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The Millennium Development Goals call for the eradication of extreme poverty and hunger while ensuring environmental sustainability. Water is essential for food production and sanitation -key factors in poverty reduction. At the same time, it is increasingly difficult to ensure clean water to maintain ecosystem services. The challenge is to find ways of managing water in order to meet both these goals in a balanced way. This water-food-environment dilemma is exceedingly clear in the coastal zone because of increasing urban demands for water, with agriculture remaining an important component of rural livelihoods, and the dependence on water by some of the most valuable ecosystems of the world that are essential for the well-being of society.Driving forces affecting this water-food-environment nexus are increases in population and income and changing dietary patterns, which highly influence food production and water-use patterns. In response, there have been many positive trends such as overall better nutrition, an increase in overall food production and water productivity, and increased global trade in food products, thus helping in food distribution. On the other hand, there are some very disturbing trends. South Asia and sub-Saharan Africa still fall below the level required to 'lead a healthy and reproductive life' and water could be much better used for providing food security. An increased number of water bodies are becoming depleted, polluted and non-productive, negatively affecting both aquatic and terrestrial ecosystems.Coastal zones are particularly vulnerable as they are susceptible to rapid changes both from within the area and from outside -shock events like tsunamis plus consistent pressure from upstream water development and use. Coastal zones bear the brunt of upstream water development, reduced flows and pollution loads, yet river basin water management has been concentrated in upstream areas and very often the coastal zone is neglected or considered separately. Thus, in order to achieve and maintain healthy coastal zones, agricultural water management has to be able to respond to rapid changes from within coastal zones to maintain a balance of food, livelihood and environmental interests, and coastal zone interests must be firmly represented in overall river basin management.

Halimeda opuntia and Diplosoma virens are common marine organisms in the Indo-Pacific. Halimeda grows to dense populations, and the ability of didemnids to overgrow coral has been well documented. In the light of their abundance in the Hikkaduwa Nature Park in Sri Lanka, this study investigated the effect of these two associates on the growth and survival of the commonly occurring staghorn coral, Acropora formosa. The results showed that both affected the growth rates of the host coral colonies significantly (P ¼ 0.11 at 0.15 error level). The two associates also displayed a strong negative correlation between the spreading rate and the host growth rate (20.71 for H. opuntia and 20.55 for D. virens). The results show that D. virens could have serious implications on coral survival with a population bloom.

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