MARICULT Research Programme: background, status and main conclusions

The human population is expected to reach about 10 billion by 2050, and it can be questioned how we can provide the food and the essential nutrients that will be needed. The ultimate goal of MARICULT was to provide a basis for the evaluation of environmental constraints and the potential for increased sustainable provision of food, raw materials and energy from the ocean. The Programme has primarily addressed fundamental questions on the marine ecosystem, because new concepts of harvesting and mariculture must be based on knowledge, and the environmental impact of new concepts should always be elaborated together with their production potential. The work has involved studies of food web structure and its functioning in the marine ecosystem as well as more applied research and testing of concepts for increasing the harvesting potential. There is a relatively tight connection between the nutrient supply rate and the primary production of phytoplankton, but the response of single species of animals is less predictable, especially for single populations on high trophic levels. There is, however, an empirical positive relationship between nutrient supply and secondary production, including fishery yields, on a regional scale. The low contribution of fisheries and aquaculture to human food compared to the contribution by agriculture is due to the fact that we primarily exploit first and higher carnivores. The general strategy to increase the marine harvesting potential is therefore to harvest and cultivate organisms at lower trophic levels. A number of harvesting and production concepts that may allow enhanced availability of marine resourses are proposed. These involve (1) harvesting of herbivore zooplankton resources, (2) cultivation of benthic, herbivore/omnivore animals, (3) enhancement of production potential by the creation of artificial up-welling systems, (4) strategic fertilization or use of available nutrient resources, and (5) further exploitation of biomass from macro-algae. All concepts involve harvesting or cultivation at low trophic levels, and some may readily be combined. It is important to note that some methods are not feasible for all coastal regions. In spite of great similarities, there are some clear differences in how the ecosystems react to enhanced nutrients in European marginal seas (Baltic Sea, Mediterranean Sea) and in Atlantic waters. Negative ecological effects caused by enhanced nutrient supply to pelagic ecosystems may occur if the primary production is not being grazed efficiently by zooplankton or benthic grazers. Dispersion by advection or retention in deepwater are important modifying factors. Loss of integrity in food web function seem to occur above a certain nutrient loading rate, suggesting a critical nutrient-loading rate for the maintenance of food web integrity. The Programme has contributed to a conceptual platform for assessment criteria of the state of the ecosystem and the water quality in pelagic coastal waters that are potential components in nutrient management models. The western principles of removing nutrient wastes from biological cycling is hardly sustainable. The counter-measure strategy that is still not explored and implemented is to reduce the ecological effects of uncontrolled nutrient emission in the coastal zone by using these nutrients for mariculture production. A more holistic ecological view in management and resource exploitation, where we recognize that we are also components in the ecosystem, is well accepted in eastern Asian countries, but not in the West. A holistic perspective may contribute to more concern for the marine environment.