长江口及邻近海域高营养层次生物群落功能群及其变化

通过对2006年6、8和10月在长江口及邻近海域3次调查采集样品的分析,对该水域的高营养层次生物群落的功能群组成及其变化进行了研究.结果表明：长江口及邻近海域高营养层次生物群落包括鱼食性、蟹食性、虾食性、底栖动物食性、浮游生物食性和广食性6个功能群.由于受海洋环境变化以及鱼类洄游活动的影响,各月份长江口及邻近海域高营养层次生物群落的组成及营养级都有较大的变化.6月高营养层次以鱼类、毛虾类和蟹类为主,以浮游生物食性功能群为主要功能群,营养级最低,为3.06;8月高营养层次以鱼类为主,虾食性功能群为主要功能群,营养级达到最高,为3.78;10月高营养层次虽仍以鱼类为主,虾蟹类比例增大,功能群以浮游动物食性和底栖动物食性功能群为主,营养级为3.58.     

基于稳定同位素技术的保安湖食物网结构特征研究

文章利用碳、氮稳定同位素技术对江湖阻隔典型湖泊-保安湖的食物网结构进行了研究。结果表明保安湖中鱼类消费者的主要营养级范围为2.1—3.3, 在调查到的16种鱼类中, 顶级肉食性鱼类种类很少, 杂食性鱼类的种类最多。保安湖食物网主要由两条营养传递途径构成, 即由POM、浮游植物为主要食物源的浮游牧食链与沉积物为主要食物源的底栖食物链。POM、浮游植物、浮游动物和底栖动物是保安湖水域食物网中鱼类的主要食物来源, 其次是沉积物中的碎屑和水生植物等。此外, 从基于理论食性数据的食物网与BIMM模型预测的食物网结构可以看出, 从POM、浮游植物、浮游动物到杂食性鱼类的浮游牧食链在整个食物网中具有主导性, 而从水生植物、沉积物和底栖动物到杂食性鱼类的底栖食物链相对重要性较低。     

莱州湾鱼类群落同功能种团的季节变化

利用2011年5月、8月、10月和12月底拖网调查数据,对莱州湾海域鱼类同功能种团特征及其季节变化进行了研究。全年调查共渔获鱼类49种,全部为硬骨鱼类。根据鱼类的摄食习性,调查海域鱼类可划分为浮游动物食性种团、浮游动物/底栖动物食性种团、底栖动物食性种团、底栖动物/游泳动物食性种团、游泳动物食性种团、杂食性种团和碎屑食性种团共7个同功能种团,其中底栖动物食性种团种类数最多(14种),底栖动物/游泳动物食性种团次之(12种)。碎屑食性种团生物量在全年处于第一优势地位,占32.8%;其次为浮游动物食性种团,占31.6%;再次为底栖动物/游泳动物食性种团,占25.0%。同功能种团多样性(HFD)和种类多样性(Hs)季节变化趋势相同,均在夏季达到最高值,冬季达到最低值;两者关系使用指数方程拟合效果最佳。浮游动物食性种团平均营养级为3.71、浮游动物/底栖动物食性种团为3.83、底栖动物食性种团为3.43、底栖动物/游泳动物食性种团为3.75、游泳动物食性种团为3.86、杂食性种团为3.73、碎屑食性种团为3.34。与20世纪80年代、90年代调查结果相比,目前莱州湾碎屑食性种团比例明显上升,游泳动物食性种团比例大幅下;底栖动物食性种团和游泳动物食性种团的平均营养级明显下降,碎屑食性种团平均营养级有所上升。     

