Helmut Schuhmacher

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

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. After 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.Zusammenfassung1. Riffökologische Untersuchungen, von denen bisher nur wenige aus dem Roten Meer und insbesondere von der Sinaiküste des Golfes von Aqaba vorliegen, sollten an den bisher noch nicht wissenschaftlich bearbeiteten Riffen der Ostseite des Golfes ergänzt und erweitert werden. Dazu werden Angaben zur Paläogeographie, Geologie und Petrographie, Topographie, Klima und Hydrographie des Golfes von Aqaba und des näheren Untersuchungsgebietes (6 bzw. 6,75 km südlich von Aqaba) vorausgeschickt und die Methodik der Untersuchungen angegeben.2. Da die Begriffe zur Beschreibung der Rifftopographie und -struktur in der Literatur nicht einheitlich gebraucht werden, werden Definitionen der hier benutzten und dabei zum Teil neu eingeführten Termini gegeben und an Hand eines Schemas erläutert.3. Beide für die strukturelle und biophysiographische Zonierung ausgewählten Riffe sind Saumriffe unterschiedlicher Ausgestaltung. Im ersten Untersuchungsmodell, einem Ufersaumriff, schließt die Riffplattform unmittelbar an den Strandfels der Uferregion an, im zweiten Modell, einem Lagunensaumriff, ist die Riffkrone durch eine breite Lagune vom Ufer getrennt.4. Topographie, Hydrographie, Strukturen und Substrate sowie die auffälligsten Elemente von Fauna und Flora (über 200 Arten) des Ufersaumriffes werden beschrieben. Vom Ufer über Riffdach und Riffhang bis zum Vorriff lassen sich hinsichtlich der Wasserbewegungsformen und der von ihnen verursachten Oberflächenstrukturen einzelne Zonen mit charakteristischen Tier- und Pflanzengemeinschaften unterscheiden. Ihre Leitarten bestimmen wiederum die biophysiographische Zonierung des Riffes. Im Uferbereich sind dies dieHippa picta-Zone, dieEnteromorpha-Zone und dieTetraclita-Zone, während der flache Uferkanal durch einePadina-Colpomenia-Zone gekennzeichnet ist. Auf dem ufernahen toten, weitgehend eingeebneten Riffdach sind vor allem Seeigel aspektbestimmend für die folgenden Zonen:Echinometra mathaei-Zone,Tripneustes gratilla-Zone,Tripneustes-Tridacna-Zone undDiadema-Sinularia-Zone. Die letztgenannte Zone leitet zum vordersten, nunmehr lebenden Riffdachabschnitt mit einerLitophyton-Zone über. Riffkante und Riffhang kennzeichnet eineMillepora-Acropora-Platygyra-Zone, während das obere Vorriff einePorites-Litophyton-Zone und eineHalophila stipulacea-Zone umfaßt. Zwei aus dem oberen Vorriff bis zur Wasseroberfläche aufragende isolierte Pfeiler, die als Reste eines alten Riffdaches interpretiert werden, zeigen eineLitophyton-Porites-Acropora-Zone bzw. eineLitophyton-Acropora-Zone. Das anschließende mittlere Vorriff mit lockeren Korallengemeinschaften wird alsXenia-Favia-Echinopora-Acropora scandens-Zone bezeichnet. Alle genannten Befunde sind in einem Lageplan des Riffes erfaßt und zusätzlich in einem maßstabgerechten Riffprofil dargestellt. Außerdem wurde die Häufigkeit der wichtigsten Tier- und Pflanzenarten in den einzelnen Zonen nach einer fünfteiligen Skala geschätzt und tabellarisch zusammengestellt.5. Nach den gleichen Gesichtspunkten wurde die Zonierung des Lagunensaumriffes vorgenommen. Im Gegensatz zum Ufersaumriff ist hier jedoch zwischen der weiter vorgeschobenen Riffkrone und dem Ufer eine Rifflagune eingeschaltet. In Abhängigkeit vom Substrat, Kalkschlamm und -sand uferseitig sowie tote Korallenhorste oder ausgedehnte Mikroatolle seeseitig, beherbergt die Lagune vor allem Algenund Weichkorallenzonen. Das Vorhandensein einer Rifflagune sowie eines Systems von Canyons, Tunnels