菲尔德斯半岛潮间带生态系统中的食物网

菲尔德斯半岛潮间带食物链是较简单的 ,一般说来在不利环境条件下的生物群落只有很少的消费者和较少的营养级。食物链中主要的生产者是大型底栖藻类 ,主要消费者是腹足类和石鳖 ,棘皮动物中的海胆与海星 ,甲壳动物 ,鱼和海鸟 ,海鸟和鱼占营养级的上层 ,草食软体动物位于中间营养级 ,大量的固着藻类 -叶状藻类、皮壳状藻类构成营养级的底层。观测实验表明 :(1 )海鸟和鱼类减少了草食性软体动物和肉食性螺类的数量 ;(2 )肉食性腹足类减少了草食性软体动物和固着无脊椎动物的数量 ;(3 )草食性软体动物减少了叶状藻类的数量并影响到皮壳状藻类的数量 ,在不清除消费者的实验中 ,皮壳状藻类显示出与其它固着生物竞争空间的优势。作者观察了并在本文中描述了异性底质与消费者对固着生物多样性的影响。壳状藻类在低潮带岩石表面占优势 ,其它的固着生物 (叶状藻类与固着无脊椎动物 )占据洞穴和狭缝。同质岩石表面固着生物的种类与数量低于异质性的岩石表面。清除岩石表面的消费者后叶状藻类与其它固着无脊椎动物的种数就超过皮壳状藻类

THE FOOD WEB IN INTERTIDAL ECOSYSTEM OF FILDES PENINSULA

The Fildes Peninsula (Antarctic) food Web has been considered to be simple. The main producers in this food web were benthic macroalgae,variation in biomass and standing crops have been described by the authors in another paper. The major consumers were molluscs (gastropods and chitons), echinoderms (sea urchins and a seastar), crustaceas, fishes and seabirds. The most abundant mobil species included fishes and seabird which occupied the top trophic level, predaceous gastropods and herbivorous molluscs, which occupied intermediate trophic levels. The most abundant sessile organisms were foliose algae, encrusting algae, and bivalves. These were all tested in two intertidal sections. Field experiments demonstrate that (1)Seabirds and fishes reduced the abundance of herbivorous molluscs, and predaceous snails. (2) Predaceous gastropods reduced the abundance of herbivorous molluscs and sessile invertebrates. (3) Herbivous molluscs reduced the abundance of foliose algae, and altered relative abundance of the encrusting algae. The encrusting algae proved to be inferior competitors for space with other sessile organisms when consumers were experimentally excluded. In this paper we evaluate the influences of substratum heterogeneity and consumers on patterns of diversity of sessile organisms in this habitat,local substratum topography is highly variable, ranging from smooth to irregular surfaces. Algal crusts typically dominate all low zone rock surfaces,and most other sessile species (invertebrates and foliose algae) occur in holes and crevices. The number and diversity of sessile species are lower on homogeneous surface than on heterogeneous surfaces. When consumers are excluded from the general rock surface, algal crusts are overgrown by foliose algae and sessile invertebrates.