Response of rocky invertebrate diversity, structure and function to the vertical layering of vegetation

- Rocky invertebrate abundance is strongly favoured by canopy forming algae.
- Epiphytic invertebrates, such as hydroids and bryozoans, are positively correlated with canopy algae.
- Taxonomic and functional diversities are linked and are dependent on canopy algae.
- Basal forming algae favour detritivore abundance and shelter poor invertebrate assemblages.
- Low levels of taxonomic redundancy exist in functional groups correlated with vegetation structure.

Macroalgae comprise a prominent part of the rocky benthos where many invertebrates develop, and are believed to be undergoing severe declines worldwide. In order to investigate how the vegetation structure (crustose, basal and canopy layers) contributes to the diversity, structure and function of benthic invertebrates, a total of 31 subtidal transects were sampled along the northeast Atlantic coast of Spain. Significant positive relationships were found between the canopy layer and faunal abundance, taxonomic diversity and functional group diversity. Canopy forming algae were also related to epiphytic invertebrates, medium size forms, colonial strategy and suspensivores. By contrast, basal algae showed negative relationships with all variables tested except for detritivores. Multivariate multiple regression analyses (DISTLM) point to crustose as well as canopy layers as the best link between seaweeds and invertebrate assemblage structure. A close relationship was found between taxonomic and functional diversities. In general, low levels of taxonomic redundancy were detected for functional groups correlated with vegetation structure. A conceptual model based on the results is proposed, describing distinct stages of invertebrate assemblages in relation to the vertical structure of vegetation.

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