基于碳氮稳定同位素的南海中西部海域春季中上层渔业生物群落营养结构

根据2018年春季于南海中西部海域进行的灯光罩网渔业生物调查,本研究采用碳氮稳定同位素技术,分析了南海中西部海域中上层渔业生物的碳氮稳定同位素基本特征,构建了连续营养谱,划分了营养功能群,并比较了不同营养功能群间的营养结构特征。结果表明: 采集的23种渔业生物δ¹³C均值最大为鲯鳅,(-17.58±0.21)‰,最小为六带线纹鱼,(-19.86±0.33)‰;δ¹⁵N均值的变化范围为8.31‰(琉璃玉鲳)～(12.46±0.74)‰(宝刀鱼)。连续营养谱分析表明,采集的中上层渔业生物营养级介于3.01～4.23,其中19种渔业生物(占总渔获种类的83%)的营养级位于3.0～4.0。23种渔业生物可划分成浮游生物食性、游泳生物食性和混合生物食性3个营养功能群。稳定同位素标准椭圆面积(SEA)分析显示,浮游生物食性功能群占据的营养生态位宽幅最大(SEA=1.56‰²),其次为混合生物食性功能群(SEA=0.99‰²)和游泳生物食性功能群(SEA=0.31‰²)。混合生物食性功能群分别与游泳生物食性功能群和浮游生物食性功能群存在17%和26%的营养生态位重叠度,而游泳生物食性功能群与浮游生物食性功能群不存在生态位重叠。     

黄海生态系统高营养层次生物群落功能群及其主要种类

根据2000年秋季和2001年春季在黄海的两次大面调查,选取生物量占总生物量90%的生物种类为研究对象,分析了黄海生态系统以及3个生态区(冷水团海域、近岸水域和黄海南部水域)春秋两季高营养层次生物群落的功能群组成及其主要种类.结果表明,黄海生态系统高营养层次生物群落包括6个功能群.按生物量排序为:浮游生物食性功能群、底栖动物食性功能群、鱼食性功能群、虾食性功能群、广食性功能群和虾/鱼食性功能群,各功能群营养级范围分别为3.22～3.35、3.30～3.46、4.04～4.50、3.80～4.00、3.38～3.79和4.01.黄海生态系统的主要功能群为浮游生物食性功能群和底栖动物食性功能群,占总生物量的79.6%;主要种类包括13种:小黄鱼、鳀、细巧仿对虾、银鲳、细点圆趾蟹、带鱼、黑鳃梅童、黄鲫、龙头鱼、双斑蟳、细纹狮子鱼、三疣梭子蟹和凤鲚,约占总生物量的70.6%.从不同季节看,春季黄海不同生态区高营养层次的营养级接近,而秋季差别较大,这主要与生物繁殖和索饵群体组成及摄食习性相关.从不同生态区看,黄海冷水团海域高营养层次生物群落以浮游生物食性功能群为主,受季节变化的影响较小,其高营养层次的营养级接近.黄海近岸水域和黄海南部水域高营养层次生物群落功能群组成受季节的影响较大,秋季的营养级均高于春季的营养级.这表明黄海冷水团海域较近岸水域和南部水域稳定,是黄海的一个典型的生态区域.     

基于生态通道模型的长江口水域生态系统结构与能量流动分析

利用Ecopath with Ecosim在前期研究的基础上构建了3个时期(2000年秋、2006年秋、2012年秋)长江口水域生态系统的生态通道模型,分析对比了三峡工程蓄水前中后期,长江口水域生态系统结构与能量流动特征。模型将长江口水域生态系统划分为鱼类、虾类、蟹类、头足类、底栖动物、浮游动物、浮游植物、碎屑等17个功能组,基本覆盖了长江口生态系统能量流动的主要途径。模型结果分析表明:蓄水前中后期,长江口水域生态系统各功能组营养级组成和分布相近,但由于长江口渔业过度捕捞,蓄水中后期多数功能组的生态营养转换率被动提高。长江口渔获物的组成未发生明显变化,但渔获物的平均营养级降低,渔获量减少。蓄水中后期,生态系统中牧食食物链的重要性增加,碎屑食物链的重要性降低,这与蓄水之后长江入海径流改变、泥沙量减少、陆源污染增加关系密切。结果表明,蓄水前中后期,生态系统均处于不成熟阶段,蓄水后生态系统总生物量、初级生产量及流向碎屑的能量呈降低趋势,但系统的净效率和再循环率升高。     

