Differential coping capacities underlie the overall resistance of temperate seagrasses to herbivory

Overgrazing events impart long-lasting changes in vegetated ecosystems. How ecosystems respond to herbivory depends on the ecological and evolutionary histories of their foundational species. The overall functioning and biodiversity depend on these responses and there is still little understanding of the intensity and duration of how herbivory interact. We experimentally tested the change in three seagrass species with distinct life-history traits to increasing intensities of herbivory. Specifically, we assessed structural responses (i.e. canopy height and shoot density) to reflect the ecosystem state. Additionally, we used mechanistic models to assess induced and constitutive responses in the seagrasses. Results show that seagrasses coped with herbivory differentially in relation to their life-history traits. The persistent Posidonia oceanica was more resistant than C. nodosa (colonising) and Z. noltei (opportunistic/colonising). Seagrasses also differed in the type of structural response, with the colonising species experiencing reductions in shoot density and the persistent P. oceanica registering declines in canopy height. After months of exposure to cumulative herbivory, all three species showed signs of stability. Interestingly, none of the species disappeared completely even when exposed to extreme herbivory. Mechanistic models indicate that herbivory-induced responses are a potential explanation for these patterns. This study suggests that given the long evolutionary history of herbivory, some seagrasses may be remarkably well adapted to both intense and cumulative herbivory.