The most controversial issue to be discussed is perhaps deep sea mining. For more than a decade countries have been trying to agree how deep sea mining in international waters could work - how resources could be shared and environmental damage could be minimised. But in April President Trump bypassed those discussions and signed an executive order saying he would permit mining within international waters. China and France called it a breach of international law, although no formal legal proceedings have yet been started. Scientists have warned that too little is understood about the ecosystems in the deep sea and therefore no commercial activities should go forward without more research. "Deep sea biology is the most threatened of global biology, and of what we know the least. We must act with precaution where we don't have the science," said Prof Peter Haugan, Co-chair of the International Science Council Expert Group on the Ocean.