Symbiosis in seaweeds from Argentina: Rhodymenia pseudopalmata and Hymenena falklandica.

GAUNA, M. CECILIA; PARODI, ELISA R.; CÁCERES, EDUARDO J.

Dartmouth, Canada

Workshop; ACCESS: Atlantic Canada Coastal and Estuarine Science Society; 2008

Atlantic Canada Coastal and Estuarine Science Society

The environment of seaweeds includes both biotic and abiotic factors. At one end of the spectrum of biotic relationships are seaweed epiphytism and endophytism. These interactions and their temporal and spatial distribution are key elements in the functioning of seaweed communities. Some instances of epiphytism are highly host specific, and epiphytism is one solution to the space problem that can also be resolved through endophytism. Epiphytism and endophytism of seaweeds represent symbioses that vary from mutualistic to parasitic. The effects of epiphytes generally are to increase drag on the fronds and to shade the anchor species. This impedes gas and nutrient exchange, and thereby decreases host growth rate. Various factors can mitigate these effects: for instance, small grazers often remove epiphytes while leaving the host macroalga intact. Some algae may avoid epiphytism simply because of their very rapid growth and the changes in pH at the thallus surface caused by a rapid metabolic rate. When the growth of such species slows, epiphytes soon cover them. Many macrophytes deter epiphytes either through periodic sloughing of their surfaces or by production of antibiotic chemicals. Since 2004 we have studied several epiphytic and endophytic symbioses on benthic seaweeds from the Argentinean coast of South America. The particular aim of this work is giving some aspects of symbiosis in Rhodymenia pseudopalmata and Hymenena falklandica seaweeds from Patagonian coast of Argentina.