Regrowth of the seagrass Thalassia testudinum into propeller scars

Abstract

Regrowth of turtle grass, Thalassia testudinum Banks ex Konig, into existing propeller scars and artificial cuts was studied in a mangal estuary located in Tampa Bay, Florida. Sediments from scars and cuts and adjacent grass beds were not significantly different in relation to particle size distribution and levels of calcium carbonate. Significantly lower concentrations of total organic matter and extractable ammonium but not phosphate were detected in scars. Increases in ammonium levels coincided with the expansion of T. testudinum into a propeller scar. Seagrass blade morphology and productivity did not significantly differ in short shoots growing along the edges of scars or cuts relative to those in adjacent seagrass beds. Rhizome architectural studies revealed that apical meristems were few in number (19 to 38% of rhizomes) and randomly orientated in undisturbed grass beds (31 to 53% oriented toward center). In contrast, a greater percentage of apical meristems (78 to 88%) along the edges and in scars or cuts were directed towards the center. Full regrowth required an average of 3.5 to 4.1 years in existing propeller scars and could take up to 7.6 years in artificial cuts. The lack of changes in shoot productivity and limited production of rhizome meristems in T. testudinum result in slow regrowth in propeller cuts. The management implication is that turtle grass meadows will show long-term damage from propeller scars if not protected.