Sheath length as a monitoring tool for calculating leaf growth in eelgrass (Zostera marina L.)

Recent advances have improved ease and accuracy in seagrass growth measurements. Despite these improvements, seagrass leaf growth can be difficult to measure effectively; current methods are destructive to the plants and require at least two site visits per growth period. We used the "previous growth" of Ibarra-Obando and Boudouresque [Ibarra-Obando, S.E., Boudouresque, C.F., 1994. An improvement of the Zieman leaf marking technique for Zostera marina growth and production assessment. Aquat. Bot. 47, 293-302.] to develop a relationship between sheath length and leaf growth in eelgrass, Zostera marina L., and we demonstrated that a simple, non-destructive method allows reliable calculation of eelgrass leaf growth (mg shoot^-1 day^-1) based on sheath length. We measured eelgrass sheath length and leaf growth for 18 months, from November 1999 to April 2001, at a site in Portsmouth Harbor on the border of New Hampshire and Maine, USA. Regression analyses showed a high coefficient of determination between sheath length and leaf growth, demonstrating that sheath length reliably reflected eelgrass leaf growth. We also showed that four seasonal measurements were sufficient to establish a significant relationship between sheath length and leaf growth. After a regression of sheath length and leaf growth has been established for a site, eelgrass sheath length can be measured in situ to accurately calculate leaf growth, eliminating both the need for destructive growth measurements and the need to mark and relocate plants.