und Siphonen, welches die Riffkrone zerlegt, deutet auf einen fortgeschrittenen Alterungsprozeß dieses Riffes hin. An ihm fanden sich folgende biophysiographische Zonen zwischen Ufer und Vorriff: Den Uferbereich kennzeichnen eineHippa picta-Zone und eineEnteromorpha-Zone, den Uferkanal eineLyngbya aestuarii-Zone. In der Lagune folgen seewärts hintereinander eineHalodule uninervis-Zone, eineSargassum dentifolium-Zone, eineStypopodium zonale-Zone, eineSinularia-Cladiella-Zone, eineLitophyton arboreum-Zone, eineFavia-Goniastrea-Litophyton-Zone und einePlatygyra-Goniastrea-Litophyton-Zone. Das Rückriff ist alsPlatygyra-Favia-Porites-Zone, die Riffplattform alsLithothamnion-Fungia-Zone zu bezeichnen, während das Kanalysystem eineAcropora-Seriatopora-Zone darstellt. Die Riffkante wird von einerMillepora dichotoma-Zone eingenommen, der Riffhang von einerAcropora variabilis-Zone. Im oberen Vorriff fand sich einePorites-Acropora variabilis-Zone und im mittleren Vorriff eineXenia-Favia-Echinopora-Acropora scandens-Zone. Auch die Zonenbildungen des Lagunensaumriffes einschließlich der sie bedingenden hydrographischen, topographischen und strukturellen Gegebenheiten wurden kartiert und die Häufigkeitsverteilung der wichtigsten Tier- und Pflanzenarten wiederum angegeben.6. Bei einem Vergleich der einzelnen Zonen sowohl innerhalb jedes der beiden Untersuchungsmodelle als auch zwischen den beiden Riffen konnten Präferenzen einzelner Arten mit dem Einfluß spezifischer abiotischer Gegebenheiten begründet werden.7. Als maßgeblicher Faktor bei der Verteilung der Riffauna erwies sich neben der Licht-Schatten-Verteilung vor allem die Wasserbewegung: Mäßige Strömungswerte, zusammen mit geringen Temperaturschwankungen und noch ausreichenden Lichtwerten, sorgen für ein „ausgeglichenes ökologisches Klima“ im oberen und mittleren Vorriff und ermöglichen eine große Artenvielfalt in diesem Biotop. Dagegen beschränken starke Brandungsdrucke und Rücklaufströme die Artenzahl an der Riffkante auf wenige, vor allem schnellwüchsige Formen wieMillepora dichotoma-undAcropora-Arten. Gelegentlich auftretende Niedrigebben führen auf dem Riffdach zum Entstehen von Mikroatoll-Wuchsformen massiger Korallenarten.8. Der unterschiedliche Ausbildungsstand der beiden Riffabschnitte wird jeweils als charakteristisches Stadium in einem hypothetischen Entwicklungszyklus des Saumriffes gedeutet: Unter der Voraussetzung eines gleichbleibend hohen Meeresspiegels entwickelt sich zunächst aus einem schmalen Riffsaum ein Ufersaumriff mit gleichmäßig ausgebildetem Riffdach. Mit zunehmendem Vorrücken des lebenden Riffbereiches (nahe der Riffkante) gegen das offene Meer hin wird der rückwärtige Teil des Riffdaches allmählich abgetragen, und es entsteht eine Lagune. Der seewärtige Abschnitt des nunmehr gebildeten Lagunensaumriffes, die Riffkrone, wird durch Erosion allmählich in Einzelpfeiler zerlegt, wie dies im zweiten Untersuchungsmodell der Fall ist. Schließlich kann nach weitgehendem Abbau der Riffkrone unter dem Einfluß der erneut wirksamen Uferbrandung wieder ein junges Ufersaumriff entstehen. Als solches mit den gleichzeitig vorgelagerten älteren Restpfeilern der vorangegangenen „Riffgeneration“ wird der erste Untersuchungsabschnitt interpretiert. Meist jedoch wird ein solcher Riffentwicklungszyklus durch Meerestrans-und -regressionen modifiziert.9. Bei einem Vergleich der Saumriffe entlang der jordanischen Ostküste des Golfes von Aqaba mit denen anderer Riffregionen läßt sich folgendes feststellen: Die Riffe bei Aqaba sind breiter, vielgestaltiger und insgesamt besser entwickelt als die auf der entsprechenden Höhe der Sinaiküste. D

