Phytoplankton communities, from lakes to oceans, are changing with anthropogenic nutrient loading and climate change. So, too, are the tools by which phytoplankton are quantified and characterized, yielding a torrent of new data and new types of data that can be related to ecosystem function. New insights have been gained about the physiology of resource acquisition by phytoplankton, allowing new relationships between phytoplankton biodiversity and function to be developed. Despite years of emphasis on the use of inorganic substrates in support of phytoplankton nutrition, it is now well understood that phytoplankton rely on a broad suite of substrates, both dissolved and particulate. Simple characterizations of limiting nutrients are not sufficient to understand how phytoplankton biodiversity is changing, or may change, in future conditions. Ecological theory is also advancing. Ecological stoichiometry brings the seemingly divergent concepts of nutrient limitation and trophic interactions together by recognizing that different organisms both within and between trophic groups have fundamentally different elemental requirements, that food web structure is a function of not only food quantity but also food quality, and that these interactions result in a complex suite of feedbacks that shape community composition. Trait-based (functional response) approaches are increasingly applied in characterizing ecosystem function and response, and new models are also emerging allowing new genomic data to be incorporated in models of ecosystem function. Climate change and altered nutrient loads should continue to motivate both new dynamic balance model architectures and new experimental investigations that support them. This article uses the metaphor of ecological theater to convey contemporary trends and themes against the backdrop of a changing world. There is potential for the outcome of the aqueous play to be characterized as tragedy with more harmful taxa emerging, but with continued science advancements—and if efforts to reduce nutrient pollution and control climate change become global priorities—there can be optimism in the face of tragedy.