Duration of prolonged simulated green turtle grazing affects Thalassia testudinum regrowth dynamics following grazing cessation in a subtropical Caribbean ecosystem

Populations of the green turtle ( Chelonia mydas ), a megaherbivore that maintains distinct areas of seagrass via cultivation grazing, are recovering worldwide. Evaluating seagrass regrowth dynamics in grazed areas following prolonged, known-durations of herbivory is challenging in situ, but is critical to understand ecosystem function as meadows return to a natural grazed state. Based on a 27-month study in a subtropical Caribbean seagrass meadow (The Bahamas; 23.46° N, 76.06° W), we evaluate Thalassia testudinum regrowth dynamics over 11 months following two durations of simulated green turtle grazing (11 and 16 months; 11clip and 16clip, respectively). By the end of the clipping treatments, simulated grazing had induced significant changes in most T. testudinum leaf morphology and nutrient variables in clipped plots compared to reference plots, while belowground biomass and nutrient content were unaffected. However, most leaf variables in clipped plots returned to levels comparable to reference plots by 6.5 months after the cessation of clipping, with the exception of leaf area index (LAI) and leaf width. The effects of grazing duration on regrowth in clipped treatments were evident in 11clip and 16clip plots. In 11clip plots, LAI increased to reference plot levels within 6.5 months after cessation of clipping, while leaves did not rewiden until 11 months post-clipping. However, LAI in 16clip plots did not reach reference plot levels until 11 months post-clipping, and leaves remained significantly narrow throughout the experiment. These regrowth patterns indicate the capacity of T. testudinum to rebound following prolonged, repetitive cropping of leaf biomass by green turtles, and that decreased leaf width and LAI after cessation of grazing may be a lingering effect of shifts in plant growth allocation in grazed systems. This study provides a valuable contribution to understand the effects of cultivation grazing and grazing duration on T. testudinum regrowth dynamics and tolerance to herbivory.