Reef-building corals and coral communities of the Yemen Red Sea

Abstract

The types of reef forms and the composition, diversity, zoogeographic affinities and ecological status of coral communities of the Yemen Red Sea were assessed between 1996 and 1998. Contemporary coral growth occurs as true accreting reefs fringing the mainland coast and islands, submerged patch reefs, and in non-accreting coral assemblages typically associated with three forms of substrate: “red algal reefs”; relic Pleistocene to Holocene reefs; and lava flow terraces and volcanic rock pinnacles. Together these structures host a moderately diverse stony coral fauna of ca 221 scleractinian species (54 genera, 15 families), including Red Sea endemics and species previously unknown from Arabian seas. Zoogeographic affinities of the northern area of the Yemen Red Sea appear similar to the more adjacent Red Sea coast of Saudi Arabia (e.g. Farasan Islands). The southern area shares more similarities with the Gulf of Aden (Belhaf - Bir Ali area). Local coral populations are acclimated, and perhaps genetically adapted, to a harsh physico-chemical environment, surviving at high sea temperatures (average 31 ºC, max. 35 ºC) that typically kill conspecifics in other reef regions. Hierarchical cluster analysis derived six coral community types distributed in relation to prevailing environmental conditions: physical exposure, water clarity, sea temperature, substrate type, slope angle and depth. The communities exhibited high variability in condition, mostly related to the differential effects of coral bleaching and predation by crown-of-thorns seastars in the 1990 s, with living cover of hard corals, dead corals and macroalgae averaging 11 %, 29 % and 21 %, respectively. Because these communities occur near the tolerance limits for coral growth and reef development, any additional impacts may prove catastrophic. Management should focus on conserving the healthy reefs of the offshore islands (e.g. Hanish and Zubayr groups), as these may be the main source of coral recruits for the recovery of mainland coastal and nearshore coral populations, which have been severely damaged in the last decades. They may act as ‘stepping stones’ for gene flow connecting populations in the Red Sea more generally.