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INFLUÊNCIA DA TEMPERATURA, SALINIDADE E NUTRIENTES DISSOLVIDOS (N e P) NO CULTIVO DE MICROALGAS DE ÁGUA ESTUARINA E COSTEIRA. INFLUÊNCIA DA TEMPERATURA, SALINIDADE E NUTRIENTES DISSOLVIDOS (N e P) NO CULTIVO DE MICROALGAS DE ÁGUA ESTUARINA E COSTEIRA.

by Meinerz, Lisandra Isabel

Abstract (Summary)
The development of commercial microencapsulated food has contributed to the feeding management of crustacean, mussel and fish larvae. However, the use of microalgae in natura is still essential for the high quality production of cultivated organisms. Microalgae have been employed not only in direct feeding but also indirectly, as for zooplankton production and water quality maintenance in green water systems. From a biotechnological perspective, the use of microalgae varies from the production of chemical and pharmaceutical substances to food industry. Besides, some research has been conducted aiming the conversion of lipids extracted form microalgae in biofuel. Despite the high production costs, microalgae shows high growth rates and tolerates a wide range of extreme environmental conditions, thus allowing intensive production in small facilities using either salt or brackish water. Nevertheless, in order to minimize production costs, research is needed in order to select more productive species, with high nutritional quality and better growth rates. In the present study the growth of the microalgae Thalassiosira weissflogii (Grunow) Fryxell & Hasle 1977 and Nannochloropsis oculata (Droop) Hibberd 1955 were accessed under various conditions of temperature, salinity and nutrients (N:P ratios). These species are considered as highly productive and are widely employed in some larvicultures. Additionally, a non-identified species of Skeletonema, isolated from the South Brazilian coastal area (Rio Grande do Sul State) and called here as Skeletonema sp., was also subject to testing. The experiments were performed on the maximum necessary time for determination of the growth curve, using 200 mL Erlenmeyer flasks under three distinct temperatures (20ºC, 25ºC and 30ºC), salinity (10, 20 and 30) and N:P ratios (Guillard culture medium f/2 - 8:1, 16:1 and 24:1). The experimental design employed was a factorial 3x3x3, resulting in 9 treatments, with 3 replicates each. These 27 sample units were randomly distributed in DBO chamber, under 12C/12D photoperiod and optimal irradiance for each species. The microalgae responses were evaluated by estimation of chlorophyll a (?g/L) and cellular density (104 cell.ml-1) from which the rates of cellular growth, doubling time, performance and chlorophyll/cell relation (Chla/cell) were calculated. Considering the cellular growth, T. weissflogii grew under all tested temperatures with best growth rate and highest chlorophyll a concentration at 25ºC and 30ºC, respectively, and a good Chla/cell relationship (4,73 ± 1,99 pg Chla/cell). Nevertheless this species exhibited lower yield and cellular growth rate, and high doubling time in comparison to the other species, meaning that its massive culture potential is restricted. Thus, according to our results, mass production of T. weissflogii is suggested to be conducted during spring and summer. N. oculata was the species with highest cellular growth and smallest doubling time, showing higher potential for massive production. Further, this species did not exhibit restrictions regarding temperature, salinity and nutrient conditions. On the other hand, Skeletonema sp., also exhibit high growth potential because of its high growth rate and short doubling time, however it does not reach the same cellular density values of N. oculata. Moreover, Skeletonema sp., exhibited a restricted growth potential under high (30ºC) temperature, therefore allowing its massive production only during spring, autumn and early winter. The development of commercial microencapsulated food has contributed to the feeding management of crustacean, mussel and fish larvae. However, the use of microalgae in natura is still essential for the high quality production of cultivated organisms. Microalgae have been employed not only in direct feeding but also indirectly, as for zooplankton production and water quality maintenance in green water systems. From a biotechnological perspective, the use of microalgae varies from the production of chemical and pharmaceutical substances to food industry. Besides, some research has been conducted aiming the conversion of lipids extracted form microalgae in biofuel. Despite the high production costs, microalgae shows high growth rates and tolerates a wide range of extreme environmental conditions, thus allowing intensive production in small facilities using either salt or brackish water. Nevertheless, in order to minimize production costs, research is needed in order to select more productive species, with high nutritional quality and better growth rates. In the present study the growth of the microalgae Thalassiosira weissflogii (Grunow) Fryxell & Hasle 1977 and Nannochloropsis oculata (Droop) Hibberd 1955 were accessed under various conditions of temperature, salinity and nutrients (N:P ratios). These species are considered as highly productive and are widely employed in some larvicultures. Additionally, a non-identified species of Skeletonema, isolated from the South Brazilian coastal area (Rio Grande do Sul State) and called here as Skeletonema sp., was also subject to testing. The experiments were performed on the maximum necessary time for determination of the growth curve, using 200 mL Erlenmeyer flasks under three distinct temperatures (20ºC, 25ºC and 30ºC), salinity (10, 20 and 30) and N:P ratios (Guillard culture medium f/2 - 8:1, 16:1 and 24:1). The experimental design employed was a factorial 3x3x3, resulting in 9 treatments, with 3 replicates each. These 27 sample units were randomly distributed in DBO chamber, under 12C/12D photoperiod and optimal irradiance for each species. The microalgae responses were evaluated by estimation of chlorophyll a (?g/L) and cellular density (104 cell.ml-1) from which the rates of cellular growth, doubling time, performance and chlorophyll/cell relation (Chla/cell) were calculated. Considering the cellular growth, T. weissflogii grew under all tested temperatures with best growth rate and highest chlorophyll a concentration at 25ºC and 30ºC, respectively, and a good Chla/cell relationship (4,73 ± 1,99 pg Chla/cell). Nevertheless this species exhibited lower yield and cellular growth rate, and high doubling time in comparison to the other species, meaning that its massive culture potential is restricted. Thus, according to our results, mass production of T. weissflogii is suggested to be conducted during spring and summer. N. oculata was the species with highest cellular growth and smallest doubling time, showing higher potential for massive production. Further, this species did not exhibit restrictions regarding temperature, salinity and nutrient conditions. On the other hand, Skeletonema sp., also exhibit high growth potential because of its high growth rate and short doubling time, however it does not reach the same cellular density values of N. oculata. Moreover, Skeletonema sp., exhibited a restricted growth potential under high (30ºC) temperature, therefore allowing its massive production only during spring, autumn and early winter.
This document abstract is also available in Portuguese.
Bibliographical Information:

Advisor:Paulo Cesar Oliveira Vergne de Abreu; Clarisse Odebrecht; Sergio de Oliveira Lourenço; Leonardo Brandes Bacellar Mendes

School:Fundação Universidade Federal do Rio Grande

School Location:Brazil

Source Type:Master's Thesis

Keywords:Thalassiosira weissflogii fluviatilis Skeletonema sp.

ISBN:

Date of Publication:03/28/2007

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