Size at first maturity in females of the spiny lobster jasus verreauxi (Crustacea: Decapoda: Palinuridae)

The carapace length and total length size at first maturity in females of Jasus verreauxi (H. Milne Edwards, 1851) has been investigated by a detailed study of (a) the detection of the smallest size class with external eggs, and (b) the incidence of egg‐carrying females per size‐class interval. For the study 834 females were measured and examined at Spirits Bay, New Zealand, during mid October and late December 1966. The specimens ranged in carapace length from 12.0 cm to 23.9 cm, and in total length from 29.0 cm to 56.9 cm.

The results of the study show clearly that the females reach first maturity at a carapace length or a total length larger than the present minimum legal size, i.e. a carapace length of 10.2 cm (4.02 in.), or a total length of 25.4 cm (10.0 in.). No mature females were found less than 13.5 cm carapace length, or 32.0 cm total length. First maturity was attained by the majority (50% or more) of the J verreauxi females at a carapace length of 15.3 cm or larger, or at a total length of 38.0 cm or larger.

No undersized (smaller than the minimum legal size) females were present in the collections—yet 10.3% of the specimens were found to be immature. Immature females ranged in carapace length from 12.0 cm to 16.9 cm, or in total length from 29.0 cm to 41.9 cm. Being larger than the minimum legal size, all of the immature specimens examined were “harvested"—without having reached first maturity. It appears therefore that the stocks of small, immature female J. verreauxi are not protected by the present New Zealand minimum size regulation.     

饲料脂肪水平对三疣梭子蟹(Portunus trituberculatus)幼蟹生长及体组成的影响

采用单因素试验设计方法, 进行了不同饲料脂肪水平对三疣梭子蟹(Portunus trituberculatus)幼蟹生长及体组成影响的研究。结果表明, 低饲料脂肪水平(1.8%)组的增重率和特定生长率最低, 饲料脂肪水平为4.2%组的增重率和特定生长率最高。不同饲料处理对三疣梭子蟹蟹体的水分、粗蛋白和灰分含量无显著影响, 饲料脂肪水平为9.01%组蟹体的脂肪含量最高, 饲料脂肪水平为1.8%组的蟹体脂肪含量最低。饲料处理显著影响各处理组的性腺指数, 饲料脂肪水平为13.76%组的性腺指数最低。而不同饲料处理对各组的肝胰腺指数、壳宽、壳长和壳高无显著影响。本实验结果显示, 4.2%—13.76%的饲料脂肪水平能满足三疣梭子蟹正常生长和发育所需。     

Behavioural responses of the mangrove fiddler crabs (Ucaannulipes and U. inversa) to urban sewage loadings: Results of a mesocosm approach

The study aimed at investigating the effects of sewage loadings on the behaviour of two fiddler crabs species maintained in a system of experimental mesocosms, built in a mangrove area in Tanzania and inundated with different seawater/sewage mixtures. Our results show that sewage loads led to a modification of the overall activity budget of the crab community as a result of increased hypertrophic conditions (high COD, increased chlorophyll-a concentrations). During their activity period, crabs inside contaminated mesocosms seemed to satisfy their feeding demand faster than those of the control cells, spending a significant longer time in other activities like courtship and territorial defence. Apart from being a good biological indication of ecosystem eutrophication, such a reduced foraging activity by fiddler crabs also depresses their sediment bioturbation activity, important factor for the health of mangrove systems, suggesting practical implications regarding the efficiency of mangrove-based wetlands for treatment of domestic sewage.     

三峡库区稻田复养河蟹的农田生态系统能量特征与经济效益

在2002年四川南充稻田养蟹田间探索性试验的基础上,2003年在位于三峡库区淹没带边缘非淹区的重庆市开县竹溪镇进行稻田复养河蟹的田间试验,对种、养结合模式农田生态系统的能流与物流进行了初步探索,并进行了经济效益分析.结果表明：稻蟹复养田的光能利用率高于单作水稻田的15.7%;水稻生长期间的防病治虫用药、运作管理用工、无机肥用量、机械耗材的投入成本明显减少,总的投入比单作水稻田少4.3%,总能、无机能、有机能的产投比分别少35.1%、51.0%和31.6%;土壤全氮、氨态氮分别高于单作水稻田的21.4%和55.2%,稻田水中的氨态氮高达61.3%,这些无机态氮是培育水生生物、高等植物的营养源,又是供应河蟹生长的饵料,而硝态氮则要低得多;河蟹的甲壳质及其排泄物经分解矿化后,是提高土壤有效养分,供应水稻生长的主要肥源.稻田养蟹后,虽然稻谷产量比单作水稻低10.1%,投入成本且低于20.0%,而利润比单作水稻增加77.8%;河蟹的产投比1.54：1,获利润6 381.49元/hm^2;稻田复养河蟹的净利润为7104.19元/hm^2,是单作水稻的44.3倍.     

