Spatial and temporal characteristics of trophic structure of the southern Huanghai Sea fish communities

The spatial and temporal characteristics of trophic structure of fish communities in the southern Huanghai Sea were examined based on the data sampled from bottom trawl surveys conducted during the autumn of 2000 and the spring of 2001. Hierarchical agglomerative cluster method and bootstrap randomization were used to identify significant trophic groups for each fish assemblage in the southern Huanghai Sea. A total of six major trophic groups were identified within this system, which classified predators based upon location in the water column or prey size （ i. e. , benthic to pelagic predators or fish to small invertebrate prey predators）. The similarity level used to identify significant trophic groups in each assemblage ranged from 24% to 34%. Although planktivores were the dominant trophic group in each assemblage （60% - 79% ）, there were spatial and temporal variations in the trophic structure, which reflected the differences in the abundance and availability of dominant preys. Simplified food webs were constructed to evaluate the most important trophic relationships between the dominant prey taxa and the fishes in each assemblage within this system. Although there were some differences in the key prey species among different food webs, pelagic prey items （mainly euphausiids and copepods） represent the most important energetic link between primary producers and higher trophic level predators. The trophic level for most fishes was between 3 and d, and the weighted mean trophic level for each assemblage ranged from 3.3 to 3.4. Compared with previous study in the mid-1980s, there was an obvious downward trend in the trophic level for most fish species, which resulted mainly from the fluctuation in key prey species in the Huanghai Sea. The decrease in the importance of Japanese anchovy seems to be offset by other abundant prey species such as Euphausia pacifica and copepods （ mainly Calanus sinicus ） .     

豆油替代鱼油对赤点石斑鱼(Epinephelus akaara)生长、体组成及体脂肪酸组成的影响

以鱼粉和酪蛋白为蛋白源,玉米淀粉为糖源,以豆油分别替代25%、50%、75%和100%的鱼油,配制4组等氮(50.26%—51.03%)、等能(20.82—21.01k J/g)实验饲料,每组饲料设3个平行,每个平行20尾鱼,进行为期6周的生长实验。实验结果表明,过高的豆油替代会引起生长的下降。随着豆油替代水平的升高,饲料转换系数(FCR)呈现先下降后上升的趋势,最高值(1.96±0.42)出现在全豆油替代水平组,而蛋白质效率(PER)表现为相反的结果。全豆油替代组呈现相对最高的肝体比(HSI)值,但各处理组之间没有显著性差异(P0.05)。全鱼水分和蛋白含量没有明显差异(P0.05)。投喂25%替代水平组的全鱼脂肪含量最高(P0.05),但是在50%—100%替代水平处理组之间没有显著差异(P0.05)。赤点石斑鱼鱼体脂肪酸组成明显受到饲料脂肪酸组成的影响。随着饲料豆油水平的升高,全鱼鱼体中的亚油酸(C18:2n6)含量显著升高(P0.05),ARA(C20:4n6)、EPA(C20:5n3)和DHA(C22:6n3)含量在全豆油替代组最低。总之,饲料豆油替代水平不宜超过75%,过高的豆油替代水平可能会对赤点石斑鱼生长产生不利影响,并影响鱼的品质。     

