Population age structure and rhizome growth of Cymodocea nodosa in the Ria Formosa (southern Portugal)

Abstract

The population age structure and derived population dynamics (recruitment, growth and mortality), rhizome growth and flowering effort of Cymodocea nodosa in the Ria Formosa (south of Portugal) were examined using reconstruction techniques. The horizontal rhizome elongation rates were low (13.8–30.7 cm year⁻¹), which is consistent with the low population growth rate (−2.35 to 0.29 year⁻¹). The vertical elongation rate was proportional to the horizontal growth except for one stand that was subjected to sand movements and had higher elongation rates. The mean leaf production varied from 11.8 to 14 leaves year⁻¹. The average shoot age varied from 0.70 to 1.04 years, and the oldest shoot found was 7.6 years. The mortality rates were the highest as yet reported for this species (0.99–3.70 year⁻¹). Observed low growth and high mortality are possibly associated with the development of eutrophic conditions in the Ria Formosa. The flowering probability found in Ria Formosa stands (<0.009–0.90 shoots⁻¹ year⁻¹) was comparable to that found in the Mediterranean and off the Canary Islands. Only two stands with flowering events were found inthe Ria Formosa population, which indicates that the stands are highly dependent on clonal growth to maintain themselves inthe Ria Formosa.