鮸鱼幼鱼在不同水温下摄食的初步研究

以冰鲜桡足类为饵料对鮸鱼幼鱼在不同水温时的摄食进行了研究.在水温10、15和20℃时,幼鱼消化道饵料系数和食物消化时间呈线性回归方程,曲线斜率为食物消化速度;消化时间各为16、19和12h;摄食率各为100%、100%和85%;消化道饵料系数均在45-60min之内达到最大值;饱食系数各为3.11%、7.84%和8.42%;提出鮸鱼幼鱼的日摄食量指数公式为:日摄食指数=饱食系数 (12×消化道饵料系数与消化时间曲线方程一次项系数),得到日摄食量指数各为5.92%、15.19%和22.29%.     

三亚湾秋季桡足类分布与种类组成及对浮游植物现存量的摄食压力

秋季(11月底),桡足类针刺拟哲水蚤(Paracalanusaculeatus)和拟哲水蚤(Paracalanus)幼体为三亚湾优势种;强额孔雀哲水蚤(Pavocalanuscrassirostris)对浮游植物现存量的平均日摄食压力最大,各站平均为叶绿素a的(6.79±6.82)%,其次是针刺拟哲水蚤,平均为(5.97±5.67)%,亚强次真哲水蚤(Subeucalanussubcrassus)对浮游植物现存量的摄食压力较低,平均为(2.20±2.33)%,桡足类在秋季对浮游植物的日摄食压力占叶绿素a的(22.31±18.92)%。三亚湾属于生产力偏低的海区,对初级生产力的摄食压力以中型浮游动物针刺拟哲水蚤、锯缘拟哲水蚤(Paracalanusserrulus)、红纺锤水蚤(Acartiaerythraea)、微驼背隆哲水蚤(Acro calanusgracilis)和驼背隆哲水蚤(Acrocalanusgibber)为主,小型浮游动物的摄食压力也占一定的比例。     

Seasonality of occurrence,foods and food preferences of ichthyoplankton in Biscayne Bay,Florida

Ichthyoplankton and microzooplankton were collected twice monthly for one year at a single station in Biscayne Bay, Florida. Based on approximate 10-m³, 333-μm mesh bongo net samples, the mean annual densities were 17·7 m^?3 and 1·8 m^?3 for fish eggs and larvae, respectively. Ichthyoplankton was most abundant in spring-summer. The most common fish larvae were bay anchovy (Anchoa mitchilli), spotted dragonet (Callionymus pauciradiatus), thread herring (Opisthonema oglinum) and gobies (Gobiidae), which comprised 50% of all larvae collected. A comparison of 35-μm and 333-μm mesh, bongo net collections revealed that mean densities of fish larvae were 8·5 times higher in the smaller mesh. The most abundant microzooplankton, based on 35-μm bongo net collections, were copepod nauplii, <100 μm in width, which averaged 90·41^?1 and tintinnids which averaged 168·51^?1. The mean density of microzooplankton <100 μm wide, potentially suitable food for first-feeding fish larvae, was 104·91^?1, exclusive of tintinnids, and 273·41^?1 including tintinninds. Excepting tintinnids, seasonal variability in microzooplankton abundance was low relative to that for ichthyoplankton. High microzooplankton densities, combined with low seasonal variability, indicated that feeding conditions for fish larvae were usually good in Biscayne Bay. Copepods, especially nauplii, were the predominant food of fish larvae (71% of all food items). Only mollusc veliger larvae (18% of all food items) were highly preferred prey but they were a small component of most larval fish diets. Average width of prey eaten by first-feeding larvae was 74 μm. Prey size increased in relation to larval length.     

