Simulation and quantification of enrichment and retention processes in the southern Benguela upwelling ecosystem

Important environmental processes for the survival and recruitment of early life stages of pelagic fishes have been synthesized through Bakun's fundamental triad as enrichment, concentration and retention processes (A. Bakun, 1996, Patterns in the Ocean. Ocean Processes and Marine Population Dynamics. San Diego, CA, USA: University of California Sea Grant). This conceptual framework states that from favourable spawning habitats, eggs and larvae would be transported to and/or retained in places where food originating from enrichment areas would be concentrated. We propose a method for quantifying two of the triad processes, enrichment and retention, based on the Lagrangian tracking of particles transported within water velocity fields generated by a three‐dimensional hydrodynamic model. We apply this method to the southern Benguela upwelling ecosystem, constructing putative maps of enrichment and retention. We comment on these maps regarding main features of the circulation in the region, and investigate seasonal variability of the processes. We finally discuss the results in relation to available knowledge on the reproductive strategies of two pelagic clupeoid species abundant in the southern Benguela, anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). Our approach is intended to be sufficiently generic so as to allow its application to other upwelling systems.     

A microcomputer program for stimulating effects of physical transport processes on fish larvae

A simple microcomputer program uses Lagrangian particle tracking to simulate the fates of individual larvae subject to wind- and tide-driven advection fields and diffusion. Space/time advection patterns are provided to the program as inputs; thus, the program can use results from various hydrodynamic models. The program can simultaneously track several groups of larvae that are assigned varying attributes, including (1) body size, to allow simulation of effects of variation in growth rates; (2) spawning locations and times; (3) vertical migration behavior; and (4) settlement strategy (duration of larval period, depth conditions for settlement). The model is intended as an exploratory tool to help identify alternative hypotheses that might explain observed life history patterns and causes of inter-annual variation in recruitment rate. For English sole in the Hecate Strait, B.C., the model leads us to hypothesize that observed spawning locations have resulted from a tradeoff between places that would provide the best feeding opportunities and places that would minimize risk of advective export to unfavorable rearing habitats.     

Transport of 17α,20β-dihydroxy-4-pregnen-3-one in brook troutSalvelinus fontinalis ovarian follicles

Extremely low levels of the maturation inducing steroid (MIS) 17,20-dihydroxy-4-pregnen-3-one (17,20-DHP) were found in the ooplasm and ovarian follicle membranes of Atlantic salmonSalmo salar ouananiche, a finding that is at variance with the elevated blood levels of the steroid. The uptake of MIS at physiological concentrations into brook trout follicles occurred by passive diffusion. Uptake of the steroid into the ovarian follicle membrane, consisting of zona radiata and the attached follicle cells, deviated from linearity in a double reciprocal plot. These results suggest that 17,20-DHP is binding to a receptor-like protein in the ovarian follicle or the zona radiata membrane surrounding the oocyte, and extend our previous demonstration of 17,20-DHP receptor-like activity in the zona radiata membrane of the late stage brook trout oocytes. An oocyte cytoplasmic receptor gave subunits on SDS PAGE that were similar to the membrane and cytosol receptors previously described.     

Cortisol stimulates intestinal fluid uptake in Atlantic salmon (Salmo salar) in the post-smolt stage

The fluid uptake rate of the posterior intestine of salmonids increases during the parr-smolt transformation. Intestinal fluid uptake in post-smolt Atlantic salmon was investigated after treatment with cortisol and growth hormone (GH), alone or together. Two replicate experiments were conducted in August 1991 and August 1992. Cortisol was emulsified in vegetable shortening and vegetable oil (1:1) and implanted into the peritoneal cavity. GH was administered as intraperitoneal injections in a saline vehicle on days 0 and 2. On days 5 and 6, plasma cortisol levels, gill Na⁺,K⁺-ATPase activity, andin vitro measurements of fluid transport rate (J_v) across the posterior intestine were measured. Implants of cortisol elevated the plasma cortisol levels within a physiological range, and resulted in elevated gill Na⁺,K⁺-ATPase activity, as expected. The fluid uptake rate across the posterior intestine was roughly doubled by cortisol treatment. GH treatment did not affect intestinal fluid transport, gill Na⁺,K⁺-ATPase activity, or plasma cortisol concentrations. The seawater-adapting increase in the rate of fluid uptake by the posterior intestine of smolting salmon is probably stimulated by elevated plasma cortisol concentrations.     