关于生态系统中食物链、营养级的几个问题

在生态系统内,各类生物之间存在着一系列的吃与被吃的关系。这种以食物营养为中心,生物个体之间捕食与被捕食的链条关系,称为食物链。食物链是一环扣一环的。各种生物体分别位于食物链的不同环节上(按食性划分)。食物链的每一个环节称为营养级,食物链长短不一,营养级的数目也不一样。由于各种生物的营养关系复杂,一种消费者常常不只吃一种食物,而一种生物又可被不同消费者所吃,这样就决定了在一个生态系统内有许多食物链。这些食物链彼此相互交结,紧密相联,构成     

长江口及其邻近水域鱼类浮游生物群落的时空格局

根据2007年长江口及其邻近水域4个航次调查资料, 探讨了该水域的鱼类浮游生物群落物种组成和多样性的季节变化特征。结果表明, 2007年共捕获鱼类浮游生物6,463个, 隶属12目28科45种, 以鳀科丰度最高, 占总丰度的76.5%。长江口鱼类浮游生物包括4种生态类型: 淡水型(2种), 半咸水型(14种), 沿岸型(10种)和近海型(16种)。 其中, 近海型物种个体数量最多, 占2007年长江口鱼类浮游生物总丰度的74.55%。鳀(Engraulis japonicus)在4个季节均有出现, 对长江口鱼类浮游生物丰度贡献最大。鱼类浮游生物在物种组成上存在明显的季节变化: 白氏银汉鱼(Allanetta bleekeri)在春季占绝对优势, 鳀是夏季优势度最高的种类, 秋季除鳀外, 前颌间银鱼(Hemisalanx prognathus)成为优势种; 鱼类浮游生物丰度高度集中在优势种上, 各季节优势种对总丰度贡献超过89%。群落物种数量、丰度、丰富度指数、均匀度指数和多样性指数, 在夏季最高, 春季和秋季次之, 冬季最低。长江口鱼类浮游生物群落物种组成和多样性的季节变化特征体现了鱼类繁殖迁移策略和鱼类对环境变异的响应。     

长江口水域中华鲟幼鱼与6种主要经济鱼类的食性及食物竞争

根据2004年6月至8月和2005年6月至8月在长江口崇明岛东滩水域插网所获取的鱼类样本,对东滩水域中华鲟(Acipenser sinensis)幼鱼和其它6种主要经济鱼类的食性、食物竞争状况进行了研究。结果表明:中华鲟、窄体舌鳎(Cynoglissus gracilis)为底栖生物食性;中国花鲈(Lateolabrax maculatus)为游泳生物食性;刀鲚(Coilia ectenes)和凤鲚(Coilia mystus)为浮游动物食性;鲻(Mygil cephalus)和鮻(Liza haematochiela)为腐屑(有机碎屑)食性。中华鲟幼鱼及6种主要经济鱼类食性按照相对重要性指标(IRI)大小排列:中华鲟(IRI):鱼类端足类多毛类蟹类;窄体舌鳎(IRI):虾类瓣鳃类鱼类;中国花鲈(IRI):鱼类虾类等足类蟹类;刀鲚(IRI):糠虾类虾类桡足类鱼类;凤鲚(IRI):糠虾类桡足类虾类鱼类;鲻(IRI):有机碎屑底栖藻类瓣鳃类桡足类;鮻(IRI):有机碎屑底栖藻类瓣鳃类桡足类。长江口崇明东滩中华鲟与6种经济鱼类饵料重叠系数显示,中华鲟与窄体舌鳎的饵料重叠系数达到了0.4,而与其余5种鱼类的饵料重叠系数均小于0.12。这表明窄体舌鳎对中华鲟幼鱼的食物有一定的竞争力,其余5种鱼类对中华鲟幼鱼的食物竞争强度较低。     

