Interannual Variation In The Keystones Species Of Fish Community In The Laizhou Bay

Under the multiple pressure of human activity(Environmental pollution, overfishing et al.) and climate change(global warming, ocean acidification et al.), the biological resources structure of the Laizhou Bay has changed. Now, the imminent is that how to slow down the speed of biodiversity loss and keep the community structural stability. However, keystone species play a decisive role in community structure and stability, and the keystone species study has both important theoretical and practical significance for the entire ecosystem. In this paper, we discuss the methods to filtrate the keystone species from the fish community in the Laizhou Bay based on the bottom trawl survey data in May, 2011. And combined with historical data from 1959 to 2004, the interannual changes of the fishery resource structure and the keystone species in the Laizhou Bay were analyzed. The main results were as follows:The methods to filtrate the keystone species: Firstly, we establish a relationship network of the 24 fish species according to the predation relationships among fish populations. Then 13 network important indices, i.e. Degree(D), In-Degree(Din), OutDegree(Dout), Betweenness Centrality(BC), Closeness Centraliy(CC), Information Centrality(IC), Hubbell Influence Index(Hout and Hin), Topological Importance Index(TI1 and TI7), Keystone Indices(K), Bottom-up Keystone Index(Kb) and Top-down Keystone Index were calculated using the Ucinet6 and Co SBi Lab Graph1.0 software. A hierarchical clustering was conducted to show the relationships between 13 network indices, and 3 Key Player Problem parameters, i.e. Fragmentation(F), Distanceweighted Fragmentation(DF) and Distance-weighted Reach(DR), were calculated using keyplayer 1.44 programme. The result showed these 13 indices can be divided into 4 different information groups: a(D, CC, IC, TI1 and TI7), basic information group; b(Din, Hin and Kt), input information group; c(Dout, Hout and Kb), output information group; d(BC and K), control information group. The species were identified as the keystone species based on the information of 13 indices and 3 Key Player Problem parameters. Liparis tanakae(D, Din, BC, CC, IC, Hin, TI1, TI7, K, Kt, F, DF and DR) and Amblychaeturichthys hexanema(Dout, H, Hout and Kb) had the highest rank among the 24 study species, and closely tied to others in the fish community, controlled the structure and energy flow of the community, indicating that they were the keystone species in fish community in the Layzhou Bay. And L. tanakae was the keystone predator which could control the density of the predators and other competitors in fish community while A. hexanema was the keystone prey which could restrict the density of other prey species by maintaining the density of the predator.The interannual variations in fish community structure of the Laizhou Bay: During 1959-2004, the highest number of fish species in 1982, 48 species, belong to 8 orders and 24 families, the lowest in 2004, 22 species, belong to 4 orders and 15 families. The higher quality and economics value dominant populations, Trichiurus lepturus, Cynoglossus semilaevis et al. were gradually replaced by the lower quality and economic value populations, Chaeturichthys stigmatias, Pholis fangi et al. 17-46 different nutrition populations constituted 6 fish communities, and there were 51-296 feeding relationships among the communities, the highest in 1982, the lowest in 2004, the mean was 134.57; the food-web topological structure density of feeding relationship was 0.155-0.333, the highest in 2004, the lowest in 1982, the mean was 0.235; the connectance was 0.140-0.182, the highest in 1993, the lowest in 1982, the mean was 0.161; the clustering coefficient was 0.188-0.326, and the weighted clustering coefficient was 0.185-0.253, the mean were 0.260 and 0.218.The interannual variations of the fish keystone species in the Laizhou Bay: the keystone species were Amblychaeturichthys hexanema, Lateolabrax japonicas, Scomberomorus niphonius and Lophius litulon, 1959; Engraulis japonicas, Lophius litulon and Larimichthys polyactis, 1982; Trichiurus lepturus, Engraulis japonicas and Scomberomorus niphonius, 1993; Engraulis japonicus, Larimichthys polyactis, Saurida elongate and Nibea albiflora, 1998; Liparis tanakae, Engraulis japonicas and Lophius litulon, 2003; Liparis tanakae and Amblychaeturichthys hexanema, 2004. Trophic structure of the keystone species from the form of a single species at low trophic level with multiple species of high trophic level coexistence to the form of a single species at low trophic level with a single species at high trophic level coexistence. The dominant species of keystone species alternately appearance, the most was 1982,Larimichthys polyactis and Engraulis japonicas, one half of the number of the keystone species, in contrast the keystone species were not the dominant species in 1959 and 2003. The economic value of the keystone species were lower than previous, and the high-value species(Lateolabrax japonicas and Scomberomorus niphonius) were replaced by the low-value species(Amblychaeturichthys hexanema and Liparis tanakae). The habitat environment has changed from the habitat mode of the pelagic fish(Lateolabrax japonicus and Scomberomorus niphonius) lived with bottom fish(Amblychaeturichthys hexanema and Lophius litulon) to the mode of a single bottom fish.