A mass balanced model of trophic structure and energy flows of a semi-closed marine ecosystem

The marine ecosystem of the Jiaozhou Bay has degraded significantly in fisheries productivity and its ecological roles as spawning and nursery ground for many species of commercial importance has been declining in recent years. A mass-balanced trophic model was developed using Ecopath with Ecosim to evaluate the trophic structure of the Jiaozhou Bay for improving ecosystem management. The model were parameterized based on the fisheries survey data in the Jiaozhou Bay in 2011, including 23 species groups and one detritus group according to their ecological roles. The trophic levels of these ecological groups ranged from 1（primary producers and detritus） to4.3（large demersal fishes）. The estimated total system throughput was 12 917.10 t/（km^2·a）, with 74.59% and25.41% contribution of the total energy flows from phytoplankton and detritus, respectively. Network analyses showed that the overall transfer efficiency of the ecosystem was 14.4%, and the mean transfer efficiency was 14.5%for grazing food chain and 13.9% for detritus food chain. The system omnivory index（SOI）, Finn＇s cycled index（FCI） and connectance index（CI） were relatively low in this area while the total primary production/total respiration（TPP/TR） was high, indicating an immature and unstable status of the Jiaozhou Bay ecosystem. Mixed trophic impact analysis revealed that the cultured shellfish had substantial negative impacts on most functional groups. This study contributed to ecosystem-level evaluation and management planning of the Jiaozhou Bay ecosystem.

Food web structure and trophic levels in a saltwater pond sea cucumber and prawn polyculture system

The food sources of aquacultured Apostichopus japonicus and the trophic levels of organisms in a sea cucumber（A. japonicus） and prawn（Penaeus japonica） polyculture system in a saltwater pond in Zhuanghe, Liaoning Province were examined using carbon and nitrogen stable isotopes. Across organisms, δ13C ranged from（–25.47±0.20）‰ to（–16.48±0.17）‰（mean±SD）, and δ15N ranged from（4.23±0.49）‰ to（12.44±0.09）‰. The δ13C and δ15N contents of A. japonicus, P. japonica and Fenneropenaeus chinensis were comparatively higher than those of other organisms. Values of δ13C and δ15N revealed that P. japonica, Hemigrapsus sanguineus and Neomysis japonica comprised the largest component of the diet of A. japonicus. The mean trophic level of the organisms in this saltwater pond polyculture system was（2.75±0.08）. P. japonica, A. japonicus, F. chinensis,Synechogobius hasta and Neomysis japonica were in the 3rd trophic level（2–3）; jellyfish, H. sanguineus and zooplankton were in the 2nd trophic level（1–2）; and Enteromorpha prolifera, benthic microalgae, periphyton and suspended matter primarily consisting of phytoplankton, bacteria and humus were in the primary trophic level（0–1）.

Seasonal variability in free-living marine nematode community structure in a sandy beach of the Taiping Bay of Qingdao,China

Nematode assemblage composition, trophic structure and biodiversity were followed over an annual cycle in a sandy beach of the Taiping Bay of Qingdao, China. Nematode assemblage in the sandy beach maintained a high genus diversity （75 genera）. Mlero- laimus and Bathylaimus were the dominant genus of the nematode assemblage, accounting for 66% of the total nematode abundance. The nematodes＇ dominant trophic structure changed seasonally as a response to the seasonal changes in food quality. Epigrowth-feeder nematodes （2A） were the dominant trophic groups in the trophic structure with the highest abundance in spring because of phytoplankton bloom, while the feeding type （ 1 B） showed higher abundance in summer that was due to the increasing of sediment detritus after spring bloom. Furthermore, species diversity and evenness calculated on nematodes identified to the genus level displayed significant temporal changes, which was also reflected by the index of trophic diversity. According to the cluster analysis, the nematode community structure of the whole year was clearly separated into two periods （A and B）. Biota-Envlron- ment matching （BIOENV） results showed that seawater temperature, sediment Chl a and grain size were responsible for the nema- tode community structure variation in spring and summer period （Period A）. However, seawater/interstitial water temperature, interstitial water dissolved oxygen concentration,interstitial water salinity, and sediment Ph a a were more important in constructing the autumn and winter period （Period B） nematode community structure.

An evaluation of underlying mechanisms for“fishing down marine food webs”

Since the concept of ＂fishing down marine food webs＂ was first proposed in 1998, mean trophic level of fisheries landings（MTL） has become one of the most widely used indicators to assess the impacts of fishing on the integrity of marine ecosystem and guide the policy development by many management agencies. Recent studies suggest that understanding underlying causes for changes in MTL is vital for an appropriate use of MTL as an indicator of fishery sustainability. Based on the landing data compiled by Food and Agriculture Organization（FAO） and trophic information of relevant species in Fishbase, we evaluated MTL trends in 14 FAO fishing areas and analyzed catches of upper and lower trophic level groups under different trends of MTL and found that both the cases of a recovered MTL trend and a generally increasing MTL trend could be accompanied by decreasing catches of lower trophic level species. Further, community structure and exploitation history should be considered in using MTL after excluding species with trophic levels lower than 3.25 to distinguish ＂fishingthrough＂ from ＂fishing-down＂. We conclude that MTL used as an indicator to measure fishery sustainability can benefit from a full consideration of both upper and lower trophic level species and masking effects of community structure and exploitation history.

Soil under dead or live organic matter systems:Effect of European shag(Phalacrocorax aristotelis L.)nesting on soil nematodes and nutrient mineralization

Here we studied whether soil systems differ if they are under the influence of live(plants)or dead organic matter systems(nest)in terms of C and N mineralization,microbiological characteristics and nematode trophic group structure.We analyzed physicochemical and microbiological properties of soils inside and outside nests of the European shag(Phalacrocorax aristotelis L.)on the Cies Islands(NW Spain).We sampled fresh soil below dead(nests)and live organic matter(plants)(paired samples,n=7).Soil of nests had lower organic matter and higher electric conductivity and dissolved organic C and extractable N contents than the soil of plants.Microbial biomass and activity were greater in soil of nests than in soil of plants.The abundance of nematode trophic groups(bacterivores,fungivores,omnivores and herbivores)differred between soils of nests and plants,and the soil of plants supported a more abundant and diverse nematode community.The present results points to that source of organic matter promote differences in the decomposer community,being more efficient in soil of nests because C mineralization is greater.Further,this occurred independently of the complexity of the systems,higher in the soil of plants with more groups of nematodes.