Egypt: Coral Survival under Extreme Conditions

Provided by Zaki Moustafa, Duke University

Photo credit: Mary Lou Frost

Zaki’s Reef is a small, shallow fringing reef 55 km south of the Suez Canal in the Red Sea off the coast of Egypt, and is situated at the northernmost limit of coral reefs’ geographic range. The reef is located adjacent to a desert with one of the highest evaporation rates in the world. Trade winds blow year-round, rainfall is minimal, air temperatures are extreme, and freshwater inputs are nearly non-existent. These conditions result in extremely high salinities (36 to 41 ppt) and fluctuations in water temperature (14 to 16 °C seasonally). Organisms that thrive here must be able to tolerate environmental extremes. Of the estimated 335 species of corals found in the Red Sea, only 35 coral taxa live in the Gulf of Suez;¹ with only 6 making up 94 percent of the coral cover on Zaki’s Reef.²

Zaki’s Reef is under local pressure from fishing, shipping, and coastal development. Local fishermen cross the reef daily and anchor directly on the beach behind the reef, causing noticeable coral damage. A major shipping port lies 5 km north, and oil tankers offload daily 2 km from the reef, causing increased sedimentation from ship traffic in shallow water and risk from oil spills. A coastal highway runs parallel to the reef and localized sewage runoff from nearby resort areas, as well as industrialization, also threaten this reef.

Zaki’s Reef had survived several decades of tanker traffic and was extraordinarily healthy in 2004. However, after a major oil spill and a bleaching event in 2005, there was a marked increase in coral disease, water turbidity, organic nutrients, and sedimentation levels, all signifying a decrease in reef health. Between 2004 and 2007, dead coral cover increased by 50 percent, sea urchin counts increased by 58 percent, and fish abundance decreased.

However, data from 2008 point to signs of improved reef health, possibly indicating that the reef is rebounding from the 2005 oil spill and bleaching event. Incidences of coral disease decreased in 2008, and the growth of new corals was documented over major portions of the reef. Although signs of stress are still evident, corals on Zaki’s Reef appear to be tolerating the newly added stressors.

The continued existence of reefs in this region demonstrates that certain corals are resilient and can survive extreme conditions. Recent data from Zaki’s Reef suggest that this ecosystem may be adapting to new stressors by shifting dominant corals and accessory reef populations. Determining the reasons this ecosystem manages to survive, despite extreme environmental conditions and additional stressors, may hold the key to the preservation of reefs elsewhere.

Back to Reef Stories >>>