Abstract
Spatial and temporal distribution of two species of adult´s ostracods (Cyprideis sp. and Cyprideis salebrosa) were studied as a function of the rainfall patterns in the Guanabara Bay, Rio de Janeiro, Brazil. Samples were taken in ten stations, along six surveys representing three periods (Dry, Early and Late Rainy) for two years. Stations were nested in four areas (Outer, Central, EPA Guapimirim and Impacted). The bottom water (temperature, salinity, dissolved oxygen and oxygen saturation) were measured in each area to characterize the influence of seasonal variations by rainfall. Cyprideis sp. and Cyprideis salebrosa showed patterns distribution to seasonality/surveys (p = 0,002 and p <0,001, respectly). The spatial distribution of Cyprideis sp was significantly different areas studied (p <0.001) indicated well defined areas and distribution in along of the surveys. However, C. salebrosa showed homogeneous distribution in along of the areas within of each survey (p <0.001). Redundancy Analysis (RDA) for the two years evidenced environment preference of the Cyprideis sp. for areas with marine conditions (high influence for channel central) and C. salebrosa for brackish water (high influence of the rivers). This observation reinforces of the existence of areas created by the seasonality of pluviometric regime, a possible dispersion of the adult's ostracods and possibility the use with bioindicators.
Highlights
In tropical estuaries, benthic biological processes are usually strongly influenced by the characteristics of the water mass above the communities, as well as the granulometric bottom structure (Day et al, 1989; Little, 2000; Gray and Elliot, 2009)
The lowest salinity was always observed in the inner areas during early rainy season (ER1 and ER2), whereas higher temperatures and lower levels of both dissolved oxygen and oxygen saturation occurred in late rainy season (LR1 and LR2) (Figure 3)
A clear spatial gradient was apparent on bottom water characteristics with salinity constantly decreasing and seasonal variation increasing towards the entrance (Outer) to the inner bay (Impacted), where the lower and temporally variable salinities are indicators of the seasonal inflow of river water inside the bay itself (Figure 3)
Summary
Benthic biological processes are usually strongly influenced by the characteristics of the water mass above the communities, as well as the granulometric bottom structure (Day et al, 1989; Little, 2000; Gray and Elliot, 2009) Communities parameters reflect these conditions through variations in species composition and relative dominance, due to species-specific physiological tolerance to several factors, allied to particular dispersion pattern strategies (Day et al, 1989; Gray and Elliot, 2009; Echeverría et al, 2010; Neves et al, 2013; Pereira et al, 2013; Magalhães et al, 2014). This balance between marine input, regulated by river-runoff, and tide amplitude, results in a characteristic seasonal variation in Guanabara Bay, which presents an extremely wide watershed (Mayr et al, 1989; Amador, 1997; Kjerfve et al, 1997; Amador, 2012)
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