Macroalgal structural complexity as a key driver of intertidal epifauna composition

Abstract

Habitat complexity is one of the most important factors structuring biotic assemblages and is of great importance in different ecosystems. Macroalgae are a clear example of this idea. They constitute ecosystems that harbor a high biodiversity because they provide a unique physical habitat to support production, making them dense, diverse and productive faunal assemblages. Thalli provide a substrate for the growth of epiphytic microalgae that feed food webs and a refuge for invertebrates and fish that reach substantially higher densities than in unvegetated benthic habitats and also provide essential shelter from predation. The present work studies the structural complexity of algae as an important factor driving the structure of epifaunal assemblages associated with marine macroalgae. For this purpose, three algal species were selected for their similar structural complexity, Cystoseira humilis, Halopteris scoparia and Stypocaulon scoparium. They harbor a rich epifauna and the small differences of the studied algae in terms of structural complexity generate a different epifaunal community. Crustaceans were the most abundant group in the epifaunal community, followed by polychaetes, mollusks and echinoderms. The maximum number of individuals was found in Stypocaulon scoparium whilst the minimum number of individuals was found in Cystoseira humilis. The intermediate number of individuals was found in Halopteris scoparia. On the other hand, the maximum number of species was found in H. scoparia and the minimum number of species was found in C. humilis. The intermediate diversity of species was found in S. scoparium. A total of 94 species were identified. In turn, multivariate analyses showed that there are significant differences in epifaunal composition amond the studied algae. The MDS analysis showed that the epifaunal community of each alga is different; that is, there is a high spatial variability within the three macroalgae. In turn, through the Permutational Multivariate Analysis of Variance (PERMANOVA) it was possible to verify that there were significant differences between the algae studied, specifically between the algal epifauna due to the different structural complexity of each one. These differences were due to the fact that the dominant species varied and in turn to the fact that there were several species that were only found in one of the three algae. Therefore, it is demonstrated that there is a clear relationship between the structural complexity of the algae and the abundance and richness of the associated fauna.