The deep-sea ecosystem engineerGeodia barretti(Porifera, Demospongiae) maintains basic physiological functions under simulated future ocean pH and temperature conditions

Abstract

AbstractGlobal ocean warming and acidification will alter the physicochemical conditions in the deep North-Atlantic Ocean. Here, extensive sponge grounds, often dominated by the demosponge speciesGeodia barretti, provide three-dimensional structure, habitat and significantly contribute to benthic-pelagic coupling and nutrient cycling processes in the deep sea. It is unknown ifG. barrettiremains physiologically functional under the future physicochemical properties of an Anthropocene ocean. In this study, individuals ofG. barretticollected from 300 m water depth in the Barents Sea, were exposed to four treatments resembling future ocean conditions (no treatment, 4 °C increase in seawater temperature, decrease of seawater pH by 0.3, and a combination of the high temperature, low pH). Over the course of 39 weeks, oxygen consumption, dissolved inorganic nutrient fluxes, and bacterioplankton clearance rates were measured as indicators of metabolic activity. We found that all indicators within each sponge individual and per treatment were highly variable over time and no effect of manipulated seawater treatments on these parameters could be demonstrated. Oxygen consumption rates in all groups closely followed a seasonal pattern, potentially caused by (a)biotic cues in the seawater flowing through the experimental aquaria. While similar metabolic rates across all treatments suggest thatG. barrettiphysiologically coped with simulated future ocean conditions, observed tissue necrosis in experimental animals might indicate that the response of the complex, high microbialG. barrettisponge (i.e., sponge host and microbial symbionts) to future ocean conditions may not be reflected in basic physiological processes.