Recruitment of Thalassia testudinum seedlings into physically disturbed seagrass beds

Abstract

Thalassia testudinum seedling recruitment, survival, and growth were examined within physically disturbed seagrass beds in the Florida Keys. Two separate studies were conducted. In the first, a large-scale study, T. testudinum seedlings were surveyed and collected from a large seagrass disturbance (1560 m2), 4.8 yr after the initial impact from a motor-vessel grounding. In the second, a smaller-scale study, T. testudinum seedling recruitment was examined over a 2 yr period within 9 smaller motor-vessel disturbances located within intact T. testudinum beds. In the large-scale study, we reconstructed the age of the seedlings based on shoot production rates from a previous study and from the small-scale study. A total of 79 seedlings were collected that varied in age from young of the year to 4.8 yr old; 6 different seedling cohorts were identified. The average density and rhizome-elongation rate for 1 yr old seedlings were 1 m-2 and 6.6 cm yr-1, respectively. In the small-scale study, we surveyed and permanently marked all newly recruited seedlings; monitoring was conducted 5 more times over a 2 yr period. The average seedling survival after Year 1 was 42%; after Year 2, average survival dropped to 20%. The average seedling density after Year 1 was 0.071 m-2; after Year 2, average density dropped to 0.026 m-2. The average rhizome-elongation rate and shoot-production rate of 1 yr old seedlings were 6 cm yr-1 and 1.8 shoots yr-1, respectively. The results of this study suggest that T. testudinum seedlings are a regular and reliable source of new recruits on seagrass banks in the Florida Keys.