COMlMUNITY CONSEQUENCES OF HABITAT USE AND PREDATION BY COMMON EIDERS IN THE INTERTIDAL ZONE OF PASSAMAQUODDY BAY A thesis Presented to The Faculty of Graduate Studies of The University of Guelph by DIANA JEANNE HAMILTON In partial fulfilment of requirements for the degree of Doctor of Philosophy November, 1997 0 Diana J. Hamilton, 1997 NationaI Library Bibliothèque nationale du Canada Acquisitions and Acquisitions et Bibliographie SeMces services bibliographiques 395 Wellington Street 395, nie Wellington OttawaON K1AW OttawaON KtAON4 Canada canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, disûiiute or sell reproduire, prêter, distribuer ou copies of this thesis in microfoq vendre des copies de cette thèse sous pqer or electronic formats. la fome de microfiche/fïlm, de reproduction sur papier ou sur fomat électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimes reproduced without the author's ou autrement reproduits sans son permission. autorisation. ABSTRACT COMMUNTY CONSEQUENCES OF HABITAT USE AND PREDATION BY COMMON EIDERS IN THE INTERTIDAL ZONE OF PASSAMAQUODDY BAY Diana Jeanne Hamilton Advisor: University of Guelph, 1997 Professor T. D. Nudds 1 investigated interactions between Common Eiders (Somaterza mollissima) and the intertidal invertebrate comrnunity in Passamaquoddy Bay. New Brunswick. 1 determined that young duckiings were dependent on rockweed (AscophyfIumnodosum), a perenniai macro aiga, to obtain food, as indicated by their feeding methods and timing, but that feeding by older duckiings was unaffected by tide level. Commercial harvest of rockweed may therefore be detrimental to the youngest duckhgs, but have little effect on older birds. 1 also found that care of ducklings constrained female behaviour and habitat use. This may be a local effect caused by very high predation pressure exerted on duckiings at this site. Addt eiders were site-selective predators of blue mussels (Mytzhs eduiis), and preferences varied depending on season and prey availability. Selection of prey corresponded with predictions of the sheil mass minimization hypothesis and also with the nsk-averse foraging hypothesis. Using a series of predator exclusion cages, 1 found that in musse1 beds, ducks had little effect on species richness or diversity, but sigdicantly reduced total biomass by feeding primarily on blue mussels. Biomass effects persisted throughout the experiment in sites subjected to abiotic disturbance, but disappeared in undishirbed sites within a year. Exclusion of ducks led to an increase in dogwhelks (Nucella hpzllus) under natural site cages, and by feeding on blue mussels they obscured the effect of eider predation. This indirect effect is an example of compensatory predation by a formerly redundant predator. Effis of eider predation on rockweed bed invertebrate biornass were small, and again duck predation did not influence species nchness or diversity. Harvest of rockweed had no effect on invertebrate abundance, and little eff'on predation by ducks. DiBerences in results between the two areas can be attributed to habitat heterogeneity and relative abundance of whelks. Although the effect on biomass was not measurable, predation by ducks may have contnbuted to maintenance of rockweed habitat. When ducks were excluded, substrate cover by blue mussels increased and rockweed declined. These redts indicate that ducks are signifiicant predators in this community, and that waterfowl should not be neglected as predators in community studies. ACKNOWISDGEMENTS 1 am gratefid to mam, people for helping me with various aspects of this research. First, 1 would like to th& my advisor, Tom Nudds, for his advice, support, encouragement, and patience during the past four years. 1am grateful to my advisory committee members, Dave Ankney, Eiizabeth Bodding, and Peter Yodzis for advice and suggestions throughout rny degree, and for helpfbl comments on my thesis. I would also like to thank John FryxeLI for helpful comments and insightfbl questions at various times, which ultimately improved the thesis. 1 am gratefid to members of my examination conmittee, Sandy Middleton, Tim Wootton, John Fryxe11, Peter Yodzis, and Tom Nudds for helpfid changes to the thesis. Thanks to Claudia Schubert-Kuener, Mark mer, Carey Bergman, Brent Gurd, and Chris McLaughlin for quizzing me before my quakfjmg exam, making usefbi suggestions, and providing much needed distractions when 1 was in Guelph. I received a great deal of help with the field and lab components of this research. Co~aBrdar, Andrea Cox, Danielle Downing, Jim Godfiey, Jennifer Neate, Kim Smith, and especiaily Cindy Doherty provided excellent field assistance. Biii Hogans provided adult ducks, and Glyn Sharp, Ian Barkhouse, and Pat Kehoe provided ducklings for food habits analysis. Discussions with GIyn Sharp and Pat Kehoe early in the study were helpful. The Engineering department at the University of New Brunswick (Saint John) aiiowed me to use the tensometer to cmsh blue mussels and Cedric Boone provided assistance. 