Flowering frequency of Philippine seagrasses

The flowering frequency of the Philippine seagrasses Thalassia hemprichii (Ehrenb.) Aschers., Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., and Enhalus acoroides (L.f.) Royle, growing on a reef flat in Bolinao (Pangasinan Province, The Philippines) was examined based on examination of flowering scars on the seagrass shoots. The flowering frequency of C rotundata and T. hemprichii was low (0.064 flowers shoot^-1 yr^-1 and 0.125 flowers shoot^-1 yr^-1, respectively), indicating that only a fraction of the shoots of these species will flower during their life spans. Shoots of these species required a maturation period of between half a year and one year before flowering. In contrast, most of the E. acoroides shoots examined had flowered several times, producing, on average, 2.8 flowers shoot^-1 yr^-1. Examination of the past flowering of E. acoroides revealed substantial interannual differences in flowering frequency in the period 1985-1992, with a maximum in 1987. Because of the large flowers of this species, the estimated biomass allocated to flowering was orders of magnitude greater for E. acoroides (35.8 g dw m^-2 yr^-1) than for C rotundata (0.021 g dw m^-2 yr^-1) and T. hemprichii (3.56 g dw m^-2 yr^-1). These results indicate that sexual reproduction could be a minor sink of resources for C rotundata and T. hemprichii (< 1% of the annual above-ground production), while it may represent a dominant source of losses of resources acquired by E. acoroides (up to 50% of the annual above-ground production). The implications of these contrasting strategies in the flowering effort of the seagrass species examined are, however, unclear, but the large output of sexual propagules of E. acoroides, compared to the other two species, should confer this species a greater capacity to recover after disturbance.