太湖贡湖湾食物网特征研究

应用稳定性同位素技术(13C和15N)研究了太湖贡湖湾食物网特征, 结果显示由于食物来源变化多样性影响, 导致贡湖的食物网结构和营养级关系变化较为复杂, 贡湖主要生物类群13C、15N值表现出较大的种间差异。消费者13C值从摇蚊幼虫的-32.3到锯齿米虾的-22.1, 其值大小与营养级的关系没有规律性。消费者平均15N值从褶纹冠蚌的10.3到位于顶端间下鳙的19.0, 随营养级位置而升高。群落中所有种类的15N、13C值之间没有相关性(r=0.1835, P0.05), 表明该食物网是非线性食物网。研究结果验证了杂食性生物有机体普遍存在于富营养化的贡湖水域生态系统中, 且13C结果表明, 浮游植物、固着藻类以及沉水植物为贡湖食物网中大多数生物有机体的主要碳源。贡湖食物链长度为4.44营养级。     

Predator diversity enhances secondary production and decreases the likelihood of trophic cascades

We manipulated the diversity of top predators in a three trophic level marine food web. The food web included four top benthic marine fish predators (black goby, rock goby, sea scorpion and shore rockling), an intermediate trophic level of small fish, and a lower trophic level of benthic invertebrates. We kept predator density constant and monitored the response of the lower trophic levels. As top predator diversity increased, secondary production increased. We also observed that in the presence of the manipulated fish predators, the density of small gobiid fish (intermediate consumers) was suppressed, releasing certain groups of benthic invertebrates (caprellid amphipods, copepods, nematodes and spirorbid worms) from heavy intermediate predation pressure. We attribute the mechanism responsible for this trophic cascade to a trait-mediated indirect interaction, with the small gobiid fish changing their use of space in response to altered predator diversity. In the absence of top fish predators, a full-blown trophic cascade occurs. Therefore the diversity of predators reduces the likelihood of trophic cascades occurring and hence provides insurance against the loss of an important ecosystem function (i.e. secondary production).     

Benthic-pelagic trophic interactions within the fish assemblage in the western Bering Sea shelf area according to stomach content analysis and ratios of C and N stable isotopes

The composition, abundance, diet and trophic status of zooplankton, bottom invertebrates, fish and nekton were analyzed based on the data collected by the staff of the TINRO-Center during complex bottom trawl catches on the Bering Sea shelf in the fall of 2004. The stomach contents of mass fish species were analyzed and the nitrogen and carbon isotopic composition of 36 mass species of plankton, benthos, nekton and nektobenthos, which together make up the basis of pelagic and bottom communities, was determined. It was found that zooplankton noticeably differ from benthic invertebrates in carbon isotopic composition: δ¹³C values in zooplankton varied from −20.3‰ to −17.9‰; in benthos—from −17.5‰to −13.0‰; and in fish—from −19.2‰ (juvenile walleye pollock) to −15.3‰ (saffron cod). The levels of ¹³C isotope in the tissues of fish depended mostly on the share of pelagic or benthic animals in their diet. δ¹⁵N values in the studied species ranged from 8.6‰ (in sea urchins) to 17.2‰ (in large Pacific cods), which corresponds to a trophic level of 2.8. Obviously the δ¹⁵N values reflect the degree of predation and generally show the ratio of primary, secondary and tertiary consumers in a fish’s diet. Trophic interactions manifest a high degree of interdependence between benthic and pelagic communities (even without taking into account such lower components of the food web as phytoplankton, bacteria, and protozoa) occurring in most nektonic species that depend on both bottom and pelagic food.     

Diet diversity among five co-existing fish species in a tropical river: integration of dietary and stable isotope data

Diets were estimated from stomach contents and the MixSIR model using stable isotope values for five co-existing and abundant benthic fishes in relation to potential prey from a riffle habitat in a tropical river in eastern Thailand. Collectively, aquatic insects were of greatest dietary importance based on stomach contents and, except for one fish species, predicted from the MixSIR. The most prominent functional feeding insect groups in fish diets were collector-filterers and scrapers and, to a lesser extent, predators. MixSIR predicted shrimp to be the most important single dietary constituent for all fishes in contrast to stomach contents, which indicated they are a major item for only one species. MixSIR predicted plant material to be more important in fish diets than stomach contents where the composition of detritus was a concern. Differences in temporal feeding schedules, prey availability, species adaptations and others are important in understanding diet and in the construction of food webs. Stable isotope and dietary analysis provides a more accurate assessment of the food web structure and dynamics of tropical river ecosystems than either method alone.     

