Influence of spatial competitor on asexual reproduction of the marine sponge Cinachyrella cf. cavernosa (Porifera, Demospongiae)

Competition for resources, which often results in resource tradeoffs, is intense among sessile benthic organisms. In this investigation, we tested the tradeoffs between the primary and secondary functions by studying the influence of spatial competitor Zoanthus sansibaricus on the reproductive outcome of the sponge Cinachyrella cf. cavernosa. Field studies were carried out at a rocky intertidal beach at Anjuna, Goa, India, from October 2013 to September 2015. C. cf. cavernosa reproduces asexually via ‘budding’ that comprises three stages (Stage I–III) with distinctive morphological and skeletal characteristics. The budding frequency was positively regulated by temperature of the rock pool water and negatively by the substrate cover of Z. sansibaricus. In the absence of the spatial competitor Z. sansibaricus, there was a significant increase in budding frequency (10–30%), bud count per sponge (45–60%), bud settlement probability (60–80%) and physiological activity (RNA/DNA ratio) of buds (10–35%). Over-expression (75–80%) of heat shock protein 70 (stress response) was observed in the sponge during the competitive interaction. This investigation shows that spatial competition adversely affects asexual reproduction of C. cf. cavernosa, and it supports the earlier observations of tradeoffs between the primary and secondary functions.