Adenylate energy charge: A possible trophic index for management of oyster intensive aquaculture

• 1.1. O. edulis and C. gigas both exhibit a seasonal variation in AEC with minimum values in summer. Two factors, food and temperature, were examined to explain these low summer values.
• 2.2. The AEC level varied with food level but a seasonal pattern was still observed. Two age groups of oysters were tested, giving a similar response.
• 3.3. The effect of temperature on the seasonal variations in AEC was confirmed by a significant correlation between AEC and temperature. This relationship allows us to calculate an AEC standard that only retains the trophic information.
• 4.4. Different trophic levels were identified in Marennes-Oléron Bay with AEC standard but growth rate was not related to them. So, AEC may inform on the carrying capacity of a given area but does not predict growth performances which will depend on other parameters.

     

基于稳定同位素技术的海州湾海洋牧场食物网基础及营养结构的季节性变化

基于稳定同位素技术对2015年春季海州湾海洋牧场海域采集的中小型生物消费者,包括鱼类、虾类、蟹类、头足类、螺类和双壳类等与其潜在碳源样品进行分析,利用IsoSource模型计算该海域消费者碳源贡献率,并对2014年夏季生物学样品与2015年春季样品比较,分析食物网营养结构的季节性变化,根据稳定同位素测定结果绘制二维双标图,计算出6种营养结构的量化指标.结果表明: 2015年春季海州湾海洋牧场海域消费者的δ¹³C值范围为-18.9‰～-17.1‰,3种潜在碳源[浮游植物、悬浮颗粒有机物(POM)、沉积物(SOM)]的δ¹³C值范围为-18.1‰～-23.4‰,根据模型计算得出浮游植物对消费者的平均碳源贡献最大,为80.8%,其余依次为SOM和POM,分别为10.8%和8.4%.2014年夏季生物样品与2015年春季样品的δ¹³C值存在显著差异,而δ¹⁵N值无显著性差异;6种量化指标表明群落营养结构存在季节性差异, 2014年夏季的δ¹³C比值范围(CR)、总面积(TA)、平均最邻近距离(NND)和平均最邻近距离标准差(SDNND)均大于2015年春季,δ¹⁵N比值范围(NR)和平均离心距离(CD)无明显变化,夏季群落营养结构冗余度小于春季,且食源多样性水平高于春季,存在季节差异.     

Disruption of seasonality in growth hormone-transgenic coho salmon (Oncorhynchus kisutch) and the role of cholecystokinin in seasonal feeding behavior

Seasonal variation in daily food intake is a well-documented phenomenon in many organisms including wild-type coho salmon where the appetite is noticeably reduced during periods of decreased day length and low water temperature. This reduction may in part be explained by altered production of cholecystokinin (CCK) and growth hormone (GH). CCK is a hormone produced in the brain and gut that mediates a feeling of satiety and thus has an inhibitory effect on food intake and foraging behaviour. Growth hormone (GH) enhances feeding behaviour and consequently growth, but its production is reduced during winter. The objectives of this study were: first, to compare the seasonal feeding behaviour of wild and GH-transgenic coho salmon; second, to determine the behavioural effect of blocking the action of CCK (by using devazepide) on the seasonal food intake; and third, to measure CCK expression in brain and gut tissues between the two genotypes across seasons. We found that, in contrast to wild salmon, food intake in transgenic salmon was not reduced during winter indicating that seasonal control of appetite regulation has been disrupted by constitutive production of GH in transgenic animals. Blocking of CCK increased food intake in both genotypes in all seasons. The increase was stronger in wild genotypes than transgenic fish; however blocking CCK in wild-type fish in winter did not elevate appetites to levels observed in the summer. The response to devazepide was generally faster in transgenic than in wild salmon with more rapid effects observed during summer than during winter, possibly due to a higher temperature in summer. Overall, a seasonal effect on CCK mRNA levels was observed in telencephalon with levels during winter being higher compared to the summer in wild fish, but with no seasonal effect in transgenic fish. No differences in seasonal CCK expression were found in hypothalamus. Higher levels of CCK were detected in the gut of both genotypes in winter compared to summer. Thus, CCK appears to mediate food intake among seasons in both wild-type and GH-transgenic salmon, and an altered CCK regulation may be responsible at least in part for the seasonal regulation of food intake.     

