The Coastal Zone is the transition between terrestrial and marine environments, which
are known for their high biomass production and ability to support major fish stocks.
Inserted in this context, is the phytoplankton community, which forms the basis of the
aquatic food chain. The study of the composition and temporal distribution of such a
community is crucial to understand the main mechanisms of functioning of aquatic
ecosystems. This study aims to characterize the structure and dynamics of
phytoplankton community and its spatial-temporal variation along the estuary of the river
Marapanim (Pará, Brazil). To achieve this goal were collected during the
September/2006 and February/2007 in two sampling profiles distributed throughout the
estuary. Samples for the qualitative study were obtained from trawls horizontal subsurface
water, while those for the quantification of chlorophyll was obtained through
direct collection. The structure of the phytoplankton community of the estuary of the river
Marapanim was represented by four divisions: Cyanophyta, Chlorophyta, Dinophyta and
Bacillariophyta, which is the group with higher taxonomic richness, with emphasis on
species such as Rhizosolenia setigera, Dimeregramma minor, Chaetoceros sp. and
Bacillaria paxillifera. Diatoms were frequent and dominant in both seasonal periods, was
recorded the presence of marine planktonic species nerítica, marine planktonic oceanic,
coastal and marine planktonic marine-nerítica ocean. Already the phytoplankton
biomass showed higher rates in the rainy season, which may be related to the high
concentration of nutrients brought by continental drainage. In the period studied was
possible to observe that the rainfall regime exercised significant influence on the
composition and phytoplankton biomass (chlorophyll a), which can be considered the
main factor controlling the dynamics of these organisms in the estuary of the river
Marapanim.
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