A mesocosm experiment was conducted to quantify the eff ects of reduced pH and elevated temperature on an intact marine invertebrate community. Standardised faunal communities, collected from the extreme low intertidal zone using artifi cial substrate units, were exposed to one of eight nominal treatments (four pH levels: 8.0, 7.7, 7.3 and 6.7, crossed with two temperature levels: 12 and 16 ° C). After 60 days exposure communities showed signifi cant changes in structure and lower diversity in response to reduced pH. Th e response to temperature was more complex. At higher pH levels (8.0 and 7.7) elevated temperature treatments contained higher species abundances and diversity than the lower temperature treatments. In contrast, at lower pH levels (7.3 and 6.7), elevated temperature treatments had lower species abundances and diversity than lower temperature treatments. Th e species losses responsible for these changes in community structure and diversity were not randomly distributed across the diff erent phyla examined. Molluscs showed the greatest reduction in abundance and diversity in response to low pH and elevated temperature, whilst annelid abundance and diversity was mostly unaffected by low pH and was higher at the elevated temperature. Th e arthropod response was between these two extremes with moderately reduced abundance and diversity at low pH and elevated temperature. Nematode abundance increased in response to low pH and elevated temperature, probably due to the reduction of ecological constraints, such as predation and competition, caused by a decrease in macrofaunal abundance. Th is community-based mesocosm study supports previous suggestions, based on observations of direct physiological impacts, that ocean acidifi cation induced changes in marine biodiversity will be driven by diff erential vulnerability within and between diff erent taxonomical groups. Th is study also illustrates the importance of considering indirect eff ects that occur within multispecies assemblages when attempting to predict the consequences of ocean acidifi cation and global warming on marine communities.
The activities of a diverse array of sediment-dwelling fauna are known to mediate carbon remineralisation, biogeochemical cycling and other important properties of marine ecosystems, but the contributions that different seabed communities make to the global inventory have not been established. Here we provide a comprehensive georeferenced database of measured values of bioturbation intensity (Db, n = 1281), burrow ventilation rate (q, n = 765, 47 species) and the mixing depth (L, n = 1780) of marine soft sediments compiled from the scientific literature (1864–2018). These data provide reference information that can be used to inform and parameterise global, habitat specific and/or species level biogeochemical models that will be of value within the fields of geochemistry, ecology, climate, and palaeobiology. We include metadata relating to the source, timing and location of each study, the methodology used, and environmental and experimental information. The dataset presents opportunity to interrogate current ecological theory, refine functional typologies, quantify uncertainty and/or test the relevance and robustness of models used to project ecosystem responses to change.
The importance of individual species in mediating ecosystem process and functioning is generally accepted, but categorical descriptors that summarize species-specific contributions to ecosystems tend to reference a limited number of biological traits and underestimate the importance of how organisms interact with their environment. Here, we show how three functionally contrasting sediment-dwelling marine invertebrates affect fluid and particle transport - important processes in mediating nutrient cycling - and use high-resolution reconstructions of burrow geometry to determine the extent and nature of biogenic modification. We find that individual functional effect descriptors fall short of being able to adequately characterize how species mediate the stocks and flows of important ecosystem properties and that, in contrary to common practice and understanding, they are not substitutable with one another because they emphasize different aspects of species activity and behavior. When information derived from these metrics is combined with knowledge of how species behave and modify their environment, however, detailed mechanistic information emerges that increases the likelihood that a species functional standing will be appropriately summarized. Our study provides evidence that more comprehensive functional effect descriptors are required if they are to be of value to those tasked with projecting how altered biodiversity will influence future ecosystems.
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