In‐stream habitat suitability criteria for feeding inanga (Galaxias maculatus)

Inanga (Galaxias maculatus Jenyns) are the basis of an important recreational and commercial freshwater fishery that has declined over the past 100 years, probably because of habitat degradation in developed areas. Maintenance of suitable stream flows for inanga is one means of protecting the fishery. Observations of habitat use by drift‐feeding inanga were made in three streams. Most feeding inanga were stationary in the current taking food items from the drift and sometimes from the surface. Drift‐feeding locations were related to current patterns and water velocity, with inanga feeding at locations where the current concentrated food, and where water velocities were sufficiently low to allow the fish to hold position. The mean feeding velocity did not vary significantly between streams, although the range of velocities used did. Optimum feeding velocities were 0.03–0.07 m s^‐1, and were comparable with brown trout (Salmo trutta) feeding velocities, when adjusted for the differences in fish size. Depth use was very different between streams and this was attributed to the variation in available habitat. Depths greater than 0.3 m were optimum, with some use of depths between 0.1 and 0.3 m. It is suggested that inanga suitability criteria are dictated by biological factors, such as swimming ability and bio‐energetic requirements, rather than the river the fish is living in and that it is necessary to collect habitat use and availability data in a wide range of stream types to define optimal habitat and suitability criteria for generalised application.     

Diel changes in the abundance and size composition of invertebrate drift in five rivers in South Island,New Zealand

Drift was collected over 24‐h periods in five rivers in South Island, New Zealand, to determine whether diel periodicity was consistent across a range of river types, and whether the pattern was similar for different life stages/sizes of selected taxa. Total drift density (numbers per 100 m³ ) of aquatic invertebrates was greater at night than during the day in all rivers; peak abundance occurred shortly after sunset in clear water rivers and shortly before sunrise in a turbid, glacier‐fed river. Densities of drifting Deleatidium spp., Nesameletus spp. (both Ephemeroptera), Aoteapsyche spp., and Hydrobiosidae (both Trichoptera), were generally greater at night than during the day. However, the timing of peak abundance in the drift for other common taxa varied between rivers. Larger Deleatidium spp. larvae (> 1.00 mm head width) were more common in the drift at night than during the day in all rivers. However, this was not apparent for Aoteapsyche spp. and Hydrobiosidae, for which diel differences in the size of drifting animals were not consistent even within the same river. The propensity for some aquatic invertebrates to drift at night may influence fish feeding behaviour, particularly with respect to the timing of feeding and the species or life history stages of their prey.     

Fine‐scale patterns in the day,night and crepuscular composition of a temperate reef fish assemblage

The distribution, abundance and composition of marine fish assemblages are influenced by changes in behaviour and movement associated with the diel cycle. The majority of studies exploring day–night differences have demonstrated that there is a greater abundance and diversity of fishes during diurnal compared with nocturnal hours, and that fish assemblage composition varies with time of day or night. We investigated fine‐scale (hourly) diel cycles in the composition and relative abundance of temperate reef fishes using unbaited remote underwater video systems. We observed short crepuscular changeover periods with the hours around dawn and dusk sharing many species, some of which are nocturnal and others diurnal. Diurnal surveys recorded a greater number of individuals (16,990) and species (70) than nocturnal surveys (1053 individuals and 19 species). There was a clear difference between the diurnal assemblage, which was characterized by benthic invertivores, and the nocturnal assemblage composition, which contained zooplanktivores and generalist feeders. Within the diurnal period the hourly temporal variation was relatively homogenous, indicating that standardization of diurnal sampling to a particular time of day may not be necessary.     

Influence of tidal regime,diurnal phase,habitat and season on feeding of an intertidal crab

The relationship between diet and feeding activity of intertidal crabs, and environmental cycles (tidal, daily and seasonal), habitat and level of the intertidal zone (high/low) was studied using Neohelice granulata (Brachyura, Varunidae) as a model. This is a semi‐terrestrial burrowing crab occupying different habitats in the Southwestern Atlantic coasts and estuaries from bare low intertidal mudflats to high intertidal salt marshes, and from fine, organic matter rich sediment to very coarse sediment with low content of organic matter. The study was carried out in two contrasting habitats of three sites with diverse sets of physical and biological conditions. Diet and feeding of adult N. granulata were indirectly studied through the proportion of food items and the presence/absence of food in crab stomachs, respectively. This species has a dual mode of feeding: predominantly herbivorous (live plants or plant litter in salt marshes) or deposit feeder (superficial sediment and detritus in mudflats), but the quantity and quality of ingested food varies among habitats and sites. A trend to omnivory (including algae and conspecifics) was detected in relation to low quality of resources. Feeding activity modulated by a complex interaction of factors varied according to spatial and/or temporal changes in some natural cycles. Males and non‐ovigerous females fed preferably after dark and during submersion periods, but also after emersion periods if mudflat sediment remained wet; salt marsh crab feeding is somewhat independent of light and tidal cycles. Ovigerous females almost never fed. Both diet and feeding activity of this crab seem to be flexible traits adapted to different combinations of physical and biological factors.     

