Geomorphological Zones Research Articles

Torcal de Antequera – stony town from Andalucia

The Torcal de Antequera is one of the best-preserved karst landscapes in Europe developed in Jurassic, oolithic, brecciated and detrital limestones. The rock formation is wellbedded and cut by a dense, regular fracture system. A relatively small area (20 km2) comprises four distinct geomorphological zones. At the surface visitors can recognize a variety of landforms produced by water and wind erosion whereas underground there exists a labirynth of karst forms: deep shafts, meandering galleries and huge caves. Since 1978 the Torcal de Antequera has been protected as a Natural Park and since 1989 it has become a Nature Site. The park combines a collection of remarkable geological valours and an exceptional biodiversity.

Contrasting fluvial styles of the Paraguay River in the northwestern border of the Pantanal wetland, Brazil

The Upper Paraguay drainage basin is situated mainly in west-central Brazil, near the Bolivian border. Flowing from north to south, the Paraguay is the trunk river of an alluvial depositional tract characterized by complex geomorphologic zonation that resulted from an intricate geologic evolution since the Late Pleistocene. This paper focuses on the geomorphology of the Paraguay River at the northwestern border of the Pantanal wetland, where two broad geomorphologic zones were distinguished. North from the Pantanal wetland, the Paraguay River flows in an aggradational fluvial plain, 5 km wide and incised into older alluvial deposits. The river exhibits a meandering style over most of its course, but sinuosity drops from 2.2 to 1.1 near the northwest border of the Pantanal wetland where the river has been forming the Paraguay fluvial megafan since the Late Pleistocene. The river deflects 90° eastward at the entrance into the Pantanal, changing its fluvial style because of a progressive loss of confinement downstream of the point where the river reaches lowland plains. The river becomes more sinuous, adopts a distributary pattern within the wetland and brings about the creation of the modern depositional lobe characterized by higher topographic gradient and active sedimentation likely linked to increased accommodation space allowing progradation. Fluvial discharge diminishes in the Pantanal wetland because of channel overbank flow during the rainy season and frequent levee crevassing. Avulsion belts and channel–levee complex are preserved on the floodplain as relict forms. South of the convergence of the two main channels that define the Taiamã Island, a loss of gradient marks the base of the depositional lobe. Further downstream, the Paraguay River returns to a meandering fluvial style, but crossing a large fluvial plain populated by hundreds of small lakes and seasonally flooded that characterizes the Pantanal wetland.

Geomorphology of Jeddah Governate, with Emphasis on Drainage Systems

Jeddah Governate comprises three distinct geomorphological zones; the Red Sea and shore features, the coastal plain, and coastal hills and pediments. The last zone lies east of the municipal Jeddah city and consists of low lying hills, and an elongated N-S oriented depression, forming a basin that lies within the coastal hills. The Red Sea displays landforms that characterize prograde shorelines; implying that the Red Sea is recently in regression. Such features include flat lying sandy beaches, lagoons, sabkhas, sea islands, bars and spits, as well as the raised dead coral terraces and marine limestones exposed inland. The drainage in the area consists of a large number of systems; twelve of which were considered to be major systems that were delineated, described and analyzed morphometrically. These systems are, from north to south: Wadi Al-Kura', Wadi Muraygh and Wadi Ghuraiyah, Wadi Um Hablayn, Wadi Burayman, Wadi Hutayl, Wadi Bani Malik, Wadi Mirayyikh, Wadi Quwayzah, Wadi Ushayr, Wadi Ghulayl, Wadi Al-Khumrah and Wadi Fatimah. All of these systems drain westwards towards the Red Sea, except Wadi Fatima that abruptly diverts direction to the north at its lower course along the coastal plain and this could be attributed to active faulting. A large number of wadi channels, both major and minor, terminate within the coastal plain at a distance from the Red Sea shore. This phenomenon could be attributed to one or more factors, such as active neotectonics, human activities and shore drift. Almost all of the drainage systems in the area exhibit parallel patterns along the coastal plain, whereas they display dendritic to

Geomorphological evidence for a changing tectonic regime, Pasinler Basin, Turkey

The Pasinler Basin, in the ‘East Anatolian Contractional Province’, features a suite of geomorphological zones, visible in the field, air photographs and Landsat and Shuttle Radar Topography Mission (SRTM) digital elevation model imagery. These zones reflect past and current tectonically influenced processes. Relicts of the Erzurum–Kars Plateau representing Mio-Pliocene volcanism, associated with transtensional tectonics, have been modified by two stages of drainage development: an earlier, shallow valley network, which was modified following uplift and tilting to form the present system characterized by deep narrow valleys that supply alluvial fan complexes. These fans discharge onto the present, aggradation-dominated basin floor. Initial normal faulting induced massive slope failures on the basin's northern margin. This extensional phase within the basin was reversed by the Late Pleistocene, with thrust faults modifying and producing landforms, and affecting sediment sequences, along both its northern and southern margins. The shift from a transtensional regime, and the associated volcanism, to normal faulting in the Pliocene to Early Pleistocene, and then to the present regime of compression-induced thrusting appears to correspond to a regional tectonic shift resulting from the collision of the Eurasian and Arabian plates and the subsequent westwards movement of the Anatolian microplate.

