Distinct developmental and morphological differences between
populations of Sargassum muticum growing in different environments
became apparent in this study. The stunted growth of tide
pool plants was reflected in low biomass production, but receptacle
development and seasonal pattern of photosynthetic activity was
similar to that of open shore plants, irrespective of morphological
differences. Photosynthetic yields were always higher in tide pool
plants possibly due to an adaptation to local light, temperature and
salinity environment. There was some limited evidence of selfthinning
resulting in a decrease in plant numbers at Letterard,
which was the most exposed site, coinciding with an increase in
frond numbers, and dislocation of individuals could have added to
this effect. The high site-specific variability in S. muticum growth
and reproductive development suggests that potential interactions
with native species are likely to vary between sites and depend on
the local competitiveness of S. muticum. These impacts require
continued monitoring.