Herbivory is an important determinant of macroalgal distribution on both tropical and temperate reefs (1). As oceans warm and species shift poleward, 'tropicalized' communities are rapidly forming which can produce novel herbivory dynamics and alter reef structure and function (2). However, with reef herbivory research primarily focused on fishes, benthic invertebrate contributions to between realm variability remains unresolved, leaving fundamental gaps in our understanding of this important process, amidst rapid ecological change (3,4,5).
Using standardized macroalgal assays across 2-12m depths, fish-only and fish-plus-invertebrate herbivory sources were measured on replicate tropical and temperate reefs. Fish-only assays revealed anticipated trends between realms, with 35% consumption on tropical and 4.3% on temperate reefs, indicating reduced fish function on temperate reefs. However, when including invertebrates, consumption patterns became surprisingly similar (35% tropical, 27% temperate), with both realms exhibiting a negative relationship between consumption and depth.
Challenging previous fish-based paradigms, that feeding decreases with latitude by demonstrating consumption can occur at similar levels across realms, but with fundamental differences in how it is delivered, being more diffuse on tropical reefs and becoming benthically constrained on temperate reefs. This fundamental difference suggests that as temperate reefs tropicalize, herbivory will likely shift toward a more diffuse process.