BrainPOP uses a great game titled iBiome Wetland (developed by Springbay Studio Ltd.) to help students review concepts of ecosystems and basic food chains. They will practice determining which organisms are producers and which ones are consumers. They will add these one at a time to develop their own wetland ecosystem.
Disclaimer: This game is to review concepts by putting them to practical use. This game does not explicitly teach these concepts. Lastly, this is a shortened demo version, so students do not get to include larger predators into their ecosystem. It appears that an extended version and an ocean ecosystem game is available to purchase for iPads.