The benefits and downsides of building into the sea

From BBC Future, 1 November 2016:

All around the world, cities are edging further into the sea. Plans are afoot to build huge islands and giant constructions in coastal areas, featuring the dredging and dumping of million of tonnes of material.
What are the implications for ocean life and ecosystems as we build more and more into the ocean? This is one of the questions that will be discussed at the BBC Future’s World-Changing Ideas Summit in Sydney in November. Read more.