Award: OCE-1435205

Loss of species that are ecosystem engineers can have dramatic impacts on primary and secondary production, biodiversity, and ecosystem functioning. Nowhere is this as dramatic as in the coastal Aleutian Archipelago. Here, large declines in forest-forming ecosystem engineers (e.g., kelps) have occurred in recent decades due to overgrazing by the dominant consumer (e.g., sea urchins), ultimately because of the loss of a keystone species (e.g., sea otters). While the Aleutian coastal habitats are now dominated by urchin barrens, small patchy forests persist in some areas along with "transition forests", which have lower kelp abundances and little else other than sea urchins. Together, these habitats provide excellent opportunities for comparisons to explore how the loss of an ecosystem engineer impacts ecosystem functioning. In this research, we asked two highly integrated questions: 1) How does the widespread loss of ecosystem engineers impact benthic primary and secondary production across the Aleutian Archipelago? 2) How does the widespread loss of ecosystem engineers impact both coastal and offshore benthic biodiversity and community structure? For our first question, we learned that gross ecosystem production and community respiration were both reduced throughout the archipelago with the loss of kelp forests, though this was spatially and temporally variable. In contrast, net ecosystem production was not affected by kelp forest loss. We also learned that with the loss of kelp forests, sea urchin recruitment and their environmental controls, specifically temperature, became more important to patterns of sea urchin density and size structure, which together had affected ecosystem respiration, with larger urchins respiring exponentially more than smaller urchins. While exploring drivers of sea urchin recruitment in both urchin barrens and kelp forests, we found that specific macroalgal and invertebrate taxa drove sea urchin recruitment across both habitats. In relation to our second question, we demonstrated that the loss of some algal guilds (but surprisingly not the dominant forest-forming kelp) reduced biodiversity and changed community structure, but that this varied on opposing sides of some large oceanic passes. One pass, Samalga, was particularly important for delineating coastal communities. Unlike coastal communities, this pass was not a biogeographic break for the offshore benthic communities we examined and were not predictable based on coastal community structure. Together, our research has increased our understanding of the Aleutian ecosystem and has broadened our awareness of the role that foundation species play for ecosystem production and coastal community structure. We suggest that substantial changes will occur to ecosystem functioning as a result of the loss of ecosystem engineers but that these results are geographically variable. Broader impacts: We highlighted the results of this research through different venues. We worked with an educator from the Alaska Sea Grant?s Marine Advisory Program (Melissa Good), who joined us on a cruise and assisted in the development of a travelling museum exhibit on changes in the Aleutian coastal ecosystem. This exhibit opened at the Museum of the Aleutians in summer 2017, and has since been travelling around rural Alaska. So far, this exhibit has visited five communities in Alaska of various sizes (Unalaska, St. Paul, Adak, Homer, and Kodiak) and was at the Urban Unangax̂ (Aleut) Culture Camp in Anchorage. It has been viewed by ca 4,000 visitors but is still travelling with its next visit to the remote island city of Atka, which is nearly entirely Aleut and has a population of ca 60. In addition to this exhibit, we reached the public through YouTube videos and our project website. Here, a series of videos were presented on the Aleutian ecosystems and our understanding of them. For K-12 and college students, we worked with a San Diego high school teacher to integrate our findings into classroom activities and involved these students in our research. Further, one of Edwards? students developed an outreach program (project Pegasus) where he worked with high school students to build an ROV that was used to survey rocky reef ecosystems on one of the project cruises and is now being used for further outreach activities in San Diego. This has since led to OPEN ROV donating an additional ROV to use in educational outreach activities. Educational/research opportunities were offered to undergraduate and graduate students from SDSU and UAF who adopted portions of this project for their thesis research, took part in the field work, and/or assisted in manuscript preparation. Our two years of field work included eight graduate students and one undergraduate student (who then became a graduate student at UAF) aboard the R/V Oceanus. Four of these students were female and one was an underrepresented minority. Three of the SDSU graduate students and three UAF graduate student have since defended their graduate theses and graduated. All PIs and students involved in this project have given multiple presentations at various local, national, and international meetings and been co-authors on mulitple peer-reviewed publications. Last Modified: 10/01/2019 Submitted by: Brenda H Konar