THE EFFECTS OF HARVESTING MACROCYSTIS PYRIFERA ON UNDERSTORY ALGAE IN CARHEL BAY, CALIFORNIA by Robert Scott Kimura A thesis submitted in partial fulfillment of the requirements for the degree of Haster of Arts in the Department of Biology California State University, Fresno December 1980 ACKNOWLEDGMENTS I offer my deepest gratitude to the late Dr. Torn Thompson; without his stimulus and encouragement I might never have become interested in marine plants. Thanks also are in order to my horne campus committee members Drs. Keith Woodwick and Gina Arce for their assistance and comments on my thesis; and to my off-campus committee member Dr. Mike Foster (California State University, Hayward) at Moss Landing Marine Laboratories for his technical guidance. I also extend my appreciation to Doug Hunt, my dive partner, Dan Miller, Kim McCleneghan, and Jim Houk of the California State Department of Fish and Game, Monterey, and fellow divers of Moss Landing Marine Laboratories. Without their assistance, this field work would have been a difficult undertaking. This research was funded by the University of California Sea Grant College Project R/CZ-21, under the direction of the late Dr. Torn W. Thompson. ABSTRACT In Carmel Bay, the Macrocystis pyrifera surface canopy undergoes a natural annual cycle of summer luxuriance and winter storm-related removal. Commercial harvesting activities normally occur during the summer months when surface canopies are best developed. To determine the effects of canopy removal on M. pyrifera and understory vegetation the abundances of 29 algal species were followed for a 1-year period in three study areas. One study area was harvested in June and a second area in October to deter­ mine if canopy removal during different harvestable months would produce different results. A third area was an unhar­ vested control. All study areas were established adjacent to one another at depths ranging from 15 to 18 meters in locations known to have not been previously harvested. In January, 6 months following the June canopy harvest, the abundances of juvenile Macrocystis pyrifera and Pterygophora californica sporophytes increased signifi­ cantly in the June harvested area. No new juveniles were noted during this time in the unharvested area. Recruitment in the latter area did not occur until 5 months later. Most of the winter-appearing juveniles in the June harvested area were quickly lost due to early storm-related mortalities. Therefore, the enhanced recruitment of the M. pyrifera and vi ~· californica populations did not contribute more adults to the June area relative to the unharvested area which lacked winter recruitment. Harvesting in October had a smaller effect on recruitment. In the October harvested area, M. pyrifera and ~· californica juvenile abundances· also increased substantially 6 months following canopy removal, but this occurred 1 month prior to natural recruitment in the unharvested area. This closer coincidence of recruit­ ment probably occurred because the October harvest was closer to the time of natural canopy thinning in the uncut area. The different recruitment periods are assumed to be the result of increased submarine illumination caused by surface canopy removals. Seasonal trends for all other species in the harvested areas were similar to those in the uncut area. In addition, annual harvesting operations have not disrupted the natural seasonal oscillations in total surface canopy coverage for the entire kelp bed from 1973 to 1979. CONTENTS Page LIST OF TABLES . viii LIST OF FIGURES X INTRODUCTION l LOCATION AND METHODS 5 Study Site 5 Methods 8 RESULTS 18 Substrate Composition 18 Species Composition 18 Algal Layering Structure 2l Trends in Algal Percent Cover 21 Trends in Algal Density 34 The Effects of a June Harvest 72 The Effects of an October Harvest 77 DISCUSSION . 81 The Effects of Harvesting on Understory Algae 81 The Effects of Harvesting on Adult Macrocystis pyrifera . 91 General Community Overview 94 CONCLUSIONS 102 LITERATURE CITED 104 LIST OF TABLES Table Page 1. Sampling Frequencies and Sample Sizes (N) for the 10m2 Quadrat and Random-Point- Contact Methods . 15 2. Species Encountered in the Unharvested, June and October Harvested Areas Over the Course of the Study Period . 20 3. Percent Cover of Minor Species in the Unharvested Area Over Time . 26 4. Percent Cover of Minor Species in the June Harvested Area Over Time 27 5. Percent Cover of Minor Species in the October Harvested Area Over Time . 28 6. Percent Frequency of Occurrence Values for l-!acrocys tis hyrifera Adults and Juveniles in Eac of the Unharvested, June, and October Harvested Areas Over Time . .... 35 7. Percent Frequency of Occurrence Values for Pterygophora californica Adults and Juveniles in Each of the Unharvested, June, and October Harvested Areas Over Time . .... 36 8. Percent Frequency of Occurrence Values for Juvenile Laminariales in Each of the Unharvested, June, and October Harvested Areas Over Time 37 9. Percent Frequency of Occurrence Values for Cystoseira osmundacea Adults and Juveniles in Each of the Unharvested, June, and October Harvested Areas Over Time .. 