Factors Affecting the Marine Ecosystem of a Pristine Coral Reef Lagoon in the Northern Red Sea

The Red Sea Project (RSP) area, recently announced as one of the Saudi Arabia's hot spot touristic plans, is a lagoon-like basin surrounded by a chain of extensive coral reef matrices and small islets. It is part of the Al Wajh bank that extends between the towns of Al Wajh and Umluj in the northern Red Sea. Physical, chemical, and biological characteristics were investigated over the RSP broader area through four seasonal oceanographic surveys along with current measurements at four selected sites. The reef-lagoon exchanges water with the open sea through two main natural channels and extensive shallow coral reefs, mainly on its northern and western side. The water exchange with the open sea, critical for the ecosystem status, is governed by the tidal cycles and the prevailing wind. In the absence of any significant anthropogenic pressure, the lagoon's water flushing time is the most influential factor affecting its sensitivity and ecosystem status. The natural embracement of coral reefs that separates the RSP lagoon from the open sea, the numerous small islands and islets, and the complicated bottom topography determine the water circulation routes and the breath of the different parts of the basin. In this way, the parts of the lagoon that easily communicate with the open sea differ significantly from those of sluggish water renewal. The eastern and especially the morphologically isolated southeastern part of the reef-lagoon present the highest salinity values throughout the year, evidence of their slow water ventilation rate. Biochemical properties show that the open sea around the reef-lagoon and most of the lagoon are characterized by low nutrient and chlorophyll-a values indicating, typical for the northern Red Sea, oligotrophic conditions in the study area.