Spatial and temporal variations of macroalgal vegetation in the north-western Red Sea

Abstract Macroalgae play a vital role in marine ecosystems, but human effects are threatening the composition and structure of algal communities. In the present investigation, the spatial and temporal variations of species composition, functional groups and percentage macroalgal cover were studied in relation to seasonal fluctuations of some physicochemical parameters, to determine the ecological status of macroalgae in coastal waters along the coast of the northwestern part of the Red Sea, from November 2020 to October 2021. Fifty-five species of macroalgae were collected and identified from the sites studied. Five functional groups of macroalgae were recognized. Among these were two turf-forming species, 34 species of upright fleshy algae, and three crustose algae. There was a large variation in the cover, as well as in the species richness and assemblage structure of the macroalgae in different sites and seasons. Seasonal changes, determined by environmental conditions, led to small changes in macroalgal cover at different sites, with the growth of some brown macroalgae suppressed by high sea temperatures, whereas some green and red macroalgae, increased in response to increasing temperature and salinity.