Environmental Aspects of Seaweed Culture

The impact of aquaculture on the environment and effects of environment on aquaculture production have become important issues in recent years. There is evidence from many countries that environmental deterioration is a major threat to aquaculture production and product quality. There is also evidence that marine and freshwater aquaculture can cause environmental change, which in some cases may adversely affect the long-term viability of the aquaculture operation itself, or result in serious conflicts with other users of aquatic resources. These problems have led to a need to consider aquaculture as one component in the aquatic ecosystem and to plan aquaculture development in a way which makes efficient use of resources. There have been several recent reviews of impacts associated with finfish (Beveridge, 1984; NCC, 1989), mollusc (ICES, 1989; NCC, 1989) and crustacean (Phillips et al, 1990) culture but there is little information on seaweed culture.

The main environmental impacts caused by aquaculture have been reviewed in several recent publications (NCC, 1989; ICES, 1989; NCC, 1990) and can be summarised as follows:

i. physical effects, including effects on water movement, the physical structure of terrestrial and aquatic habitats and aesthetic impacts;

ii. ecological effects, including changes in water quality, primary and secondary productivity and native fisheries.

These effects have arisen in many forms of aquaculture, although impacts vary considerably depending on the nature of the culture system and species cultured, plus the environment where the culture system is located. The main impacts and problems come from intensive aquaculture with high stocking densities and supplementary feeding, but problems have also arisen in extensive aquaculture systems.

Seaweed culture has expanded rapidly over the past few years, and in 1987 3,139,473 tons (wet weight) of seaweed were produced throughout the world, the bulk produced in Eastern Asia (FAO, 1989). This expansion has brought benefits in terms of income, employment and foreign exchange, but has also been accompanied by some conflicts with other users of the coastal zone and concerns over potential environmental impacts. The aim of this review is to consider some of the environmental implications associated with seaweed culture and ways in which issues may be resolved.