湛江硇洲岛文昌鱼(Branchiostoma belcheri)的食性研究

于2006年4~7月在湛江硇洲岛海域采集文昌鱼,进行春夏季节不同性别、不同体长组等的胃含物观察分析。结果表明,湛江硇洲岛文昌鱼消化道残留食物成分以泥沙碎屑为主,可辨生物成分有34种,大部分为底栖硅藻,占58.8%,也有少量甲藻、瓣鳃类幼虫、底栖桡足类幼虫和原生动物等。春夏季节的文昌鱼的摄食喜好不尽相同,饵料生物的出现率随着季节的变化有所变化。不同性别文昌鱼的摄食喜好比较相近。文昌鱼到了性腺成熟后才开始进食动物性食物。研究结果表明,文昌鱼摄食藻类、微生物等而自身转化为其他动物的较高营养层次食物,在海洋食物网中具有一定的重要作用。     

Variations in the Number of Intestinal Loops in Scaphopoda (Mollusca)

Abstract. The intestinal loops of two species of the genus Bathoxiphus (Entalinidae) and of Cadulus aberrans (Gadilidae) have been reconstructed from serial sections. The results are compared to the 'textbook scaphopod' Antalis dentalis having the hindgut coiled in three loops. Bathoxiphus ensiculus has four or five intestinal loops, B. sp. S 153 four, and C. aberrans two. The buccal pouch contents included Foraminifera in all species, with agglomerates of sediment being found only in Bathoxiphus and Antalis. The mean ratio of intestinal length to body length ranges from 1.05 in B. ensiculus , over 0.98 in the four-looped B. sp. S 153, to 0.7 in A. dentalis and 0.6 in the twice-looped C. aberrans. The correlation of intestinal length with diet—additional deposit-feeding in Bathoxiphus and highly specialized 'carnivory' in C. aberrans —is probable. Despite the differences in feeding ecology, the elongated hindgut of both deep-sea species of Bathoxiphus resembles the adaptations of some bivalves to poorly nutritious deep-sea sediments.     

冬季大连砂质潮间带自由生活海洋线虫群落结构及多样性的比较

本研究于2015年12月在濒临渤海的大连夏家河子沙滩和濒临黄海的大连金沙滩采集海洋线虫样品,对两处砂质潮间带海洋线虫群落结构及多样性特征进行了研究。研究结果表明,两处砂质潮间带海洋线虫丰度、优势种、摄食结构及多样性差异显著。夏家河子海洋线虫平均丰度为(592.0±318.9) ind./(10 cm²),金沙滩海洋线虫平均丰度为(54.6±53.8) ind./(10 cm²),显著低于夏家河子。共鉴定海洋线虫43种,共有种13个。夏家河子沙滩海洋线虫优势种为Daptonema sp.1、Daptonema sp.2、Theristus sp.1、Setosabatieria sp.1、Prochromadorella sp.1、Daptonema sp.3、Paracyatholaimus sp.1、Sabatieria breviseta,以非选择性沉积食性线虫为主;金沙滩海洋线虫优势种为Oncholaimus sp.1、Chromadorita sp.1、Theristus sp.2, Neochromadora sp.1、Enoplus sp.1、Prochromadorella sp.1,以杂食性或捕食性线虫为主。两处砂质潮间带海洋线虫种数S、丰富度指数d和香农−威纳多样性指数H'存在极显著的差异,其值均表现为夏家河子显著高于金沙滩。相似性分析结果显示,两处沙滩的海洋线虫群落结构存在显著差异。间隙水pH、沉积物有机质含量及中值粒径是引起海洋线虫群落结构及多样性差异的主要因子,其中,沉积物中值粒径对线虫群落特征的影响最为突出。就两处沙滩潮区差异而言,受沉积物粒径特征及pH的影响,夏家河子海洋线虫群落特征在不同潮区之间也存在差异,其低潮带海洋线虫多样性高于高、中潮带,杂食者和捕食者丰度高,反映其海洋线虫群落结构较复杂。金沙滩不同潮区的环境因子无显著差异,线虫群落结构及多样性潮区差异不显著,较为均一。此外,水动力对海洋线虫群落结构沙滩差异和潮区差异也产生重要影响。一方面,水动力通过影响不同粒径沉积物的沉积影响海洋线虫群落特征;另一方面,水动力可影响线虫的分散性,进而对其潮区分布产生影响。     

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.     

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.