Within-thallus variation in chemical and physical defences in two species of ecologically dominant brown macroalgae from the Antarctic Peninsula

Results from D. anceps, a highly differentiated species, were consistent with the Optimal Defence Theory (ODT) in that the most valuable tissue component (the primary stem) was the most strongly chemically and physically defended. The holdfast, also with a high tissue fitness value, was strongly physically defended. Laterals, which are replaceable and assigned a lower fitness value, were moderately chemically defended. No significant differences were detected in the palatability of the differing thallus parts in D. menziesii, although the holdfast and primary stem were tougher than the lateral branches. These results remain consistent with the ODT as D. menziesii displays less differentiation between the primary stem and the lateral branches and were assigned a similar fitness value.