Conservation status and reproduction of the critically endangered freshwater pearl mussel (Margaritifera margaritifera) in Northern Ireland

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褐菖鲉幼鱼对贻贝养殖生境的利用规律初探

嵊泗海域规模庞大的贻贝养殖生境发挥着养护幼鱼的海洋牧场功能,而探查当地趋礁鱼类在幼体阶段对该生境的利用规律可为当地海洋牧场的设计提供重要参考,为此2018年5—7月对舟山北部枸杞岛贻贝场的褐菖鲉幼鱼、附着生物进行了逐月调查,使用自制网具采集目标生物样品,应用相对密度指数和相关分析法分析了褐菖鲉幼鱼在该生境中的栖息密度、栖息方式和空间分布特征,采用胃含物分析法确定其食性特征,并结合耳石轮纹探究其利用该生境的生长周期。结果显示,褐菖鲉幼鱼的栖息密度时空特征上,5—7月在养殖区贻贝串上的栖息密度分别为(10±6)、(7±5)和(5±5)个/串,时间上呈现逐月递减趋势,随时间的推移养殖区外侧幼体逐渐迁移至内侧近岸区直至消失。栖息方式选择上,褐菖鲉幼鱼栖息数量与贻贝串孔隙大小和附着海藻生物量之间皆呈正相关,但并不显著。饵料利用上,养殖区褐菖鲉幼鱼总体维持较高的摄食强度,各月份平均摄食强度皆高于对照区,主要摄食对象为麦秆虫和钩虾,重量百分比为70.9%和28.3%。栖息周期上,养殖区内褐菖鲉幼鱼耳石平均轮纹数为(57±12)个,其利用养殖贻贝串的周期一般约为2～3月,且该生境中幼鱼耳石纹路间距均匀性和条纹清晰度均明显优于岩礁生境。研究表明,枸杞岛的贻贝养殖生境成为褐菖鲉幼鱼额外的栖息环境,在增殖养护褐菖鲉资源方面发挥了积极作用,因此嵊泗海域在建设海洋牧场时可依据贻贝养殖生境的资源养护原理,通过设置浮体结构强化海洋牧场的饵料场和庇护功能,以提高褐菖鲉种群的补充量,为当地休闲海钓的持续发展提供部分保障。     

新型滚筒式贻贝清洗设备设计

为了提高贻贝清洗工序的自动化程度和清洗效果,降低工人劳动强度,设计了一种集打散和清洗工序为一体的新型滚筒式贻贝清洗设备,利用摩擦清洗方式代替当前使用的振动清洗方式,清洗后的贻贝表面附着物和足丝连接更少,该设备提高清洗加工自动化程度和降低加工人员配置的同时,设备占地面积更小。采用Solidworks软件和Simulation模块对设备进行三维建模和相关零部件的有限元仿真,并对该设备进行样机制作和相关试验。结果显示:清洗过程中,贻贝破损数量和滚筒转速成正比,清洗所用时间和滚筒转速成反比,结合破损数量和清洗时间两曲线,确定滚筒最佳转速为30 r/min,最佳清洗时间为32s,清洗速度为375颗/min(约25 kg/min)。该设备对发展贻贝船上加工模式具有借鉴意义。     

Productive performance of brown mussels Perna perna (Linnaeus, 1758) cultivated on ropes at low densities in Caraguatatuba,Brazil

In Brazil, mussel seed are not a plentiful natural resource, and so the efficient use of seeds by reducing stocking densities should be considered. There are very few studies addressing the relationship between seeding density and growth of mussels in tropical conditions. This work aimed to determine the influence of low seeding densities on the productive performance of Perna perna (Linnaeus) mussels cultivated on ropes in Caraguatatuba, Brazil. In October 2014, 12 ropes, one metre in length each, were seeded at the densities of 200, 300 and 400 mussels/m (four ropes for each density) and suspended on a long line. After 226 days of growing, mussels were harvested and their performance at each density was evaluated in terms of mean weight and length, production, culture efficiency, condition index, survival, amount of recruited seed, amount of fouling on the ropes and morphometric relationships. We observed no significant differences (p > .05) for these indicators among the densities tested, except for mussel biomass, which was significantly higher (p < .05) at the greater densities. A partial budget analysis showed that the density of 400 m^?1 showed better profitability and should be recommended, even in case of seed shortage.     