1 am grateful to ail these people. 1 would also keto thank the staff of Huntsman Marine Science Centre for assistance while conducting research there, and the biology department at the University of New Brunswick (Saint John) for aliowing me to use slide making equipment. 1 wish to acknowledge and thank the foiiowing organkitions for providing research funding for this project: Institute for Wetland and Waterfowl Research (IWWR), Delta Waterfowl Foundation, Natural Sciences and Engineering Research Council (NSERC)(research grant to T. D. Nudds), New Brunswick Department of Fisheries and Aquaculture, Canadian Wddlife Service University Research Support Fund. Personal fiinding was provided through: NSERC Postgraduate Fellowship, Ontario Graduate Scholarship, Bomeycastle FeUowship (MrWR), Elgin Card Avian Ecology Scholarship (University of Guelph), Hunt sman Graduate Scholarship (Huntsman Marine Science Centre), Faculty of Graduate Shidies Scholarship (University of Guelph) . FinaUy, 1 would like to thank my husband, Matthew Litvak. He helped me with the field work that nobody else wanted to do, read and commented on my thesis, gave me many helpfùl suggestions, and supported and encouraged me throughout. LIST OF TABLES 1.1 .Redts of MANOVAS of duck age and tirne of day on behaviour ...........................15 1-2 O Results of MANOVAS of duck age and tide level on behaviour ..............................-22 1-3 .Results of ANOVA of duck feeding time................................................................. -29 2.1 - Redts of x2 analyses of prey seleetion experiments................................................ -51 3.1 - Effects tested in ANOVA and MANOVA models ....................................................84 3 -2- Results of ANOVAs of total biomass, species diverzity, and species richness ......... 93 3 -3 - Results of MANOVA of cornmon species dry tissue biomass .................................. 96 4.1 - Results of ANOVAs of total biornass and biomass of periwinkles and whellcs ..... -141 4.2 - Resuks of analyses of blue musse1 and rockweed cover in cages and controls...... -157 4.3 - Cornparison of rockweed and musse1 bed habitat .................................................. -163 LIST OF FIGURES Figure Page 1.1 .Behaviour of ducklings and adults at the four tide levels .......................................... 18 1 -2 .Behaviour of eiders at different times of the day ...................................................... -21 1 -3 - Behaviour of ducklings and adults at dBerent hesof the day ............................... 25 1.4 - The spent feediag for ducks in each age group .............................................. 31 2.1 - Tiles used in prey selection experiments.................................................................. -46 2.2 - Size fiequency distributions of mussels collected at Indian Point and Barr Road -34 2.3 - Tissue content of mussels collecteci at different times of the year .......................... 36 2.4 - Regressions of sheli thickness and cmsbg resistance on shell length ..................... 59 2.5 - Shell mass eaten by ducks and profitability of mussels of difEerent sizes................. 61 3.1 - Diagram of an experimental site............................................................................... -79 3 -2- Dry tissue biornass in cage and control areas ............................................................ 87 3 -3 - Species richness in cage and wntrol areas ................................................................ 90 3 -4- Species diversity in cage and control areas ................................................................ 92 3 -5 - Dq tissue biomass of blue mussels in cage and control areas................................ 100 3.6 - Dry tissue biomass of wheks in cage and control areas........................................ -102 3 -7- Average musse1 length in cage and control areas................................................... -105 3.8 - Size fiequency distributions of mussels collected from cages and wntrols ............ 107 3 -9 - Dry tissue biomass in cage and control areas