This study observed the spatial and temporal distributions of molluscs in a Halodule wrightii meadow, verifying if they respond satisfactorily to seasonal changes in this seagrass ecosystem. Twenty-four species were identified. Chitons were rare, bivalves had greater number of species (11), followed by gastropods (9) which were also the most abundant class (73%). All classes were more abundant in the belowground. The most common species was Tricolia affinis, especially in aboveground. The occurrence of some species in both strata or out of the expected stratum may have been influenced by shallow layer of the sediment considered in this study, hydrodynamic, and low biomass of the studied meadow. According to univariate and multivariate analyses, despite of molluscan descriptors had been related to variables associated with rainfall, the seagrasses had an important role on the seasonal and vertical variations of the molluscan fauna. The biomass of the epiphyte Hypnea musciformis was correlated to temporal variations of the species from aboveground, indicating its secondary role for this community. The molluscs were sensible to environmental variations, and also reflected seasonal changes of the seagrass, showing that damages on these meadows reflect even at lower levels of the marine food web.

ABSTRACT. The diff erent microhabitats provided by seagrasses and the habit of the species determinate the vertical distribution of crustaceans. This study verifi ed the infl uence of the seasonality on the spatial distribution of the crustacean community associated with a Halodule wrightii meadow. From April 2006 to July 2007, we performed fi fteen samplings in Goiabeiras Beach, Ceará State, each with fi ve sectioned replicates in belowground and aboveground. Cumaceans and the amphipod Hyale media (Dana, 1853) had a higher frequency, density, and dominance than the other taxa, in both strata. The community exhibited gradual changes along the study, in both the belowground and aboveground strata, but the seagrass structure was not suffi cient to explain the vertical distribution of the crustacean fauna along the time.KEYWORDS. Seagrass, shoal grass, benthic communities. RESUMO. Variação sazonal da fauna de crustáceos nos estratos subterrâneo e aéreo em uma pradaria de Halodule wrightii do nordeste do Brasil.Os diferentes microhabitats proporcionados pelas pradarias marinhas e o habito das espécies determinam a distribuição vertical de espécies de crustáceos. Este estudo verifi cou a infl uência da sazonalidade sobre a distribuição espacial da comunidade de crustáceos associada a uma pradaria de Halodule wrightii. De abril de 2006 a julho de 2007, foram realizadas 15 amostragens na praia das Goiabeiras, estado do Ceará, em cada uma com cinco amostras seccionadas em partes aérea e subterrânea. Cumáceos e o anfípode Hyale media (Dana, 1853) tiveram a maior frequência, densidade e dominância em relação a outros táxons, em ambos os estratos. A comunidade exibiu mudanças graduais ao longo do estudo, em ambos os estratos aéreo e subterrâneo, mas a estrutura da pradaria não foi sufi ciente para explicar a distribuição vertical da fauna de crustáceos ao longo do tempo.PALAVRAS-CHAVE. Pradarias marinhas, capim marinho, comunidades bentônicas.