海洋浮游微食物网结构及其影响因素

微食物环是海洋生态系统中重要的物质和能量过程,是传统食物链的有效补充。微食物环研究是当前海洋生态学研究的热点之一,但对其结构的系统研究较少,海洋微食物网结构在2000年才被Garrison提出。尽管微食物网各个类群的丰度在不同海洋环境中有相对变化,但是这些变化都处于一定的范围之内,其丰度结构约为纤毛虫10 cell ml-1、鞭毛虫103 cell ml-1、微微型真核浮游生物104 cell ml-1、蓝细菌104-5 cell ml-1、异养细菌106 cell ml-1、病毒107 particle ml-1。海洋浮游食物链中捕食者和饵料生物粒径的最佳比值为10:1,实际研究中该比值会略低,例如纤毛虫与其饵料的粒径比值为8:1,鞭毛虫为3:1。Pico和Nano浮游植物的丰度比（Pico:Nano）是研究微食物网结构的指数之一,该指数具有不受研究尺度影响的优点,可用于研究区域性和全球性微食物网结构。近年来,学者们从多角度对海洋微食物网的结构开展了研究,不同海区微食物网各类群丰度、生物量的时间和空间变化研究有很多报道,微食物网的结构可受空间、季节、摄食、营养盐等多种因素影响。在对不同空间微食物网的研究中,学者往往研究不同物理性质的水团中各类群生物丰度的不同,以此来表征微食物网结构的不同;同一海区微食物网结构的季节变化也是使用各个类群丰度和生物量的变化来表示,该变化主要受水文环境因素影响。摄食者对微食物网各类生物的影响通过三种途径：1. 中型浮游动物摄食;2. 中型浮游动物摄食微型浮游动物,通过营养级级联效应影响低营养级生物;3. 中型浮游动物通过释放溶解有机物、营养盐影响细菌和低营养级生物。浮游植物通过产生化感物质和溶解有机物影响微食物网结构,而营养盐的浓度及变化则可以对微食物网产生直接或间接影响。     

海洋寄生性甲藻——阿米巴藻Amoebophrya spp.的研究进展

寄生性甲藻阿米巴藻Amoebophrya是一类广泛寄生于纤毛虫类、放射虫类、甲藻类等海水浮游生物的原生生物,在北大西洋、北太平洋和地中海等营养盐丰富、宿主密度较高的河口和近海水环境中普遍存在,是海洋浮游食物网的重要组成部分。这类寄生性甲藻能够特异性感染海洋浮游甲藻,在有害藻华(harmful algal bloom,HAB)的发生过程中起下行控制作用,将逃脱了浮游动物摄食的浮游植物补充到微食物环(microbial loop)中去。Amoebophrya在近海海洋生态系统中的独特作用日益受到国际上越来越多研究者的关注和重视,并逐渐成为国际上海洋微型生物研究的新热点之一。近年来,已有初步调查研究表明这类寄生性甲藻在我国近海海域广泛存在;然而,目前我国尚缺乏该类寄生性甲藻的相关研究。本文系统综述了国际上该类寄生性甲藻的研究进展,针对目前研究中存在的问题并结合我国有害藻华发生机制相关研究的现状做出了分析和展望,以期推动我国该类寄生性甲藻的相关研究,为进一步阐释寄生性甲藻等海洋微型生物在有害藻华消长过程和海洋微食物环中的作用奠定基础。     

温度、饵料种类对中华哲水蚤(Calanus sinicus)油脂积累与生长发育的影响

中华哲水蚤(Calanus sinicus)C5期幼体的油脂积累是种群在黄海冷水团中得以顺利度夏的关键过程。本研究对温度(10°C和19°C恒温,10—19°CⅠ和10—19°CⅡ变温)与饵料种类(硅藻饵料,自然饵料)双因子培养实验进行研究,探讨温度和饵料种类对中华哲水蚤油脂积累与生长发育的影响作用。结果表明,不同的温度和饵料种类对C5期幼体的油脂积累均有影响。C5期幼体在变温组的油脂积累是10°C组的31%—102%,是19°C组的1.8—6.1倍,低温有利于C5期幼体降低个体代谢消耗以增加油脂的积累。在恒温培养下,C5期幼体在硅藻饵料组的油脂积累是自然饵料组的2.8倍,硅藻饵料比自然饵料更有利于油脂的积累。雌体的体长和油囊体积均随着温度的升高而减小。与硅藻饵料相比,在自然饵料组中雌体的性腺发育速度更快,性腺成熟度更高(繁殖指数:58%—65%)。     

Evaluation of the “fishing down marine food web” process in the north-west of Persian Gulf(Khuzestan Province) during the period of 2002–2011

The worldwide increase in commercial fisheries and its impact on ecosystems as well as inefficient fishery management have led to overfishing and frequent breakdown of traditional fish stocks.In this context,an analysis of Khuzestan inshore fisheries data covering the years 2002–2011,was conducted in reliance on testing for occurrence of the fishing down marine food webs(FDMFW) phenomenon in the North of Persian Gulf Large Marine Ecosystem(LME).In this study,the mean trophic level(m TL) and the fishing-in-balance(FIB)-index of Khuzestan landings during this period of time were estimated using the trophic level of 47 fishery resources.Increase in total landings(Y) was observed,which explained the high fishing yield in major fishery resources(especially demersal).Moreover,the moderates decreasing trend in m TL per decade,and the increasing trend in FIB-index were observed.The status of fishery resources in Khuzestan inshore waters(under exploited but not overexploited),the rise in Y,FIB and slightly drop in m TL can be considered as indirect indicators of the fishing impacts on the trophic structure of marine communities.Based on this result,probability occurrence of FDMFW process in Khuzestan inshore waters is low to some extent.However,we suggest that the goal of management programs in Khuzestan inshore waters should prevent the continuance of this trend in the long-term using an ecosystem-based approach.     