What is hermatypic

The term hermatypic, as widely used in the literature of extant and fossil Scleractinia, includes, by definition (Wells 1933), the confusing generalization of equating reef-building with containing zooxanthellae. In course of time the use of the term diverged into denoting organisms which are either reef-building (including calcareous Rhodophyta) or those that contain zooxanthellae (including soft Alcyonaria). The equation: reef-building corals harbour zooxanthellae and vice-versa, is invalidated by reviewing the various ecological categories of corals such as: reef-building species without the support of zooxanthellae, zooxanthellae-containing corals which inhabit but do not build reefs, zooxanthellae-containing, non-reef-building corals beyond the bathymetric and latitudinal limits of reefs, and framework-erecting corals in deep waters without zooxanthellae. Former attempts to improve the original definition of hermatypic are shown to be insufficient to match the ecological diversity of corals. A strict terminological separation of the properties zooxanthellae-containing, reef-building and (more generally) framework-building is provided by the use of the revised, respectively new terms zooxanthellate, hermatypic and constructional (with the respective antonyms azooxanthellate, ahermatypic and nonconstructional). This terminology also applies to non-scleractinians.

Mass Diving Tourism – A New Dimension Calls for New Management Approaches

Diving has become a booming branch of the tourism business. The economies of many countries with reef-lined coasts depend on high numbers of tourist divers; the resultant degradation of reefs by mechanical damage is accepted due to the short-term gain from the tourism business. Many activities of recreational diving do not particularly require coral reefs – any varied three-dimensional structure (e.g. a wreck) may be sufficiently attractive. The conflict between the needs of nature conservation and the economic interests of diving tourism can be mitigated by the formation of artificial underwater attractions as reef substitutes. Based on experiments in the northern Red Sea, we propose to deposit calcium minerals from the seawater in situ by electrolysis on a template of any desired shape. After transplantation of living coral fragments, a diverse community will develop. With this method different modules can be designed and formed on the seabed which can serve different needs such as diver training, environmental education and recreation as well as reef rehabilitation. By a combination of such modules, a recreational underwater park can be formed well suited to function as a DAD (diver aggregation device) and therefore, divert diver pressure from the natural reef.

Interspecific hybridization and restricted trans-Pacific gene flow in the Tropical Eastern Pacific Pocillopora

Coral reefs in the Tropical Eastern Pacific (TEP) are among the most isolated in the world. This isolation has resulted in relatively low species diversity but comparatively high endemism. The dominant reef‐building corals of the TEP are the Pocillopora corals, a ubiquitous Indo‐Pacific genus commonly regarded as inferior reef‐builder. In addition to being the dominant reef‐builders in the TEP, the Pocilloporids have undergone a reproductive shift from internally brooding larvae through most of their Indo‐Pacific range to free‐spawning in the TEP. Using genetic data from the internally transcribed spacer (ITS) regions of the nuclear ribosomal DNA gene cluster, we show here that this apparent reproductive shift coincides with interspecific hybridization among TEP Pocillopora species. We document a pattern of one‐way gene flow into the main TEP reef builder P. damicornis from one or both of its TEP congeners —P. eydouxi and P. elegans. Our data provide preliminary evidence that trans‐Pacific gene flow in P. damicornis between the Central and Eastern Pacific is restricted as well (ΦST = 0.419, P < 0.0001). In combination, these results suggest that Eastern Pacific corals exist in relative isolation from their Central Pacific counterparts and interact with each other differently via hybridization.