Influence of tidal regime,diurnal phase,habitat and season on feeding of an intertidal crab

The relationship between diet and feeding activity of intertidal crabs, and environmental cycles (tidal, daily and seasonal), habitat and level of the intertidal zone (high/low) was studied using Neohelice granulata (Brachyura, Varunidae) as a model. This is a semi‐terrestrial burrowing crab occupying different habitats in the Southwestern Atlantic coasts and estuaries from bare low intertidal mudflats to high intertidal salt marshes, and from fine, organic matter rich sediment to very coarse sediment with low content of organic matter. The study was carried out in two contrasting habitats of three sites with diverse sets of physical and biological conditions. Diet and feeding of adult N. granulata were indirectly studied through the proportion of food items and the presence/absence of food in crab stomachs, respectively. This species has a dual mode of feeding: predominantly herbivorous (live plants or plant litter in salt marshes) or deposit feeder (superficial sediment and detritus in mudflats), but the quantity and quality of ingested food varies among habitats and sites. A trend to omnivory (including algae and conspecifics) was detected in relation to low quality of resources. Feeding activity modulated by a complex interaction of factors varied according to spatial and/or temporal changes in some natural cycles. Males and non‐ovigerous females fed preferably after dark and during submersion periods, but also after emersion periods if mudflat sediment remained wet; salt marsh crab feeding is somewhat independent of light and tidal cycles. Ovigerous females almost never fed. Both diet and feeding activity of this crab seem to be flexible traits adapted to different combinations of physical and biological factors.     

Spatio‐temporal variation in biomass of the deep‐sea red crab Chaceon affinis in Gran Canaria Island (Canary Islands,Eastern‐Central Atlantic)

The spatial and temporal biomass distribution of Chaceon affinis and its vulnerability to fishing activity in Gran Canaria (Canary Islands) were investigated. The first goal was to assess the influence of the slope steepness and substrate on the size of crab patches, size of the crabs, and crab biomass. The second goal was to evaluate spatial and temporal variation in the biomass over a 15‐month period. The last goal was to assess the influence of fishing activity upon the reduction in the biomass over the same 15‐month period. Only two or three locations in the sampling area generated high‐biomass contour patches. When these patches were superimposed on the isobath lines, they were coincident with the main depth range described for the species in the area. The map of the biomass values clearly showed three structures with cores of the highest biomass in both muddy and rocky‐muddy areas. The biomass was higher on muddy than on rocky‐muddy bottoms. Biomass was twice as high when steepness was reduced to one third between isobaths of 500 and 900 m. The size of crab patches increases linearly with the decrease in slope steepness. The spatial structure of crabs remained fairly stable over time, showing that biomass changes with depth over time. Maps of the estimated biomass values over the 15‐month period showed the same two main patches over time with the cores of highest biomass separated by a distance of between 4.2 and 4.5 km. Although the bathymetric distribution by sexes showed temporal changes, with a displacement to deeper areas made by both sexes over the studied period, only a partial temporal segregation between males and females was observed. During the study period, crabs underwent a significant decline in biomass and this was consistent with the combined catches of both commercial and experimental fishing in the area. Due to its low mobility, C. affinis is highly vulnerable to local depletion by intensive fishing efforts.     

生物活动对黄河口潮滩表层沉积物扰动作用的研究

以螃蟹扰动作用下黄河口刁口地区潮滩表层沉积物为例,对沉积物的物理力学性质及其运移进行了试验研究,结果表明:螃蟹扰动作用使表层20 cm以内沉积物的含水率明显增加,渗透性略有提高,表层30 cm以内土体贯入强度降低,下层土体贯入强度增高;螃蟹每日掘出的细粒物质达502.08 g/m2(干重),远大于螃蟹洞穴在涨落潮过程中所捕获的细颗粒物质,并使潮滩表层沉积物细化。从螃蟹扰动对沉积物组成、性质和运移产生的作用,可以得出生物活动对黄河口潮滩的稳定性具有一定的影响。