Could the annual Saccorhiza polyschides replace a sympatric perennial kelp (Laminaria ochroleuca) when it comes to supporting the holdfast-associated fauna?

Kelp forests dominate temperate rocky shores worldwide but are declining globally with consequences for organisms that depend on them. In NW Iberia, the golden kelp (Laminaria ochroleuca) commonly occurs alongside a fast-growing annual that, unlike the golden kelp, does not seem to have receded in recent times (Saccorhiza polyschides). Here, we assessed whether the bulbous holdfast of S. polyschides could replace the intricate holdfast of L. ochroleuca as epifaunal habitat provider. Richness, diversity and total abundance of epifauna was similar in both seaweeds, while colonial/encrusting fauna was more abundant in L. ochroleuca. More importantly, each host supported a distinctive assemblage structure, indicating that S. polyschides seems an unsuitable replacement for L. ochroleuca as habitat provider for holdfast epifauna. Therefore, while S. polyschides may contribute substantially to the kelp forest canopy in some seasons, a regional decline of L. ochroleuca will likely alter the patterns of biodiversity within kelp stands.