Effects of fish herbivory on seagrass meadows of Guang-guang, Mati City, Philippines

Abstract

This study provides information on the effects of fish grazing on a seagrass bed that was dominated by Thalassia hemprichii in Guang-guang, Dahican, Mati City, Davao Oriental, Philippines. We tested the assumption that herbivore exclusion keeps the growth of seagrass shoots up to a minimum length. Fish visual census was used to count the abundance of fish in the area during high tide at a distance of 5 m away from the treatment cages with a 15 m transect length. Among all species, Siganus fuscescens was the most abundant (499) followed by S. guttatus (153), while Thalassoma jansenii was the less abundant (13). The result of the weekly fish count in the seagrass bed showed highly significant variations in the number and census of species present in the area (df = 11, MS = 2.88, F = 30.10, p < 0.001). Analysis of shoot length measurement in treatment cages also exhibited highly significant differences throughout the sampling period (df = 11, MS = 726.71, F = 1,633.10, p < 0.001). Comparison between initial and final shoot counts also showed significant differences, with a higher shoot count in the full cage (X2 = 8, df = 2, p = 0.018; FC > PC > OP). This study raises clear evidence to support the assumption that herbivore exclusion positively influences the growth of T. hemprichii in this area.