Effects of geomorphological zones, reefs and seasons on coral reef fish communities of Réunion Island, Mascarene Archipelago, SW Indian Ocean

The present work analyses the spatial and temporal fluctuations of fish communities on Réunion coral reef flats on three different reefs, each comprising three geomorphological zones, over eight seasons within a 6-year period. These three reefs are subjected to different environmental conditions and displayed various percentages of live coral cover. Our objectives were not only to describe the spatio-temporal patterns, but also to organize the factors involved in variation hierarchically, and to quantify the degree of community structuring that could be monitored over various spatial and temporal scales. We also focus on fish guilds to link the spatio-temporal patterns not only to species but also to the roles fish are playing (mainly involving trophic activity). We found that spatial attributes strongly determined fish distribution, with intra-reefal zones (back-reef, inner reef flat and outer reef flat) playing a much more important role than the different reefs. This suggests that the percentage of live coral cover of a given reef was less significant than its morpho-structural organization to explain fish distribution. Seasons had only a weak role in fish distribution, although fish communities were significantly more homogeneous in winter than in summer, possibly due to the arrival of numerous juveniles belonging to various species during summer settlement events. We also identified a marked temporal persistence of the spatial patterns found over the course of the study. This is discussed in relation to the current trend of increased surface seawater temperatures involved in the possible future increase in number/intensity of ENSO events. We consider the average squared Euclidian distance as a candidate for monitoring tools to quantify future changes in fish community structuring.

Progress in the use of remote sensing for coral reef biodiversity studies

Coral reefs are hotspots of marine biodiversity, and their global decline is a threat to our natural heritage. Conservation management of these precious ecosystems relies on accurate and up-to-date information about ecosystem health and the distribution of species and habitats, but such information can be costly to gather and interpret in the field. Remote sensing has proven capable of collecting information on geomorphologic zones and substrate types for coral reef environments, and is cost-effective when information is needed for large areas. Remote sensing-based mapping of coral habitat variables known to influence biodiversity has only recently been undertaken and new sensors and improved data processing show great potential in this area. This paper reviews coral reef biodiversity, the influence of habitat variables on its local spatial distribution, and the potential for remote sensing to produce maps of these habitat variables, thus indirectly mapping coral reef biodiversity and fulfilling information needs of coral reef managers.

The impact of geology and geomorphology on cave and rockshelter archaeological site formation, preservation, and distribution in the Zagros mountains of Iran

AbstractThis paper is a first attempt to explore the impact of geological and geomorphological settings on formation processes of shelter sites in the karstic Zagros Mountains of Iran. In general, the Zagros Mountains can be divided geologically and geomorphologically into two main zones, highland and folded, which are located parallel to each other and run from the northeast to the southwest in western Iran. Both the geological and geomorphological zones have implications for the formation processes of archaeological deposits at shelter sites. These environmental differences also influence the preservation of archaeological deposits at these types of sites. It is suggested that apart from site formation and post‐depositional processes, the local geological and geomorphological structure might also have had some influence on the distribution of prehistoric sites in the region. © 2007 Wiley Periodicals, Inc.

Geomorphology, site distribution, and Paleolithic settlement dynamics of the Ma'aloula region, Damascus Province, Syria

AbstractThis survey of the geology, geomorphology, and Paleolithic archaeology of a 300 km2 area in Damascus Province, Syria, focused around the villages of Ma'aloula and Jaba'deen. The study resulted in the definition of seven geomorphological zones that trend northeast–southwest, parallel to the prevailing geological features of the region. The zones span a broad range of elevations, from a dry lake bed in the Jeiroud Basin (ca. 800 m) to the peaks of the Anti‐Lebanon Mountains (ca. 2350 m). The research focused on assessing the geological and paleoenvironmental history of the region as a backdrop for 500,000 years of Paleolithic settlement. Among the 618 archaeological sites documented thus far, all major archaeological periods from the Lower Paleolithic through the Epipaleolithic are represented. Most abundant are occurrences of the Levalloisian Middle Paleolithic, with 255 new sites documented. Nine Neolithic sites were also included in the survey. The distribution of sites varies during the Paleolithic and reflects the availability of resources, especially of flint and water, as well as the spatial patterns of erosion and deposition on the ancient land surfaces. © 2007 Wiley Periodicals, Inc.

