When one foundation species supports another: Tubeworms facilitate an extensive kelp bed in a soft‐sediment habitat

Abstract

AbstractThe role of foundation species—dominant organisms that provide habitat for other organisms—in enhancing the diversity and abundance of associated species is now well known. Less well studied are interactions between multiple, co‐occurring foundation species, which collectively provide habitat for other organisms. Here, I document a unique interaction between tubeworms (Eudistylia vancouveri) and two kelp species (Alaria marginata and Saccharina latissima). Kelps—large brown macroalgae in the order Laminariales—require hard substrates for attachment and are therefore typically restricted to rocky reefs. However, while exploring a remote coastline in southeastern Alaska, USA, I observed an extensive kelp bed, composed of both Alaria and Saccharina, growing in a location where the substrate was a mixture of mud and sand. The leathery tubes of Eudistylia formed dense hummocks that protruded from the sediment and provided a hard substratum for attachment by the kelps. Given the role that kelps, including Alaria and Saccharina, play as important facilitators of fish and invertebrates, this interaction likely represents an example of a facilitation cascade, which occurs when one species facilitates another species that subsequently enhances the diversity or abundance of associated organisms. Furthermore, the high kelp biomass likely contributes detrital inputs to the local ecosystem, potentially enhancing productivity. More generally, this observation highlights the need to understand the habitat requirements of foundation species, including the potential for other species to facilitate them.