Pollution and substrate characteristics are correlated with intertidal macroalgal community structure on the eastern Libyan coast

Abstract

This pioneering investigation relates pollution indicators and substrate characteristics to algal diversity at seven sites along the eastern Libyan coast during autumn 2018 and spring 2019. Seawater chemical composition and algal diversity exhibited marked temporal and spatial variability. High concentrations of inorganic phosphorus (Pi), nitrite (NO2−) and nitrate (NO3−), along with low dissolved oxygen (DO) were used as indicators of water pollution. Water pollution status and nature of substrate were correlated with algal distribution and diversity. The algal community was dominated by rhodophytes followed by chlorophytes and ochrophytes, whereas cyanophytes and xanthophytes were rare. Interestingly, Xanthophyta was represented by the freshwater alga Vaucheria piloboloides. Chlorophytes, particularly Ulva spp, were associated with polluted sites, whereas rhodophytes and ochrophytes dominated the more pristine sites. Chlorophytes, rhodophytes and xanthophytes were more abundant in the cold season (October–December), whereas cyanophytes and ochrophytes were found in greater abundance in the warm season (March–May). In addition to the effect of pollution and climate, the nature of the substrate had a profound influence on algal diversity. The agreement between frequency of occurrence and percentage cover observed in cyanophytes, chlorophytes and ochrophytes was less evident in rhodophytes. The present work concludes that the enhanced urbanization at the eastern Libyan coast, with emergence of point source pollution mainly of municipal and industrial origins, has impacted the diversity of algal communities, leading to dominance of Chlorophyta, particularly Ulva spp, over the other algal groups at polluted sites.