基于稳定同位素方法的闽江口常见鱼类群落营养结构的季节性变化

为了解闽江口常见鱼类群落的营养结构特征,于2015年冬季(1月)、春季(5月)、夏季(8月)、秋季(11月)采集闽江口底拖网渔业资源样品,利用稳定同位素分析闽江口常见鱼类群落营养结构特征及其季节性变化,并计算了基于δ¹³C-δ¹⁵N量化的7个营养结构的群落范围指标.结果表明: 闽江口常见鱼类群落除夏季和秋季的δ¹³C值之间不存在显著性差异,其余各季节之间δ¹³C值均差异显著;δ¹⁵N值春季与其余3个季节都表现出显著性差异,而其余3个季节δ¹⁵N值互相之间均无显著性差异.稳定同位素的量化指标表明: 闽江口常见鱼类群落的营养结构存在季节差异,春季的生态位总空间(TA)、核心生态位空间(SEAc)、鱼类基础食物来源(CR)、营养长度(NR)、鱼类营养多样性(CD)均为四季的最大值;从夏季至秋季再到冬季,生态位总空间(TA)、核心生态位空间(SEAc)、鱼类基础食物来源(CR)、营养长度(NR)、鱼类营养多样性(CD)和营养位置差异(MNND)均逐步上升.闽江口常见鱼类群落营养结构的季节差异可能与鱼类生殖洄游和群落内食源多样性的变化密切相关.     

Water temperature determines strength of top-down control in a stream food web

1. We examined effects of water temperature on the community structure of a three trophic level food chain (predatory fish, herbivorous caddisfly larvae and periphyton) in boreal streams. We used laboratory experiments to examine (i) the effects of water temperature on feeding activities of fish and caddisfly larvae and on periphyton productivity, to evaluate the thermal effects on each trophic level (species‐level experiment), and (ii) the effects of water temperature on predation pressure of fish on abundance of the lower trophic levels, to evaluate how temperature affects top‐down control by fish (community‐level experiment). 2. In the species‐level experiment, feeding activity of fish was high at 12 °C, which coincides with the mean summer temperature in forested streams of Hokkaido, Japan, but was depressed at 3 °C, which coincides with the mean winter temperature, and also above 18 °C, which coincides with the near maximum summer temperatures. Periphyton productivity increased over the range of water temperatures. 3. In the community‐level experiments, a top‐down effect of fish on the abundance of caddisfly larvae and periphyton was clear at 12 °C. This effect was not observed at 3 and 21 °C because of low predation pressure of fish at these temperatures. 4. These experiments revealed that trophic cascading effects may vary with temperature even in the presence of abundant predators. Physiological depression of predators because of thermal stress can alter top‐down control and lead to changes in community structure. 5. We suggest that thermal habitat alteration can change food web structure via combinations of direct and indirect trophic interactions.     

Use of Metabolic Inhibitors to Characterize Ecological Interactions in an Estuarine Microbial Food Web

Understanding microbial food web dynamics is complicated by the multitude of competitive or interdependent trophic interactions involved in material and energy flow. Metabolic inhibitors can be used to gain information on the relative importance of trophic pathways by uncoupling selected microbial components and examining the net effect on ecosystem structure and function. A eukaryotic growth inhibitor (cycloheximide), a prokaryotic growth inhibitor (antibiotic mixture), and an inhibitor of photosynthesis (DCMU) were used to examine the trophodynamics of microbial communities from the tidal creek in North Inlet, a salt marsh estuary near Georgetown, South Carolina. Natural microbial communities were collected in the spring, summer, and fall after colonization onto polyurethane foam substrates deployed in the tidal creek. Bacterial abundance and productivity, heterotrophic ciliate and flagellate abundance, and phototrophic productivity, biomass, and biovolume were measured at five time points after inhibitor additions. The trophic responses of the estuarine microbial food web to metabolic inhibitors varied with season. In the summer, a close interdependency among phototrophs, bacteria, and protozoa was indicated, and the important influence of microzooplanktonic nutrient recycling was evident (i.e., a positive feedback loop). In the fall, phototroph and bacteria interactions were competitive rather than interdependent, and grazer nutrient regeneration did not appear to be an important regulatory factor for bacterial or phototrophic activities. The results indicate a seasonal shift in microbial food web structure and function in North Inlet, from a summer community characterized by microbial loop dynamics to a more linear trophic system in the fall. This study stresses the important role of microbial loops in driving primary and secondary production in estuaries such as North Inlet that are tidally dominated by fluctuations in nutrient supply and a summer phytoplankton bloom.     