淮北平原降雨入渗补给系数随地下水埋深变化特征

水文地质参数对地下水资源评价起着至关重要的作用。其中,降雨入渗补给系数是影响浅层地下水水量、水质的重要参数。它对研究区域水量转化和水量平衡也十分重要。但是由于受降雨量、土壤类型、植被、地下水埋深等诸多因素的影响,准确判断降雨入渗补给系数存在很大困难。如果没有考虑这些因素的影响,尤其是降雨量和地下水埋深的影响,所推求的降雨入渗补给系数就会存在较大误差。结合安徽省淮北平原区五道沟水文实验站观测的降雨量、地下水补给量、地下水水位资料,利用两种不同的方法推求了不同降雨量等级的次降雨入渗补给系数。根据统计学理论研究了不同降雨量条件下,次降雨入渗补给系数随地下水埋深变化的分布规律,建立了次降雨入渗补给系数与地下水埋深的回归模型,并进行了相应的检验。研究表明,在控制地下水埋深的条件下,次降雨入渗补给系数随地下水埋深的变化符合指数分布;在地下水位自由变动的条件下符合伽玛分布。     

Spatio-temporal variability of small copepods (especially Oithona plumifera) in shallow nearshore waters off the south coast of South Africa

Although small copepods are one of the main dietary sources for many commercially important fish, their role in the pelagic trophic dynamics has traditionally been underestimated due to the methodology commonly used in plankton sampling. Temporal variation in abundance of adults and nauplii of small copepods (particularly Oithona plumifera) in nearshore waters on the south coast of South Africa was investigated fortnightly over 14 months at site (km) and location (100 m) scales. Sampling was within <500 m of the shore, where depth was ca. 10 m, using vertical hauls of an 80-μm mesh plankton net from 1 m above the seabed to the surface. Twenty-seven adult copepod taxa were recorded, but Oithona spp. was consistently the most abundant. Taxon richness was 7–19 on each sampling occasion. There was strong temporal variation (Oithona varied between 0 and 2300 m⁻³), but much of this was short-term variability (e.g. between consecutive sampling sessions), with no seasonality or other long-term discernable patterns. There were periods of consistently low numbers, but very high numbers often followed samples with low abundances. Nor was there spatial structure at the location scale, though numbers differed between sites. Despite considerable variability at the location scale within sites, Kenton consistently showed higher densities than High Rocks. Separate analyses, with Bonferroni adjustment, showed that this difference was significant on eight out of 21 occasions for Oithona, six for other pelagic copepods and three for nauplii. This suggests that hydrodynamics favour aggregation of plankton at Kenton. A high degree of short-term variability, with a tendency for aggregation of small zooplankton at certain sites has implications for both pelagic processes and food-web links between the benthic and pelagic environments.     

Effect of native and invasive cordgrass on Macoma petalum density, growth, and isotopic signatures

Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass (Spartina alterniflora × Spartina foliosa) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C₄ plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ¹³C and δ¹⁵N) composition of the clam Macoma petalum (=M. balthica) among native marsh, hybrid Spartina, and mudflats in central San Francisco Bay. We found higher densities (individuals m⁻²) of M. petalum on mudflats compared to either native or hybrid Spartina (p < 0.001). Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 (p = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ¹³C but not δ¹⁵N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina. Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa, despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C₄ carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum.     

Assessment of spatial variation in carbon utilization by benthic and pelagic invertebrates in a temperate South African estuary using stable isotope signatures

Stable isotope analyses (δ¹³C and δ¹⁵N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ¹³C values of Zostera capensis and surface sediments near the salt marsh, the δ¹³C and δ¹⁵N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ¹³C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ¹³C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ¹⁵N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ¹³C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.     

Food Preferences of Dominant Salt Marsh Herbivores and Detritivores

Abstract. Food preferences of six dominant salt marsh invertebrates were studied to identify detritivores and to assess differences in their diets. Animals fed on agar suspensions of dead and live foods in petri dishes with four compartments. Only two foods were included in each dish. Relative palatability was assessed by measuring the amount of suspension removed or by counting the number of feeding marks left on the surface of the suspensions.
Feeding marks reflected differences in mouth parts and feeding mechanisms of the six invertebrates. Melampus bidentatus, Orchestia grillus , and Philoscia vittata preferred dead litter over live tissues of marsh graminoids, blue-green algae, and sulfur bacteria. No preference for detritus from different graminoids was shown by M. bidentatus. Orchestia grillus fed preferentially on Spartina patens detritus. Philoscia vittata preferred detritus from S. alterniflora and S. patens. Blue-green algae and sulfur bacteria were preferred over detritus by Littorina saxatalis , but detritus was preferred over live graminoids. Littorina saxatalis fed preferentially on Juncus gerardi detritus. Blue-green algae, sulfur bacteria, and live graminoids were preferred over detritus by L. littorea. Talorchestia longicornis also preferred blue-green algae.
On the basis of their food preferences, Littorina saxatalis, Melampus bidentatus, Orchestia grillus , and Philoscia vittata were classified as detritivores. Feeding on detritus from different plant species could result in a partitioning of this food resource in the detritus-based food chains of the salt marsh ecosystem.