The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea

Abstract

The Saudi Arabian Red Sea (SARS) contains diverse shallow water coral reef systems that include attached (fringing and dendritic reefs) and detached (platform, patch, tower, ribbon, and barrier reefs) reef systems extending up to 90 km offshore. To better understand the current status of coral reefs in SARS, the Living Oceans Foundation conducted assessments of representative reef environments in the Farasan Islands (2006), Ras Al-Qasabah (2007), Al Wajh and Yanbu (2008), and the Farasan Banks (2009). A combination of belt transects and quadrats was used to assess the diversity, size structure, partial mortality, condition, and recruitment of the dominant reef-building corals. Most sites had high structural complexity, with up to 52 genera of scleractinian corals recorded from a single region. Living corals varied in abundance and cover by region, habitat, and depth, with the highest species richness documented in the south (Farasan Banks), followed by Al Wajh and Yanbu and lowest at Ras Al-Qasabah. On most reefs, a single species was dominant. The reef architecture was constructed by massive and columnar Porites, with unusually large (1–4 m diameter) colonies in shallow water (up to 80 % live cover in 2–10 m depth) and a deeper reef Porites framework that was mostly dead. Porites lutea was the single most abundant coral throughout SARS, and the dominant species on leeward reef crests and slopes, while reef slopes and deeper coral carpets were predominantly Porites columnaris and P. rus. Faviids (Goniastrea and Echinopora) were the next most abundant corals, especially in areas that had experienced a disturbance, although these were small (most <15 cm diameter) and made up a small fraction of the total live coral cover. Multi-specific Acropora assemblages often formed large thickets, but these were restricted in distribution. Pocillopora was the dominant taxon in Yanbu, widespread in Al Wajh, and much less common in northern and southern sites. Coral cover throughout the region averaged about 20 %, with higher cover (often >50 %) in shallow water and rapid decline with increasing depth. In each region, many reefs (15–36 %) showed signs of damage and had less than 5 % live coral cover. These degraded sites were characterized by extensive dead skeletons in growth position, substrates colonized by thick mats of turf algae and soft corals (Xenia), and surviving massive and plating corals that were subdivided by partial mortality into numerous small (<10 cm) ramets. Mortality was attributed to bleaching events, disease, and outbreaks of corallivores occurring over the last 10–15 years. Several sites also exhibited signs of recent mortality from crown of thorns sea stars (Acanthaster), coral-eating snails, and coral disease. In many cases, the Porites framework had been recolonized by faviids, acroporids, and other corals and these had subsequently died. Most degraded areas appeared to be rebounding, as substrates had high cover of crustose coralline algae (CCA), little macroalgae, and high numbers of coral recruits and juvenile corals.