastal crab fishery. Juvenile Dungeness crabs are dependent on limited intertidal epibenthic shell for refuge habitat during early benthic life and experience increased mortality on open sand and mud as a result of predation by fish and birds. Early juveniles throughout the subtidal are similarly at risk due to predation by fish and especially adult conspecifics. Laboratory experiments and infrared video observations revealed that juvenile green crab displace Dungeness crab of equal size from shelters during one-on-one competition. Green crab also consistently win nocturnal foraging trials in which the species compete for fresh, damaged clams. Field and laboratory enclosure experiments show that juvenile Dungeness crab emigrate from oyster shell habitat as a result of competition and predation by adult green crab. Depending on the extent to which the two species overlap, interactions with the dominant nonindigenous species could have a negative influence on juvenile Dungeness crab survival and could conceivably impact recruitment to the fishery. However, current evidence indicates that the distribution of green crab in Washington State is far removed from nursery areas of Dungeness crab.     

Mud crabs (Xanthidae) in Chesapeake Bay: claw characteristics and predation on epifaunal bivalves

Abstract. We examined claw characteristics of mud crabs (Eurypanopeus depressus, Rhithropanopeus harrisii) to determine if one crab species was potentially more powerful than the other. We related our findings to the abilities of individuals of each species to open epifaunal mytiliform bivalves (Ischadium recurvum; Mytilopsis leucophaeata) that occur on beds of eastern oysters (Crassostrea virginica) in mesohaline Chesapeake Bay. There were high correlations between claw width or height and claw length, and between claw length and carapace width for both mud crab species. The mechanical advantage or “grip strength’ of the crusher and cutter claws of both species did not change with crab size (carapace width) and did not differ between sexes in each species, nor did the cutter data differ between species. However, individuals of E. depressus had a significantly stronger crusher claw grip than did those of R. harrisii. Data on mechanical advantage for both species were similar to values reported in the literature for members of other xanthid crab species. These values in turn overlapped those reported for calappid, cancrid, majid, and grapsid crabs, and were greater than those of various species of portunid crabs and individual species of fiddler crab, lobster, crayfish, and ghost shrimp. When simultaneously presented with the two species of bivalves, the mud crabs E. depressus chose mussels of M. leucophaeata first and crabs of R. harrisii chose mussels of I. recurvum first about two‐thirds of the time; ultimately, the crabs ate both bivalve species in >50% of the choice experiments. The size range in E. depressus was greater than that in R. harrisii, and crabs of E. depressus opened larger bivalves than did crabs of R. harrisii, although similar‐sized individuals of the two crab species overlapped in their ability to open bivalves of both species. In Mytilopsis leucophaeata, there is probably no size refuge from predation by the mud crabs whereas the larger mussels of I. recurvum do have a refuge in size.     

Impact scenario for the invasive red king crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> (Tilesius, 1815) (Reptantia,Lithodidae) on Norwegian,native, epibenthic prey

Large invasive predators like the king crab, Paralithodes camtschaticus, deserve particular attention due to their potential for catastrophic ecological impact on recipient communities. Conspicuous, epibenthic prey species, such as the slow growing commercial scallop Chlamys islandica, are particularly exposed to the risk of local extinction. A research program integrating experiments and field monitoring is attempting to predict and track the impact of invasive king crab on scallop beds and associated fauna along the north Norwegian coast. The claw gape of the crab shows no limitations in handling the flat-bodied scallop. However, the potential impact of the crab on scallop may depend on the availability of other calcified prey associated with scallop beds, such as the sea star, sea urchin, and blue mussel, all species recorded in the diet of P. camtschaticus. To address this issue, a laboratory experiment on foraging behaviour of P. camtschaticus was conducted. The experimental results show that all size classes of red king crab prefer scallops, but small juveniles and medium sized crabs demonstrate active selection for starfish (Asterias rubens) that equals or surpasses the electivity of the large crab. The selection of sea urchin (Strongylocentrotus droebachiensis) and blue mussel (Mytilus edulis) is slightly positive or neutral for the three crab size classes. These results suggest that scallop beds with a rich associated fauna are less vulnerable to red king crabs predation and possibly more resilient than beds with few associated species. Also, crab size distribution is likely relevant for invasion impact, with increasing abundance of small and medium sized crabs being detrimental for alternative calcified prey associated with scallop beds. Successive stages of crab invasion will see an acceleration of scallop mortality rates associated with (i) decreasing availability of alternative prey, due to protracted predation pressure intensified by recruitment of juvenile crabs, and (ii) increased number of large crabs. Estimates of crab density and intake rates suggest that the accelerated loss rates will eventually endanger scallop beds persistence.     

WSSV对锯缘青蟹的致病性及血清酶指标影响

锯缘青蟹(Scylla serrata)俗称青蟹,是我国重要的海水养殖蟹类.近年来,浙江、福建、广东等青蟹主要养殖地区出现了严重的青蟹病害.对浙江省养殖青蟹的发病原因和流行病学调查发现,白斑综合征病毒(white spotsyndrome virus,WSSV)与青蟹发病存在较大相关性.为进一步研究WSSV对青蟹的致病性和发病机理,作者采用白斑综合征病毒的除菌过滤液,以1:10-1:10000稀释度注射感染青蟹,结果表明1:10、1:100感染组的青蟹死亡率达100%,1:1000感染组死亡率为66.7%,1:10000感染组死亡率为38.9%.根据攻毒悬液的病毒浓度计算出WSSV对青蟹的LD50为1.19×104拷贝/只(7.93×103拷贝/g组织);取WSSV感染青蟹血淋巴进行PCR检测,攻毒死亡青蟹的WSSV检出率为100%,表明WSSV对青蟹有很强的致病力.分析病毒感染濒死蟹的血清酚氧化酶(PO)、过氧化物酶(POD)、超氧化物歧化酶(SOD)、碱性磷酸酶(ALP)、谷丙转氨酶(GPT)、符草转氨酶(GOT)等主要酶指标,发现病毒感染青蟹的PO、POD和SOD活力明显低于对照组,而ALP、GPT和GOT的活力则明显高于对照组;用WSSV单克隆抗体对感染蟹进行免疫组化分析,发现WSSV主要侵染青蟹的鳃、甲壳下表皮、心脏、肠、胃等组织的上皮细胞,尤其以鳃上皮细胞损害最为严重.