The phytoplanktons are organisms that have limited locomotion about the current being drift in aquatic environment. Another characteristic of phytoplankton their growth and energy are result about photosynthetic process. It is important to emphasize that the phytoplankton is the main primary producer of aquatic environment, it means that, it is the base the aquatic food chain . The organic material produced by phytoplankton is responsible in provide the material and energy which sustains the growth of fish, crustaceans and mollusks, in marine ecosystems. Because of this, it is important to know the factors that interfere with their accumulation in environments mainly in fishing regions. In this way, this study tries to demonstrate the importance of retention time, often caused by hydrological issues, in the variation of phytoplankton biomass in the estuary of the Patos Lagoon (ELP), in Rio Grande/RS. To do that, we created one model that simulates this environment, using techniques of multi-agent-based simulation and its implementation was done with the NetLogo tool.
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Plankton (in Greek – plágchton) means wandering because of its power of locomotion be void against the current, and so it is “no moviment” in the aquatic environment. The Plankton can be divided into two distinct categories which are: the animals (zooplankton) and plants (phytoplankton) (Lalli and Timothy 1997). Thus, the focus of this study is to determine the variation of phytoplankton biomass in the estuary of the Patos Lagoon (ELP) in response to hydrologic conditions.
Many studies (Howarth et al. 2000, Jassby, 2008) have as the aim to know the factors that control the amount of phytoplankton biomass in aquatic environment. The tasks have been doing in this area show some factors as light nutrients and predation for the production of phytoplankton. There are other studies (Abreu et al. 2010; Lucas, Thompson and Brown, 2009) show the interference of waters movement and the process of accumulation, mainly when it refers to retention or transport time.
The previous mentioned studies are divided by types of aquatic environments and they are related to rivers, lakes, sea, estuaries and others. In our studies, we will work with estuaries. They are transitional environmental between fresh water and salty water (Pritchar, 1967). The estuary which will be used as an example for this proposal is the Estuary of the Patos Lagoon (ELP).
Estuaries are environments where mixing occurs between fresh water coming from the continent and marine waters (Pritchar, 1967). The ecological processes of estuaries are similar to other aquatic environments such as oceans, lakes and rivers. The ELP is located in the extreme south of Brazil and it is included by Patos Lagoon and its connection with Atlantic Ocean by a canal about 800 meters wide. That region has approximately 900 square kilometers and it is an environment of low depth 75% of this area has less than two deep meters (Seeliger & Odebrecht 1997). By having a close link with the sea and to be near an anfidromic point (it is a point where the tide is null), the tides are small amplitudes. Another feature about this estuary is that it is surrounded by two big cities, Pelotas and Rio Grande. Moreover, in this place is situated the Port of Rio Grande, one of the biggest of Brazil (Seelinger & Odebrecht 1997).
There is a lot of phenomena involved in the growth of phytoplankton and a great diversity of phenomena involved with estuaries and it becomes difficult to have conclusive data which determine the control factors of the variation of the biomass of phytoplankton. At present, the collection is carried out intensively in time and the space through sensors. However, these sensors must have periodic maintenance and the cost is high.
These factors are of great importance for the life of the species located in the estuary because of the low depth ensures that sunlight is not a limiting factor for the photosynthetic activity of the primary producers and the action of man ensures excess nutrient needed the development of life in this environment (Lalli & Timothy 1997). Because of this, studies have sought other factors influencing phytoplankton biomass accumulation in the ELP. These studies are directed mainly to abiotic factors such as the wind and rain, which act directly on the hydrology of this ecosystem (Odebrecht, Abreu, & Carstensen, 2015).