红海湾远海梭子蟹Portunus pelagicus的食物组成及营养位置分析

利用稳定同位素技术;分析了2015年5月在红海湾海域采集的远海梭子蟹Portunus pelagicus及其潜在食物的碳（δ13C）和氮（δ15N）稳定同位素比值;通过稳定同位素混合模型（SIAR）;估算不同食物对远海梭子蟹食性的相对贡献。结果表明:远海梭子蟹的δ13C值在-18.1‰~-14.1‰之间;δ15N值的范围为9.8‰~13.8‰;平均值分别为-16.9‰±1.3‰和12.1‰±2.3‰。δ13C和δ15N值的变化范围均较大;表明远海梭子蟹食物来源广泛、多样。远海梭子蟹的食物主要由双壳贝类、螺类、鱼类、头足类、虾类、蟹类和藻类组成。SIAR模型计算结果显示:藻类为远海梭子蟹的主要食物;其平均贡献为32.5%;双壳贝类的相对食性贡献为21.9%;虾类、螺类、鱼类和蟹类的平均贡献差异较小;分别为9.7%、9.7%、9.6%和9.3%;头足类的贡献最低;仅为7.3%。此外;根据δ15N值及营养位置的计算公式得出:远海梭子蟹在红海湾海域位于2.91±0.68营养级。远海梭子蟹的7类潜在食物中;藻类的营养位置最低;为1.21±0.58;其次为双壳贝类;为2.00±0.25;蟹类、螺类、虾类和鱼类的营养位置分别为2.85±0.33、2.87±0.26、3.01±0.16和3.08±0.18;头足类的最高;为3.41±0.17。     

Prey characteristics and dietary composition in intertidal Astrostole scabra (Echinodermata: Asteroidea)

Dietary composition in juvenile Astrostole scabra at Kaikoura, New Zealand (42°25′S, 173°42′E), changed qualitatively with increased seastar size so that food was partitioned amongst starfish size classes according to a combination of prey species and size. Small A. scabra fed more frequently than large specimens. Size‐discriminant feeding was evident as large Turbo smaragdus and Risellopsis varia, small Melagraphia aethiops, and intermediate sized Micrelenchus dilatatus, Ischnochiton maorianus, Onithochiton neglectus, and Amaurochiton glaucus were consumed in proportions greater than those found in the habitat. Major prey species have both spatial and size refuges from predation.     

Application of DNA metabarcoding to characterize the diet of the moon jellyfish Aurelia coerulea polyps and ephyrae

Dietary studies of polyps and ephyrae are important to understand the formation and magnitude of jellyfish blooms and provide important insights into the marine food web. However, the diet of polyps and ephyrae in situ is largely unknown. Here, prey species of the polyps and ephyrae of the moon jellyfish Aurelia coerulea in situ were identified using high-throughput DNA sequencing techniques. The results show that A. coerulea polyps and ephyrae consume a variety of prey items. The polyps consume both planktonic and benthic prey, including hydromedusae, copepods, ciliates, polychaetes, stauromedusae, and phytoplankton. A. coerulea ephyrae mainly feed on copepods and hydromedusae. Gelatinous zooplankton, including Rathkea octopunctata and Sarsia tubulosa, were frequently found as part of the diet of A. coerulea polyps and ephyrae. The utilization of high-throughput sequencing technique is a useful tool for studying the diet of polyps and ephyrae in the field, complementing the traditional techniques towards a better understanding of the complex role of gelatinous animals in marine ecosystems.     

饲料脂肪含量对施氏鲟生长及其肝脏脂质组成的影响

本文报道了饲料中不同脂肪含量对施氏鲟生长及其肝脏脂质组成的影响结果，试验饲料是以酪蛋白质，鱼粉，糊精和纤维素等为主要原料配制而成的等氮和等能量的半精制饲料，以等量混合的海水鱼油，豆油作为肪源，试验周期为25d，结果表明；施氏鲟饲料中脂肪适宜含量为5．6－11．4％，最适合含量为7．5％左右，肝脏脂质含量和中性脂质含量随着饲料脂肪添加量的增加而升高，但在饲料脂肪适宜含量范围内各组间却无显著差异。     

Dietary Shifts in the Queen Triggerfish, Balistes vetula, in the Absence of its Primary Food Item, Diadema antillarum

Abstract. The long-spined sea urchin Diadema antillarum has been reported to be the major food item of the queen triggerfish, Balistes vetula in the Caribbean. This sea urchin has undergone a massive mortality on reefs throughout the Caribbean during 1983. The dietary habits of twenty-three queen triggerfish from patch reef habitats in Belize were examined. It was found that crabs and chitons now form the major dietary items when D. antillarum is not available. It is suggested that this predator, which was previously specialized on a single food item, is able to shift resource utilization in the absence of its primary food source, and that the queen triggerfish can capture diverse prey from a wide variety of habitats.     

