Seaweed-based ecosystems are amongst the most productive on Earth (Mann et al. 1980, Leigh et al. 1987). Therefore it is a good opportunity to investigate if seaweeds can form a sink to trap nutrients in swallow eutrophic seas like the Baltic-, Adriatic- and Nort Sea were N and P are delivered by rivers like the Rhine in order to avoid a further eutrophication of our oceans like the Atlantic Ocean.
Enhancement of the growth of seaweeds has been observed under certain situations in coastal marine waters polluted by sewage (Causey et al. 1945, Sawyer 1956; Tewari et al. 1972). Also in disturbed systems with large amounts of nutrients like in Brittany (France) (REF) and the Venice lagoon (REF) Ulva sp, can bloom.
To get information about the effects of nutrients on seaweed growth rate and the possibility if seaweeds can be used to trap phosphorus and by harvesting bring back this compound to the terrestial agriculture we made a study at the N:P ratio in seaweeds.
The mean C:N:P ratio of 92 benthic plant samples from five phyla and nine locations worldwide is about 700:35:1, the median is about 550:30:1 (Atkinson & Smith 1983).
Our misfitted diet
There is a relation between a “hunter-gatherer” diet and chronic degenerative diseases. The hominids (including modern man: Homo sapiens) exist for two million years and according to evolutionary biologist and nutritionist we still have the “metabolic machinery” of the early hominids living on a paleolithic diet (see A). So the question arises if we can feed the estimated 9.2 billion people living at our planet in 2050 (UNFPA: United Nations 2008) with a substitute sea-based paleolithic diet. The Earth globe consist for 30% out of land and for 70% out of oceans. Global human population is rapidly increasing, especially since the second half of the 20th century. It is currently estimated by the United Nations Population Fund in their State of World Population 2008 that 9.2 billion people will live on our planet in 2050 (UNFPA: United Nations, 2008). Mankind has never experienced these population numbers before, and both economic and ecological consequences may be huge.
Even applying recently developed biotechnology tools for improved food crops it is generally believed our on freshwater based terrestrial agricultural system will be unable to feed this estimated amount of people (Worldwatch Report 176, 2008). Shortages may occur due to an increasing demand resulting from a growing population with an appetite for meat, dairy and fish protein. Given the growing world population and increasing demand for qualitative and quantitative food, the present sources of food supply will almost certainly be insufficient in the near future (FAO/FWT 2006). Recent studies predicted a rapid worldwide depletion of fish populations. Already 29% of edible fish and seafood species has declined by 90%, which indicates a collapse of fisheries and salt-water fish extinction by the year 2048.
Therefore, new sources for n-3 and n-6 Fatty Acids have to be explored from which Integrated Multi-Trophic Aquaculture (abbreviated IMTA) is a strategy, which is presently being explored for its economic and agronomic feasibility. Sea farming in marine off-shore systems of seaweeds forms part of this approach. Already at this stage of development a production for seaweeds of about 50 tons per ha is achieved and this yield will increase when the potential of using off-shore farming seaweed agriculture are further optimized.
Because 70% of our globe is covered with ocean, seaweeds are a durable and virtually inexhaustible, additional source for PUFAs, but also of amino acids and other useful bioactive ingredients, which are undeniably also accessible for developing countries. Still it can be the questioned if for food quantity (in energy compounds) the FAO goal of 3,000 kcal per caput can be reached in 2050. For reaching the quality of the different food compounds to oppose the unhealthy chronic anti-inflammatory Westernized diet, the Paleolithic diet seems to be an acceptable substitute. Although a terrestrial approach seems to be impossible (Worldwatch Report 176, 2008).