Otherwise, the logical to me conclusion is that there are additional non-photosynthetic sources of oxygen.    From Wordnik.com.  [Unthreaded #21 « Climate Audit] Reference

Microheterotrophs are non-photosynthetic microorganisms.    From Wordnik.com.  [Featured Articles - Encyclopedia of Earth] Reference

Photosynthetic sponges are abundant and diverse in temperate WA, with comparable percentages of photosynthetic to non-photosynthetic sponges to tropical zones.    From Wordnik.com.  [BioMed Central - Latest articles] Reference

Using the metaphor of fitness landscapes (Don't read this book unless you want to think, warns the back cover), Niklas offers a careful exploration of the vital nodes in an oft overlooked branch of life, without which non-photosynthetic metazoans like you and me would wither like blooms in autumn.    From Wordnik.com.  [The annotated budak] Reference