1959–2011年莱州湾渔业资源群落食物网结构的年间变化

通过对1959–-2011年莱州湾渔业资源摄食习性、营养级的分析, 构建了莱州湾生态系统简化食物网。结果表明, 莱州湾渔业资源群落食物网经历了“以鱼食性种类为主的食物网—以浮游动物食性种类为主的食物网—以浮游动物食性种类和底栖动物食性种类为主, 但浮游动物食性种类占比大于底栖动物食性种类的食物网—以浮游动物食性种类和底栖动物食性种类为主, 但底栖动物食性种类占比大于浮游动物食性种类的食物网—以底栖生物食性种类为主的食物网” 5个阶段的演变过程。中低营养阶层生物替代高营养阶层生物成为莱州湾生态系统食物网的顶级捕食者, 食物链越来越短, 食物网通过碎屑食物链传递的能量成为食物网能流的主体。在1959–-2011年期, 莱州湾渔业资源群落平均营养级从4.4下降到3.4, 平均以每10年0.19的速度下降, 高于整个渤海生态系统的下降速度; 种类组成的变化、个体小型化, 以及摄食食物种类的变化是引起莱州湾生态系统营养级波动的主要原因。

Interannual variation in the food web of commercially harvested species in Laizhou Bay from 1959 to 2011

We used stomach content analysis to evaluate the feeding habits of the dominant fish species in Laizhou Bay. The species were classified into one of five feeding habits, including zooplanktivores, benthivores, piscivores, omnivores, and generalist predators. , and is omnivorous; , Chaeturichthys stigmatias are benthivorous; Synechogobius hasta and are generalist predators. Of the species that are harvested commercially, fish were the dominant taxa in the food web from 1959 to 1993. However, the biomass of invertebrates, including , has gradually increased and constituted 42.8% of the total biomass in 2008 and 72.1% in 2011. Thus, invertebrates are now the dominant taxa among harvested species. The food web in 1959 included benthivores, piscivores, and generalist predators, among which piscivores accounted for 78.7% of the biomass. More recently, piscivores have been absent from the food web in Laizhou Bay, except in 2008. Zooplanktivores were the dominant species in 1982 and 1993, accounting for 71.1% and 72.2% of the biomass, respectively. From 1998 to 2008, the biomass of zooplanktivores declined and the biomass of benthivores increased dramatically. In 2011, the food web in Laizhou Bay included only benthivores and generalist predators, among which benthivores accounted for 82.6% of the biomass. Using cluster analysis and a simplified version of the food web from 1959 to 2011, we showed that the food web in Laizhou Bay has experienced five stages of evolution, changing from a piscivore-dominated system to a zooplanktivore-dominated system, to a zooplanktivore and benthivore system (with a higher proportion of zooplanktivores), to a benthivore and zooplanktivore system (with a higher proportion of benthivores) to a benthivore-dominated system. The species at low and medium trophic levels have replaced the species at higher trophic levels and have become the top predators in the Laizhou Bay ecosystem. The food chain is now considerably shorter and energy transfer occurs primarily through the detritus food chain. The mean trophic level declined from 4.4 to 3.4 between 1959 and 2011, which is more rapid than in the Bohai Sea. Variation in dominant species composition, individual miniaturization, and intraspecific changes in feeding are the primary factors explaining the decline in the trophic level in Laizhou Bay.