Costa, R.M. da, Matos, J.B., Pinto, K.S.T., Pereira, L.C.C., 2013. Phytoplankton of a dynamic Amazon sandy beach
The present study was developed to characterize the structure and the temporal variation of the phytoplankton of the surf zone of Atalaia beach (Pará, Brazil) and to investigate the effect of certain environmental variables on this community. Nyctemeral sampling was carried out in November/08, March/09, June/09 and September/09. Ninety- eight taxa were identified. The diatoms dominated the local microphytoplankton with the species Coscinodiscus perforatus Ehrenberg, Dimeregramma minor (Gregory) Ralfs, Ditylum brightwellii (West) Grunow and Odontella sinensis (Greville) Grunow having the highest frequency of occurrence and relative abundance. The maximum phytoplankton density was 1,723 ± 257 ×103 cell L−1 in September/09 (F=18.8; p <0.05), while biomass (chlorophyll-a content) was significantly higher in November/08 (U= 0.00; p <0.05). The highest densities of D. minor in September resulted in the lowest observed diversity and evenness. Cluster Analysis showed the formation of three groups, with 55% similarity. The separation of the groups was influenced primarily by the seasonal distribution of samples. Overall, rainfall and consequently variation in salinity showed a strong influence on local phytoplankton composition, density and biomass. Furthermore, the strong local hydrodynamics, as well as the action of the winds and currents promoted the ressuspension of tychoplankton species that characterized the structure of the local phytoplankton.