Temporal variation of biomass and productivity of Thalassia testudinum (Hydrocharitaceae) in Venezuela, Southern Caribbean

ABSTRACT

Annual biomass and productivity of Thalassia testudinum were determined during a year at a seagrass bed located in the Parque Nacional Morrocoy, Venezuela. Leaf, rhizome and root biomass were determined monthly, together with short-shoot density, from February 1992 to January 1993, from nine replicated core samples. Productivity was measured using the methodology by Zieman (1974) with minor modifications, and leaf turnover rate was calculated. Leaf biomass values ranged between 101.73 dry g m(-2) in February and 178.11 dry g m(-2) in August. Productivity ranged from 1.69 dry g m(-2) d(-1) in April and October to 3.30 dry g m(-2) d(-1) in July, showing two annual peaks one in July and one in March. The leaf turnover rate showed the highest value in June (2.41% d(-1)) and the lowest in May (1.23% d(-1)). Sampling time differences in leaf biomass, productivity and turnover rate were statistically significant. Short-shoot density values varied between 811.10 shoots m(-2) in April and 1226.08 shoots m(-2) in December, but the differences were not significant along the year. These results indicated seasonal trends for leaf biomass, productivity and turnover rate of T. testudinum in the Southern Caribbean (latitude 10 degrees N).

RESUMEN

Durante un año se determinaron mensualmente la productividad foliar, la densidad de tallos cortos y la biomasa de hojas, tallos cortos, rizomas y raíces de Thalassia testudinum, en una “pradera” localizada en el Parque Nacional Morrocoy, Venezuela. Los valores de biomasa foliar estuvieron entre 101.73 g/m2 en febrero y 178.11 g/m2 en agosto, los de productividad foliar se ubicaron entre 1.69 g/m2/d en abril y octubre y 3.30 g/m2/d en julio, mostrando dos picos anuales, uno en julio y otro en marzo. La tasa de recambio foliar mostró el mayor valor en junio (2.41%/d) y el menor en mayo (1.23%/d). Tales diferencias fueron estadísticamente significativas durante el año para todas estas variables. La densidad de tallos cortos fluctuó entre 811.10 tallos/m2 en abril y 1 226.08 tallos/m2 en diciembre, pero las diferencias no fueron significativas a lo largo del año. Estos resultados indicaron una tendencia estacional para la biomasa foliar, la productividad foliar y la tasa de recambio de las hojas de T. testudinum en el Caribe Sur, a 10º N de latitud.