Marine macroalgal forests are highly productive and iconic ecosystems, which are seriously threatened by a number of factors such as habitat destruction, overgrazing, ocean warming, and pollution. However, the effect of chronic, but low levels of pollutants on the long-term survival of the canopy-forming algae is not well understood.

This study tested the effects of low concentrations (found in good quality water-bodies) of nitrates, heavy metals copper (Cu) and lead (Pb), and herbicides (glyphosate) on both adults and recruits of Carpodesmia crinita, a Mediterranean canopy forming macroalga.

The results showed that although adult biomass, height and photosynthetic yield remain almost unaffected in all the assays, low Cu levels completely suppress adult fertility. In addition, all the assays had a strong and negative impact on the survival and growth of recruits, and in particular glyphosate.

The authors conclude that the obtained results suggest that the long-term viability of C. crinita may be severely compromised by low pollutant levels that are not affecting adult specimens. They also stress that the results provide important data for a better understanding of the present-day threats to marine canopy-forming macroalgae and for the design of future management actions aimed at preserving macroalgal forests.

Caralt et al. (2020) Differential effects of pollution on adult and recruits of a canopy-forming alga: implications for population viability under low pollutant levels. Scientific Reports 10: 17825.