Fringing Red Sea Corals Survival: Is It Tide or Local Wind?

Abstract

In this paper, we obtain tidal constituents and discuss observations of tidal and wind variations and its impact on water surface elevation at Zaki’s Reef; a fringing coral reef located in the Red Sea-Gulf of Suez. This manuscript focuses on investigating if tidal forces are playing a key role to keep the area’s unique coral reefs alive and well. Determining the reasons why coral species and community of organisms found here survive despite all stressors is critical, and such information may hold the key to the preservation of reefs elsewhere. Phase and amplitude for 35 tidal constituents were deducted from observations of water surface elevation at the study site (first of its kind). The main tidal constituents based on their amplitudes are: M2, N2, S2, K1, NU2, K2, 2Ns, L2, and MU2. The first five tidal constituents of the aforementioned list are enough to reproduce accurate predictions of tides at this location (R2 variance = 87.54% and RMS = 0.167). The Tidal Form number (0.07) at Zaki’s Reef indicates a fully semidiurnal dominated tidal regime. Moreover, the Sa and Ssa constituents obtained from nearby stations made no improvements on tidal prediction results. Spectral analysis results of the white noise (residuals) from observed water surface elevation are dominated by daily frequency, suggesting that local wind plays a key role in circulation at study site. Local wind generated southerly long-shore and year-round offshore wind stress with a mean of -0.36 & 0.35 , respectively. The persistent longshore and offshore currents help transport oil patches/spills, from the two nearby ports, away from the reef. Yet, offshore wind stress, pushing water away from the shore, may cause more exposure of the reef to extreme atmospheric conditions. We hypothesize that the repeated reef exposure to the combined effect of tides and offshore wind stress over many years may have played a key role in selecting and then enhancing corals ability, through training, to become more adaptable to those harsh conditions. Training of corals over the years, may have led to the dominance of only six species, out of 35 coral species known to exist in the gulf. Those heat-adopted dominant species can be used to stimulate and revive impacted coral sites elsewhere.