Trophic interactions, ecosystem structure and function in the southern Yellow Sea

The southern Yellow Sea is an important fishing ground, providing abundant fishery resources. However, overfishing and climate change have caused a decline in the resource and damaged the ecosystem. We developed an ecosystem model to analyze the trophic interactions and ecosystem structure and function to guide sustainable development of the ecosystem. A trophic mass-balance model of the southern Yellow Sea during 2000–2001 was constructed using Ecopath with Ecosim software. We defined 22 important functional groups and studied their diet composition. The trophic levels of fish, shrimp, crabs, and cephalopods were between 2.78 and 4.39, and the mean trophic level of the fisheries was 3.24. The trophic flows within the food web occurred primarily in the lower trophic levels. The mean trophic transfer efficiency was 8.1%, of which 7.1% was from primary producers and 9.3% was from detritus within the ecosystem. The transfer efficiency between trophic levels II to III to IV to V to >V was 5.0%, 5.7%, 18.5%, and 19.7%–20.4%, respectively. Of the total flow, phytoplankton contributed 61% and detritus contributed 39%. Fishing is defined as a top predator within the ecosystem, and has a negative impact on most commercial species. Moreover, the ecosystem had a high gross efficiency of the fishery and a high value of primary production required to sustain the fishery. Together, our data suggest there is high fishing pressure in the southern Yellow Sea. Based on analysis of Odum’s ecological parameters, this ecosystem was at an immature stage. Our results provide some insights into the structure and development of this ecosystem.     

Preliminary analysis of the Jimo coastal ecosystem with the ecopath model

The Jimo coast encompasses an area of 2157 km~2, and the ecosystem is valuable both socially and economically with regional fisheries substantially contributing to the value. A mass-balanced trophic model consisting of 15 functional ecological groups was developed for the coastal ecosystem using the Ecopath model in Ecopath with Ecosim(Ew E) software(version 6.4.3). The results of the model simulations indicated that the trophic levels of the functional groups varied between 1.0 and 3.76, and the total production of the system was estimated to be 5112.733 t km~(-2) yr~(-1) with a total energy transfer efficiency of 17.6%. The proportion of the total flow originating from detritus was estimated to be 48%, whereas that from primary producers was 52%, indicating that the grazing food chain dominated the energy flow. The ratio of total primary productivity to total respiration in the system was 3.78, and the connectivity index was 0.4. The fin cycling index and the mean path length of the energy flow were 4.92% and 2.57%, respectively, which indicated that the ecosystem exhibits relatively low maturity and stability. The mixed trophic impact(MTI) procedure suggested that the ecological groups at lower trophic levels dominated the feeding dynamics in the Jimo coastal ecosystem. Overfishing is thought to be the primary reason for the degeneration of the Jimo coastal ecosystem, resulting in a decline in the abundance of pelagic and demersal fish species and a subsequent shift to the predominance of lower-trophic-level functional groups. Finally, we offered some recommendations for improving current fishery management practices.     

Compound-specific isotopes of fatty acids as indicators of trophic interactions in the East China Sea ecosystem

The composition and compound-specific isotopes of fatty acids were studied within food webs in the East China Sea.Lipid-normalized stable carbon isotopes of total organic carbon had a good correlation with trophic level.Variations in fatty acid compositions among different species were observed but were unclear.Different dietary structures could be traced from molecular isotopes of selected fatty acids in the Shiba shrimp(Matapenaeus joyneri),the coastal mud shrimp(Solenocera crassicomis) and the northern Maoxia shrimp(Acetes chinensis).Both M.joyneri and S.crassicomis are mainly benthos feeders,while A.chinensis is a pelagic species,although they have a similar fatty acid composition.There was a good correlation for isotopes of arachidonic acid(C20:4n6;ARA) and docosahexaenoic acid(C22:6n3;DHA)among pelagic species from higher trophic levels.The isotopic compositions of DHA in benthic species were more negative than those of pelagic species at the same trophic level.The fact that the diet of benthic species contains more degraded items,the carbon isotopes of which are derived from a large biochemical fraction,may be the reason for this variation.A comparative study of benthic and pelagic species demonstrated the different carbon sources in potential food items and the presence of a more complex system at the watersediment interface.     

