Luci Cajueiro Carneiro Pereira

Diel variation in the productivity of Acartia lilljeborgii and Acartia tonsa (Copepoda: Calanoida) in a tropical estuary (Taperaçu, Northern Brazil)

ABSTRACT Magalhães, A., Nobre, D.S.B., Bessa, R.S.C., Pereira, L.C.C. and Costa, R.M. da, 2013. Diel variation in the biomass and productivity of Acartia tonsa (Copepoda: Calanoida) in a tropical estuary (Taperaçu, northern Brazil). In: Conley, D.C., Masselink, G., Russell, P.E. and OHare, T.J. (eds.) Diel variation in the productivity of the copepods Acartia lilljeborgii and Acartia tonsa was investigated in the Taperaçu estuary in July (rainy season) and October (dry season), 2004. The estimated productivity of A. lilljeborgii (min-max: 3.932,385.41 mg C m−3 d−1; mean: 246.60 mg C m−3 d−1) and A. tonsa (min-max: 0.32–160.21 mg C m−3 d−1; mean: 16.99 mg C m−3 d−1) highlight the importance of their contribution to zooplankton production in the Taperaçu estuary. The absence of significant short-term variation in the productivity of A. lilljeborgii and A. tonsa in relation to the period of the day may be related to the combined effect of the shallow depth of the waters of this estuary and its strong tidal currents. These factors rendered the water column homogeneous, reducing the effect of the vertical migration of the zooplankton as a potential factor responsible for oscillations in the density of these organisms during the course of the day. The influence of tidal variation (flood/ebb) on the dynamics of these two species was also unclear in this study due to a number of morphological and morphodynamic characteristics of the estuary, such as the absence of any measurable fluvial discharge and the small catchment area, which resulted in an minor and infrequent inflow of freshwater into the estuary.

Phytoplankton of a dynamic Amazon sandy beach

ABSTRACT 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.