Feeding patterns of the dominant benthic and demersal fish community in a temperate estuary

The diet and feeding relationships of the 12 most abundant benthic and demersal fish species of the Mondego Estuary, Portugal, were studied between June 2003 and May 2006. Fishes were caught during the night using a 2 m beam trawl. The stomach contents were analysed for prey identification, counting and weighing. According to prey importance in diets, three main feeding guilds were identified: (1) invertebrate feeders, (2) invertebrate and fish feeders and (3) plankton and invertebrate feeders. Besides these main feeding guilds, some fishes also presented fractions of algae and zooplankton in their stomach contents. The most abundant prey items were macroinvertebrates, with several polychaetes ( Nephtys spp., Capitellidae, Spionidae and Eunicidae), Corophium spp. and Crangon crangon among the dominant prey. Pomatoschistus spp. were the most preyed on fishes. Several fish species showed a tendency for a specialized diet, but almost all also showed some degree of opportunistic feeding by preying on other food resources. High diet overlap was found between some fish species, yet exploitative competition could not be concluded.     

Feeding habits and seasonal trophic guilds structuring fish community in the bay mouth region of a tropical estuarine habitat

Understanding trophic relationships of fish in estuarine ecosystem is an important element for sustainable resource management. This study examined the feeding habits of 29 dominant fish species, characterized the trophic guilds, assessed the impact of season and clarified the role of diets in structuring the fish community in the mouth region of Pattani Bay, Thailand. Samples of 5792 fishes collected monthly by gillnets from March 2019 to February 2020 were used for stomach content analyses. It was found that the number of food types and fullness index differed between fish taxa (P < 0.001). Most fishes were specialist feeders feeding on specific food components and were categorized into five trophic guilds: piscivore, shrimp-fish feeder, polychaete feeder, zooplanktivore and planktivore. Six species were piscivorous, considered as apex predators, that fed almost entirely on fishes. High diet overlaps among some species (>0.6) were recorded. Not much variation in seasonal guilds was observed: four guilds in the dry season, three in the moderate rainy season and four in the rainy season. Some species remained in the same guild the whole year round, but some fishes changed seasonally. Two fish communities from different regions of the bay were segregated based on feeding habits. The inner bay community comprised mainly copepod and plankton feeders, but there were more piscivores in the deeper bay mouth area. Results from this study help us to understand the feeding habits and trophic guilds of dominant fish species at the mouth of this tropical estuarine bay.     

汞在新建水库食物网中生物累积与风险评价研究进展

汞是唯一参与全球循环的液态重金属。1974年,自美国学者Smith首次报道水库中鱼类总汞含量高于邻近自然湖泊以来,水库中鱼类汞升高的风险成为新建水库环境影响评价中的重要内容之一。汞在水库生态系统生物组分和非生物组分中含量升高的现象先后在世界各国报道,包括加拿大、美国、芬兰、泰国和巴西等。通过对系列的野外研究进行回顾,表明了水库形成后生态系统中汞的甲基化过程发生了变化。水库形成对汞在食物网中的鱼类、底栖生物、浮游生物的累积产生影响。水库中汞的生物累积、迁移转化主要与被淹没土壤和植物腐解过程有着直接或间接的关系。水库形成后,总汞、甲基汞和甲基汞比例在生态系统食物网各组分中的变化并不一致。蓄水后,水体中总汞变化较小,甲基汞和甲基汞比例上升明显;浮游生物尤其是浮游动物中总汞升高,但甲基汞和甲基汞比例升高更为明显;与浮游动物类似,底栖水生昆虫中总汞升高,甲基汞和甲基汞比例升高也更为明显;鱼类作为食物网顶级消费者,甲基汞比例一般在80%以上,在水库形成后鱼类总汞和甲基汞均明显升高,但甲基汞比例变化已经不大。这些变化揭示了水库形成后甲基汞在食物网传递的两个主要可能途径,一是微型生物食物网。通过悬浮颗粒物、浮游植物、浮游动物这一环节,甲基汞和甲基汞比例有明显的增加。第二个途径是底层生物食物网。通过悬浮颗粒物、细菌、碎屑食性底栖水生昆虫、肉食型底栖水生昆虫环节,甲基汞和甲基汞比例明显增加。这两种途径均能导致以水生昆虫、小鱼、甲壳类等为食的肉食性鱼类汞含量增加。水库形成后,生态系统中汞的甲基化发生了明显的"加速"过程。这种"加速"过程最直接的因素是成库后大量土壤淹没使得汞的甲基化平衡被打破。这个过程主要有两方面的影响。一方面是直接影响,被淹没土壤和植被在腐解过程中主动或被动地将甲基汞释放到水库生态系统中;另一方面是间接影响,被淹没土壤和植被的腐解使水库底部形成厌氧环境,有利于无机汞从被淹没土壤和植被中溶出,为甲基化反应提供充裕的、可供甲基化的无机汞,同时腐解产生的大量营养物质为微生物提供丰富食物来源,使硫酸盐还原菌大量繁殖,促进无机汞的甲基化。在我国,有关汞在新建水库食物网中生物累积和风险评价的研究有待进一步加强。     

