The diversity of sessile invertebrates of coral reefs is highly dependent upon spatial association and interactions among species. In this report we describe biotic substratum-associated effects on the growth and survival of the sponge Desmapsamma anchorata Carter 1882. Special attention is given to associations and interactions of Desmapsamma with various gorgonian species on which the sponge dwells. With the exception of relatively high abundances of Desmapsamma on Briareum asbestinum Pallas 1766, associations with gorgonian taxa were not species-specific. In contrast, interactions were often species-specific with gorgonians and other taxa, the nature of which ranged from (1) mutualistic (with Briareum), (2) to neutral (non-interactive) with other sponges, (3) to negative (competitive) with a variety of other organisms. Negative interactions included (1) overgrowth, (2) competitive standoff, and (3) allelochemical effects. Other results show that wave action plays an important role in the growth and survival of Desmapsamma individuals. These results indicate that the reciprocal action of physical and biological factors play a key role in structuring and organizing coral reef communities.