SPONGES AS IMPORTANT SPACE COMPETITORS 

 IN DEEP CARIBBEAN CORAL REEF COMMUNITIES 



1 



Thomas H. Suchanek 

 Robert C. Carpenter 

 Jon D. Witman 

 C. Drew Harvel 1 



2 

 West Indies Laboratory 



Fairleigh Dickinson University 



Chri stiansted , St. Croix 



U.S. Virgin Islands 00820 



D 

 deep 

 encr 



di ve 

 quad 

 120' 

 aggr 

 (Cho 



cant 

 f req 

 cont 

 comm 



ABSTRACT 



emosponges are diverse and aggressive competitors for space in 



open-reef habitats. Sponges comprise nearly half (30/63) of al 

 ustinq taxa recorded in this study and are significantly more 



rse than corals at 90' and 120' (p < .001). Analyses of m 

 rats (total N = 111) from depths of 10', 30', 60', 90', and 



reveal that a gorgonacean ( Erythropodium ) was the most frequent 

 essor at 10'. Below this depth, four genera of demosponges 

 ndri 1 1 a , Hemectyon , I rci ni a and V e r o n g i a ) were the most signifi- 



aggressors. Below 30', scl eracti ni an corals were the taxa most 

 uently overgrown. Sponges should be recognized as important 

 ributors to the organization and dynamics of open coral reef 

 unities. 



INTRODUCTION 



1 



Competition for space has gained the attention of a wide variety 

 of investigators interested in making long-range predictions about 

 community structure (Dayton, 1971; Lang, 1973; Jackson & Buss, 1975; 

 Osman, 1975). In tropical coral reef communities, heavy emphasis has 

 been placed on the transitive nature of competitive interactions 

 between scl eracti n ian corals and the contribution of such "competi- 

 tive hierarchies" to the structure of these communities (Lang, 1973; 

 Sheppard, 1979). Although other invertebrate groups are well-known 

 to exist within these communities, they are known mostly from the 

 crypto fa una (those species that inhabit the undersides of foliaceous 

 corals or cave-like environments) where competition has been reported 

 to be non-transitive in nature, producing "competitive networks" 

 (Jackson & Buss, 1975; Buss & Jackson, 1979). 



For "open-reef" assemblages (defined here as those reef species 

 existing out in the open, as opposed to those in cryptic habitats) 

 relatively little attention has been given to non-scleractinian 

 components of the community and their contribution to reef diversity 

 and dynamics. 



Contribution #109 of the West Indies Laboratory, St. Croix, U.S. V.I. 



2 Current Addresses : T.H.S. - 4124 Tami Way, Carmichael, Calif. 95608; 



R.C.C. - Institute of Ecology, Univ. of Georgia, Athens, Ga. 30602; 



J.D.W. - Dept. of Zoology, Univ. of New Hampshire, Durham, N.H. 03824; 



C.D.H. - Dept. of Zoology, Univ. of Washington, Seattle, Wash. 98195 



55 