Bathymetry, biota and sediments on the Hirota Reef, Tane‐ga‐shima – the northernmost coral reef in the Ryukyu Islands

Abstract Investigations were conducted on bathymetry, reef biota and sediments on the Hirota Reef, Tane‐ga‐shima, North Ryukyus, near the northern limit for coral‐reef formation. A bathymetric profile from shore to the reef edge was depicted along an approximately 420‐m transect on the Hirota Coast of this island. A total of 20 quadrats (1 m × 1 m) were analyzed along the profile at 10‐ or 20‐m intervals to clarify distribution of macrobenthos inhabiting the reef. The Hirota Reef is divided into four geomorphologic zones according to their depth, gradient, surface roughness, substrate and characteristic macrobenthos. They are, from shore to offshore, shallow lagoon, seaward reef flat, reef edge and reef slope. The shallow lagoon comprises a shoreward depression (∼160 m wide on the transect) with a sand/gravel bottom that inclines gently toward offshore, and a seaward patch zone (∼70 m wide). The patches (<2 m high) are covered with fleshy algae, coralline algae and hermatypic corals. The seaward reef flat (∼190 m wide) is a flat plane that is constructed by biogenic carbonates and is covered with turf algae, with hermatypic corals scattered. Although the seaward reef flat of the Hirota Reef cannot be differentiated into different geomorphologic zones, similar seaward reef flat areas in the Central and South Ryukyus can be clearly subdivided into inner reef flat, reef crest and outer reef flat. This difference may be attributed to a lower reef growth rate and/or the later reef formation of the Hirota Reef in Holocene time than the southern examples. The coral fauna on the Hirota Reef is delineated by low diversity and characterized by taxa typical of high‐latitude, non‐reefal communities. The algal flora consists of tropical to subtropical species associated with warm‐temperate species. These faunal and floral characteristics may be related largely to lower water temperature in Tane‐ga‐shima than those in typical coral‐reef regions.

Erratum

Journal of BiogeographyVolume 34, Issue 2 p. 278-278 Free Access Erratum This article corrects the following: Tree distribution on a steep environmental gradient in an arid savanna Edmund C. February, Steven I. Higgins, Rosemary Newton, Adam G. West, Volume 34Issue 2Journal of Biogeography pages: 270-278 First Published online: September 11, 2006 First published: 29 September 2006 https://doi.org/10.1111/j.1365-2699.2006.01640.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Figure 5 in February et al. (2006) was published incomplete, with species names and geomorphological zones missing. The upper two panels show, from left to right, P. violacea stem growth in the Streamside and Near stream geomorphological zones. The lower three panels show, also from left to right, C. mopane stem growth in the Near stream, Far stream and Savanna upland geomorphological zones. References February, E.C., Higgins, S.I., Newton, R. & West, A.G. (2006) Tree distribution on a steep environmental gradient in an arid savanna. Journal of Biogeography, doi: DOI: 10.1111/j.1365-2699.2006.01583.x. Volume34, Issue2February 2007Pages 278-278 ReferencesRelatedInformation

A comparison of mud- and sand-dominated meanders in a downstream coarsening reach of the mixed bedrock-alluvial Klip River, eastern Free State, South Africa

Along a 28 km reach of the Klip River, eastern Free State, South Africa, mud- and sand-dominated meanders have developed in close proximity within a floodplain wetland up to 1.5 km wide, providing an unusual opportunity to compare their characteristics under similar hydrological conditions. Throughout the reach, the channel bed is grounded on sandstone/shale bedrock although the banks are alluvial, and most river activity occurs during summer high flows. The reach can be divided into three geomorphological zones: Zone 1 (0–11 km), a muddy proximal part with a single meandering channel (w/d < 10) and near-permanent standing water in oxbows and backswamps; Zone 2 (11–17.5 km), a transitional mud-to-sand part with one main channel (w/d ∼ 20–30), a number of sinuous palaeochannels and oxbows, and only limited standing water; and Zone 3 (17.5–28 km), a sandy distal part with a single meandering channel (w/d ∼ 15–30), scroll bars and oxbows, and little standing water. Each zone also has a distinctive sedimentology: Zone 1 is characterised by an ∼ 3–4 m thick succession of basal sand and minor granules overlain by dominantly muddy sediment deposited primarily by oblique accretion in meander bends; Zone 2 is characterised by < 4 m of interbedded sand and mud deposited primarily by lateral point-bar accretion, although a history of avulsions also attests to the importance of abandoned-channel accretion; and Zone 3 is characterised by < 3 m of dominantly sand deposited primarily by lateral point-bar accretion. This unusual downstream sediment coarsening trend, and the associated changes in channel and floodplain character, are independent of sediment inputs from tributaries, and result from a downstream increase in bankfull unit stream power from < 3.5 W m − 2 (Zone 1) to ∼ 4–10 W m − 2 (Zone 3). Mud is deposited primarily in low-energy Zone 1 but is conveyed in suspension more effectively through higher energy Zones 2 and 3, only forming drapes over sandy lateral accretion deposits during waning flood stages. The downstream increase in unit stream power is controlled in part by a slight downstream increase in floodplain gradient that may be related to a subtle variation in the erosional resistance of the bedrock underlying the channel bed. These findings add to previous work on meandering rivers by demonstrating that mud-dominated meanders can occur in long-term erosional settings where the channel bed is grounded on bedrock, and that downstream fining trends may be reversed locally.

