Distribuição espaço-temporal da comunidade zooplanctônica no estuário do Taperaçu (Bragança-Pará-Brasil): biomassa e produção secundária das principais espécies de copépodos

Abstract

This study aimed to determine the composition and distribution of zooplankton in the estuary Taperaçu evaluating, in temporal and spatial scales, the contribution of the main species of copepods for biomass and production in terms of organic carbon in the environment under study. Therefore, samples were taken bimonthly (zooplankton and hydrologic variables) from June 2012 to June 2013, in three fixed stations located along the estuary, totaling 45 samples. The zooplankton community was apparently homogeneous. With regard to biological attributes, significant variations related to circadian cycles (day/night) and tidal periods (flood/ebb) were not detected. High values of abundance of Paracalanus quasimodo, Labidocera fluviatilis and Pseudodiaptomus marshi were observed. The absence of a nichtemeral and tidal patterns, was possibly related to the morphodynamic characteristics of the estuary Taperaçu, such as the presence of sandbanks in its central portion, the absence of a river discharge, the small catchment area, low depths and strong tidal currents, which facilitate the processes of horizontal and vertical mixing of the water column. When analyzed on a monthly and spatial scale, it was observed the influence of seasonal periods on the dynamics of these organisms, these being directly related to variations in salinity, turbidity and chlorophyll-a concentrations. The zooplankton community was dominated by copepods, especially Acartia tonsa (22,230.9±46,145.7 ind.m ), Acartia lilljerborgi (4,011.6±10,326.5 ind.m -3 ), P. quasimodo (9,270.7±17,593.3 ind.m -3 ), P. marshi (3,267.3±4,565.1 ind.m-3) and Oithona oswaldocruzi (30,221.9±28,328.4 ind.m-3-3), together with Oikopleura dioica (15,284.6±26,060.6 ind.m-3). The average diversity of species ranged from 2.0±0.6 bits.ind-1 to 3.8±0.4 bits.ind-1, while the evenness ranged from 0.5±0.1 to 0.7±0:03. Overall, the temporal variability (monthly and temporal) and spatial observed in the structure and dynamics of zooplankton population was mainly related to fluctuations in precipitation rates, which directly affect the salinity of the water and consequently the abundance of these organisms. In addition, it was also concluded that the presence of typically marine species such as P. quasimodo and O. dioica may be related to the significant increase in salinity as a result of reduced rainfall in 2012. Biomass and production A. tonsa and A. lilljeborgi were directly related to the local rainfall since, A. tonsa showed high values throughout the period, not only in the rainy season as previously observed in this same estuary. The immature stages (C1-C5) of A. tonsa were the dominant forms, especially the C4 stage (839.88±1518.80 mgC.m), while for A. lilljeborgi the highest values were obtained for adults (1,347.84±499.95 mgC.m-3). The obtained rates of secondary production were higher than those described for other estuaries located around the world, and these results are associated with the high temperatures recorded during the year as well as the observation of water rich in nutrients and particulate organic matter derived from adjacent to mangroves Taperaçu. In general, the results indicate that the influence of climate changes on the hydrological variables especially temperature, salinity, as well as the concentration of chlorophyll-a were the main responsible for the dynamics of mesozooplanctônicas species identified in the estuary of Taperaçu.