Read about ‘Heatwave-driven Rewiring of Food Webs’

When the sea heats up, who eats whom? Marine heatwaves, periods of unusually warm seawater, are becoming more frequent, intense and prolonged with global warming, threatening coastal biodiversity and ecosystem functioning. Understanding their effects on ecosystems means looking beyond individual species responses. Marine heatwaves do more than put individual species under stress. They can change how species interact, including who eats whom, potentially rewiring entire food webs. These relationships help determine how ecosystems function, how stable they are, and how they respond to future heatwaves. In the coastal Baltic Sea, bladderwrack forms underwater habitats that provide food and shelter for small animals such as snails, isopods and shrimp. These animals are connected through an invisible web of feeding relationships. When heatwaves strike, do predators such as shrimp eat more to meet their increased energy needs, switch prey or struggle to find enough food? And how do these changes ripple through the food web? At Tvärminne Zoological Station, a group of researchers are investigating these questions by studying how coastal communities respond to marine heatwaves. They transferred bladderwrack and its associated organisms from the nearby coast into large experimental tanks, then exposed them to heatwaves of different intensities. The experiment was repeated in early and late summer to explore whether the seasonal timing of a heatwave matters. The researchers are measuring changes in the abundance and biomass of organisms, alongside key ecosystem processes such as decomposition and oxygen production and consumption. They will combine these observations with food web modelling to explore how warming could rewire feeding relationships and alter ecosystem functioning. As marine heatwaves become more frequent and intense, understanding these hidden ecological connections can help anticipate the future of coastal Baltic Sea ecosystems.

This project is funded by the Research Council of Finland through an Academy Research Fellowship (2024–2028).