Positive relationship between two conspicuous intertidal components, the sponge Hymeniacidon sp. and the algae Ulva lactuca?

GASTALDI, M.; DALEO, P.; NARVARTE, M.; IRIBARNE, O.

Mar del Plata

Congreso; CERF's Inaugural International Conference of the Americas; 2012

Sponges and algae are common components of intertidal  ecosystems all over the world and their ecological relationships have  notbeen extensely studied.  Most of studies, performed in subtidal environments, indicate that macroalgae out-compete and displace sponges causing their death through smothering, shading or release of allelochemicals. The main goal of this study was to evaluate the relationship between the sponge Hymeniacidon sp. and the algae Ulva lactuca in a stressful intertidal environment of Patagonia. In order to assess whether the abundance of the sponge is affected by the presence of algae we examined, during the spring of 2011 in four sampling times, the variation in sponges cover in plots at sites with and without algae. Also, to evaluate if the survivorship of sponges? colonies is determined by the presence of algae, we carried out a transplant experiment. Results showed that at in early spring, sponges cover was higher in plots without algae. However, this difference was substantially reduced in the subsequent time samples. The transplant experiment showed that survivorship of sponge colonies with algae was71-78%, and that of sponge colonies without algae was 29-32%. These results show a negative effect of the algae on the sponge cover at the beginning of the spring, but as temperature rises (and the dessication stress increases) the effect of the algae becomes positive both on sponges cover and its survivorship. Future experiments will evaluate this relationship seasonally, both in intertidal and subtidal environments.