Application of stable isotope techniques in studies of carbon and nitrogen biogeochemical cycles of ecosystem

Stable isotope techniques have been proved useful as tools for studying the carbon (C) and nitrogen (N) biogeochemical cycles of ecosystem. This paper firstly introduced the basic principles and the distribution characteristics of stable isotope, then reviewed the recent advances and applications of stable isotope in the C and N biogeochemical cycles of ecosystem. By applying the 13 C natural abundance technique, ecologists are able to understand the photosynthetic path and CO 2 fixation of plants, the CO 2 exchange and C balance status of ecosystem, the composition, distribution and turnover of soil organic C and the sources of organic matter in food webs, while by using the 13 C labeled technique, the effects of elevated CO 2 on the C processes of ecosystem and the sources and fate of organic matter in ecosystem can be revealed in detail. Differently, by applying the 15 N natural abundance technique, ecologists are able to analyze the biological N 2 -fixation, the N sources of ecosystem, the N transformation processes of ecosystem and the N trophic status in food webs, while by using the 15 N labeled technique, the sources, transformation and fate of N in ecosystem and the effects of N input on the ecosystem can be investigated in depth. The applications of both C and N isotope natural abundance and labeled techniques, combined with the elemental, other isotope ( 34 S) and molecular biomarker information, will be more propitious to the investigation of C and N cycle mechanisms. Finally, this paper concluded the problems existed in current researches, and put forward the perspective of stable isotope techniques in the studies on C and N biogeochemical cycles of ecosystem in the future.     

湖、库营养状况影响因素统计分析

采用常规统计方法,对影响湖、库营养状况的12项因素数据进行了分析。从因素数值在同一营养型内分布的稳定性、在不同营养型间的差异显著性以及因素彼此间的相关性出发,为各因素在湖、库营养型划分中的作用提供参考。结果表明,就所讨论的因素而言,浮游植物产量、总氮、有机物耗氧最为重要,浮游动物量、浮游植物现存量、无机氮、总磷有一定作用;pH盐量、活性磷无甚价值。     

Temporal and spatial distribution of virioplankton in large shallow freshwater lakes

Virioplankton dynamics at seven sample sites (from two freshwater lakes) with different trophic states were monitored over the period of a year. Water was sampled monthly from August 2004 to July 2005, and the abundances of viruses and bacteria were measured using direct epifluorescence microscopy counting. Results indicated that both natural and anthropogenic factors could influence the distribution of virioplankton. Temporally, viral abundance was significantly correlated to bacterial density and water temperature. Spatially, viral abundance was significantly correlated to trophic state. This in turn indicated that viral abundance was directly dependant on host abundance in eutrophic lakes, while trophic state and temperature could drive the distribution of virioplankton. The virus-bacteria ratio was significantly lower in less productive water-bodies. The result implied that the control of virioplankton on their hosts may change according to the host density.     

Estimating the budgets of nutrients for phytoplankton bloom in the central Yellow Sea using a modified lower tropic ecosystem model

A modified lower trophic ecosystem model (NEMURO) is coupled with a three-dimensional hydrodynamic model for an application in the central Yellow Sea. The model is used to simulate the horizontal distributions and annual cycles of chlorophyll-a and nutrients with results consistent with historical observations. Generally, during the winter background and spring bloom periods, the exchange with neighboring waters constitutes the primary sources of nutrients. Howerver, during the winter background period, the input of silicate from the layer deeper than 50 m is the most important source that contributes up to 60% to the total sources. During the spring bloom period, the transport across the thermocline makes significant contribution to the input of phosphate and silicate. During the post spring bloom period, the relative contribution of relevant processes varies for different nutrients. For ammonium, atmospheric deposition, excretion of zooplankton and decomposition of particulate and dissolved nitrogen make similar contributions. For phosphate and silicate, the dominant input is the transport across the thermocline, accounting for 62% and 68% of the total sources, respectively. The N/P ratio averaged annually and over the whole southern Yellow Sea is up to 51.8, indicating the potential of P limitation in this region. The important influence of large scale sea water circulation is revealed by both the estimated fluxes and the corresponding N/P ratio of nutrients across a section linking the northeastern bank of the Changjiang River and Cheju Island. During the winter background period, the input of nitrate, ammonium, phosphate and silicate by the Yellow Sea Warm Current is estimated to be 4.6×10¹⁰, 2.3×10¹⁰, 2.0×10⁹ and 1.2×10¹⁰ mol, respectively.     

