Human impacts on ecosystems are resulting in unprecedented rates of biodiversity loss worldwide. The loss of species results in the loss of the multiple roles that each species plays or functions (i.e., “ecosystem multifunctionality”) that it provides. A more comprehensive understanding of the effects of species on ecosystem multifunctionality is necessary for assessing the ecological impacts of species loss. We studied the effects of two dominant intertidal species, a primary producer (the seaweed Neorhodomela oregona) and a consumer (the shellfish Mytilus trossulus), on twelve ecosystem functions in a coastal ecosystem, both in undisturbed tide pools and following the removal of the dominant producer. We modified analytical methods used in biodiversity-multifunctionality studies to investigate the potential effects of individual dominant species on ecosystem function. The effects of the two dominant species from different trophic levels tended to differ in directionality (+/-) consistently (92% of the time) across the twelve individual functions considered. Using averaging and multiple threshold approaches, we found that the dominant consumer – but not the dominant producer – was associated with ecosystem multifunctionality. Additionally, the relationship between abundance and multifunctionality differed depending on whether the dominant producer was present, with a negative relationship between the dominant consumer and ecosystem function with the dominant producer present compared to a non-significant, positive trend where the producer had been removed. Our findings suggest that interactions among dominant species can drive ecosystem function. The results of this study highlight the utility of methods previously used in biodiversity-focused research for studying functional contributions of individual species, as well as the importance of species abundance and identity in driving ecosystem multifunctionality, in the context of species loss.

This dataset contains the raw data from a removal experiment, which includes the physical characteristics of the tide pools (water depth, volume, surface area, etc.) and details about the removal manipulation (e. g., mass of removed algae). It also includes the data from seven sets of community biodiversity surveys, in which the surface area of all non-mobile species were measured (recorded in measurements of “squares”, each of which is equal to 100cm²) and the number of individuals of mobile species were counted in each tide pool. Additionally, the data collected during two sets (before and after removal) of light/dark productivity trials, in which the tide pools were incubated under opaque tarps for a period of time to assess photosynthetic activity and respiration, are included. Initial measurements were collected prior to incubation, “dark” measurements were collected immediately following the incubation, and recovery measurements were taken approximately 30 minutes after the end of the incubation. All measurements taken during the trials (light, salinity, dissolved oxygen, temperature, and pH) are included. Finally, the data collected across four water samplings were included. Each water sampling consisted of a series of measurements (light, salinity, dissolved oxygen, temperature, and pH) and samples collected (for analysis to determine pH and nutrient concentration) across all ten experimental tide pools, across three time points, over the course of ~3 hours. Two of the four water samplings were conducted prior to the algae removal manipulation (day and night) and two were conducted following algal removal (day and night).

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