FACTORS CONTROLLING HOLOCENE REEF GROWTH - AN INTERDISCIPLINARY APPROACH

SummaryThis interim report deals with investigations on key factors controlling reef growth by zoophysiologists, ecologists, paleontologists and geologists. The different levels of emphasis are the coral animal and the reef community. The main study area is the Red Sea which reaches over 20°C latitude up to the northernmost margin of the global coral reef belt. Supplementary results on microborer ecology are provided from the Bahamas.The desert enclosed Red Sea, not influenced by land runoff and only minimally by anthropogenic (urban and touristic) nutrient inputs, is predestined for a study on the principal influence of light on calcification within bathymetrical and latitudinal gradients. Hence, on the level of the zooxanthellate scleractinian animal phototrophic and heterotrophic energy supply and its bearing on calcification are being measured in different coral species—in particular inPorites sp., one of the most important reef builders.The growth of 15 zooxanthellate scleractinians in the Gulf of Aqaba correlates with the annual light cycle. This correlation is observable down to 40 m depth. Other growth promoting factors seem to have less influence on coral extension. The availability of organically enriched sediments in shallow water probably yields nutritional value, in particular for filter feeding species, thus restricting their distribution to those areas. Zooxanthellae, when isolated fromMycedium elephantotus, are different in their dependence on depth in maximum rates of photosynthesis and photosynthetic efficiency (-slope). Increasing concentrations of pigments as a function of depth could be determined. Maximum rates of photosynthesis of zooxanthellae in vivo, collected at corresponding depth, have been 4 times higher. Structural and physiological adaptations improving heterotrophic and phototrophic energy intake are highlighted. Porites sp. was the subject of annual growth studies at locations extending from Aqaba in the North over the northern and southern Egyptian coast and islands, Sanganeb Atoll and Wingate reef offshore Sudan to the Gulf of Tadjoura in the Gulf of Aden (Djibouti). Mean growth rates in the shallow water zone increase with decreasing latitude and are highest at the southernmost studied reefs in the Gulf of Tadjoura. However, the observed latitutdinal growth reduction is restricted to the upper ca. 15 m of the water column. The upper limit of growth potential decreases with depth parallel to the decrease of light availability. Highest growth rates are recorded in shallow depth (10–2.9 mm yr−1). This zone reaches at Aqaba (29°30′N) to a depth of ca. 10 m. At the southern Egyptian reefs (24°30′N) this zone extends to ca. 15 m water depth. This effect is probably a result of the stronger reduction of winter light levels and water temperature in the northern regions. Compared to other oceans the decrease of growth with increasing latitude of Red SeaPorites corals is far less, and growth rates at Aqaba are the highest observed at these latttudes.On the level of the community of reef inhabitants four principal topics are addressed:The first one is the dynamics of the proportions of hermatypic and ahermatypic organisms and open space. The occurrence of stony and soft corals and the sharing of empty space in different reef sections at Aqaba and on Sanganeb Atoll were quantified. Soft corals, mainlySinularia- and xeniid species, occupy decreasing shares with depth. Among theXenia species a bathymetrical zonation pattern was detected.The next issue is the growth impeding role of soft corals and gastropod parasites and predators on scleractinians. Experimental and field observations showed xeniid soft corals to be opportunistic i.e. occupying rapidly open space rather than to attacking and outcompeting stony corals. An increasingly specialized behaviour was detected among corallivorous gastropods of the family Coralliophilidae to exploit their coral hosts. Whereas these snails are more or less sessile and depend for a long time on the surrounding host polyps the mobileDrupella cornus (Thaididae) forms feeding aggregations which denude mainly branching corals on shallow reef parts.Furthermore, the role counteracting reef growth of macro- and microbioeroders is investigated.Diadema setosum is a major destructive agent on reefs at Aqaba (not in the central Red Sea). The grazing sea urchins do not only keep potential colonization area free but also erode carbonate material (e. g. 1468 g/m2/year, 10 m depth). Demographic and bathymetric patterns in the sea urchin population are analyzed including their bearing on bioerosion of the reef. Investigations on microboring organisms in carbonate material have started in the Red Sea; initial results, however, are only available from similar studies near Lee Stocking Island, Bahamas.Three major environments have been identified based on the distribution of the different microborers. These are1)the intertidal environment dominated by boring cyanobacteria.,2)reef sites from 2 to 30 m water depth dominated by a diverse assemblage of boring cyanobacteria and chlorophytes, and3)the deep reef slope from 100 to 300 m dominated by boring green algae and heterotrophs. The boring chlorophyte genusPhaeophila appears rapidly and dominates at sites from 2 to 30 m, but it leaves vacated borings and is replaced byOstreobium quekettii after 1 year. Different substrate types show very different rates of colonization by microborers. The greatest excavation rates (100 g/m2/3 months) occur in fine-grained limestone, while the slowest rates (0.5 g/m2/3 months) occur in calcite crystals. Molluscan shell material shows intermediate rates of excavation. Light conditions appear very important in determining the growth rate and distribution of different microborers between the sites, however, the interaction of light with other factors, such as substrate, time period of exposure, and water quality conditions may be involved.

