Otters, sea stars, and glacial melt: top-down and bottom-up factors that influence kelp communities Item Type Thesis Authors Traiger, Sarah B. Download date 07/10/2021 21:31:28 Link to Item http://hdl.handle.net/11122/7903 OTTERS, SEA STARS, AND GLACIAL MELT: TOP-DOWN AND BOTTOM-UP FACTORS THAT INFLUENCE KELP COMMUNITIES By Sarah B. Traiger, B.S. A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Marine Biology August 2017 APPROVED: Brenda Konar, Committee Chair Sarah Hardy, Committee Member, Chair Department of Marine Biology Stephen Okkonen, Committee Member Matthew Edwards, Committee Member Wayne Litaker, Committee Member Bradley Moran, Dean College of Fisheries and Ocean Sciences Michael Castellini, Dean o f the Graduate School ABSTRACT Kelp beds are important features of the Alaska coastline and provide habitat, protect coastlines, and support commercial and subsistence harvests. Kelp beds are affected by top-down and bottom-up factors, which are changing due to human and climate-related impacts. The influences of these top-down and bottom-up factors on kelp beds are investigated in three chapters. My first chapter investigated the influence of glacial discharge on recruitment and early community development in subtidal kelp communities by monitoring benthic sessile algae and invertebrates on cleared rocks across a glacial gradient along with various physical and biological parameters in the summers of 2013-2014. It has been predicted that Alaska’s glaciers will lose 30-60% of their volume by 2100. The melt from glaciers increases sedimentation and lowers salinity, impacting important habitat-providing kelp. I found that sites upstream from glacial discharge had higher kelp recruitment than downstream sites, and that up to 72% of the variation in community development was related to mobile invertebrates and kelp in the surrounding community. Glacially-influenced environmental factors did not explain any variation that was not already explained by biological factors. My second chapter explored whether patterns in the recruitment of the dominant canopy kelp,Nereocystis luetkeana and the subcanopy kelp, Saccharina latissima were a result of dispersal limitation or failure to grow to macroscopic size. My goals were to determine 1) whether glacial melt conditions affect adult fecundity (spore production) of either species, 2) how sedimentation affects early gametophyte growth and survival in each species, and 3) whether competitive interaction between species at the gametophyte stage is altered by sediments. I found that glacial melt conditions did not affect the fecundity of either species, but sedimentation affected survival and competition.Saccharina latissima was the superior competitor under high sediment conditions. Because glacially- iii influenced coastal areas often have little exposed hard substrate and predation by sea otters and sea stars on clams can provide hard substrate for kelp colonization, my third chapter examined methods for determining predation on clams by these predators without direct observation. I found that foraging pits of sea otters and sea stars could not be distinguished using quantitative measurements. In contrast, shell litter proved useful in quantifying relative foraging rates. Clam consumption by sea otters and sea stars was equal at all but one site. Collectively, my thesis chapters provide information on the effects of glacial discharge on microscopic and early kelp life stages in Alaska which can be incorporated into management practices. iv TABLE OF CONTENTS Page TITLE PAGE..........................................................................................................................................i ABSTRACT..........................................................................................................................................iii TABLE OF CONTENTS......................................................................................................................v LIST OF TABLES.............................................................................................................................viii LIST OF FIGURES.............................................................................................................................. x ACKNOWLEDGEMENTS............................................................................................................... xii GENERAL INTRODUCTION.............................................................................................................1 LITERATURE CITED......................................................................................................................... 6 CHAPTER 1: INITIAL RECRUITMENT AND EARLY COLONIZATION OF KELP- ASSOCIATED BENTHIC COMMUNITIES VARIES IN RELATION TO GLACIAL DISCHARGE....................................................................................................................... 11 1.1 ABSTRACT...............................................................................................................................11 1.2 INTRODUCTION..................................................................................................................... 12 1.3 METHODS.................................................................................................................................14 1.3.1 Study Site.............................................................................................................................14 1.3.2 Environmental factors.........................................................................................................15 1.3.3 Biological factors................................................................................................................ 17 1.3.4 Patterns of initial recruitment and early community development................................. 17 1.3.5 Data Analysis ...................................................................................................................... 18 1.4 RESULTS ...................................................................................................................................20 1.4.1 Environmental factors....................................................................................................... 20 1.4.2 Biological factors .............................................................................................................. 21 1.4.3 Patterns of community development................................................................................ 21 1.4.4 Correlations with environment and surrounding community......................................... 23 1.5 DISCUSSION ........................................................................................................................... 25 1.5.1 Patterns of early community development.......................................................................26 1.5.2 Factors correlated with community development...........................................................27 1.5.3 Implications........................................................................................................................ 32 1.6 LITERATURE CITED.............................................................................................................33 1.7 TABLES AND FIGURES....................................................................................................... 38 1.8 APPENDIX A ........................................................................................................................... 58 v CHAPTER 2: SUPPLY AND SURVIVAL: GLACIAL MELT IMPOSES LIMITATIONS AT THE KELP MICROSCOPIC LIFE STAGE.....................................................................60 2.1 ABSTRACT.............................................................................................................................. 60 2.2 INTRODUCTION..................................................................................................................... 61 2.3 MATERIALS AND METHODS.............................................................................................64 2.3.1 Study site............................................................................................................................ 64 2.3.2 Fecundity Comparison....................................................................................................... 65 2.3.3 Competition-sedimentation experiments..........................................................................67 2.3.4 Single Species Response to Sedimentation......................................................................68 2.3.5 Mixed Species Response to Sedimentation......................................................................69 2.3.6 Data analysis....................................................................................................................... 71 2.4 RESULTS ...................................................................................................................................72 2.4.1 Fecundity did not differ between sites upstream and downstream of glacial discharge ..................................................................................................................................................... 72 2.4.2 Competition-sedimentation experiment...........................................................................73 2.4.2.1 Nereocystis andSaccharina gametophyte survival and growth are similar