Growth dynamics of the seagrass Halophila johnsonii from a subtropical estuarine lagoon in southeastern Florida, United States of America

Biomass, net production, turnover, and decomposition of the seagrass Halophila johnsonii were studied in the Lake Worth Lagoon, Palm Beach County, Florida, USA. Biomass and apical meristem density averaged 8.0 g dry wt/m^2 and 1122/m^2, respectively. Mean net productivity was 0.00154 g dry wt/shoot/day or 0.45cm/shoot/day with one new leaf pair for every 0.97 cm of shoot growth. Estimated turnover time was 4.6 days. Mean weight loss in plant material was 72% after three days and 88% after seven days. No evidence was found of sexual reproduction. Halophila johnsonii's growth dynamics in the intertidal and shallow subtidal zones are characterized by low biomass, substantial apical meristem density, regular leaf pair production, rapid turnover, and rapid decomposition. Halophila johnsonii's growth in these zones provides an additional level of biomass and detritus to the shallow lagoon system.