Population dynamics of a mutualistic interaction between the sponge Haliclona caerulea and the red alga Jania adherens

Abstract

A population of the association between the haplosclerid sponge Haliclona caerulea and the red algae Jania adherens was studied in the Bay of Mazatlan (east tropical Pacific Ocean, Mex- ico), along a spatial gradient (from 1 to 5 m depth) and over time (from February 2001 to September 2003). No clear seasonality was found in the abundance (from 0.5 to 17 ind. 25 m -2 ), volume (from 741 to 7241 cm 3 25 m -2 ), recruitment (up to 9 new ind. 25 m 2 mo -1 ) and mortality (50% loss mo -1 average). The population was capable of recovering after 50% of the specimens were lost; abundance and volume recovered after 7 and 17 mo, respectively. Recruitment was determined in part by asexual propagation through fragmentation, and the relationship with abundance suggested that the popula- tion was self-sustaining. Seasonality was only evident in the sexual reproduction of the sponge, which occurred when water temperature increased: from May to September in 2001, from March to July in 2002, and from April to October in 2003. An important feature was that axial conceptacles of J. adherens living in association with the sponge were never found. The association was permanent over time and the interaction affected the abundance, survival and distribution of the 2 partners in the association. J. adherens was found growing independently in the intertidal zone, which is out of the range of distribution for the association, but we did not find any evidence of sponge living in iso- lation, although in association it is one of the dominant members of the shallow rocky ecosystem in the Bay of Mazatlan. The association was very highly specific; other coralline algae such as Amphi- roa spp. were found in the same habitat, but H. caerulea only associated with Amphiroa spp. in less than 3% of the samples studied. The advantages for J. adherens can be deduced from the fact that it spreads and persists below 1 m thanks to its association with the sponge. The sponge benefits from the fact that it can persist and colonize shallower zones by living in association with the alga. Thus, we conclude that this association is mutualistic.