Participation of lysine-sensitive aspartokinase in threonine production by S-2-aminoethyl cysteine-resistant mutants of Serratia marcescens.

S-2-Aminoethyl cysteine (AEC) reduced both growth rate and final growth level of Serratia marcescens Sr41. The growth inhibition was completely reversed by lysine. AEC inhibited the activity of lysine-sensitive aspartokinase to a lesser extent than lysine. The AEC addition to the medium lowered not only the level of lysine-sensite aspartokinase but also those of homoserine dehydrogenase and threonine deaminase, whereas lysine repressed the aspartokinase alone. To select mutations releasing lysine-sensitive aspartokinase from feedback controls, AEC-resistant colonies were isolated from strains HNr31 and HNr53, both of which were previously found to excrete threonine on the minimal plates but not on the plates containing excess lysine. Two of 280 resistant colonies excreted large amounts of threonine. Strains AECr174 and AECr301, derived from strains HNr31 and HNr53, respectively, lacked both feedback inhibition and repression of lysine-sensitive aspartokinase. These strains produced about 7 mg of threonine per ml in the medium containing glucose and urea.     

Metabolic rate and food availability of the Antarctic amphipod <Emphasis Type="Italic">Gondogeneia antarctica</Emphasis> (Chevreux 1906): seasonal variation in allometric scaling and temperature dependence

Among the few existing works on seasonal variation in metabolic rate of polar species, most have been conducted during summer due to logistic constraints and have been focused on species that cease feeding during winter. In this work, we present the first extensive data set on the seasonal variation in metabolic rate of G. antarctica, an abundant amphipod that feeds throughout the year, and its relationship with body size, potential food availability and temperature. We measured the resting metabolic rate (RMR) of groups of individuals during 6 months from late summer through winter at 4 experimental temperatures and for a wide range of body size. RMR had a negative allometric scaling with body size and showed a tendency to increase with temperature as expected. However, temperature and body size effects on RMR showed a significant temporal variation, and an increase in temperature decreased scaling exponents. RMR at the mean seawater temperature throughout the study showed a strong seasonal variation following food availability: RMR decreased from the end of summer through winter, coinciding with a reduction in microphytobenthos stock, but recovered summer values in August, when an epontic algae boom occurred. The seasonal factorial aerobic scope (×2.37) is lower than benthic Antarctic invertebrates that cease feeding during winter, in agreement with what is expected based on theoretical grounds. Results suggest that seasonal variation of RMR would allow G. antarctica to achieve a high efficiency in energy utilization, while maintaining the ability to exploit sudden changes in food supply.     

不同时期北部湾日本带鱼营养生态位差异

基于2008—2009年和2018年对北部湾日本带鱼的采样,通过测定碳氮稳定同位素,计算其营养级、营养生态位等指标,对比分析10年前后日本带鱼营养生态位的差异,探究其生态适应能力的变动。结果表明: 2个时期北部湾日本带鱼碳稳定同位素(δ¹³C)值差异明显,2018年δ¹³C值范围变窄,平均值变小,推测日本带鱼食物来源由偏中上层向偏中下层水域转变;氮稳定同位素(δ¹⁵N)值的范围和平均值基本保持不变,营养级范围和平均值(3.38和3.43)变化不明显,说明近10年来北部湾日本带鱼在生态系统中的营养层次比较稳定。日本带鱼δ¹³C值与肛长相关性不显著,δ¹⁵N则为极显著正相关性。在营养生态位方面,2018年的生态位指标均出现不同程度的下降,下降幅度的范围为1.1%~32.1%;生态位总面积和核心生态位面积分别由20.20和4.68缩小至14.20和3.18,说明北部湾日本带鱼的营养生态位发生了显著变化,对资源利用能力和环境适应能力下降。推测,10年来北部湾日本带鱼的营养级变化不明显,但由于食物来源发生变化,营养来源多样性下降,营养生态位变小。     

Participation of lysine-sensitive aspartokinase in threonine production by S-2-aminoethyl cysteine-resistant mutants of Serratia marcescens.

