Surface complexity and gastropod exclusion drive colonization of an intertidal eco‐engineered structure

Abstract Seawalls modify and homogenize marine shoreline habitats but are necessary coastal defences in many regions. Ecological engineering (eco‐engineering) aims to counteract reduced biodiversity by adding microhabitats such as pits and crevices. We tested the effects of increased habitat complexity, designed to enhance biodiversity, alongside invertebrate grazing to understand what drives community structure and ecosystem functioning, estimated by measuring carbon dioxide flux during emersion using infrared gas analysis. Sessile invertebrate species richness increased significantly with habitat complexity, while macroalgae abundance and richness was primarily controlled by invertebrate grazing. Gross community productivity was more strongly influenced by macroalgae cover than habitat complexity. Synthesis and applications . Our findings demonstrate the value of adding microhabitats to coastal defence structures, while underscoring the nuanced relationship between habitat complexity, community composition and ecosystem functioning. A mosaic of different habitats that includes flat and varying microhabitat surfaces may provide the greatest overall ecological benefit.