three major habitats exist in the sea in this region, two of them distinguished by the nature of the substrate. the substrate, or base material, is important in that it provides a base to which an organism can anchor itself, which is vitally important for those organisms which need to stay in one particular kind of place. rocky reefs provide a firm fixed substrate for the attachment of plants and animals. sedimentary bottoms are a relatively unstable substrate and cannot anchor kelp or many of the other benthic organisms. finally there is open water, above the substrate and clear of the kelp forest, where the organisms must drift or swim. mixed habitats are also frequently found, which are a combination of those mentioned above.