In situ survival and development of Posidonia oceanica (L.) Delile seedlings

The sexual reproductive success of the marine phanerogam Posidonia oceanica (L.) Delile was evaluated in two different beds along the Tuscan coast, It aly. Seed germination and the development of seedlings was followed in situ over a period of 2 years. In addition, a pilot study was set up on the eff ect of depth and substratum on seedlings survival and development. During t he study period the density of seedlings decreased from initial values of a bout three seedlings m(-2) to 1.9 in the two beds. The rhizome length incre ased from about 2 cm at the beginning to about 5 cm at the end of the obser vation period. The average length of the longest leaves reached maximum val ues during summer and a minimum in autumn, while the number of leaves did n ot show a clear seasonal trend. The analysis of variance performed showed s ignificant differences in survival, Linked both to substratum (dead matte > rock > gravel) and to depth (10 m > 2 m). The analysis also showed signifi cant differences in rhizome growth linked to depth (10 m > 2 m). The result s showed the importance of the post-germination phases in determining the r eproductive success of P. oceanica particularly during the first year of li fe. These phases seem to be closely Linked to the environmental characteris tic of the settlement area; in particular we observed that seedling establi shment, survival and growth strongly depended on depth and on substratum ch aracteristics. (C) 1999 Elsevier Science B.V, All rights reserved.