Species numbers alone do not fully capture how ecosystems are changing. In a global study, scientists analyzed long-term data from nearly 15,000 marine and freshwater fish communities. They found that fish food webs have changed substantially over recent decades, even in places where the number of species (species richness) has remained stable. Published in Science Advances, the study shows consistent shifts in species composition, body size, and feeding relationships, highlighting that changes in species traits such as body size and interactions can alter ecosystem structure without obvious changes in species richness.