A mesocosm concept for the simulation of near-natural shallow underwater climates: The Kiel Outdoor Benthocosms (KOB)

Abstract

Biogenic, seasonal, and stochastic fluctuations at various scales characterize coastal marine habitats and modulate environmental stress. The relevance of most past studies into climate change impacts is weakened by the usually intentional exclusion of fluctuations from the experimental design. We describe a new outdoor mesocosm system for benthic research (“benthocosms”) which permit the control and manipulation of several environmental variables while admitting all natural in situ fluctuations. This is achieved by continuously measuring the relevant variables (e.g., temperature, pH, O2, CO2) in situ, defining these in real time as reference values in the control software and simulating target climates by delta treatments. The latter constitute the manipulative addition of predefined changes (e.g., “warming”, “acidification”) to the reference values. We illustrate the performance of the system by presenting the environmental data of four seasonal experiments which together represent an entire year. The “Kiel Outdoor Benthocosms” allow realizing near‐natural climate change experiments on complex benthic communities under controlled scenarios.

Effect of temperature rise and ocean acidification on growth of calcifying tubeworm shells (<i>Spirorbis spirorbis</i>): an in situ benthocosm approach

“…The absorption of the dye into newly grown tubes provides a well-defined starting point for growth under the experimental conditions. After 3 days of staining, 12 individual Fucus plants were transplanted into the 12 subunits of the Kiel Outdoor Benthocosms (Wahl et al, 2015), fixed on a plastic grid at the bottom of the basins under 0.4 m of water. The incubations started immediately after staining.…”

“…Kiel Fjord and Eckernförde Bay are narrow coastal embayments in the western Baltic Sea. Surface water data from Kiel Fjord show a seasonal pH range from 7.3 to 8.5 (NBS scale) with pCO 2 varying from 385 to 2500 µatm (Thomsen et al, 2010(Thomsen et al, , 2013Wahl et al, 2015). Significant variations in pH and pCO 2 were observed along the coast line of the Kiel Bight (Winde et al, 2017).…”

“…Reynaud et al, 2003;Marshall and Clode, 2004;Veron et al, 2009;Saderne and Wahl, 2013;Wisshak et al, 2013;Cornwall et al, 2016;Wahl et al, 2016). However, only few studies investigated combined effects of simultaneously increased temperature and CO 2 on entire ecosystems (Wahl et al, 2015). To study the combined impact of temperature rise and elevated CO 2 on typical marine calcifiers from the Baltic Sea, we carried out experiments in the Kiel Outdoor Benthocosms (KOB, Wahl et al, 2015) to investigate calcification of the serpulid tubeworm Spirorbis spirorbis under near-natural habitat conditions as sessile epibionts on the thalli of Fucus seaweeds.…”

“…Our results also provide new information about the life cycle and shell microstructure of S. spirorbis. The growth experiments were carried out in the Kiel Outdoor Benthocosms under near-natural conditions, exposed to the weather and water conditions of the Kiel Fjord, by using a flow-through setup with water pumped directly from the fjord (Wahl et al, 2015).…”

What are the type, direction, and strength of species, community, and ecosystem responses to warming in aquatic mesocosm studies and their dependency on experimental characteristics? A systematic review protocol

“…Benthic mesocosms have long been used in shallow freshwater ecosystems to establish mechanistic relationships between various stressors and population, community, or ecosystem dynamics [10]. More recently, benthic mesocosms have also been developed for marine environments to test the effect of warming, acidification, eutrophication and hypoxia on shallow coastal ecosystems while allowing for natural fluctuations, thus increasing realism [11].…”