What organisms would you use to create a self-sustaining ecosystem

You can create other self-sustaining ecosystems including those in water. Include a producer (i.e., algae), a consumer (e.g., water flea) and a decomposer (e.g., protozoans) and plenty of sunlight.

don't know sorry

Explanation:

Case studies are in-depth investigations of a single person, group, event or community. Typically, data are gathered from a variety of sources and by using several different methods (e.g. observations & interviews). In psychology, case studies are often confined to the study of a particular individual.