S-2-Aminoethyl cysteine (AEC) reduced both growth rate and final growth level of Serratia marcescens Sr41. The growth inhibition was completely reversed by lysine. AEC inhibited the activity of lysine-sensitive aspartokinase to a lesser extent than lysine. The AEC addition to the medium lowered not only the level of lysine-sensite aspartokinase but also those of homoserine dehydrogenase and threonine deaminase, whereas lysine repressed the aspartokinase alone. To select mutations releasing lysine-sensitive aspartokinase from feedback controls, AEC-resistant colonies were isolated from strains HNr31 and HNr53, both of which were previously found to excrete threonine on the minimal plates but not on the plates containing excess lysine. Two of 280 resistant colonies excreted large amounts of threonine. Strains AECr174 and AECr301, derived from strains HNr31 and HNr53, respectively, lacked both feedback inhibition and repression of lysine-sensitive aspartokinase. These strains produced about 7 mg of threonine per ml in the medium containing glucose and urea.     

The relative influence of temperature and food on the metabolism of a marine invertebrate

Many benthic marine invertebrates exhibit a seasonal cycle in activities such as feeding, growth and reproduction. In temperate regions, this seasonality is typically correlated with coincident cycles in photoperiod, temperature and food availability and it can be difficult to determine which of these environmental factors is the key driver. Polar regions are characterised by greatly reduced seasonal variation in temperature, and an enhanced seasonality of food availability; they therefore form a natural laboratory for distinguishing the ecological effects of food from those of temperature. Here, we report a study of the common shallow water urchin Sterechinus neumayeri from Rothera Point, Antarctica. This species exhibits a marked seasonal variation in metabolic rate and feeding activity (which ceases completely in winter). In this study the metabolic rate of urchins collected in late winter and held in the laboratory without food was compared with that of wild urchins undertaking the transition to summer feeding and growth. Starved urchins showed a small rise in metabolic rate in summer which could be explained entirely by the small increase in temperature (Q(10)=2.5). At the same time, the wild population showed a much larger increase in metabolic rate related largely to the costs of feeding and growth. Rates of nitrogen excretion were also much larger in wild urchins, and the O:N atomic ratio indicated that starved urchins were depending to a greater extent on lipid and carbohydrate. Gut mass and test organic content showed no change in starved urchins, indicating that metabolic substrate was being provided by the gonad. The data suggest that in wild S. neumayeri only 15-20% of the summer increase in metabolism is caused directly by the temperature rise whereas 80-85% is caused by increased physiological activity associated with feeding, growth and spawning.     

Influence of seston quantity and quality on growth of tropical cladocerans.

The seston of the small, shallow, and tropical lake Monte Alegre was tested for quantity and quality for cladocerans by growth bioassays, which were carried out in spring (Daphnia gessneri and Moina micrura), summer (D. gessneri, M. micrura, Ceriodaphnia cornuta, and Simocephalus mixtus), and winter (D. gessneri and D. ambigua). Cohorts of newborns originating from ovigerous females collected in the lake or from laboratory cultures were submitted, at a room temperature of 23 degrees C to the following treatments: (1) the chlorophytes Ankistrodesmus falcatus and/or Scenedesmus spinosus; (2) lake seston; and (3) lake seston + chlorophytes. Growth rate, clutch size, and fecundity were evaluated. Seston alone was not the best food for promoting cladoceran growth. There were seasonal differences in food quantity and quality with spring and summer seston being better for growth than that of the winter. Adding chlorophytes to the seston increased clutch size and fecundity for most species in summer and winter, but not in spring. Energy limitation seems to be the most important factor influencing cladoceran growth in summer and especially in winter.     

