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Daya Bay, is one of the largest and most important semi-closed bays along the southern coast of China. Due to the favorable geomorphological and climatic conditions, this bay has become an important conservation zone of aquatic germplasm resources in South China Sea. To characterize the trophic structure, ecosystem properties and keystone species, a food-web model for Daya Bay has been developed by the means of a mass-balance approach using the Ecopath with Ecosim software. The mean trophic transfer efficiency for the entire ecosystem as a whole is 10.9% while the trophic level II is 5.1%. The primary- and secondary-producers, including phytoplankton, zooplankton and micro-zoobenthos demonstrated the important overall impacts on the rest of the groups based on mixed trophic impact (MIT) analysis and are classified as the keystone groups. The analysis of ecosystem attributes indicated that ecosystem of Daya Bay can be categorized as an immature one and/or is in the degraded stage. A comparison of this model with other coastal ecosystems, including Kuosheng Bay, Tongoy Bay, Beibu Gulf and Cadiz Gulf, underpinned that the ecosystem of Daye Bay is an obviously stressed system and is more vulnerable to the external disturbance. In general, our study indicates that a holistic approach is needed to minimize the impacts of anthropogenic activities to ensure the sustainability of the ecosystem in the future. [ABSTRACT FROM AUTHOR]

To examine trophic dynamics over different size classes, an isotopic study of sailfish Istiophorus platypterus life-history stages was carried out. Samples were collected from eastern Taiwan and the South China Sea during April 2009 and February 2012. A total of 263 samples (111-245 cm, lower jaw fork length, LLJFL) were examined for changes in trophic structure in relation to LLJFL by using stable isotope analysis of carbon ( δ13C) and nitrogen ( δ15N). The δ15N values for I. platypterus ranged from 7·51 to 14·19‰ (mean ± s.d. = 12·06 ± 1·16‰) and the δ13C values ranged from −22·04 to −15·48‰ (mean ± s.d. = −17·62 ± 1·10‰). The δ15N values were positively dependent on LLJFL ( r2 = 0·377), whereas δ13C were negatively dependent on LLJFL ( r2 = 0·063). There were significantly different seasonal changes in nitrogen and carbon isotopic concentration, but no significant differences in concentrations between eastern Taiwan and the South China Sea were reported. The trophic level ( TL) of each LLJFL class was correlated, starting from 2·84 TL for size class I ( LLJFL < 140 cm) and reaching 5·03 TL for size class VI ( LLJFL > 221 cm). The mean ± s.d. TL was 4·43 ± 0·19 for all samples. The results reveal that I. platypterus occupies a wide range of trophic levels and different size classes occupy different trophic positions in the pelagic ecosystem. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]