The value of algae as a substrate for intertidal invertebrates in the White Sea
The paper is devoted to researching zoobenthos communities of the intertidal zone, where the role of the substrate is represented by littoral phytobenthos. Macrophytes are subject to changes in time and are part of the trophic structure of marine communities as comparing with an inert ground substrate. The comprehensive study of littoral biocenoses allows reveal interrelation of benthic organisms with the vegetable substrate where they inhabit. The aim of the work is the investigation of structure and distribution features of epibenthic communities on the littoral macrophytes of the Chupa inlet (the White Sea). The investigations were conducted at The White Sea Biological Station "Kartesh" (WSBS) during the summer period of three years (2012-2015). The material was being collected on the intertidal zone of the Levaya bay, Kruglaya bay, and Sel'dyanaya bay of the Chupa inlet by the method of vertical transects using the accounting frame (0.25 m<sup>2</sup>) in the three-fold repetition. In the processing of samples, the abundance of algae and epibionts has been defined; the biomass and number of macrophytes and invertebrates have been measured. In the course of the work, it has been revealed that Fucus algae create a favorable habitat for epibenthos including moving animals. A variety of seaweed substrates contributes to increase of invertebrates' biomass. The only exceptions are parts of the bays, where seaweed Ascophyllum nodosum and Pelvetia caniculata are abundant. These algae are not favourable substrate for most of epibenthic organisms and serve as habitat mainly of sedentary invertebrates due to the morphology of the thallus. Mussels Mytilus edulis are dominant invertebrates in the communities, where Fucus is the substrate. Filamentous algae contribute to active development of Hydrobia ulvae communities.