38 10. Percent Frequency of Occurrence Values for Schizymenia pacifica in Each of the Unharvested, June, and October Harvested Areas Over Time 39 ix Table Page 11. Percent Frequency of Occurrence Values for Weeksia reticulata in Each of the Unharvested, June, and October Harvested Areas Over Time 40 12. Percent Frequency of Occurrence Values for Opuntiella californica in Each of the Unharvested, June, and October Harvested Areas Over Time . 41 13. Two-Tailed Kruskal-Wallis Test of Macrochstis hyrifera Juvenile Abundances in Eac of t e Unharvested, June and October Harvested Areas . 73 14. Newrnan-Kuels Multiple Comparisons Test of Macrosystis pyrifera Juvenile Abundances in the June Harvested Area .. 73 15. Newrnan-Kuels Multiple Comparisons Test of Macrocystis pyrifera Juvenile Abundances in the Unharvested Area .... 74 16. Two-Tailed Kruskal-Wallis Test of Pterygophora californica Juvenile Abundances in Each of the Unharvested, June and October Harvested Areas . 76 17. Newrnan-Kuels Multiple Comparisons Test of Pter~gophora californica Juvenile Abun ances in the Unharvested Area . 76 18. Two-Tailed Kruskal-Wallis Test of Juvenile Laminariales Abundances in Each of the Unharvested and June Harvested Areas 78 19. Newrnan-Kuels Hultiple Comparisons Test of Juvenile Laminariales Abundances in the Unharvested Area . ... 78 20. Newrnan-Kuels Multiple Comparisons Test of Macrocystis pyrifera Juvenile Abundances in the October Harvested Area 80 LIST OF FIGURES Figure Page 1. Carmel Bay Kelp Bed and Study Area Locations 36°33'N. & 121°57'W 6 2. Vertical Layering in the Carmel Bay Kelp Forest (Most Abundant Species within Each of Seven Layers) 7 3. Mean No. Plants/10m2 = 95% Confidence Intervals Versus Increasing Sample Size 13 4. Overall (Annual) Percent Composition of Substratum Types for Each of the Study Areas 19 5. Mean No. Layers/Point and Sample Sizes for Each of the Study Areas 22 6. Pre-Harvest (Summer) Percent Cover Values Per Species for Each of the Study Areas 24 7. Plocamium cartilagineum Percent Cover ±95% Confidence Intervals and Sample Sizes in Each of the Study Areas 29 8. Calliarthron tuberculosum Percent Cover ±95% Confidence Intervals and Sample Sizes in Each of the Study Areas 30 9. Bossiella californica ssp. schmittii Percent Cover ±95% Confidence Intervals and Sample Sizes in Each of the Study Areas 32 10. Crustose Corallines Percent Cover ~95% Confidence Intervals and Sample Sizes in Each of the Study Areas 33 11. Mean No. of Macrocystis pyrifera (adults)/ 10m2 ±95% Confidence Intervals in Each of the Study Areas 42 12. Mean No. Macrocystis pyrifera (juveniles)/ 10m2 ~95% Confidence Intervals in Each of the Study Areas 44 xi Figure Page 13. Relative Changes in Macrocystis pyrifera Canopy Cover for the Carmel Bay Kelp Bed from 1973 to 1979 46 14. Macrocystis pyrifera Mean Canopy Frond Lengths in Each of the Study Areas . 47 15. Macrocystis pyrifera Mean No. Stipes/10m2 in Each of the Study Areas . 49 16. Mean No. Pterygophora californica (adults)/ 10m2 ~95% Confidence Intervals in Each of the Study Areas . 51 17. Pterygophora californica (adults) Relative Percent Composition of Four Morphological Categories in the Unharvested Area .. 52 18. Pterygophora californica (adults) Relative Percent Composition of Four Morphological Categories in the June Harvested Area 53 19. Pterygophora californica (adults) Relative Percent Composition of Four Morphological Categories in the October Harvested Area . 54 20. Mean No. Pterygophora californica (juveniles)/ 10m2 ~95% Confidence Interval in Each of the Study Areas . 57 21. Mean No. Laminariales (juveniles)/10m2 ~95% Confidence Intervals in Each of the Study Areas 59 22. Mean No. C~stoseira osmundacea (adults)/ 10m2 ~95" Confidence Intervals in Each of the Study Areas . 61 23. Cystoseira osmundacea (adults) Relative Percent Composltlon of Three Morphological Categories in the Unharvested Area . 63 24. Cystoseira osmundacea (adults) Relative Percent Composltlon of Three Morphological Categories in the June Harvested Area 64 25. Cystoseira osmundacea (adults) Relative Percent Composltlon of Three Morphological Categories in the October Havested Area 65 xii Figure Page 26. Mean No. Cystoseira osmundacea (juveniles)/ 10m2 ±95% Confidence Intervals in Each of the Study Areas . 67 27. Mean No. Schizymenia pacifica/10m2 ±95% Confidence Intervals in Each of the Study Areas . 68 2 28. Mean No. Weeksia reticulata/10m ±95% Confidence Intervals in Each of the Study Areas . 70 29. Mean No. Opuntiella californica/10m2 ±95% Confidence Intervals in Each of the Study Areas 0 • • • • • • • • 0 • • • • • • • • 71 INTRODUCTION Algal community structure in kelp forests has been described by Neushul (197la) and Foster (1972). The campo- nents, based on plant size, are vertically layered and thus act as shading agents reducing the amount of light reaching the bottom. Shading effects produced by Macrocistis pyrifera surface canopies are well known to suppress under­ story algal species composition and abundance. Dawson et al. (1960) noted only six species within a dense M.