Response of rotifer community to environmental changes in five shallow lakes in the middle reach of Changjiang River,China

We evaluated the response of a rotifer community to environmental changes in five shallow lakes in the middle reach of the Changjiang （Yangtze） River in summer and autumn 2010. These five lakes differed in trophic status and rotifer community structure. Twenty-nine rotifer species were collected, of which Keratella cochlearis, Polyarthra dolichoptera, and Trichocerca elongate were dominant. The mean density, Shannon-Wiener diversity, and equitability among the five lakes differed significantly （P〈0.05）. The mean rotifer density was positively correlated with trophic state. The diversity was higher in lakes with high macrophyte coverage. The composition of rotifer species was closely associated with the trophic gradient. Five environmental variables, Secchi depth, conductivity, TN, NHa-N, and TP, significantly affected the composition of rotifer species. Keratella quadrata, Brachionus calyciflorus, and B. forficula were more common in eutrophic conditions. Our results suggest that eutrophication has a significant influence on the rotifer community structure and highlight the potential for using rotifer community structure as an indicator of trophic status in subtropical lakes.     

Trophic ecology of sharks in the mid-east Pacific ocean inferred from stable isotopes

As apex predators, sharks are of ecological and conservation importance in marine ecosystems. In this study, trophic positions of sharks were estimated using stable isotope ratios of carbon and nitrogen for five representative species caught by the Chinese longline fleet in the mid-east Pacific, i.e., the blue shark(Prionace glauca), the bigeye thresher shark(Alopias superciliosus), the silky shark(Carcharhinus falciformis), the scalloped hammerhead(Sphyrna lewini), and the oceanic whitetip shark(Carcharhinus longimanus). Of these species, oceanic whitetip shark has the lowest trophic level and mean δ15N value(3.9 and 14.93‰± 0.84‰), whereas bigeye thresher shark has the highest level/values(4.5 and 17.02‰± 1.21‰, respectively). The bigeye thresher shark has significantly higher δ15N value than other shark species, indicating its higher trophic position. The blue shark and oceanic whitetip shark has significantly higher δ13C values than bigeye thresher shark, silky shark and scalloped hammerhead, possibly due to different diets and/or living habitats. The stable isotope data and stomach content data are highly consistent, suggesting that stable isotope analysis supplements traditional feeding ecology study of sharks, and thus contributes to understanding their trophic linkage.     

Relative abundance of biotic communities of plankton and zoobenthos in three ox-bow lakes of Eastern India

We made comparative studies of three tropical ox-bow lakes in India with different trophic states. The species number of zooplanktons was negatively correlated with the degree of water eutrophication, and lakes of similar trophic status had higher similarity of species. The most significant differences of species composition were observed with rotifers and zoobenthos. The density and biomass of phytoplankton, rotifers, oligochaetes and chironomids tended to increase with increasing nutrients. We observed a significant difference of dominant species in different waters, especially the eutrophic lake, which was dominated by a few species of oligochaetes. The abundance of Tanypus bilobatus showed a highly significant correlation with the degree of eutrophication. Rotifers and zoobenthos showed considerably lower biodiversity in the eutrophic lake.     

Assessing the effects of oyster/kelp weight ratio on water column properties: an experimental IMTA study at Sanggou Bay,China

Journal of Oceanology and Limnology - Integrated Multi-Trophic Aquaculture (IMTA) is an effective method for sustainable aquaculture as species from different trophic levels could reduce negative...     

Assessment of trophic status in Changjiang （Yangtze） River estuary

The integrated methodology for the assessment of estuarine trophic status (ASSETS), which was extended and refined from the United States National Estuarine Eutrophication Assessment (NEEA), is a multi-parameter assessment system and has been widely used in eutrophication assessment in estuarine and coastal waters. The ASSETS was applied to evaluate the trophic status of the Changjiang (Yangtze) River estuary, one of the largest estuaries in the world. The following main results were obtained: (i) The estuarine export potential is "moderate susceptibility" due to the "moderate" dilution potential and "moderate" flushing potential; (ii) The overall human influence (OHI) index classified the impact of nutrients in the system as "high" due to the high level of nutrient discharge by the river which channels anthropogenic impacts in the catchments to the estuarine system; (iii) The overall eutrophic condition (OEC) in the estuary was classified into the "high" category due to frequent occurrence of nuisance and toxic algal blooms in the mixing and seawater zones; (iv) Since the nutrient loadings (e.g., DIN) in the river is expected to continue to increase in the near future following the population increase and rapid economic growth throughout the drainage basin, the nutrient-related symptoms in the estuary are likely to substantially worsen, which leads to the "worsen high" category for the definition of future outlook (DFO). The combinations of the three components (i.e., OHI, OEC, and DFO) lead to an overall grade as "bad" for the trophic status in the Changjiang River estuary.     

