Analysis of Seagrass Recovery in Experimental Excavations and Propeller-Scar Disturbances in the Florida Keys National Marine Sanctuary
Kenworthy WJ, Fonseca MS, Whitfield PE, Hammerstrom KK. 2002. Analysis of Seagrass Recovery in Experimental Excavations and Propeller-Scar Disturbances in the Florida Keys National Marine Sanctuary. Journal of Coastal Research (JCR). (Special Issue No. 37):75-85
We investigated recovery of seagrasses in two types of mechanical sediment disturbances associated with motor vessel injuries: (1) artificial excavations where we removed all seagrasses in three size categories, 0.25 m², 1.0 m² and 2.25 m²; and (2) propeller scars of known age. We simulated mechanical sediment disturbance in the three excavation sizes in Thalassia testudinum, Syringodium filiforme, and Halodule wrightii meadows growing on soft, carbonate mud banks in the Florida Keys National Marine Sanctuary. After 700 days, results confirmed the long-standing paradigm that H. wrightii and S. filiforme recover significantly faster than T. testudinum. Results from the experimental excavations in monotypic seagrass meadows indicate that there were no significant differences in recovery rates between size categories for each of the species. In monotypic T. testudinum, H. wrightii, and S. filiforme excavations, recovery was predicted to be 1.9, 1.5 and 10.5 years, respectively. Adjusted for a typical scar width of 0.45 m, recovery in propeller scars is estimated to be 9.5 years for T. testudinum, 1.7 years for H. wrightii, and 1.4 years for S. filiforme. In mixed species seagrass communities the subdominant, but pioneering and opportunistic species, H. wrightii or S. filiforme, sometimes colonized the artifical gaps as fast or faster than T. testudinum, suggesting that physical disturbance from motor vessels can alter the relative abundance of seagrass species on a bank. For the 15 existing propeller scar injuries, the rate of recovery predicted for T. testudinum was faster than in the excavations, 6.9 years versus 9.5 years. These results suggest that injury recovery models and restoration strategies for vessel injuries should consider species composition of the injured site as well as the physical dimensions of the injury, including the excavation depth.
- Type
- Journal Article
- Authors
- Kenworthy, W; Fonseca, Mark; Whitfield, Paula; Hammerstrom, Kamille
- Units
- GULN
- Keywords
- Analysis, Background, Center, Coastal, comparison, Design, Disturbances, excavation, Excavations, Experimental, Experimental, Fisheries, Florida, grounding, Habitat, keys, Marine, Methods, National, Objective, overburden, propeller, Recovery, Recovery, Research, Sanctuary, scar, Seagrass, Site, Study, typical, vessel