Biogenic habitats as drivers of invertebrate benthic community variability in Tongoy Bay (SE Pacific coast): implications of macroalga harvesting

Habitat biogenic complexity is thought to exert a significant positive influence on benthic communities. We examined the link between the seasonal variability of macroinvertebrate community structure (species and trophic richness, diversity and biomass) and habitats with different macroalgal assemblages. We identified macroinvertebrates and algae from 336 samples spread over four types of habitat: sand, mud, sand-gravel and seagrass meadows. Considering the whole macroalgal and macroinvertebrate assemblage, we confirmed that macroinvertebrate community variability within and among habitats can be mainly (but not only) explained by a few macroalgal structuring species. The variability of macroinvertebrate communities between habitats and seasons depended on the changes in the relative contribution of the explanatory biostructuring species in the overall algal community. Biomass, trophic behaviour and species richness remained stable in habitats with conspicuous macroalgal communities in contrast with habitats devoid of macroalgae. However, invertebrate species richness and biomass remained stable only in habitats whose dominant species did not change between seasons and not in those where dominant structuring species shifted. The seasonal change in a key structuring macroalgal species (Condracanthus chamissoi), probably as a result of harvesting, led to a major reduction in invertebrate community biomass and richness both in the particular habitat and in those nearby at species level. These consequences are especially important for invertebrates linked by trophic relationships and targeted by fisheries.