A case study of conventional and organic marine shrimp farms located at Guaraíra Lagoon, Rio Grande do Norte State, Brazil.

Description

Introduction

 

The rapid development of marine aquaculture in the last years has greatly contributed to increase in the amount of marine shrimps traded in the world market. Most of the marine shrimp production from aquaculture comes from developing countries where it has become a significant economic activity. Despite its economic relevance shrimp farming still attracts controversies due to its linkage to several socio-economic and environmental problems such as considerable negative effects on the livelihoods of fishing communities who use the mangrove as nursery for fish stocks and for artisanal fishing; euthrophisation of  the waters close to marine shrimp farms and water pollution.

Given the economic importance of marine shrimp farming and the conflicting public concerns regarding environmental effects of this activity, there is a growing interest in more sustainable management practices in marine shrimp farming. Organic aquaculture is therefore emerging as one of the sustainable approaches aimed at mitigating some of the problems facing the aquaculture industry. Compared to practices in agricultural sector, organic aquaculture lags behind in terms of quantities and diversity of certified organic products as well as in terms of scientific research.

In Brazil, the first organic shrimp farm was certified in 2003 by IBD (Instituto Biodinamico, Brazil). This farm is located at Guaraíra Lagoon in Rio Grande do Norte State. Organic aquaculture is a technological innovation in the context of marine shrimp farms in Brazil. At present, there are no studies on economic and environmental aspects of organic aquaculture in comparison to conventional shrimp production.

 

Objectives

The general objective of this research is to explore and evaluate relevant management aspects of conventional and organic marine shrimp farms at Guaraíra Lagoon as the food management, pond preparation, phases of the rearing cycles including or not the use of nursery ponds and fertilization practices. Specific objectives of this study were:

• Study the macrobenthos dynamics from an intensive, semi-intensive and organic marine shrimp ponds during the rearing cycle and its relations with the environment stress caused by each management practices;
• Study the soil and water characteristics from each farming system;
• To analyse the organic and conventional marine shrimp ponds using an emergetic approach.

 

Progress so far

The different management practices affected shrimp production (intensive pond 2 510 kg/ha/yr; semi-intensive pond 2 060 kg/ha/yr; organic pond 650 kg/ha/yr) as well as the concentrations of organic matter, nitrogen, and phosphorus in the soil at the bottom of the pond. The soil from the organic pond showed significantly lower levels of organic matter and phosphorus as compared to the two conventional systems. A balance of organic matter inputs and outputs of the different systems revealed that while the conventional systems release large amount of nutrients into the environment, the organic system is a sink of nutrients from the Guaraira Lagoon ecosystem.

The population of macrobenthos is an indicator of pollution and environmental stress in aquatic systems. Macrobenthos are aquatic animals living in the bottom of the body of water, which are larger than 1 mm. The organic pond showed higher (p<0.05) macrobenthos density inside the pond at the beginning of the rearing cycle (141.5 animals /m²). At the end of the cycle the density of the opportunistic species Polydora cornuta was virtually absent inside the organic pond while it occurred at high densities in the semi-intensive pond (43.3 animals /m²), indicating lower environmental stress in the organic pond. The density of Capitela capitata similarly indicates better environmental conditions in the organic pond. The density was significantly lower (p<0.05) in the middle of the rearing cycle in the organic pond (19.7 animals /m²) as compared to the intensive pond (37.0 animals/m²). In the outlet of the organic pond the density of this opportunistic species (< 0.1 animals/m²) was also lower (p<0.05) compared to the outlet of the semi-intensive pond (11.8 animals/m²).

An emergetic analysis revealed strong differences between the organic and semi-intensive systems. The emergetic analysis allows the comparison of production systems by transforming different types of inputs to a common form (solar energy equivalents) that allows for meaningful comparisons across organic and semi-intensive system. Several energy indicators indicated  higher sustainability of the organic pond. However, others showed that improvements are necessary in order to ensure economical sustainability of the organic system. In organic agriculture systems, by applying scientific approaches the productivity could be substantially improved without loosing ecological sustainability.

Through this study, the soil characteristics, macrobenthos population and emergy flows have been shown to be efficient tools for the comparison between different aquaculture systems. The same methodology could be applied in future studies covering a higher number of marine shrimp farms.