An ecological model of the artificial ecosystem (northern Hangzhou Bay,China): analysis of ecosystem structure and fishing impacts |
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Authors: | Zuozhi Chen Shannan Xu Peimin He |
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Institution: | (1) Key Laboratory of Mariculture, Ecology and Quality Control, Ministry of Agriculture, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, No. 231 Xingang West Road, 510300 Guangzhou, China;(2) College of Fisheries and Life Science, Shanghai Ocean University, 201306 Shanghai, China |
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Abstract: | The artificial ecosystem is a large-scale enclosure in northern Hangzhou Bay, China. Using the Ecopath with Ecosim software,
a trophic structure model is constructed for 2006–2007 to characterize the food web structure, functioning, and describing
the ecosystem impacts of fishing. Input information for the model were gathered from published and unpublished reports and
from our own estimates during the period 2006–2007. Pedigree work and simple sensitivity analysis were carried out to evaluate
the quality and the uncertainty of the model. Results show that the food web in the enclosed sea area was dominated by a detritus
pathway. The trophic levels of the groups varied from 1.00 for primary producers and detritus to 3.90 for piscivorous fish
in the artificial system. Using network analysis, the system network was mapped into a linear food chain, and five discrete
trophic levels were found with a mean transfer efficiency of 9.8% from detritus, 9.4% from primary producer within the ecosystem.
The geometric mean of the trophic transfer efficiencies was 9.5%. Detritus contributed 57% of the total energy flux, and the
other 43% came from primary producers. The ecosystem maturity indices-TPP/TR (total primary production/total respiration),
FCI (Finn cycling index), A (ascendancy) and TB/TDET were 2.672, 25%, 31.5%, and 0.013, respectively, showing that the artificial
system is at developmental stage according to Odum’s theory of ecosystem development. The ‘Keystoneness’ result indicates
that herbivorous zooplankton was identified as keystone species in this system. Furthermore, a simple dynamical simulation
was preformed for varying fishing mortality over 10 years. The biomass of most fish groups has a small increase when the fishing
mortality at current level. Increasing fishing mortality by twofold resulted in a marked decrease in biomass of piscivorous
fish accompanied by an increase in that of other fish groups, notable zooplanktivorous fish. Generally, this study represents
the first attempt to evaluate the food web structure and the potential effects of fisheries in the artificial coastal ecosystem.
It is concluded that this model is a potential tool for use in the management of the artificial ecosystem in northern Hangzhou
Bay. |
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