Impacts of species depletion on the food web structure of a marine ecosystem based on topological network analysis

Single-species management ignores the interactions between species,and ecosystem-based fisheries management(EBFM)has become a main method to fisheries management.Understanding food web structures and species interactions is essential for the implementation of EBFM and maintenance of ecosystem functions.Overfishing is one of the main reasons behind the depletion,which could even lead to the depletion of some target species in local areas.So understanding the impacts of species depletion on food web structures is important for the implementation of EBFM.The impacts of species depletion can be transmitted through the food web and cause the local extinction of both target and non-target species.In this study,topological network analysis was applied to examine the impacts of species depletion on the food web structure of Haizhou Bay.Results showed that fine crayfish Leptochela gracilis,squid Loligo sp.,and Japanese snapping shrimp Alpheus japonicus have the highest numbers of outgoing links(48,32 and 31 respectively);thus,these species may be considered key prey species.Whitespotted conger Conger myriaster,fat greenling Hexagrammos otakii,and bluefin gurnard Chelidonichthys kumu were key predators with the highest number of incoming links(37,36 and 35 respectively).The competition graphs derived from the Haizhou Bay food web were highly connected(more than 40%predators sharing over 10 common prey species),and showed close trophic interaction between high trophic level fishes.Simulation analysis showed that the food web structure has small changes to the depletion of species in a highly complex food web.The most-connected target species did not necessarily indicate high structural importance;however,some species with low connectivity may demonstrate stronger trophic interactions and play important ecological roles in the food web.But most species were more sensitive to the depletion of the most-connected target species than other target species(for instance,for zooplankton,closeness centrality 13.876 in D6,but closeness centrality 82.143 in original food web).Therefore,EBFM should focus on the most-connected target species,but also on those species with few but strong links and feeding relationships in the food web.

Evaluation Method of Web Site Structure Based on Web Structure Mining

The structure of Web site became more complex than before. During the design period of a Web site, the lack of model and method results in improper Web structure, which depend on the designer's experience. From the point of view of software engineering, every period in the software life must be evaluated before starting the next period's work. It is very important and essential to search relevant methods for evaluating Web structure before the site is completed. In this work, after studying the related work about the Web structure mining and analyzing the major structure mining methods (Page\|rank and Hub/Authority), a method based on the Page\|rank for Web structure evaluation in design stage is proposed. A Web structure modeling language WSML is designed, and the implement strategies for evaluating system of the Web site structure are given out. Web structure mining has being used mainly in search engines before. It is the first time to employ the Web structure mining technology to evaluate a Web structure in the design period of a Web site. It contributes to the formalization of the design documents for Web site and the improving of software engineering for large scale Web site, and the evaluating system is a practical tool for Web site construction.

Spatial variations in food web structures with alternative stable states:evidence from stable isotope analysis in a large eutrophic lake

Food web structures are well known to vary widely among ecosystems. Moreover, many food web studies of lakes have generally attempted to characterize the overall food web structure and have largely ignored internal spatial and environmental variations. In this study, we hypothesize that there is a high degree of spatial heterogeneity within an ecosystem and such heterogeneity may lead to strong variations in environmental conditions and resource availability, in turn resulting in dif ferent trophic pathways. Stable carbon and nitrogen isotopes were employed for the whole food web to describe the structure of the food web in different sub-basins within Taihu Lake. This lake is a large eutrophic freshwater lake that has been intensively managed and highly influenced by human activities for more than 50 years. The results show significant isotopic dif ferences between basins with dif ferent environmental characteristics. Such differences likely result from isotopic baseline dif ferences combining with a shift in food web structure. Both are related to local spatial heterogeneity in nutrient loading in waters. Such variation should be explicitly considered in future food web studies and ecosystem-based management in this lake ecosystem.

Topology-based analysis of pelagic food web structure in the central and eastern tropical Pacific Ocean based on longline observer data

The tropical Pacific Ocean supports many productive commercial fisheries.However,few studies of ecosystem structure in the tropical Pacific Ocean have been carried out.In this study,we analyzed the food web structure in the central and eastern tropical Pacific Ocean based on trophic relationships of 35 pelagic species collected by Chinese tuna longline observers from June to November in 2017.Topology indices(node degree,D;centrality indices,BC and CC;topological importance indices,TI^1,TI^3;keystone indices,K,K_t and K_b)and Key-Player algorithms(KPP-1,KPP-2)were used to select key species and construct a simplified food web combined with body size data.The Kendall rank correlation and hierarchical clustering analysis indicated that different topology indices resulted in consistent rankings of key species.Most key species were the same as those selected in other studies in the Pacific Ocean,such as Shortbill spearfish(Tetrapturus angustirostris),Swordfish(Xiphias gladius),Albacore tuna(Thunnus alalunga),cephalopods and scomber.The food web would be separated into many unconnected parts(F=0.632,FD=0.795,R^D=0.957)after the removal of the five key species,indicating the key roles of these species in the food web structure and stability.Body size was considered an influential indicator in constructing the simplified food web.This study can improve our understanding of the food web structure in the tropical Pacific Ocean and provide scientific basis for further ecosystem dynamics studies.

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）.