Imagine that you are a plant propagule looking for a home. You find a nice warm sunny place where the nutrients wash over you and think that you have arrived in paradise. And, what is more, there are few other plants with which to compete. However there are many animals close by in the form of corals and sponges and a variety of animals which make up the Great Barrier Reef. If you were on land, where plants occupy much of the available surface area over which animals wander, you would seem less out of place. Yet on healthy and pristine coral reefs found on the outer shelf of the Great Barrier Reef off the north east coast of Australia, only 20–28% of the available surface area comprises plants, i.e. algae (Sweatman et al., 1998) (Figure 1). Sea grass and kelp beds are more reminiscent of the terrestrial situation. Why is this so? Maybe coral reefs are, in fact, not a good place for plants to grow. But if this were the case, why then would the space be dominated by animals reliant for much of their nutrition upon symbiotic relationships with plants such as are found in corals and their symbiotic unicellular plants, zooxanthellae. What then, keeps the number of freegrowing plants low on coral reefs relative to the land? Does chemical warfare by the animals play some role? And if so, can these chemicals be developed for use as herbicide in the terrestrial environment?