ABSTRACT
Abstract The effects of small-scale disturbance by burrowing shrimps (defoliation, shoot burial) on the growth patterns of the seagrass Thalassia hemprichii (Ehrenberg) Ascherson were examined in three manipulative experiments. Disturbance was applied in situ on apical shoots (Expt. 1) and on tank-grown seedlings (Expt. 2) and apparent shrimp activity was blocked in situ from seagrass plugs in exclosures (Expt. 3). Changes in leaf growth and rhizome elongation/ root growth rates were measured and compared after four short periods (4, 7 or 8, 14, and 25 or 28 days) in Expts. 1 and 2, while in Expt. 3, leaf growth rates of mature T. hemprichii shoots and shoot densities of coexisting species within the plugs were monitored for a year. In apical shoots, burial for at least 14 days induced accelerated leaf growth, while clipping and combined treatments had minimal effects on module growth. Clipping did not cause module growth differences with control seedlings. Burial, alone and combined with clipping disturbance, however, significantly and continuously decreased seedling growth. Exclusion from shrimp activity did not influence leaf growth rates of mature shoots. Both T. hemprichii growth and shoot densities of other coexisting seagrass species exhibited strong temporal variation as expected.