Fluctuation in the distribution of low-salinity water in the North Equatorial Current and its effect on the larval transport of the Japanese eel

Surface water in the North Equatorial Current (NEC) is composed of southern low‐salinity water diluted by precipitation to less than 34.2 psu and northern, high‐salinity tropical water greater than 34.8 psu. Analyses of 27‐year historical data, observed in winter and summer along the longitude 137°E by the Japan Meteorological Agency, shows that an obvious salinity front (34.5 psu) generated by the two water masses was usually located around 15°N. However, the salinity front has been moving northward during the past three decades. El Niño/Southern Oscillation (ENSO) affected salinity in the surface layer, while temperature changed in the middle layer. The salinity front sometimes moved southward, mainly south of 5°N, and the movement was well correlated with the southern oscillation index (SOI). Because precipitation at Yap (9.5°N, 138.1°E) fluctuated with SOI, this spike‐like southward movement of the salinity front was probably affected by reduction of low‐salinity water during El Niño in the north‐western Pacific Ocean. However, ENSO only induced such large southward movements of the salinity front when the time lag between the low precipitation and low SOI was short (within four months). This salinity front is quite important for long‐distance migrating fish such as the Japanese eel because the eels spawn just south of the salinity front in the NEC. This behaviour suggests that the movement of the salinity front associated with ENSO may control the success of larval transport from the spawning ground in the NEC to the nursery ground in East Asia. In fact, catch of the Japanese eel larvae in Japan was well correlated with fluctuation of SOI and the location of the salinity front, and lower catch occurred during El Niño. The salinity front has moved from 13°N to 17°N during the past three decades. Considering that conditions of larval transport are worse north of 15°N, we suggest that decadal‐scale linear decrease of glass eel catch during the past three decades also can be explained by the displacement of the salinity front.     

The ameliorative effect of ascorbic acid on the oxidative status,live weight and recovery rate in road transport stressed goats in a hot humid tropical environment

The ameliorative effect of ascorbic acid (AA) on live weight following transportation is vital in animal husbandry. This study investigated the influence of AA on live weight, rectal temperature (rt), and oxidative status of transport stressed goats in a hot humid tropical environment. Twenty‐four goats were divided into four groups, A, B, C and D of six animals each. Group A were administered AA 100 mg/kg intramuscularly 30 min prior to 3.5 h transportation. Group B was administered AA following transportation. Group C were transported but not administered AA as positive controls while group D were not transported but were administered normal saline as negative controls. Live weight, rt and blood samples were collected before, immediately post‐transport (pt), 24 h, 3 days, 7 days and 10 days pt. Plasma was used for malondialdehyde (MDA) analysis while hemolysates were used for superoxide dismutase (SOD) analysis. There was minimal live weight loss in group A compared to groups B and C. Group A recorded reduced MDA activities and increased SOD activities compared to groups B and C which recorded significantly high MDA activities. This study revealed that AA administration ameliorated the stress responses induced by transportation in animals in hot humid tropical environments. The administration of AA to goats prior to transportation could ameliorate stress and enhance productivity.     

农药非点源模拟研究进展：流失、传输及归趋

农药非点源污染指农药自田块流失产生经水沙传输到水体,并通过迁移转化最终进入并残留在各个环境介质中,从而对生态环境产生不利影响的污染,非点源模拟模型能为农药污染防控和管理提供更科学的理论和技术支撑。本文通过对国内外研究进行梳理,从农药环境流失、传输、归趋的角度,综述了各类模型的方法、特点和应用。对代表性模型进行综合分析,总结出现有模型存在的问题,即对农药环境行为考虑不完善、结果存在不确定性以及对决策和管理支持不足等,并从多方面对模型进行了展望,未来农药非点源模拟将向机理化、精准化、动态化和决策支撑等方向发展。     

植物离体嫁接的方法和研究进展(综述)

介绍了离体嫁接的特点和方法并且概括了其组织学和细胞学发育、同化物输导以及生化研究等方面的进展.     

基于农业冷链物流的智能监测系统的设计与实现

在冷链物流的运输过程中,很多车辆因为生产年限较早,其环境保温的稳定性差,同时对车内环境的实时监控手段缺乏。所以这些冷链物流车辆在运输过程中农产品的生理状况难以监管,最终导致产品运输到目的地时可能已经处于腐坏状态。现有的装置体积较大,造价也不菲。所以我们设计一款便携,功能齐全,造价较低的冷链物流在线监管设备,其可以通过物联网传感器,对冷链车内的环境进行监控,方便农产品的运输。     

NaCl胁迫对4个树种体内离子分布的影响

通过对木栓榆、厚叶榆、醉翁榆、黄连木4个树种盆栽苗在Na Cl胁迫下不同组织中离子动态分布的研究,结果表明:1厚叶榆、木栓榆Na+总含量均随盐处理浓度的增大而提高,醉翁榆、黄连木Na+总含量不呈单一变化趋势;Na+在4个树种中分布趋势是根最大,茎次之,叶最小。2木栓榆、黄连木、厚叶榆3树种在4 mg/g盐度以下根向茎、叶选择性地运输K+而限制Na+的运输,5 mg/g盐度后根向茎、叶选择性地运输方式正好相反;醉翁榆随盐梯度的升高,根向茎、叶选择性地运输Mg2+而限制Na+的运输。3盐胁迫总体上降低了4树种叶片K+/Na+比值,但厚叶榆和黄连木叶片K+/Na+值变化规律性不强;盐胁迫对4个树种Ca2+/Na+值的影响表现为,醉翁榆、木栓榆在低盐下有所上升,随盐浓度的升高而降低;厚叶榆和黄连木Ca2+/Na+值变化无规律。