Quantitative Analyse der Korallenbesiedlung eines Vorriffareals bei Aqaba (Rotes Meer)

Previous descriptions of the ecology and zonation of Aqaba reefs (Mergner & Schuhmacher, 1974) are supplemented by this quantitative study of a test quadrat (5×5 m in size), randomly chosen in some 10 m depth in the middle fore reef of a coastal fringing reef. Of the total surface of 25 m2 Cnidaria represent 42.31%, sponges 0.17%, calcareous algae 0.20%, dead coral rock and pebble 30.27% and sand and coral debris 26.15%. The cnidarian cover is roughly equally contributed by 50.86% Scleractinia and 48.61% Alcyonaria, mainly Xeniidae (35.81%). For each species the percentage of the total cover (measured as vertical projection), colony number, average and maximal colony size are given. A total number of 104 cnidarian species was recorded, among which the 78 scleractinian species represent 34 of the 55 coral genera known from the Red Sea. The well balanced regime of moderate light and current conditions which are tolerated both by shallow and deep water species may account for the high species number. Disturbances such as occasional sedimentation, grazing of sea urchins(Diadema setosum) and overgrowth of stony corals by xeniids result in continuous fluctuations of the coral community, in small colony size and in high colony number. Abiotic factors and biotic interactions maintain a diversity (H=3.67) which ranks among the greatest ever found in reef communities. The data obtained from the fore reef square are compared with those of a similar test square in the lagoon of the same reef and with results from transect zonations on the opposite coast of the Gulf of Aqaba. These comparisons indicate that the fore reef harbours the richest coral fauna in the reef. The inventory of coral species at the northern end of the Gulf of Aqaba, one of the northernmost outposts of the coral reef belt, is only little reduced when compared with that of the central Red Sea; this great species diversity is in contrast to the worldwide decrease of species number towards the periphery of the reef belt.

Mariculture trials with Mediterranean sponge species: The exploitation of an old natural resource with sustainable and novel methods

Abstract The growing interest in bioactive compounds for new drugs resulted in a notable research boom on secondary metabolites from marine invertebrates, especially from sponges. Some sponge species display promising antibiotic and antitumour activities. Natural stocks, however, are not capable to satisfy the potential demand by pharmaceutical industries without being heavily degraded. Within the scope of the European Commission (EC)-funded NOvel MArine TEChnologies (NOMATEC) project, a new method for farming sponges has been developed and tested in order to ensure the sustainable supply of sponge raw material without harming the marine ecosystem. Various Mediterranean sponge species with promising bioactive metabolites are tested for their suitability for aquaculture. Special trays were designed as mariculture units using metal/net grids. In total, 708 cuttings from four different species were farmed in mesh on various installations exposed off the marine biological station, Station de recherches sous marine et oceanographique (STARESO), in the Bay of Calvi, Corsica. All sponges were regularly mapped using a digital UW camera to monitor survival and health. Growth rates were determined by weighing the sponge samples (drip-wet weight, DWW) as well as by calculating their projected body area using digital imaging software. Within the first 12 months, species taken in aquaculture exhibited promising survival rates of up to 98%, indicating the general suitability of the applied farming design. In contrast to former findings, Ircinia variabilis exhibits high survival rates (75% in 12 months) and reveals remarkable growth rates (up to 200% in 12 months). A correlation between the drip-wet weight and the projected body area of cuttings from two species was detected and discussed. Based on the results of the first project year, farming design and conditions will be improved and knowledge gaps concerning sponge autecological questions will be filled during the next phases.

Artificial reefs created by electrolysis and coral transplantation: an approach ensuring the compatibility of environmental protection and diving tourism.