Seasonal variation in top-down and bottom-up processes in a grassland arthropod community

Both top-down and bottom-up processes are common in terrestrial ecosystems, but how these opposing forces interact and vary over time is poorly understood. We tested the variation of these processes over seasonal time in a natural temperate zone grassland, a field site characterized by strong seasonal changes in abiotic and biotic conditions. Separate factorial experiments manipulating nutrients and cursorial spiders were performed in the wet and dry seasons. We also performed a water-addition experiment during the summer (dry season) to determine the degree of water limitation during this time. In the spring, nutrient addition increased plant growth and carnivore abundance, indicating a bottom-up control process. Among herbivores, sap-feeders were significantly enhanced while grazers significantly declined resulting in no net change in herbivore abundance. In the summer, water limitation was predominant increasing plants and all herbivores while nutrient (N) effects were non-significant. Top-down processes were present only in the spring season and only impacted the guild of grazing herbivores. These results show that bottom-up limitation is present throughout the season in this grassland, although the specific limiting resource changes as the season progresses. Bottom-up processes affected all trophic levels and many different guilds, while top-down effects were limited to a select group of herbivores and did not extend to the plant trophic level. Our results show that the relative strengths of top-down and bottom-up processes can shift over relatively short periods of time in habitats with a strong seasonal component.     

Application of a bioenergetics model for analysis of growth and food consumption of subarctic whitefish Coregonus lavaretus (L.) in Lake Kilpisjärvi, Finnish Lapland

A bioenergetics model was used to estimate daily food consumption and growth of benthic whitefish Coregonus lavaretus (L.) of age groups 1+ to 10+, in oligotrophic Lake Kilpisjärvi, northern Finnish Lapland. Fish and zooplankton samples and water temperature data were collected twice per month from February to December 1993. Simulation results indicated wide seasonal variations in consumption and growth rates. Growth was in general slow; especially in age-group 6 the net increase in weight was slight. The fit of the model to the weight data was good, and the model was able to follow even rapid seasonal variations in the weight. There were clear changes in the diet during the year. In March, when the food intake was reduced, copepods, mainly adult calanoids, formed the bulk of the food consumed. The most intensive consumption period lasted from June to late September. Chironomid pupae and planktonic cladocerans were the major summer food items. The largest individuals fed mainly on molluscs during summer. Zooplankton survey and consumption estimates did not show directly that the population density of copepodids and adults of Eudiaptomus graciloides were affected by whitefish predation although their population density decreased in spring. Nauplii, showing the maximum population density in April, were not consumed. The role of copepod consumption in the timing of Diphyllobothrium ditremum plerocercoid transmission to whitefish was also discussed. The increased copepod consumption rate during winter results in high energy intake but also an increased risk of food transmitted parasite infection.     

Hibernation in an antarctic fish: on ice for winter

Active metabolic suppression in anticipation of winter conditions has been demonstrated in species of mammals, birds, reptiles and amphibians, but not fish. This is because the reduction in metabolic rate in fish is directly proportional to the decrease in water temperature and they appear to be incapable of further suppressing their metabolic rate independently of temperature. However, the Antarctic fish (Notothenia coriiceps) is unusual because it undergoes winter metabolic suppression irrespective of water temperature. We assessed the seasonal ecological strategy by monitoring swimming activity, growth, feeding and heart rate (f(H)) in N. coriiceps as they free-ranged within sub-zero waters. The metabolic rate of wild fish was extrapolated from f(H )recordings, from oxygen consumption calibrations established in the laboratory prior to fish release. Throughout the summer months N. coriiceps spent a considerable proportion of its time foraging, resulting in a growth rate (G(w)) of 0.18 +/- 0.2% day(-1). In contrast, during winter much of the time was spent sedentary within a refuge and fish showed a net loss in G(w) (-0.05 +/- 0.05% day(-1)). Whilst inactive during winter, N. coriiceps displayed a very low f(H), reduced sensory and motor capabilities, and standard metabolic rate was one third lower than in summer. In a similar manner to other hibernating species, dormancy was interrupted with periodic arousals. These arousals, which lasted a few hours, occurred every 4-12 days. During arousal activity, f(H) and metabolism increased to summer levels. This endogenous suppression and activation of metabolic processes, independent of body temperature, demonstrates that N. coriiceps were effectively 'putting themselves on ice' during winter months until food resources improved. This study demonstrates that at least some fish species can enter a dormant state similar to hibernation that is not temperature driven and presumably provides seasonal energetic benefits.     

