Gracilaria-Mytilus interaction on a commercial algal farm in Chile

Abstract

Mytilus chilensis is an invertebrate that competes for space with the alga Gracilaria chilensis in farmed areas in Chile and, for this reason, is considered a contaminant organism . Mussel beds are considered to play a role in the regeneration of nitrogen and, as a consequence, they could be an important source of ammonium for the algae . In this study, we manipulated the mussel cover in experimental plots, creating replicated areas with 0%, 30% and 60% coverage. In half of the plots the mussels were killed with a gas torch so their effect would be mechanical, without nutrient regeneration . After 15 days, each plot was planted with 12 G. chilensis bundles (100 g each) per square meter. Ammonium concentrations increased significantly in the waters around the mussel bed in contrast to areas without mussels or dead mussels . Mussel cover had a significant negative effect on the length of the G . chilensis bundles planted in the experimental plots . However, no significant differences were detected between experimental quadrats with live mussels and those with dead mussels during a 5 month period . These results indicate that the mechanical effect of the mussel can, to some extent, be responsible for the decline in G. chilensis abundance in farms where mussel beds have been established .

Diversity, phenomenology and epidemiology of epiphytism in farmedGracilaria chilensis(Rhodophyta) in northern Chile

“…The types of epiphyte prevailing will determine the degree of negative effects on the farmed host (Buschmann & Go´mez, 1993;Pizarro & Santelices, 1993;Buschmann et al, 2001). Whereas the main pests for Gracilaria farming in the south of Chile are Polysiphoniatype epiphytes and tube-forming herbivorous polychaetes, crustacean grazers and fouling mussels (Retamales & Buschmann, 1996;Buschmann et al, 1997a, b;Buschmann et al, 2001), the studied farm in Caldera, in the north of Chile, was mainly affected by small sized epiphytes. However, epiphytism does not only affect the host tissues, but it can also significantly depress the productivity of Gracilaria through reduction in irradiance, depletion of nutrients and the additional weight (Buschmann & Go´mez, 1993).…”