The macroalgal communities of the Suez Canal were seasonally investigated at 16 sites during 1996 and 2000. A
hundred and twenty eight taxa including 15 new records were identified. The recent reduction of navigation and
urbanization works resulted in an increase in species richness (42 species) and algal forms.
Distribution pattern, seasonal variation, and algal zonation were also examined. All were intensely
regulated by substrate, space, depth, light, and water movement during the passage of ships. Sites were clustered,
on the basis of species co-occurrence, into five groups, suggesting division of the Suez Canal into four biological
sectors. The hard substrata supported distinct algal zones. Cladophoropsis zollingeri and Bangia fuscopurpurea
characterized the littoral zone. A rich algal community dominated the infralittoral at a depth of 30-150 cm, while
a few red species with Caulerpa racemosa were found deeper. Competition for space in some sites was evident
by presence of 61 epiphytic macroalgae. A half of these were also found on hard substrata when the space was
available.
Algal succession in the canal during the past century was also discussed in the light of environmental
changes. Algal succession could have passed through four stages; including the establishment of pioneers until
1924, the maturity to a climax sometime before1953, degradation of the climax due to navigation and
urbanization constructions, and the reestablishment of the climax with the recent improvement in algal habitats.