ECOLOGY OF THE OBLIGATE SPONGE-DWELLING BRITTLESTAR Ophiothrix lineata Timothy P. Henkel A Dissertation Submitted to the University of North Carolina Wilmington in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Department of Biology and Marine Biology University of North Carolina Wilmington 2008 Approved by Advisory Committee Martin Posey ______________________________John Bruno ______________________________ Fred Scharf Ami Wilbur ______________________________ ______________________________ ______________________________Joseph R. Pawlik Chair Accepted by __________________________ Dean, Graduate School i TABLE OF CONTENTS ABSTRACT .....................................................................................................................................v ACKNOWLDEGEMENTS ........................................................................................................ viii LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ....................................................................................................................... xi CHAPTER 1: THE ASSOCIATION OF Ophiothrix lineata AND Callyspongia vaginalis: IS THE BRITTLESTAR A PARASITE ON SPONGE LARVAE? ....................................................1 ABSTRACT ...............................................................................................................................2 INTRODUCTION .....................................................................................................................3 MATERIALS AND METHODS ...............................................................................................5 Predation of sponge larvae by Ophiothrix lineata .................................................................5 Effect of Ophiothrix lineata on Callyspongia vaginalis .......................................................6 Statistical analyses .................................................................................................................9 RESULTS ................................................................................................................................10 DISUSSION .............................................................................................................................11 LITERATURE CITED ............................................................................................................16 CHAPTER 2: HOST SPECIALIZATION AND LIMITATION OF AN OBLIGATE SPONGE- DWELLING BRITTLESTAR .......................................................................................................25 ABSTRACT .............................................................................................................................26 INTRODUCTION ...................................................................................................................27 MATERIALS AND METHODS .............................................................................................30 Host choice experiments .....................................................................................................30 Effect of habitat size on growth of Ophiothrix lineata .......................................................32 ii Growth of Ophiothrix lineata living on multiple sponge hosts ...........................................34 Sex and size distribution of Ophiothrix lineata ...................................................................35 RESULTS ................................................................................................................................36 DISUSSION .............................................................................................................................37 Host specificity of Ophiothrix lineata .................................................................................37 Host Limitations and the distribution of Ophiothrix lineata ...............................................43 LITERATURE CITED ............................................................................................................45 CHAPTER 3: LIFE HISTORY TRAITS OF THE SPONGE-DWELLING BRITTLESTAR Ophiothrix lineata ..........................................................................................................................57 ABSTRACT .............................................................................................................................58 INTRODUCTION ...................................................................................................................59 MATERIALS AND METHODS .............................................................................................61 Larval development .............................................................................................................61 Morphometrics and size distribution ...................................................................................61 Growth model ......................................................................................................................62 RESULTS ................................................................................................................................64 Larval development .............................................................................................................64 Morphometrics and size distribution ...................................................................................65 Growth model ......................................................................................................................66 DISCUSSION ..........................................................................................................................66 Development of Ophiothrix lineata ....................................................................................66 Implications of direct development in Ophiothrix lineata ..................................................69 Growth of Ophiothrix lineata ..............................................................................................70 iii LITERATURE CITED ............................................................................................................73 CHAPTER 4: THE EFFECT OF AN OBLIGATE SPONGE-DWELLING BRITTLESTAR ON THE SPONGE-ASSOCIATED COMMUNITY ...........................................................................83 ABSTRACT .............................................................................................................................84 INTRODUCTION ...................................................................................................................85 MATERIALS AND METHODS .............................................................................................86 Surveys of established community ......................................................................................86 Immigration of sponge-associated community ...................................................................87 Statistical analyses ...............................................................................................................88 RESULTS ................................................................................................................................88 Surveys of established community ......................................................................................88 Immigration of sponge-associated community ...................................................................89 DISCUSSION ..........................................................................................................................90 LITERATURE CITED ............................................................................................................93 iv ABSTRACT Host specificity has long been recognized as an important means of speciation in terrestrial plant-herbivore and host-parasite interactions; however, the role of host specificity in the marine environment is less understood. On coral reefs off the Florida Keys, the sponge- dwelling brittlestar Ophiothrix lineata lives almost exclusively in the tube sponge Callyspongia vaginalis. I examined chemotactic recognition by O. lineata to assess sponge host preferences using a y-tube assay chamber. Relative to seawater controls, O. lineata preferentially selected seawater conditioned by the preferred host sponge C. vaginalis and showed no preference for seawater conditioned by the infrequent host Niphates digitalis or non-host Aplysina archeri. When offered seawater conditioned by C. vaginalis and N. digitalis, O. lineata chose C. vaginalis 78% of the time. Growth of O. lineata living in the three sponge hosts was measured in the field. Growth of O. lineata was greatest when living in C. vaginalis, though growth was similar to O. lineata living in N. digitalis. Unlike A. archeri, both N. digitalis and C. vaginalis brood larvae year round. Sponge larvae may provide an additional food source to O. lineata, which deposit-feeds on the outer surface of the sponge. Predation of sponge larvae by O. lineata was first assessed in lab feeding assays, and O. lineata readily consumed larvae from both C. vaginalis and N. digitalis. In the field, O. lineata grew faster when living in both species of brooding sponges than when living in non-brooding individuals. Larval predation by O. lineata in the field was further assessed by comparing