Biological diversity is the variety of life—from genes to species to habitats and ecosystems—that forms the intricate fabric of our planet’s natural systems, which provides many essential goods and services. Changes in this fabric—such as losses of biodiversity—may be small or set in motion a chain of events where ecosystem functions change, and goods and services are no longer available. These changes can have significant social, economic, and scientific consequences. This is why understanding and conserving biodiversity are considered among the most important research priorities and policy issues of our time. Without better understanding of what organisms make up biological communities, and how these organisms and communities interact and are interconnected to form functioning ecosystems, we are destined to continue playing a dangerous game of ecological roulette, unsure which policy decisions and management actions might produce results that sever critical threads and begin an unraveling of marine ecosystem functions.