Fatty acid composition of consumers in boreal lakes – variation across species,space and time

1. Fatty acids (FAs) have been widely applied as trophic biomarkers in aquatic food web studies. However, current knowledge of inter‐ and intraspecific variation in consumer FA compositions across spatial and temporal scales is constrained to a few pelagic taxa. 2. We analysed the FAs of 22 taxa of benthic macroinvertebrates, zooplankton and fish collected from the littoral, pelagic and profundal habitats of nine boreal oligotrophic lakes over spring, summer and autumn. We quantified and compared the FA variance partitions contributed by species identity (i.e. an integrative effect of phylogenetic origin, life history and functional feeding guild of individual taxa), site and season using partial redundancy analysis both on all consumers and on benthic arthropods alone. 3. Species identity alone contributed 84.4 and 72.8% of explained FA variation of all consumers and benthic arthropods, respectively. Influences of site, season and all joint effects accounted for 0–11.3% only. Fatty acid profiles of primary consumers differentiated below class level, but those of predators were distinguishable only when they became more taxonomically distinct (i.e. among classes or higher). 4. Pelagic and profundal consumers showed stronger reliance on autochthonous resources than did their littoral counterparts as reflected by their higher ω3 to ω6 FA ratios. Polyunsaturated FAs (PUFAs) were increasingly retained with trophic levels, and saturated FAs (e.g. FA 16 : 0) gradually reduced. Ecologically, this trade‐off enhances the trophic transfer efficiency and confirms the importance of PUFA‐rich autotrophs in aquatic food webs. 5. Our findings indicate strong interspecific differences in FA requirements and assimilation among aquatic consumers from a wide range of taxonomic levels, habitats and lakes. Consumers were able to maintain homoeostasis in FA compositions across spatial and temporal changes in resource FAs, but consumer homoeostasis did not limit the effectiveness of FAs as trophic biomarkers.     

Lake size and fish diversity determine resource use and trophic position of a top predator in high‐latitude lakes

Prey preference of top predators and energy flow across habitat boundaries are of fundamental importance for structure and function of aquatic and terrestrial ecosystems, as they may have strong effects on production, species diversity, and food‐web stability. In lakes, littoral and pelagic food‐web compartments are typically coupled and controlled by generalist fish top predators. However, the extent and determinants of such coupling remains a topical area of ecological research and is largely unknown in oligotrophic high‐latitude lakes. We analyzed food‐web structure and resource use by a generalist top predator, the Arctic charr Salvelinus alpinus (L.), in 17 oligotrophic subarctic lakes covering a marked gradient in size (0.5–1084 km²) and fish species richness (2–13 species). We expected top predators to shift from littoral to pelagic energy sources with increasing lake size, as the availability of pelagic prey resources and the competition for littoral prey are both likely to be higher in large lakes with multispecies fish communities. We also expected top predators to occupy a higher trophic position in lakes with greater fish species richness due to potential substitution of intermediate consumers (prey fish) and increased piscivory by top predators. Based on stable carbon and nitrogen isotope analyses, the mean reliance of Arctic charr on littoral energy sources showed a significant negative relationship with lake surface area, whereas the mean trophic position of Arctic charr, reflecting the lake food‐chain length, increased with fish species richness. These results were supported by stomach contents data demonstrating a shift of Arctic charr from an invertebrate‐dominated diet to piscivory on pelagic fish. Our study highlights that, because they determine the main energy source (littoral vs. pelagic) and the trophic position of generalist top predators, ecosystem size and fish diversity are particularly important factors influencing function and structure of food webs in high‐latitude lakes.     