Stable isotopes in aquatic food web of an artificial lagoon in the Hangzhou Bay, China

Stable isotope values, δ¹³C and δ¹⁵N, were determined for four primary producers and 19 dominant consumers in a small artificial lagoon located in Hangzhou Bay. Based on these results the major pathways for energy flow and trophic structure of the artificial lagoon ecosystem were characterized. The mean δ¹³C values for the 19 consumers ranged from −22.99‰ to −14.24‰. Apart from so-iny mullet Liza haematocheila, the other 18 consumers had intermediate δ¹³C values between those of epibenthic microalgae and particulate organic matter (POM). The results of a multiple source linear mixing model (IsoSource model) indicated that 50% or more of the organic carbon in the tissues of most consumers was derived from epibenthic microalgae. This indicated that these primary producers were the main food source fueling the lagoon food web. The mean δ¹⁵N values for the 19 consumers varied between 4.93‰ and 12.97‰ and indicated four trophic levels in the lagoon. Four macroinvertebrates and zooplankton represented the primary consumers, whilst the other 14 consumers occupied the secondary and tertiary consumer levels. The 19 consumers were divided into three trophic guilds (detritivores/suspension feeders, omnivores and carnivores).     

湖泊和水库营养灰色聚类分析

选取浮游植物初级产量、浮游植物现存量、有机物耗氧量、总氮、无机氮、总磷、活性磷等七项指标,由德尔菲法确定各指标的类别界限值和权重,用灰色系统理论的定权灰色聚类方法,借用计算机对23个湖泊和水库营养类型主要参数作灰色聚类分析,以建立一种划分我国湖泊和水库营养类型的有效方法,作为渔业生产的依据。     

Fatty Acid Composition of Euphausia superba,Thysanoessa macrura and Euphausia crystallorophias Collected from Prydz Bay,Antarctica

The information of trophic relationship is important for studying the Southern Ocean ecosystems.In this study,three dominant krill species,Euphausia superba,Thysanoessa macrura and Euphausia crystallorophias,were collected from Prydz Bay,Antarctica,during austral summer of 2009/2010.The composition of fatty acids in these species was studied.E.superba and T.macrura showed a similar fatty acid composition which was dominated by C14:0,C16:0,EPA(eicosapentenoic acid) and DHA(decosahexenoic acid) while E.crystallorophias showed higher contents of C18:1(n-9),C18:1(n-7),DHA and EPA than the former two.Higher fatty acid ratios of C18:1(n-9)/18:1(n-7),PUFA(polyunsaturated fatty acid)/SFA(saturated fatty acid),and 18PUFA/16 PUFA indicated that E.crystallorophias should be classified as a typical omnivore with a higher trophic position compared with E.superba and T.macrura.     

Phytoplankton community structure in reservoirs of different trophic status, Northeast China

The aim of this study was to determine the phytoplankton community structures of reservoirs of different trophic status, located in a cold region. Physical and chemical variables and the phytoplankton communities were investigated in two reservoirs (Xiquanyan Reservoir and Taoshan Reservoir) in Northeast China in 2009. The two reservoirs showed strong seasonal fluctuations in their physical and chemical composition. Results of the trophic status index indicated that Xiaquanyan Reservoir was mesotrophic, whilst Taoshan Reservoir was eutrophic. Diatoms were the dominant phytoplankton group in Xiquanyan Reservoir throughout all seasons of the study, while in Taoshan Reservoir, diatoms dominated in spring, and cyanobacteria dominated in summer and autumn. This difference was resulted from differences in local environmental factors, including nutrients and hydrology. This study suggests that in mesotrophic reservoirs, nutrients played a key role in controlling seasonal phytoplankton successions, whereas in eutrophic reservoirs water temperature was the key factor in a cold region. Notably, the dominant species in summer in the Taoshan Reservoir was Microcystis, which may produce toxins depending on the ambient conditions, and presenting a risk of local toxin contamination.     

