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Marine botanical research activities in the Western Indian Ocean region have increased significantly over the past two decades, contributing to a growing awareness and enhanced understanding of the important values and functions of the main primary producers in the coastal ecosystems of this region (UNEP 1982). Whereas a major proportion of the research has been descriptive, focusing on the distribution and general biology of mangrove, seaweed and seagrass plants and microalgae, more recent research has diversified its attention to include various other more quantitative and applied research topics (Björk et al. 1996). Throughout the region, increasing efforts are underway for coastal zone management, mangrove rehabilitation and marine conservation (e.g. Tanzania Coastal Management Partnership 1999), which call for a solid scientific knowledge base. Yet, new research initiated without a thorough review of past and recent research outputs may lead to a deficiency in the relevance of the knowledge being produced (Hatcher et al. 1989). The present review of the current status of marine botanical research (1950–2000) in the Eastern African region was made to provide a diagnosis of its strengths and weaknesses, with the aim of identifying the main research challenges to be faced to assist in the development of a solid basis for the management, conservation and wise use of the marine botanical resources in this region.

A detailed understanding of physiological and reproductive processes in seaweeds has repeatedly proven to be an essential pre-requisite in the successful development of a sustainable industry. The prime example of this was the classical discovery of the “conchocelis”- phase of Pyropia (Porphyra) by Kathleen Mary Drew-Baker in 1949. Such elegant research proved to be pivotal to the development of a globally important “nori” industry which transitioned from the simple provision of the enhanced surface area of the substrata for spore settlement to the sophisticated, mechanized and computerized operations in modern hatcheries supplied by seedling banks of selected species and their cultivars. All of the pre-requisite knowledge was acquired through intensive applied research. However, not all solutions need to be high-tech; problems caused by epiphytes and contaminants have been achieved by exposing Pyropia nets periodically and was found to be effective. This protocol was achieved based on fundamental observations by farmers which were then complemented and refined by laboratory trials. Techniques must be adapted for site-specific differences, as abiotic factors such as water current and movement, surface seawater temperature, light regime and photoperiod, nutrients dispersion and water quality are interrelated, either positively or negatively, influencing seaweed productivity and the end-use of the biomass. Unfortunately, positive techniques that have been shown in vitro/silica can prove to be impractical once attempted at large-scale cultivation and/or the return on investment is not justified by the commercial value of the resultant seaweed biomass. This chapter presents a summary of how the judicious application of knowledge based on the ecophysiological processes of common seaweed species from tropical and cold-waters can assist the future development and scale-up of the global seaweed industry

Results obtained on the changes in growth, reproduction, alginic acid and mannitol contents of Turbinoria decurrens carried out for one year from March, 1973 to February, 1974 are presented. Young plants of T. decurrens appear in May and grow to a minimum size between December and February. Branching starts from August and maximum number of branched plants occur in November. Reproductive plants were observed throughout the year. The yield of alginic acid varies from 16.3 to 26.3 % and the estimated mannitol content from 1.5 to 8.7 %. T. decurrens may be harvested in the months between December and February for extraction of alginic acid.

Seaweed farming at sea is proving an increasingly competitive biomass production alternative for food and related uses. Farmed seaweed output has been growing exponentially, reaching 24 million tons by 2012. Remarkably, 99 % of this production occurred in merely eight Asian nations. Most of the remaining 150 countries and territories with coasts are yet to begin seaweed farming. With current technology and extensive available sea areas, requiring no land, freshwater or fertilizers, seaweed production can expand sustainably to the scale of agriculture, while providing a variety of valuable ecosystem services. Following a deductive or principle-based approach, that establishes seaweed primary productivity as a basis for food production, this chapter describes the fundamentals of seaweed farming, harvest and post-harvest techniques, ecological and economic considerations and a perspective on opportunities and challenges. The objective is to provide both an overall account of the state-of-the-art on seaweed farming as well as a contribution to the industry's sustainable development.