Unexpected prey of juvenile spotted scat (Scatophagus argus) near a wharf: The prevalence of fouling organisms in stomach contents

A knowledge of fish diets can contribute to revealing the trophic role and ecological function of species in aquatic ecosystems. At present, however, there are no efficient or comprehensive methods for analyzing fish diets. In this study, we investigated the diets of juvenile Scatophagus argus collected near a wharf in Daya Bay, China, by dissection and high‐throughput sequencing (HTS) using the 18S rDNA V4 region. Microscopy disclosed large amounts of bryozoans and unrecognizable detritus. In contrast, HTS analysis indicated that the fish diets were considerably more diverse than visual inspection suggested. After eliminating fish sequences, approximately 17,000 sequences from taxa in nine phyla (Ciliophora, Bryozoa, Annelida, Bacillariophyta, Chlorophyta, Arthropoda, Dinoflagellata, Tunicata, and Phaeophyta) were identified from the analysis of stomach contents. Twenty‐one food categories were identified, most of which (95.2%) were benthic fouling organisms that could easily be collected around wharfs. These consisted of bryozoans (31.9%), ciliates (45.7%), polychaetes (14.6%), and green algae (3.0%). Therefore, to adapt to anthropogenic habitat modification, the fish had probably shifted from planktonic to benthic feeding. The prevalence of fouling organisms in the stomachs of juvenile S. argus indicates that the fish have responded to habitat changes by widening their food spectrum. This adaptation may have increased their chances of survival. The fouling organisms that inhabit highly perturbed coastal ecosystems could represent a food source for animals at higher trophic levels. Our results accordingly suggest that human activity might significantly influence fish feeding behavior and material transfer along the food chain.     

Widespread omnivory and low temporal and spatial variation in the diet of fishes in a hydrologically variable northern Australian river

This article examines the trophic ecology of freshwater fishes (22 species in 15 families) in a wet and dry tropical Australian river of high intra‐annual and interannual hydrological variability. Seven major trophic groups were identified by cluster analysis; however, four food items (filamentous algae, chironomid larvae, Trichoptera larvae and Ephemeroptera nymphs) comprised almost half of the average diet of all species. The influence of species, fish size, spatial effects and temporal effects on food use was investigated using redundancy analysis. Size, time and space accounted for little of the perceived variation. Ontogenetic changes in diet were minor and limited to a few large species. Spatial variation in trophic composition of the fish assemblages reflected the effects of the Burdekin Falls and dam, a major geographic barrier, on species distributions. Little spatial variation in diet was detected after accounting for this biogeographical effect. Temporal variations in flow, although marked, had little effect on variations in fish diet composition due to the low temporal diversity of food resources in physically monotonous sand and gravel channels. Species identity accounted for<50% of the observed variation in food choice; omnivory and generalism were pronounced. The aquatic food web of the Burdekin River appears simple, supported largely by autochthonous production (filamentous and benthic microalgae, and to some extent, aquatic macrophytes). Allochthonous food resources appear to be unimportant. The generalist feeding strategies, widespread omnivory and absence of pronounced trophic segregation reported here for Burdekin River fishes may be common to variable and intermittent rivers of subtropical and tropical northern Australia with similar fish communities and may be a general feature of rivers of low habitat diversity and characterized by flow regimes that vary greatly both within and between years.