Temperature reaction norms of Daphnia magna: the effect of food concentration

1. The effects of temperature and food concentration on the fitness of Daphnia magna were tested in a 4×4 factorial flow-through design. Food ranged from 0.1 to 1.0 mg C L⁻¹ and temperature ranged from 15 to 30 °C. 2. The juvenile growth rate ( g _j) was used to construct reaction norms for temperature at varying food concentrations. Two clones isolated from the same pond at different seasons did not differ with respect to their temperature responses. Reaction norms had the shape of an optimum curve with highest values around 20 °C. There was a significant temperature–food interaction as the temperature response was most pronounced when the food was not limiting. 3. Differences in fitness were a consequence of different responses of physiological parameters to food and temperature. Age and size at first reproduction, as well as egg numbers, decreased with increasing temperature and decreasing food concentration. 4. As the temperature effect was strongest at the highest food concentrations, it can be concluded that environmental warming may affect D. magna more through a temperature rise earlier in spring rather than in summer.     

Seasonal population dynamics and trophic role of planktonic nanoflagellates in coastal surface waters of the Southern Baltic Sea

We investigated the temporal dynamics and trophic role of different nanoflagellates in surface waters of the Gulf of Gdańsk (Baltic Sea) between April and October 2007. Two 18S rRNA gene clone libraries were constructed from samples collected in spring and summer, and weekly changes in the abundances of five phylogenetic groups were studied by fluorescence in situ hybridization with newly designed probes. Stramenopiles affiliated with MAST‐6 and Pedinellales were most numerous in spring but rare in summer. Both groups formed short‐lived blooms during a sudden drop of salinity due to riverine influx (from 7.1 to 6.2 practical salinity units). The analysis of food vacuole content suggested that MAST‐6 nanoflagellates were herbivorous, whereas bacterivory was found both in plastidic and aplastidic pedinellid populations. Members of an uncultured lineage of aplastidic, bacterivorous cercozoans distantly related to Ebria tripartita were more abundant in summer when water temperatures exceeded 17°C. Multicellular trophonts and/or free‐living single cell stages of two lineages of Group 1 parasitic Syndiniales (alveolates) were present in spring and early summer. One of these alveolate populations repeatedly peaked before and after the freshwater influx, but was conspicuously absent throughout the period of decreased salinity. Our results indicate that nanoflagellate populations in coastal surface waters may form short‐lived blooms that can only be detected by high‐frequency sampling, and that may be related both to seasonal development and to sporadic (e.g. mixing) events. In view of their trophic diversity we moreover suggest that nanoflagellates in eutrophic coastal waters should not be regarded as a single functional unit.     

Nutrient Dynamics of Estuarine Invertebrates Are Shaped by Feeding Guild Rather than Seasonal River Flow

