The antonyms for the word "more spawning" are "less breeding" or "decreased reproduction." These words imply a decrease in the rate of breeding or spawning, indicating a decline in the population of species that reproduce in large numbers. Such a situation can cause a decline in biodiversity, with potential negative impacts on the ecosystem. Factors such as habitat destruction, pollution, and overfishing can all contribute to a decrease in breeding rates for fish, amphibians, and other species, leading to a decline in numbers over time. Efforts to conserve habitats and reduce human impact on natural ecosystems are essential to maintain healthy populations of various species, including those that rely on spawning for reproduction.