Changes in the macroalga taxa and zonation at the Content Keys, Florida

Macroalgal zonation on the exposed limestone reef of the Content Keys Florida was similar to that found between 1964 and 1968 with 65 of the 87 species in common. The number of macroalgae appears to have declined in the past 28 yrs with 38% Chlorophyta, 28% Phaeophyta, and 21% Rhodophyta being the same as those previously listed. Compared to the study of 28 yrs earlier, there was an upward shift in zones by 48% of the macroalgal species and a downward shift by 22% of the 65 species in common with both studies. Of the 17 species newly reported for the Content Keys, all are known from tropical to subtropical habitats. Of the newly reported species, two green and six red algae are also known from eutrophic habitats. It appears that macroalgal diversity has declined and is showing effects of nutrification, similar to that reported elsewhere in the Florida Keys.