Heatwaves can push species beyond their tolerance limits, leading to species loss and rewiring of feeding interactions with consequences for food web functioning and stability. Yet, challenges with quantifying trophic interactions currently hinder our ability to predict how food webs respond to future climate scenarios. To quantify trophic interactions and future thermal scenarios in controlled settings, we conducted mesocosm experiments combined with bioenergetic food web modelling. Temperate hard- and soft-bottom communities were sampled after four-month incubations in response to natural warming scenarios, representing a gradient of marine heatwave intensities. Body masses and allometric scaling laws were used to quantify energy fluxes in the mesocosm food webs. Our results show that higher temperatures led to food web simplification, with decreases in trophic levels and food web complexity (e.g., connectance). Shifts were observed at both the bottom and top of the food webs, due to die-offs in predatory species such as Asterias rubens and foundation species such as Fucus vesiculosus. Further, new species appeared at higher temperatures, adding trophic interactions to the mesocosm food web. These findings have important implications for our understanding of the impacts of warming and heatwave scenarios on marine ecosystems. Overall, bioenergetic modelling is a valuable tool for understanding the structure and dynamics of experimental mesocosm food webs and can provide important insights into the impacts of environmental changes on ecosystem functioning and stability.

Primary Presenter: Lucinda Kraufvelin, Åbo Akademi University (lukraufv@abo.fi)

Authors:

Lucinda Kraufvelin, Åbo Akademi University  (lukraufv@abo.fi)

Christian Pansch-Hattish, Åbo Akademi University  (christian.pansch-hattich@abo.fi)

Marie Nordström, University of Helsinki  (marie.nordstrom@abo.fi)

Martin Wahl,   ()

Jahangir Vajedsamiei, Helmholtz Centre for Ocean Research (GEOMAR)  ()

Susanne Kortsch, University of Helsinki  (susanne.kortsch@abo.fi)