Nitrogen, as a nutrient, is considered a rate-limiting factor. Additionally to the pool nutrients, abundance of particular species can be delennined by biomass of seagrass and plant architecture. including algae associated to Thalassia meadows. To test this, mree sampling stations of T. testudinum beds were studied al Morrocoy National Park Venezuela (lOO52'N-6go16W). Al each, a 20 X 20 meter plot was markedpennanently and, alleast, ten random quadrats were sampled moothly during 13 months. Nitrogen colltents in sediments and biomass of H. opunlía influence positively me abundance of Potamilla sp. (A= 21.49; B= 6.0; C= 1.05). Both parameters showed the following gradient: A>B>C (r= 0.6549; p<0.0l). The influence of me algae was noled particulary on me Morisita dispersion index (Ig).