Temperate Intertidal Ecosystems are Functionally Richer but More Vulnerable to Loss Than Tropical Ecosystems

Gastropods are major contributors to a range of key ecosystem services on intertidal rock platforms, supporting trophic structure in both terrestrial and marine contexts and manipulating habitat complexity. However, the functional structure of these assemblages is rarely examined across broad spatial scales. Here, we describe patterns in gastropod functional diversity, redundancy and vulnerability to functional loss across a latitudinal gradient following the west coast of Australia (18° S-34° S). Specifically, we created a trait matrix based on six categorical traits for 186 gastropod species from 39 sites to examine how trait composition varied with latitude. We found there was no latitudinal gradient in either functional richness or distinctiveness despite clear gradients in species richness and taxonomic distinctiveness, which both increased towards the equator. We delineated two distinct functional bioregions, a temperate south (34° S-27° S) and a tropical north (24° S-18° S), and found that the temperate bioregion had greater functional richness and uniqueness but lower redundancy compared to the tropical bioregion. Our findings show that gastropod assemblages in the temperate bioregion are more vulnerable to functional loss as their functional entities are supported by fewer or even single species. Comparatively, the tropical bioregion reported higher redundancies, which could provide a buffer against future change. Understanding the functional structure of intertidal ecosystems is vital as gastropods face the uncertain impacts of coastal tropicalisation, range shifts and sea level rise.