Responses to Predation Cues and Food in Two Species of Sympatric, Tropical Sea Urchins

Abstract. We examined the responses of two tropical sea urchins, Lytechinus variegatus and Tripneustes ventricosus, to cues from predators, simulated predation events and food. Cues released from damaged conspecifics, heterospecifics and heteroclassics (holothurian) were used to simulate predation events in field experiments. Responses to the presence of seagrass, spiny lobster or both were tested in tanks. Findings were supplemented by natural history observations of dispersion patterns off Bermuda. In field experiments, neither species formed groupings in the presence of conspecific, heterospecific or heteroclassic cues. Flight responses were greatest in conspecific treatments; responses to heterospecific cues were intermediate to control and conspecific cues. Urchins in pre‐assembled associations remained in groups in control trials but dispersed when exposed to predation cues. Lytechinus exhibited greater sensitivity to predation cues than Tripneustes. Cues from a damaged sea cucumber invoked a response from Lytechinus but not Tripneustes. Both species employed a two phased response to cues from damaged conspecifics: initially a rapid, but ephemeral (2 min), alarm response followed by a slower (≈ 35 % lower) sustained flight phase for 6+ min, which in nature would disperse urchins downstream and away from a predator. In tank experiments, Lytechinus formed groupings only around food or food + predators. The presence of a predator reduced the aggregation response to food, suggesting that Lytechinus employed a risk aversion strategy. Tripneustes exhibited escape or refractory behavior in both control and experimental treatments in laboratory tanks.     

Water Quality Improvements in Liverpool Docks: The Role of Filter Feeders in Algal and Nutrient Dynamics

Abstract. The redevelopment of disused docks around Liverpool into areas suitable for shops, offices, housing and recreational watersports has necessitated the maintenance of good water quality in these areas. The main source of water to the docks is the River Mersey, which contains high concentrations of nutrients, encouraging algal blooms - including potentially nuisance species - in the enclosed dock basins. Since 1988 an extensive monitoring programme has been run sampling the hydrography, plankton and benthos of the docks. During this period there has been an improvement in water quality, including a reduction in summer phytoplankton biomass and anoxic bottom water. There are strong indications that phytoplankton biomass has been severely reduced by the filter feeding of Mytifus edulis . Changes in the composition of the benthic community since 1988 suggest that the large population of M. edulis is now suffering from limited recruitment. The long-term development and stability of the system is discussed with reference to community succession and its link to ecosystem functioning.     

An Experimental Investigation of the Palatability of Kelp Bed Algae to the Sea Urchin Parechinus angulosus LESKE

Abstract. The relative palatability of 13 algae common in the kelp beds of the west coast of the Cape Peninsula, South Africa, is experimentally investigated with respect to feeding by the sea urchin Parechinus angulosus.
We investigated 2 hypotheses: 1) that this important herbivore would feed selectively on these algae and 2) that Desmarestia firma, one of these algae, would be unattractive to Parechinus on account of the H₂S0₄ in the thallus.
Algal preferences are determined from 3 types of feeding experiment, results of which support our first hypothesis, and allow us to group the algae into 3 arbitrary categories: "preferred", "intermediate", and "non-preferred". To explain these patterns, we measured "relative astringen-cy" of each species (essentially a phenol measurement), and phenol content of 4 species (FOUN-DENIS method). Rates of feeding on single species are negatively correlated with relative astringen-cies (r = 0.76, P = 0.99). The high relative astringency of D. firma is caused by its high (18 % per dry mass) H₂S0₄ content, and it is non-preferred. Our results therefore support our second hypothesis. Other implications of these results are discussed.     

Diel Fluctuations of a Shallow Water Fish Community in the Inner Oslofjord, Norway

Abstract. A shallow water fish community in the inner Oslofjord, Norway, was sampled with a beach seine at 4h intervals over two 36 h periods (25-26th May and 28-29th September, 1982). Night length varied from 1 h in May to 11 h in September. Differences in the community composition were observed between May and September. The diversity of the fish community changed between the two months although the interpretation of the change was dependent on the method used to analyse the community. The three dominant species ( Gasterosteus aculeatus, Sprattus sprattus , and Ammodytes tobianus ) showed diel variations in catch rate which were out of phase with each other. The percentage overlap in abundance of the dominant species was low. The summation of the individual periodicities resulted in aperiodicity at the community level. There were fluctuations, over a diel cycle, in all the community parameters (number of individuals, number of species, species diversity [H'J, species richness [D] and evenness [J']) which affect measures of resource partitioning in fish communities and which should therefore be considered in ecological studies. Diel fluctuations in abundance of some individual shallow water species varied between seasons causing problems in population estimates.     

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.