Frank Melzner1,2, Jahangir Vajedsamiei1,3, KOB 2022 Consortium1
1GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany - 2Kiel University, Germany - 3Leibniz Institute for Baltic Sea Research Warnemünde, Germany
In order to better predict which future summer heat waves can lead to coastal habitat degradation, we exposed macroalgae (Fucus) reef and seagrass (Zostera) communities to twelve heat wave scenarios using the Kiel Outdoor Benthocosm (KOB) facility. KOB is unique in that it permits high water flow rates of unfiltered Kiel Fjord water containing phytoplankton and larval stages to the experimental tanks using gentle peristaltic pumps, thus enabling establishment of diverse species assemblages. Tanks were stocked with adult and juvenile Fucus, as well as mussels (Mytilus), snails (Littorina) and seagrass (Zostera). All other organisms were recruited as planktonic life stages that settled in our experimental tanks. Following a two-month establishment period under ambient temperature conditions, we subjected our experimental systems to gradually increasing heat waves (from ambient to +5.5°C above ambient temperature) during the summer of 2022 and sub-sampled both biomes directly after the heat waves in autumn to analyze growth performance of foundation species, diversity and biomass of associated species (macrofauna, meiofauna, microbial communities). Foundation species growth and abundance was severely impacted by temperature increases of 2.5-3.5°C, and correlated with reductions in species abundance of many associated taxa. Other species increased in abundance with elevated temperatures, leading to strongly altered community composition at high temperatures. Our findings indicate that future summer heat waves likely to occur under Representative Concentration Pathway (RCP) 8.5 would severely damage current foundation species communities, while RCP 4.5-like summer heat wave scenarios would likely permit existence of seagrass and macroalgae with their typical associated epi- and infauna communities. Our findings underscore the critical role of stringent global carbon emission reductions and targeted conservation efforts to safeguard biodiversity and ecosystem resilience.
Biography
Frank Melzner is a Professor of Marine Ecology at GEOMAR and Kiel University. He leads the experimental ecology research unit and the Kiel Outdoor Benthocosm (KOB) facility at GEOMAR to investigate community responses to various climate change scenarios. He and his group aim to combine eco-evolutionary approaches to predict how coastal biomes may be impacted by climate change and to better understand adaptation mechanisms to warmer and more acidic oceans.