Morphologie, Ökologie und Zonierung von Korallenriffen bei Aqaba, (Golf von Aqaba, Rotes Meer)

Abstract

Morphology, ecology and zonation of coral reefs at Aqaba (Gulf of Aqaba, Red Sea). The coral reefs of the Gulf of Aqaba are among the most northern ones of the world. This study, the first concerning the east coast of this topographically and hydrographically peculiar sea, considers relationships of biophysiographical and structural reef zones to fundamental abiotic environmental factors. An introduction to paleogeography, geology, petrography, topography, climate and hydrography is followed by terminological definitions used to describe the different reef areas. The investigations were carried out on two transects crossing fringing reefs of different shape. Each transect was 20 m wide and run from the shore over nearly 200 m to the fore reef in about 30 m depth. One reef, a "coastal-fringing reef", represents an unaltered straight reef flat from shore to the reef edge 60 m away; two large pinnacles reach the surface some 125 m off the shore. The other reef, a "lagoon-fringing reef", is divided into a 100 m wide lagoon of 0.5-2.3 m depth and a reef crest separated from the former by a rear reef. The reef platform of the lagoon-fringing reef is cut by a system of channels and tunnels; the reef edge is about 135 m off shore. Such water depth, substrate, temperature, illumination and water movement were recorded, about 200 common or dominant species (plants and animals) were collected, their distribution plotted and, together with other data and structural items, charted. Indicator species characterize the biophysiographical zones. Their variation as well as that of the structural and substrate zones depend on different zones of water movement. This basic factor also controls other ecological parameters such as food and oxygen supply as well as temperature and salinity gradients between fore reef and shore. From this point of view the ecological requirements of some indicator and other species and conversely the ecological settings of different reef areas are discussed. The different shapes of both reefs are explained on the basis of a "reef development cycle" -a hypothesis applicable to fringing reefs at unchanging sea level and based on the fact that only a small surf-influenced area of "living reef" is able to compensate for reef destruction: While a young coastal fringing reef is growing outwards, its back reef is gradually altered to a reef lagoon by erosion. Aflcer stillstand of seaward expansion the reef crest, too, is cut by a channel system eroded by rip currents. This stage is represented by the lagoon-fringing reef. Isolated pinnacles remain as remnants of the former reef crest; young coastal-fringing reefs develop from the shore. This stage is examplified by the first reef studied. Extension, growth intensity, dominant frame building corals, and the number of species of the Aqaba reefs are compared with those of Eilat and with reefs of the middle Red Sea, South India, Southwest-Pacific and Jamaica.

Initial phases in reef development, studied at artificial reef types off Eilat, (Red Sea)

“…They represent a system of holes and projections exposed to abiotic and biotic influences like a natural reef. Further description, especially concerning the environmental details of the moles, can be found in a previous paper (Schuhmacher, 1974).…”

Characteristics of oceanographic processes on reefs of the Seychelles Islands

“…The shape of coral reefs depends to a p a t extent on the pattern of surface currents (Brown and Dunne 1980). Underwater geomorphological features of reef slopes and plateaus (buttress and reef-flat systems) abounding in spurs, coral columns, hollows, channels and tunnels are primarily the result of abrasive wave forces (Munk and Sargent 1954, Storr 1964, Mergner and Schuhmacher 1974. In sinr measurements and aerial photography have revealed the existence of areas of vortex formation near islands with fringing reefs as well as zones with strong currents that affect the accumulation of sediments and development of benthic communities , Hamner and Hauri 1981, Roberts et al 1981.…”

“…of wind drift, roughness, long gravity waves, upwelling and coastal sewage on the structure of currents and thermohaline conditions inside reef lagoons. Some authors (Storr 1964, Mergner andSchuhmacher 1974) stress that wave and current action are the main factors causing biotic zonation of patterns on coral reefs.…”

Distribustion of the macro- and meiobenthic assemblages in the littoral soft-bottoms of the Gulf of Aqaba (Jordan)

“…In same times, shallow and deep coral assemblages in the Gulf were finely described (Loya 1972, Mergner & Schuhmacher 1974, Fricke & Hottinger 1983, Fricke & Schuhmacher 1983.…”

“…Recent studies were devoted to : (1) the sandy beach assemblages (Hulings 1975a, b, Wahbeh 1976, D. Dexter 1979-survey, first data in Por 1983, Amoureux 1983 ; (2) the littoral communities of enclosed lagoons along the Sinal peninsula (Jplrgensen 1973, Kristensen 1973, Por & Tsurnamal 1973, b, Por 1974, Por & Dor 1975a, b, Por et al 1977 ; (3) the shallow terrigeneous and coral bare sandy biota (Lawrence & Ferber 1971, Clarke 1972, Mergner & Schuhmacher 1974, Holthuis 1975, Ferber 1976, Mastaller 1979, Yaron 1979, Karplus et al 1981, de Vaugelas & Saint-Laurent 1984 (4) the Halophila meadow epi-and endofauna (Hulings 1979b, Lipkin 1979, Zohary et al 1980, Hulings & Kirkman 1982, Wahbeh 1982; (5) the deep slope infauna from Por's & Fishelson's dredgings (Bratcher & Burch 1967, Bonaduce et al 1976, Schmalbach & Por 1977, Wagele 1981.…”