GRACILARIA-MYTILUS INTERACTION ON A COMMERCIAL ALGAL FARM IN CHILE

Mytilus chilensis is an invertebrate that competes for space with the alga Gracilaria chilensis in farmed areas in Chile and, for this reaso n, is considered a contaminant organism. Mussel beds are considered to play a role in the regeneration of nitrogen and, as a consequence, th ey could be an important source of ammonium for the algae. In this stu dy, we manipulated the mussel cover in experimental plots, creating re plicated 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 mechani cal, without nutrient regeneration. After 15 days, each plot was plant ed with 12 G, chilensis bundles (100 g each) per square meter. Ammoniu m concentrations increased significantly in the waters around the muss el bed in contrast to areas without mussels or dead mussels. Mussel co ver had a significant negative effect on the length of the G. chilensi s bundles planted in the experimental plots. However, no significant d ifferences were detected between experimental quadrats with live musse ls 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 whe re mussel beds have been established.