Aquaculture

Cyanobacteria culture

In a recent review, Borowitzka (1999) consider that many species of marine cyanobacteria are proving to be excellent sources of novel compounds with pharmacological activities such as anti-neoplastic compounds and plant growth regulators, and it is possible that in the near future some of these cyanobacteria will be grown commercially as industrial sources of these compounds. Marine cyanobacteria could also find application as producers of biochemicals such as polyols, polysaccharides and phycobilins and as large-scale sources of fixed nitrogen. They could also be a source of renewable energy in the form of hydrogen and as CO₂ absorbers. Marine cyanobacteria are also being developed as feed in aquaculture.

The commercial large-scale culture of cyanobacteria (blue-green algae) is a relatively new phenomenon, despite the fact that some cyanobacteria such as Nostoc commune and Spirulina spp. have been used as food in Asia and Africa for a long time (Ciferri, 1983; Martinez, 1988) Commercial large-scale culture was first developed for Spirulina (S. platensis, S. maxima) for use as a human health food and nutritional supplement. The first problem in scaling up Spirulina production to very large farms is water and there aren’t many places in this world where those doing conventional irrigation farming would want to give up amount of fresh water to algae farming (Fox, 1999) However, Spirulina can be grown in seawater (Materassi et al., 1984; Tredeci et al., 1986; Wu et al., 1993) and there are now several culture plants in the world where Spirulina is grown in a seawater-based medium.

Picocyanobacteria in aquaculture ponds

In inter-tropical coastal waters dominated by picocyanobacteria (<1µm) aquaculture of commercial species has to take into account the existence of a microbial loop. Indeed, as observed in Takapoto lagoon, pearl oysters (Pinctada margaritifera) are not able to retain particles <3 µm. These particles have to be first ingested by protozoan, which can be ingested by oysters. (Pouvreau, 1999) The estimation of the transfer rate between picocyanobacteria and protozoan and between protozoan and pearl oysters is necessary to calculate the culture capacity of these waters.  

 

A European Union Project: The Mekong delta (Vietnam)

Long-term objectives The overall objective of the project is to make shrimp brackishwater aquaculture, an essential economic activity in the Mekong delta, sustainable in order to increase households revenues and reduce rural depopulation, while protecting the ecosystem. Short-term objectives Five detailed objectives have been identified : F  To confirm on a significant sample of sites quantifiable relationships between shrimp production and ecological indicators, issued from previous research work (STD3) and assess their value and reliability, F To analyse farming practices on the same sites in order to determine those allowing lowest environmental and economic costs; F To carry out mapping of mangrove vegetation, soil and salt intrusions over the selected sub-areas as well as land use by aquaculture and other activities (agriculture…). This will help validate relationships established in 1 above and value them at ecosystem unit level, F To increase capacity building of scientists, local fisheries authorities and farmers groups through a strong involvement in the programme. Vietnamese partners are expected to collect and process field data under supervision of the EU experts, follow short-term and long-term training courses, organise and participate in 3 workshops, F To provide the Vietnamese counterparts with the tools and methods making them able to devise a follow-up development.

Picocyanobacteria as bio-indicator of anthropic pollution

Picocyanobacteria abundance appears to be related to the oligotrophic level of coastal waters. Therefore, the taxonomic composition of phytoplankton could be probably used as a bio-indicator of pollution effect.

Toxicity

Trichodesmium accumulations are important to take into consideration in coastal waters because they may cause eutrophication processes at origin of grave mortalities in coral reefs (Endean, 1976) by reduction of light penetration in the water column and/or smothering by excess organic sediment load (Bell, 1992) In addition, Jones (1992) has shown that Trichodesmium of Great Barrier Coral Reef modify the chemical composition of water and the amount of suspension organic matter, whereas Preston et al. (1998) have demonstrated that frequent Trichodesmium blooms in the Gulf of Carpentaria (North Austratlia) modify and even inhibit the life of penaeid prawn larvae. Trichodesmium blooms were also reported to be at the origin of important mortalities in prawn breeding on the western coast of New Caledonia (Blanchot, personal communication), and in the Gulf of Thailand (Suvapepun, 1991)