This study aimed to determine the variability of carbon and nitrogen elemental content, stoichiometry and diet proportions of invertebrates in two sub-tropical estuaries in South Africa experiencing seasonal changes in rainfall and river inflow. The elemental ratios and stable isotopes of abiotic sources, zooplankton and macrozoobenthos taxa were analyzed over a dry/wet seasonal cycle. Nutrient content (C, N) and stoichiometry of suspended particulate matter exhibited significant spatio-temporal variations in both estuaries, which were explained by the variability in river inflow. Sediment particulate matter (%C, %N and C:N) was also influenced by the variability in river flow but to a lesser extent. The nutrient content and ratios of the analyzed invertebrates did not significantly vary among seasons with the exception of the copepod Pseudodiaptomus spp. (C:N) and the tanaid Apseudes digitalis (%N, C:N). These changes did not track the seasonal variations of the suspended or sediment particulate matter. Our results suggest that invertebrates managed to maintain their stoichiometry independent of the seasonality in river flow. A significant variability in nitrogen content among estuarine invertebrates was recorded, with highest % N recorded from predators and lowest %N from detritivores. Due to the otherwise general lack of seasonal differences in elemental content and stoichiometry, feeding guild was a major factor shaping the nutrient dynamics of the estuarine invertebrates. The nutrient richer suspended particulate matter was the preferred food source over sediment particulate matter for most invertebrate consumers in many, but not all seasons. The most distinct preference for suspended POM as a food source was apparent from the temporarily open/closed system after the estuary had breached, highlighting the importance of river flow as a driver of invertebrate nutrient dynamics under extreme events conditions. Moreover, our data showed that estuarine invertebrates concentrated C and N between 10–100 fold from trophic level I (POM) to trophic level II (detritivores/deposit feeders) and thus highlighted their importance not only as links to higher trophic level organisms in the food web, but also as providers of a stoichiometrically homeostatic food source for such consumers. As climate change scenarios for the east coast of South Africa predict increased rainfall as a higher number of rainy days and days with higher rainfall, our results suggest that future changes in rainfall and river inflow will have measurable effects on the nutrient content and stoichiometry of food sources and possibly also in estuarine consumers.     

Seasonal Ichthyodiversity and Growth Patterns of Juvenile Flatfish on a Nursery Ground in the Southern Bight of the North Sea (France)

The demersal fish community on a flatfish nursery ground, of the Southern Bight of the North Sea, was sampled monthly between May 1998 and 1999. The studied coastal area is a multispecific nursery area. Although 32 fish species were caught, only nine species had a major influence on the variation in total densities through the year and can be considered as key species. Juvenile sole and plaice exhibited similar seasonal growth patterns with rapid growth during late spring and summer, a growth arrest during autumn and winter and a restart of growth in March. Comparisons of observed growth in length with predicted maximal growth under optimal food conditions suggested that during the summer, growth of 0-group sole and plaice was only determined by prevailing mean water temperature. During autumn and winter, while growth in length of sole followed model predictions, observed length of plaice was less than model predictions, suggesting growth limitation. Analyses of the factors that may be responsible for differences between observed and expected length growth indicated that autumn and winter growth arrest of plaice was not only related to low winter water temperature. It is suggested that for visual feeders such as plaice, the interaction of decreasing food availability and day length during autumn and winter can reduce the access to food resource and therefore feeding success and growth.     

厦门同安湾定置网捕获鱼类的多样性及营养级特征

利用2012年4月至2013年3月在同安湾进行的定置网渔业资源调查资料, 探讨了该海域鱼类多样性及平均营养级特征。结果表明, 周年逐月共鉴定鱼类112种, 隶属于15目53科88属。渔获物组成以沿岸小型底层鱼类为主, 其中中上层鱼类15种, 中下层鱼类18种, 底层鱼类79种; 暖水性种类84种, 暖温性种类28种, 亚热带动物区系特征明显; 杂食性鱼类8种, 低级肉食性鱼类71种, 中级肉食性鱼类30种, 高级肉食性鱼类3种, 以低级肉食性鱼类为主。中华海鲶(Tachysurus sinensis)是夏、秋、冬三季的优势种, 六指多指马鲅(Polydactylus sextarius)、锯脊塘鳢(Butis koilomatodon)和髭缟鰕虎鱼(Tridentiger barbatus)是春、冬两季的优势种。重量和尾数多样性指数最高值均在11月, 分别为3.26和3.29; 最低值均在2月, 分别为1.78和1.77。鱼类种类存在明显的季节更替现象, 其月更替率6月最低, 为40.1%; 3月最高, 达68.6%。鱼类平均营养级也存在明显的季节变化, 其中3月最低, 为3.02; 1月最高, 为3.92; 周年平均营养级为3.52。与2003年调查资料相比, 鱼类种类数明显减少, 鱼类组成和优势种发生了很大的变化, 导致变化的主要原因可能是过度捕捞、栖息地破坏和环境污染等。