Testing the potential for improving quality of sediments impacted by mussel farms using bioturbating polychaete worms

Biodeposits from farmed mussels severely influence the biogeochemistry of sediments by increasing the levels of organic matter (OM). Mitigation of such negative impacts is important for the development of sustainable aquaculture operations. As a step towards developing methods for remediation of coastal sediments affected by mussel farming, the effects of the polychaete, Hediste diversicolor was evaluated experimentally. In a series of field‐ and laboratory experiments we tested hypotheses about the effects of polychaetes on sediment oxygen consumption, nutrient fluxes and sulphide pools under different polychaete densities and sedimentation regimes. The experimental results support the idea that polychaetes can mitigate negative effects on the benthic environment beneath mussel farms. H. diversicolor oxidized the sediment and generally enhanced the oxygen consumption, and thus the decomposition of OM. The accumulation of pore water sulphides were reduced and fluxes of nutrients across the sediment‐water interface increased. Additional calculations suggest that the effects of polychaetes were mainly indirect and driven by increased microbial activity due to the borrowing activity of the polychaetes. Trends of increasing decomposition with increasing polychaete density suggest that the decomposition could be further enhanced by higher densities. Overall, we concluded that H. diversicolor is a potentially strong candidate for remediation of mussel farm sediments. The results show that sediments inhabited by H. diversicolor have high assimilative capacity of OM and oxygen conditions are significantly improved following the addition of polychaetes at naturally occurring densities. However, technological developments are needed in order to allow the approach to be used in practice.     

Development of release methods for captive‐bred freshwater pearl mussels (Margaritifera margaritifera

1. Biodiversity loss is a global problem with freshwater bivalves considered among the most endangered biota. The freshwater pearl mussel, Margaritifera margaritifera, is declining throughout its range owing to habitat degradation and overexploitation. In most of its range, populations are regarded as reproductively non‐functional, which has led to the development of captive breeding programmes.
2. A novel method of releasing M. margaritifera was tested, with captive‐bred juveniles being released into the rivers caged in ‘mussel silos’ (protective concrete domes with ventilation creating upwelling to ensure water through‐flow).
3. In total, 240 juvenile mussels were released and survival and growth rates were monitored for 18 months after release for three size classes: A (13.01–20.00 mm); B (10.01–13.00 mm); and C (4.01–10.00 mm).
4. Two experimental treatments were tested: one in which sediment was added to each silo (allowing mussels to orientate and burrow) and one without sediment. Survival by the end of the experiment at month 18 was significantly higher for the largest size class at 97% (although growth was lowest in this cohort), and lowest for the smallest size class, at 61% (although growth was highest in this cohort). Survival and growth were unaffected by the experimental treatment suggesting that adding sediment offered no advantage. Growth was positively correlated both with water temperature and with particle size of suspended solids (both of which were collinear, peaking in summer).
5. There are many ex situ breeding programmes for freshwater pearl mussels throughout Europe and the results of this study suggest that the use of mussel silos may be a useful tool to protect juvenile mussels, allowing them to be released at a relatively early stage of development and minimizing the risk of domestication.

Copyright © 2016 John Wiley & Sons, Ltd.     

Numerical modeling of submerged mussel longlines with protective sleeves

Farmers growing mussels in offshore environments have turned to submerged longline farming as a relatively safe, reliable and profitable way to produce mussels in the exposed ocean environment. However, variations in the environmental conditions (strong currents and storms) and potential presence of predator species (e.g. eider ducks) require robust engineering approaches to design longline mussel farms and their components.This paper describes application of a mechanistic fluid-structure interaction modeling software Hydro-FE to predict the dynamic response of several mooring/longline/dropper configurations subjected to typical and extreme environmental conditions of a North Atlantic mussel farming site. Hydro-FE is a software tool that expands and modernizes the approach previously implemented in the finite element program Aqua-FE developed at the University of New Hampshire to analyze flexible structures in marine environment. The numerical model takes into account smooth variation of the hydrodynamic forces around the free surface (continuous partial submergence), Reynolds number dependence of drag coefficients of mooring lines and includes contributions of predator-protection sleeves to the overall mechanical response of mussel droppers. The simulations provide estimates of anchor forces, mooring line tensions, and time-series data on the motion of the droppers. This information can be used in the design of mussel longlines to prevent anchor failure, rope breakage, line entanglement and mussel fall-off.     

淡水珍珠蚌循环水养殖模式下分布式水质监控系统设计

为促进中国淡水珍珠养殖业由传统粗放模式向高效生态智能化改造升级,该研究针对珍珠蚌工厂化循环水养殖模式下的水质监控需求,开发了基于无线传感网络的分布式水质监控系统。系统采用感知层、传输层和应用层相结合的体系架构,由水质监测节点、气象监测节点、设备控制节点和监控中心组成。现场采用多参数传感器、ZigBee无线模块、可编程逻辑控制器(Programmable Logic Controller,PLC)和MCGS触控屏组合的方式,实现对多地点监测数据的实时采集、图形化显示和报警功能,对循环水处理设备的启停控制及藻类供饵自动控制功能;上位机采用MCGS网络版和SQL Server数据库构建监控数据中心。系统采用无线组网分布式架构,组网灵活且操作简单,简化了设备的安装和维护工作。经实际使用测试,系统工作稳定性和检测准确性均在98%以上,能够满足淡水珍珠蚌循环水养殖的监控需求,可以为珍珠蚌传统养殖模式的转变和产业生产方式的转型升级提供有利保障。