A BEHAVIORAL STUDY OF THE HAWAIIAN GOBY SHRIMP RELATIONSHIP AND THE EFFECTS OF PREDATION ON THE SYSTEM

A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTERS OF SCIENCE

IN ZOOLOGY

MAY 2005

By

Robert Paul Nelson

Thesis Committee:

Jim Parrish

Julie Bailey-Brock

Tim Tricas

We certify that we have read this thesis and that in our opinion it is satisfactory in scope and quality as a thesis for the degree of Master of Science in Zoology.

THESIS COMMITTEE

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Chairperson

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Acknowledgments:

I’d like to thank first and foremost my advisor Dr. J.D. Parrish for all his help in organizing and funding the project and reviewing my manuscript. Thanks to my committee members, Dr. Tim Tricas and Dr. Julie Bailey-Brock. Dr. Andrew Thompson helped in reviewing the manuscript. Mahalo to Casey Kaneshiro, Tyler Bouland and Rami Huiguas for collecting most of the daily rhythm cycle data. I also wish to express thanks for help from Georgi Kinsela, Jan Dierking, Katja Wunderbar, and Jeff Whitehurst.

Abstract

The belief that the relationship between certain gobies and snapping shrimp (Alpheidae) is mutualistic typically includes the assumption that predation is a selective force driving the co-evolution of the relationship. In this study, I first showed the importance of the Hawaiian shrimp goby (Psilogobius mainlandi) to the sheltering behavior of its associated alpheid shrimp. Shrimp spent 53.6 + 21.8 percent of light hours in the day outside burrows with gobies present, but only 6.9 + 3.4 percent of the time outside without gobies present. I then examined effects of predation by experimentally excluding predators on gobies from several 1.5-m square plots and observing the subsequent density and size of gobies. Over the 5 months of predator exclusion, no significant effect on goby density was detected (ANOVA; p = 0.345). The most conspicuous results of the exclusion were the changes in the size classes of gobies (ANOVA, p < 0.001). Plots with exclosures had a mean of 2.23 more large gobies (> 4 cm TL) than plots with no exclosures. In a final part of the study, I documented the daily cycle of activity of the snapping shrimp, Alpheus rapax, with an associated goby present. The results indicate that A. rapax increases foraging and burrow maintenance activities toward the end of daylight. Overall, this study was able to test the widely held assumption that predation can be a selective pressure on the goby-shrimp association.

TABLE OF CONTENTS

Acknowledgments ……………………………………………………………... ii

Abstract …………………………………………………………………………..iii

List of Tables ……………………………………………………………………. v

List of Figures …………………………………………………………………… vi

Introduction ………………………………………………………………………1

Methods ………………………………………………………………………….. 3

Results ……………………………………………………………………………. 9

Discussion …………………………………………………………………………12

References ………………………………………………………………………..16

Appendix …………………………………………………………………………32

LIST OF TABLES

Table Page

  1. Dates of data collection, corresponding sample ID numbers, and timing relative to exclosure events.
  2. Duration of behaviors in seconds (mean + SD) recorded for shrimp during five 1000-sec sampling periods in daylight
  3. Means (+ S.D.) from seven shrimp burrows with associated goby and seven burrows without: ‘bout’ length; percent of total time that shrimp were out of the burrow; percent of shrimp emergences that involved burrow maintenance
  4. Results from two-way ANOVA of numerical density of gobies (all sizes combined) for exclosure treatment and time.
  5. Mean numerical densities of gobies per plot, divided into three size classes, for each of seven data collection dates and three exclosure treatments (full, partial, none). (For ID#s, refer to Table 1.)
  6. Results from two-way ANOVA of numerical density of large gobies for exclosure treatment and time.

LIST OF FIGURES

Figure Page

  1. Placement of treatment areas, plots, and assignment of treatments in goby bay.
  2. Layout of plots within each treatment area.
  3. Mean time (+ S.D.) spent by gobies in each type of behavior at various times of day.
  4. Mean number (+ S.D.) of gobies (all sizes combined) recorded per plot for each of three treatments from February to October 2004. Exclosures were in place and functional just after ID#0 and were taken down immediately after ID#5.
  5. Mean number (+ S.D.) of large gobies (> 4 cm) recorded per plot for each of three treatments from February to October 2004. Exclosures were in place and functional just after ID#0 and were taken down immediately after ID#5.
  6. Estimated total biomass of gobies per plot for each of three treatments from February to October 2004. Exclosures were in place and functional just after ID#0 and were taken down immediately after ID#5.
  7. Changes in snapping shrimp (Alpheusspp.) behaviors throughout one day.

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