Plants and animals living in the oceans could provide new antibiotics, drug treatments and painkillers.
By Carolyn Fry
in Galway, Ireland
But scientists believe these unexplored resources may disappear before we have had the chance to tap their potential.
Fishing, climate change and pollution are altering the food chains in the ocean - reducing biodiversity.
The decline needs to be stopped before it is too late, delegates to the European Conference on Marine Science and Ocean Technology in Ireland said.
"Life originated in the oceans and has evolved over a much longer time than on land, so the diversity of life is far greater," Professor Carlo Heip, of the Netherlands Institute of Ecology, said at EurOCEAN 2004.
However, marine biodiversity is very poorly known.
Only a few hundred thousand species of marine plants and animals have been scientifically described; and in terms of micro-organisms, we are just scratching the surface of what exists.
Species have evolved several tricks to survive the rigours of the ocean environment. Many organisms produce molecules designed to give them a competitive edge, in the fight for survival.
These molecules can, for example, make the host creature taste bad, or even render them toxic enough to kill predators outright.
Some sessile creatures, unable to move location, cover themselves in secretions that prevent bacteria from colonising them.
Scientists are studying such marine organisms with a view to learning more about cell functions, and using this knowledge to develop new drugs.
One line of work has focused on diarrhetic shellfish poisoning in Europe.
The oceans' vast resources remain to be documented
Dinoflagellates produce a toxin called okadaic acid which induces cramps and sickness in humans who eat shellfish exposed to dinoflagellate blooms in seawater.
Scientists have discovered that the acid can also induce cancer and interfere with testosterone - possibly even causing sterility.
"Scientists researching anti-cancer drugs look for molecules which are designed to arrest cell growth," explained Dr Adrianna Ianora, an ecologist at Stazione Zoologica, Anton Dohrn, Italy.
"In addition toxic creatures, such as poisonous snails from the Indo-Pacific, are being explored for their potential to help produce drugs to alleviate pain."
Although the oceans have huge potential to provide us with new drugs, they are being altered by human activities.
Overfishing has depleted the number of large predators, such as sharks, affecting food webs down to microbe level.
Alien species carried out of their natural environment in the ballast water of ships are changing local ecosystem dynamics, and scientists suggest climate change may ultimately affect the acidity of seawater.
Professor Heip: Diversity of life is far greater in the ocean
No one knows what the impact of these changes will be.
"It's important to look not just at biodiversity but at how ecosystems function," said Dr Ianora.
"We need to know how biodiversity is maintained as the ocean is a very important resource for humanity."