In terrestrial systems, species diversity and abundance increase toward the equator. However, mobile marine invertebrates display a bimodal distribution with lower abundance at the equator. This pattern is attributed to declining oxygen in warm water, which can fail to meet the metabolic demands, necessitating greater food consumption for homeostasis. Declines in invertebrates may be linked to increased predation from fishes, as foraging rates tend to rise with temperatures. We test whether the signals of temperature-dependent oxygen availability and predation pressure relate to changes in marine invertebrate abundance while controlling for local site productivity and habitat complexity. We utilize systematic sampling across the Great Barrier Reef (GBR) before and after the 2016/2017 El Niño heatwave event and build a model of temperature-dependent fish consumption to test if variation in invertebrate abundance is explained by consumption and oxygen availability. Average fish consumption rates are higher in the cooler southern GBR locations and increase markedly during the heatwave. By contrast, warming at the equator dampens fish consumption rates but oxygen concentration falls below critical thresholds for invertebrates. Our findings highlight the energetic costs of marine heatwaves for invertebrates and fish and the cascading effects on invertebrate diversity that scale across latitudes.