• Sea urchin ecology: effects of food-web modification, climate change, and community structure

      Weitzman, Benjamin P.; Esler, Daniel; Konar, Brenda H.; Hardy, Sarah M.; Johnson, Mark A.; Tinker, Martin T. (2020-08)
      Ecosystem structure and function of temperate rocky reef habitats are subject to change as a result of food-web modification, climate change, and changes in biological community interactions. Sea urchins are a global driver of change in nearshore marine habitats though their ability to heavily graze marine vegetation and force rocky reef ecosystems from kelp forest to sea urchin barren ground states. The Aleutian Archipelago in southwest Alaska provided an ideal natural laboratory to study sea urchin (Strongylocentrotus spp.) ecology following the functional loss of the keystone predator, the sea otter (Enhydra lutris) during the 1990s. The objectives of this dissertation were to 1) determine the important drivers of sea urchin demographics following the functional loss of their keystone predator; 2) determine how projected ocean warming and acidification may affect sea urchin physical condition; and 3) identify biological drivers of sea urchin recruitment in both kelp forest and barren ground habitats. To determine demographic drivers, I used a time series of benthic habitat, sea urchin demographic, and environmental data, dating back almost forty years. In the absence of sea otters, environmental conditions, specifically ocean temperatures, became more important to sea urchin demographics, but recruitment was the primary process affecting the resultant abundance and size class structure over time. To understand how predicted ocean warming and acidification could impact S. polyacanthus survival, growth, calcification, gonad development, and energy content, a 108-day laboratory experiment was conducted. This experiment determined that temperature caused a greater reduction in survival than acidification, and that projected changes in temperature and acidification will result in investment trade-offs between reproduction and maintenance or growth of somatic and calcified tissues. To determine how recruitment varied between kelp forest and sea urchin habitats, fine-scale surveys of benthic community structure found that specific taxa, and not overall community structure, correlated with sea urchin recruitment. Results from this dissertation will allow managers to make predictions about how sea urchin demography will change as a result of keystone predator loss and climate change and how that will affect nearshore community structure and function. Overall, my dissertation establishes likely pathways by which coastal habitats may change over time, in a system no longer under strong top-down control.
    • Sources and effects of strontium in waterfowl eggs

      Latty, Christopher J.; Hollmén, Tuula E.; Matz, Angela C.; Powell, Abby N.; Hobson, Keith A.; Adkison, Milo D. (2021-05)
      Strontium (Sr) may be a contaminant of concern for wild birds. Because of chemical similarities to calcium (Ca), Sr is readily incorporated into calcified tissues, such as eggshells. My objectives were to determine the potential drivers of both total and radio-Sr in the eggshells of waterfowl, and to assess the relationship between eggshell Sr and thickness. I collected eggs from sympatrically nesting waterfowl species in interior Alaska from 2011-2013. I measured total and radio-Sr in eggshells, environmental chemistry, and eggshell thickness. Local water chemistry explained much of the variation in eggshell Sr for canvasback (Aythya valisineria) and northern shoveler (Spatula clypeata), but not lesser scaup (Aythya affinis). Most of the remaining variation was associated with heterogeneity among eggs in the same nest (intra-clutch variance). General trends in eggshell Sr/Ca among species aligned with what would be expected had diet and/or endogenous reserve use affected eggshell chemistry. Results were similar for radio-Sr, with local water chemistry accounting for far less ⁹⁰Sr in the eggshells of lesser scaup, compared to the other species studied. At the site where water chemistry was stable, canvasback and northern shoveler eggshell thickness was not related to eggshell Sr, but lesser scaup eggshells with more Sr were thicker. At the site where water chemistry was variable, canvasback and northern shoveler eggshells with more Sr were thicker at low to intermediate concentrations, but this effect was moderated when the source of eggshell Sr appeared to be explained by the local environment. In contrast, lesser scaup eggshells with more Sr were consistently thicker, but only at higher concentrations. The different relationships between eggshell Sr and thickness across species, and interactions with apparent Sr sources, suggest the relationship between eggshell thickness and Sr is not a simple dose-dependence. My results show that for some species like lesser scaup, factors associated with the laying hen (e.g., diet or physiology) may have a larger impact on both eggshell total and radio-Sr, as well as how Sr interacts with eggshell quality, than the local environment.