Importance of kelp-derived organic carbon to the scallop <Emphasis Type="Italic">Chlamys farreri</Emphasis> in an integrated multi-trophic aquaculture system

Bivalves and seaweeds are important cleaners that are widely used in integrated multi-trophic aquaculture (IMTA) systems. A beneficial relationship between seaweed and bivalve in the seaweed-based IMTA system has been confirmed, but the trophic importance of seaweed-derived particulate organic materials to the co-cultured bivalve is still unclear. We evaluated the trophic importance of the kelp Saccharina japonica to the co-cultured scallop Chlamys farreri in a typical IMTA farm in Sungo Bay (Weihai, North China). The dynamics of detritus carbon in the water were monitored during the culturing period. The proportion of kelp-derived organic matter in the diet of the co-cultured scallop was assessed via the stable carbon isotope method. Results showed that the detritus carbon in the water ranged from 75.52 to 265.19 μg/L, which was 25.6% to 73.8% of total particulate organic carbon (TPOC) during the study period. The amount of detritus carbon and its proportion in the TPOC changed throughout the culture cycle of the kelp. Stable carbon isotope analysis showed that the cultured scallop obtained 14.1% to 42.8% of its tissue carbon from the kelp, and that the percentages were closely correlated with the proportion of detritus carbon in the water (F =0.993, P= 0.003). Evaluation showed that for 17 000 tons (wet weight) of annual scallop production, the kelp contributed about 139.3 tons of carbon (535.8 tons of dry mass). This confirms that cultured kelp plays a similar trophic role in IMTA systems as it does in a natural kelp bed. It is a major contributor to the detritus pool and supplies a vital food source to filter-feeding scallops in the IMTA system, especially during winter and early spring when phytoplankton are scarce.     

Application and comparison of two symptom-based eutrophication-assessment methods in Jiaozhou Bay,China

Increasing numbers of approaches to assess eutrophication,such as estuarine trophic status,the Oslo-Paris Commission Common Procedure,and the Water Framework Directive,focus on the symptoms of eutrophication.In China,however,nutrient index methods dominate the assessment of coastal waters.In this study,an integrated method that includes both water quality and ecological response was compared with the Northwest Pacific Action Plan(NOWPAP)Common Procedure.Observation data from Jiaozhou Bay,Shandong,China,were used in a comparison of the two methods in a trophic status study.Overall,both clearly revealed a high level of nutrient enrichment in the bay,indicated by high nutrient concentrations.Though the two methods differed in their methodological design in the assessment of the ecological effects of nutrient enrichment,they have acquired similar results:the integrated method suggested that the status was good,and the NOWPAP Common Procedure suggested that the status was low(indicating that the bay had no serious eutrophication problem).The introduction of filter feeders(shellfish aquaculture)into the bay on a reasonable scale may have been effective in mitigating eutrophic conditions,and perhaps explains the low ecological impacts there.Our results will be useful to ecosystem-based eutrophication management in the bay and in similar areas.     

富营养化的太湖水体叶绿素a浓度模型反演

半经验模型反演叶绿素a浓度是目前遥感反演水体叶绿素a浓度的主要方法。但是,大量研究结果表明,太湖水体浑浊,富营养化严重,各种半经验模型的反演精度和模型适用性有较大差异。因此,研究一种既满足一定精度要求,又具有时间普适性的叶绿素a浓度反演算法,对提高模型适用性,促进遥感的反演应用具有重要意义。本研究通过2005年6-10月地面实测数据,建立太湖叶绿素a浓度一阶微分反演模型、波段比值反演模型和三波段反演模型,对比各模型反演效果,认为波段比值模型与三波段模型具有较好的反演效果。运用2006年11月和2007年11月实测数据对这三种模型加以检验,结果表明,三波段模型反演高富营养化的太湖水体,不仅精度高,平均误差仅为实测浓度差的8.3%,而且适用性较强,不同年份数据的检验结果证明平均误差均低于实测浓度差的20%。因此,三波段模型是这三种反演模型中效果最好的一类模型。     

Species- and tissue-specific mercury bioaccumulation in five fish species from Laizhou Bay in the Bohai Sea of China

Mercury (Hg) concentrations in the tissues (muscle, stomach, liver, gills, skin, and gonads) of five fish species (mullet Liza ha em atocheil us, flathead fish Platycephalus indicus, sea bass Lateolabrax japonic u s, mackerel Scomberomorus niphonius and silver pomfret Pampus argenteus) collected from Laizhou Bay in the Bohai Sea of China were investigated. The results indicate that Hg bioaccumulation in the five fish was tissue-specific, with the highest levels in the muscle and liver, followed by the stomach and gonads. The lowest levels were found in the gills and skin. Fish at higher trophic levels (flathead fish and sea bass) exhibited higher Hg concentrations than consumers at lower trophic levels. Mercury bioaccumulation tended to be positively correlated with fish length in mullet, silver pomfret, mackerel, and flathead fish, but was negatively correlated with fish length in sea bass. The Hg concentrations in the muscles of all fish species in Laizhou Bay were within the permissible limits of food safety set by national and international criteria. However, the suggesting maximum consumption of sea bass is 263 g per week for human health.