Coral reefs are currently being subjected to increasing pressure caused by water sports, especially scuba diving. Highly complex reef coenoses are affected by mechanical breakage and the coverage of corals by resuspended sediments. As the ecological capacity of the biocoenosis is exceeded, sensitive species are suppressed and the community is impoverished. The conflict between the needs of nature conservation and the economic interests of diving tourism can be mitigated by the creation of artificial underwater attractions as reef substitutes. Specially designed underwater structures are ideal for many diving activities, which can be diverted from sensitive natural habitats in that way. It is also possible to develop model reef communities for training and environmental education purposes. Our new concept is based on the elegant solution, proposed by Hilbertz et al. (1977), of depositing calcium minerals from the seawater in situ by electrolysis. We report on experiments conducted near Aqaba (Red Sea) showing that it is feasible to transplant living coral fragments on to the substrate being developed by electrochemical processes. In this way, the formation of a diverse community on any structure desired can be considerably enhanced.

Quantitative Analyse von Korallengemeinschaften des Sanganeb-Atolls (mittleres Rotes Meer). I. Die Besiedlungsstruktur hydrodynamisch unterschiedlich exponierter Außen- und Innenriffe

The Sanganeb-Atoll off Port Sudan is an elongate annular reef which rests on a probably raised block in the fracture zone along the Red Sea-graben. Its gross morphology was most likely formed by subaerial erosion during low sealevel conditions. Features of its topography and hydrography are described. The prevailing wind waves are from NE, Hence, the outer and inner reef slopes are exposed to different hydrodynamic conditions. The sessile benthos was analysed using the quadrat method. Four test quadrats (5×5 m each) were selected on the outer and inner slopes at a depth of 10 m along a SSW-NNE transect across the atoll. Cnidaria were by far the most dominating group; coralline algae, Porifera, Bryozoa and Ascidia, however, counted for just under 3 % living cover. Light and temperature intensities did not differ significantly at the sites studied; water movement, however, decreased in the following order: TQ IV (outer NE side of the reef ring) was exposed to strong swell and surf; TQ II (inner side of the SW-ring) was met by a strong longreef current; TQ I was situated on the outer lee of the SW-atoll ring and TQ III in the inner lee of the NE-side. This hydrodynamic gradient correlates with the composition of the coral communities from predominantly branching Scleractinia (staghorn-like and otherAcropora species andPocillopora) in TQ IV, through aLobophyllia, Porites andXenia-dominated community in TQ II, and a mixed community with an increasing percentage of xeniid and alcyoniid soft corals in TQ I, to a community in TQ III which is dominated by the soft coralsSinularia andDendronephthya. The cnidarian cover ranged between 42.4 and 56.6 % whereby the two exposed test quadrats had a higher living coverage than the protected ones. In total, 2649 colonies comprising 124 species of stony, soft and hydrocorals were recorded by an elaborate method of accurate in-situ mapping. The 90 scleractinian species found include 3 species new to the Red Sea and 11 hitherto unknown species from its central part. Only 7 cnidarian species covered large areas, forming aXenia macrospiculata-zone in TQ I, a Lobophyllia corymbosa-zone in TQ II, aSinularia-Dendronephthya-zone in TQ III and anAcropora-Pocillopora verrucosa-zone in TQ IV. Hydrodynamic exposition and ratio of genus abundanceAcropora: Montipora are closely correlated: on the windward side (TQ IV) it is 943:4, but on the leeward side (TQ I) 18:208. Apart from the taxonomic and quantitative distribution of species and colonies, types of growth form and categories of the dead substrate are given. Since soft corals do not contribute to the reef framework, the distribution of Scleractinia and Alcyonaria indicates that at Sanganeb-Atoll reef substance is mainly generated on the windward side.

A hermit crab, sessile on corals, exclusively feeds by feathered antennae

SummaryThe hermit crab Paguritta harmsi does not live in mobile shells, but occupies the calcareous tubes of the coral epibiont Spirobranchus giganteus (Polychaeta). Feathered (second) antennae are an unique adaptation to this sessile mode of life enabling the crab to utilize plankton carried by the water. The mode of filter feeding depends on the speed of water current: during stagnation of water the antennae are continuously moved fore- and backwards, during flowing water they are kept perpendicularly to the current forming a sieve. P. harmsi represents one more example to establish a specialized ecological niche in the highly complex ecosystem coral reef.