No bill, you're not wrong. Macrocystis is more abundant in the south. You'd have to go down to Puerto Montt (1000 km from Santiago) or further south for it to really become relevant. You're probably familiar with the work Carlos Moreno or Bernarbe Santelices which were around cape horn.
Here in central Chile it is present, but usually less than 5m depth in wave protected areas.
Here in central Chile it is present, but usually less than 5m depth in wave protected areas.