Does transported seagrass provide an important trophic link in unvegetated, nearshore areas?

The contribution of detritus from seagrass and other primary producers to faunal production in unvegetated nearshore areas was examined primarily using stable isotopes. Fish, macroinvertebrates, meiofauna and primary producers (seagrasses, macroalgae, seston and benthic microalgae) were sampled from sites in south-western Australia. All samples were analysed for δ¹³C and δ¹⁵N values and fish gut contents were determined. δ¹³C values for seagrasses in the region were high compared to other macrophytes, ranging from 49.9 to −8.2‰ compared to −19.8 to −12.6‰ for macroalgae. The δ¹⁵N values ranged between 4.0 and 7.7‰ for the red, brown and green algae, and between 3.2 and 5.9‰ for seagrasses. Seston and benthic microalgae samples had a mean δ¹³C value of −12.8 and −14.0‰, respectively, and their δ¹⁵N values were comparable to the macroalgae. All invertebrate fauna had mean δ¹³C values considerably lower than seagrasses. However, individual samples harpacticoid copepods and polychaetes had a value as high as −11.7‰. δ¹⁵N values for consumers were higher than those of the primary producers, except for copepods and amphipods. The δ¹³C values for fish had a relatively small range, between −16.6 and −13.1‰, and the δ¹⁵N values of fish were elevated compared to the invertebrates and primary producers, ranging mostly between 10.0 and 12.6‰. Mixing model analysis based on δ¹³C values indicated that seagrass ranked low as a likely carbon source for all invertebrates other than harpacticoid copepods at a single site and some samples of polychaetes. The δ¹³C values for fish were similar to those of a combination of harpacticoid and calanoid copepods, amphipods and polychaetes. The consumption of harpacticoid copepods by some fish species indicates that Amphibolis and Posidonia species in south-western Australia can contribute to the food web of unvegetated nearshore areas as detritus, but brown algae is likely to make a greater contribution. At least for the time of year that was sampled, the flow of detrital seagrass material into the foodweb may be mediated by specific detrivores, in this case harpactacoid copepods, rather than by all detritivores.     

Feeding ecology of Japanese Spanish mackerel(Scomberomorus niphonius) along the eastern coastal waters of China

Feeding activities provide necessary nutrition and energy to support the reproduction and development of fish populations. The feeding ecology and dietary plasticity of fish are important factors determining their recruitment and population dynamics. As a top predator, Japanese Spanish mackerel(Scomberomorus niphonius) supports one of the most valuable fisheries in China. In this study, the feeding ecology and diet composition of Japanese Spanish mackerel spawning groups were analysed based on samples collected from six spawning grounds along the eastern coastal waters of China during spring(March to May) in 2016 and 2017. Both stomach contents and stable isotope analysis were conducted. Stomach content analysis showed that spawning groups of Japanese Spanish mackerel mainly fed on fish, consuming more than 40 different prey species. Diets were significantly different among sampling locations. The most important prey species were Stolephorus in Fuzhou, Japanese anchovy Engraulis japonicus in Xiangshan, Euphausia pacifica in Lüsi, sand lance Ammodytes personatus in Qingdao and Weihai, and Leptochela gracilis in Laizhou Bay. Stable isotope analysis showed that the trophic level of Japanese Spanish mackerel was relatively high and generally increased with latitude from south to north. In the 1980 s, the diet of Japanese Spanish mackerel was dominated solely by Japanese anchovies in the eastern coastal waters of China. The results in the present study showed that the importance of Japanese anchovies declined considerably, and this fish was not the most dominant diet in most of the investigated waters. Both the spatial variations in diet composition and changes in the dominant diet over the long term indicated the high adaptability of Japanese Spanish mackerel to the environment. Combining the results of stomach analysis and stable isotope analysis from different tissues provided more comprehensive and accurate dietary information on Japanese Spanish mackerel. The study provides essential information about the feeding ecology of Japanese Spanish mackerel and will benefit the management of its populations in the future.