Chemical communication in epiphytic communities under ocean acidification

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Ocean acidification (OA) through the uptake of additional CO2 from the atmosphere into marine waters is considered a serious threat to marine ecosystems. However, there is only very little known on potential effects of OA on chemical communication of benthic invertebrates, in particular in connection to utilization of food and habitat cues. The project proposed here aims to extend our knowledge on chemical communication in benthic invertebrate communities in the globally relevant context of OA. Close to Ischia, volcanic CO2 vents have caused a gradient of pH along the coastline with ecosystem effects of natural ocean acidification on benthic communities. We will use this natural gradient to investigate effects of OA on interspecific chemical communication of primary producers and macro¬in-verte¬brates in seagrass stands. We will focus on seagrass stands at pH 8.1 (non-acidified) and pH 7.7 (acidified) to cover the range of OA that is predicted to occur until the end of the century.In earlier work we have shown that volatile organic compounds (VOCs) are important signalling molecules among primary producers and macro¬in¬verte¬brates in communities found in seagrass stands. Here we will investigate how OA affects this VOC-mediated signalling. It is hypothesized that effects on signaling will differ between invertebrate signal receiver taxa. It will be tested whether the effects of OA on the sensitivity of macroinvertebrates to VOCs are similar for (i) phylogenetically more closely related invertebrate groups, (ii) taxa that originate from the normal or the acidified habitat or (iii) taxa that share the same trophic preference. We will extract VOC bouquets from epiphytic communities and from algal strains isolated from these communities, compare them analytically via GC-MS and subject them to behavioural assays with macroinvertebrates collected from seagrass-associated communities. In the natural community on seagrass, the sex of the fairly abundant shrimp Hippolyte inermis is reverted from male to female, when young individuals feed on the diatom Coccconeis scutellum parva. We will investigate effects of OA on this unique signalling by crossing different pH-values during culturing of the diatom with different pH-values during the bioassay, and we will use a metabolomics approach to identify the inducing chemical compound, with the objective to understand the effects of OA on the level of the chemical compound. We hypothesize that OA will interfere with this diet-mediated change in sex, which at the current pH is fundamental to assure stability of natural populations of this shrimp.Overall this project will shed light on the so far neglected role of OA for important biotic interactions in marine benthic communities mediated by chemical signals.