Predicting diversity in benthic macro-scale communities associated with mussel matrices in three Pacific ecoregions

Marine mussels are ubiquitous and their tough byssal threads allow for the formation of expansive, age-aggregated mats known as mussel matrices which can host marine invertebrates and algal macro-benthic communities playing an important role in food-web dynamics. Yet, despite the significant implications for biodiversity and intertidal ecosystem functioning, the role of mussel size, individual morphology and community arrangement in determining the structure of the associated community has never been investigated. Species representative of the green, brown and red marine algal phyla as well as polychaetes, crustaceans and gastropods were sampled from mussel matrices in the Guayaquil (GUAY), Humboldtian (HWS, HNS) and North American Pacific Fjordland (NAPF) marine ecoregions. Linear mixed effects modelling (LMM) and linear effects modelling (LEM) were used to determine the effect of mussel matrices as a predictor of species diversity by incorporating variability due to ecoregion and sampling site. Shell length and stratum index demonstrated significant effect on species richness (S-obs) and Menhinick's richness (D), while stratum index demonstrated an effect on species diversity (H). In the linear mixed model analysis, shell length explained most of the variation in Menhinick's richness (D) and observed species richness (S-obs), while stratum index explained most of the variation in (D) in the linear effects model. Our findings reveal that the level of complexity in mussel assemblages plays a major role in determining species diversity.