Communities in Freshwater Coastal Rock Pools of Lake Superior, with a Focus on Chironomidae (Diptera) A Dissertation SUBMITTED TO THE FACULTY OF UNIVERSITY OF MINNESOTA BY Alexander Taurus Egan IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Advisor: Leonard C. Ferrington, Jr. May 2014 © Alexander Taurus Egan 2014 Acknowledgements Projects of this size are rarely accomplished without the assistance and support of many people. Primarily, my advisor, Len Ferrington, has been a great source of guidance and enthusiasm. My committee, Jacques Finlay, Ralph Holzenthal, and Roger Moon, have raised the bar considerably by pushing, pulling and steering me toward being a better scientist. Friends and colleagues in the Chironomidae Research Group have made my graduate experience a time I will remember fondly, with Alyssa Anderson, Will Bouchard and Jessica Miller sharing in the successes, misfortunes, and minor but important goals that come with the territory. In particular, Petra Kranzfelder often filled the roles of peer advisor and sounding board for ideas both brilliant and ridiculous. The National Park service has been very generous in many ways, and specific thanks go to Brenda Moraska Lafrançois and Jay Glase, who provided early development and direction for this project. My colleagues Mark Edlund from the Science Museum of Minnesota and Toben Lafrançois from the Science Museum and Northland College have consistently offered excellent ecological advice on what the data mean, often acting as de facto advisors. Without support from Isle Royale National Park this project would not have been possible. In particular, the technical advice, equipment loans, and logistical assistance from Paul Brown, Rick Damstra, Joan Elias, and Mark Romanski were invaluable. Additional technical support was generously provided by Ulf Gafvert and Rebecca Key from the National Park Service Great Lakes Network office. The rewards and challenges of field work were shared with many Isle Royale staff and volunteers: Meredith Bryant, Leah Ettema, Katy Goodwin, Ted Gostomski, Roger Haro, Robert Hoffmaster, Kerry Martin, Jenna McCullough, Jess Ruuti, Michael Schuldt, Lindsay Stedman and Pete Sweger. i Funding was provided to the Chironomidae Research Group by the Great Lakes Restoration Initiative, EPA Project #90, Great Lakes Northern Forest CESU Task Agreements J6067100007 and J6067100008. The Department of Entomology at the University of Minnesota provided support services for laboratory procedures and additional matching support was available through the Minnesota Agricultural Experiment Station, Project # MIN-17-018. The Alexander & Lydia Anderson Fellowship provided funding for additional summer work. Finally, thanks to Katy, who has patiently endured four years of stories, ideas, and ecological minutiae about small flies and little shoreline puddles. ii Communities in Freshwater Coastal Rock Pools of Lake Superior, with a Focus on Chironomidae (Diptera) Abstract Exposed freshwater shores have received little ecological attention. At Isle Royale, an archipelago in Lake Superior, coastal areas have a moderated climate due to the large, deep lake. This project was instigated because 1) little was known about coastal ecosystems at Isle Royale, 2) unique aquatic species were expected in this habitat, 3) potentially disastrous impacts from shipping accidents could cause population losses of sensitive species, and 4) long-term shifts in climate could influence communities via warming conditions and erratic precipitation. Focal habitats were pools on the open shore, formed in bedrock depressions from precipitation, ground water, overland flow, and wave wash. The focal study taxon was Chironomidae, a diverse family of aquatic flies, well-known for variable responses to pollution and ecological gradients. Results showed a surprisingly species-rich (n = 102) and diverse assemblage. Moderate to extreme range expansions and novel habitat use were documented. Distinct communities were observed between two vertical zones, based on distance from the lake. Differences in seasonal emergence occurred close to the lake, but emerging assemblages were similar across seasons above lake influence. Some evidence supported both biogeographic community variation based on distances between islands and control of emergence events by water temperature. However, there was no evidence that pool depth or potential for desiccation influenced chironomid occupancy. Nutrients (phosphorus, nitrogen, and carbon) were the most important factors driving chironomid assemblage differences. iii Pools higher on the shore showed nutrient input from upland habitats, while pools lower on the shore appeared to have nutrients flushed out by wave action and replaced with low-nutrient water. Comprehensive habitat mapping revealed high pool densities, with an extraordinary number on Passage Island, arguably the most threatened locality to shipping pollution. Also, Passage Island had the highest density of Pseudacris triseriata, a frog species with a remarkably narrow habitat use at Isle Royale. Overall, a diverse community was revealed in what superficially looks like unremarkable habitat. Apparent similarities to northern and western shores of Lake Superior suggest this study of basic aquatic ecology and physical structure describes reference conditions for coastal management across much of the lake. iv Table of Contents Page Acknowledgements .............................................................................................................. i Abstract .............................................................................................................................. iii Table of Contents ................................................................................................................ v Figures................................................................................................................................ ix Tables ............................................................................................................................... xiii CHAPTER I CHIRONOMIDAE (DIPTERA) IN FRESHWATER COASTAL ROCK POOLS AT ISLE ROYALE, MICHIGAN ........................................................................ 1 Summary .......................................................................................................................1 Introduction ...................................................................................................................1 Methods ........................................................................................................................2 Results...........................................................................................................................3 Discussion ...................................................................................................................23 CHAPTER II SPATIAL ARRANGEMENT AND METRICS OF FRESHWATER COASTAL ROCK POOLS APPLIED TO AMPHIBIAN CONSERVATION ............... 26 Summary .....................................................................................................................26 Introduction .................................................................................................................26 Methods ......................................................................................................................28 Study Area .............................................................................................................28 Data Collection ......................................................................................................29 Analyses .................................................................................................................31 Results.........................................................................................................................32 v General Pool Arrangement and Mapping Effort ....................................................32 Physical Pool Characteristics .................................................................................35 Amphibian Occupancy...........................................................................................36 Discussion ...................................................................................................................43 General Pool Arrangement and Mapping Effort ....................................................43 Physical Pool Characteristics .................................................................................43 Amphibian Occupancy...........................................................................................44 Threats to Coastal Systems ....................................................................................47 Conclusions.................................................................................................................48 CHAPTER III CHIRONOMIDAE (DIPTERA) OCCURRENCE AND EMERGENCE IN FRESHWATER COASTAL ROCK POOLS OF LAKE SUPERIOR ............................ 50 Summary .....................................................................................................................50 Introduction .................................................................................................................50 Methods ......................................................................................................................53 Study site ................................................................................................................53