Comparison of the influence of vertebrate predation and competition insidethe community upon the White Sea soft-bottom intertidal zoo- and phytobenthos: Caging experiments

At the beginning of June on lower littoral zone 6 cage exclosers (1 m(2) ea ch, mesh size 5 mm) were set on lower zone of soft-bottom tidal flat in the White Sea. In half of the cages density of macrobenthos was increased arti ficially in 2.5-3 times. Through 2.5 months, both total biomass of macrofau na and most of the dominant species (Mya arenaria, Hydrobia ulvae, Arenicol a marina, Littorina saxatilis) in cages exceeded the control values in some times. The similar result was received for macrophytes (mainly for Ruppia maritima). The total losses from vertebrate predators (birds and fishes) we re estimated as about 80% of the seasonal production both for macrofauna an d macrophytes. In cages with raised initial density the absolute gain of an imals biomass was maximal, but the growth rates practically of all species, except H. ulvae, were significantly lower than at cages with natural densi ty. The production of macrophytes was also lower at increased density of an imals. The conclusion is made, that the press of vertebrate predators is th e basic controlling factor for this community, keeping density of littoral macrofauna below a critical level, at which the competitive effects become significant. However there is a specifity in the individual reaction of som e species complicating the general pattern.