Simulated green turtle grazing affects structure and productivity of seagrass pastures

• Published in: Marine ecology. Progress series (Halstenbek) 2005-12, Vol.305, p.235-247
• Main Authors: Moran, Kathleen L., Bjorndal, Karen A.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Average linear density; Biological and medical sciences; Chelonia mydas; Ecological sustainability; Environmental conservation; Fundamental and applied biological sciences. Psychology; Grazing; Herbivores; Marine; Marine ecosystems; Pastures; Productivity; Rhizomes; Sea water ecosystems; Synecology; Thalassia testudinum; Turtles
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps305235

The seagrassThalassia testudinumevolved under much greater grazing pressure than exists today because overexploitation by humans caused the severe decline of green turtlesChelonia mydas, the major seagrass herbivore in the Caribbean. Understanding the effects of grazing on the structure and function of seagrass ecosystems is critical to evaluating how ecosystem processes have changed since the major herbivore was essentially removed from modern Caribbean seagrass systems. We evaluated effects of grazing on the structure and productivity ofT. testudinumpastures by simulating green turtle grazing in 3 × 3 m plots for 16 mo in the central Bahamas and comparing these clipped plots to adjacent control (unclipped) plots. Simulated grazing affected the physical structure ofT. testudinumplots, resulting in a system with reduced structural complexity. Simulated grazing resulted in compensatory growth inT. testudinum. Clipped plots maintained levels of growth comparable to unclipped plots over the 16 mo clipping trial, and specific mass growth was significantly elevated in clipped plots, even without simulating the nutrient return from green turtle feces and urine. The green turtle grazing pattern of re-croppingT. testudinumplots is sustainable for long periods—at least 16 mo. We estimated a range of carrying capacities ofT. testudinumfor green turtles of 1567 to 3748 kg turtle ha–1. Our study provides a foundation for reconstruction models and restoration plans for Caribbean seagrass ecosystems.