A Large-scale, Hierarchical Approach for Assessing Habitat Associations of Fish Assemblages in Large Dryland Rivers

Multiple-scale assessments of fish-habitat associations are limited despite the fact that riverine fish assemblages are influenced by factors operating over a range of spatial scales. A method for assessing fishhabitat assemblages at multiple scales is proposed and tested in a large Australian dryland river, the Barwon–Darling River. Six discrete mesohabitat types (large wood, smooth bank, irregular bank, matted bank, mid-channel and deep pool) nested within 10 km long river reaches were sampled. Individual reaches were, in turn, nested within four larger geomorphological zones, previously identified along the river. Fish assemblages varied significantly between mesohabitat types and at different spatial scales. Golden perch (Macquaria ambigua), Murray cod (Maccullochella peelii peelii) and common carp (Cyprinus carpio) were strongly associated with large wood, but golden perch and Murray cod exhibited higher habitat specificity than carp. Bony herring (Nematalosa erebi) were more common in shallow edgewater habitats. At the riverscale, regional differences in the fish assemblage occurred at scales closely corresponding to geomorphological zones and these differences were associated with changes in the relative abundance of species rather than the addition or replacement of species. The proposed hierarchical framework improves the efficiency of fish surveys in large rivers by viewing meso-scale fish-habitat associations in the context of larger-scale geomorphological processes.

Preliminary testing of the Integrated Habitat Assessment System (IHAS) for aquatic macroinvertebrates

Preliminary testing of the Integrated Habitat Assessment System (IHAS), a widely-used aquatic macroinvertebrate habitat assessment method in South Africa, was undertaken. Based on the sensitivity of the South African Scoring System (SASS) to biotope availability and assuming that SASS Scores at minimally-impacted reference sites are the highest Scores attainable, one would expect to find a positive relationship between SASS Scores and IHAS scores at reference sites. The preliminary testing undertaken is based on the assumption that this relationship should be linear. For data obtained from reference sites in Mpumalanga and the Western Cape, non-parametric correlation analyses were undertaken between SASS4/5 Scores and IHAS scores, using Kendall's Rank-correlation Coefficient. Separate analyses were undertaken for different geomorphological zones and biotope groups. Results were generally unsatisfactory, with non-significant correlations (P > 0.05) for two-thirds of the data sets analysed. Performance of the IHAS varied between geomorphological zones and biotope groups, with best results obtained for the Foothill: Gravel-bed Zone in Mpumalanga, particularly with the stones-in-current biotope analysed separately. Further testing is required to confirm the relative performance in different bioregions/ecoregions, geomorphological zones and biotope groups.

River avulsions on the Taquari megafan, Pantanal wetland, Brazil

The Pantanal wetland is located in a tectonically active interior sedimentary basin in west-central Brazil. The south-flowing Paraguay River is the trunk-river of an alluvial constructional landform comprising several large alluvial fans, the largest one of which is the Taquari megafan. The Taquari River flows in two distinct geomorphologic zones within the megafan. Entrenched on sediments of Pleistocene fan lobes, the Taquari River flows in a 3 to 5 km wide meander belt in the upper fan, where avulsion is hindered by entrenchment. Downstream of the intersection point, stream discharge progressively decreases and the Taquari River becomes narrow and shallow toward the Paraguay River plain. Within the distributary fan lobe, the channel–levee sandy complex is topographically higher than the adjacent floodplains and avulsion is a natural consequence of crevasses in the natural levees. Many channel avulsions have occurred during the last decades and documented cases show that significant channel changes may take place in a few years. Beginning with crevassing in 1988 and ending with the abandonment of the former channel in 1998, the river completely changed course in the lower fan. Presently, a major avulsion is occurring in the upper portion of the growing fan lobe, where many crevasses have appeared in the natural levees with associated splays onto the floodbasin. New anastomosed channels have formed north of the Taquari River, but downstream of them the flow is unconfined and the water spreads into natural floodbasins. This avulsion is still in process and allows observation of channel evolution, the geomorphic features produced, the sedimentary processes involved, and resulting effects. If the new channels do not rejoin the main channel, the river mouth may abandon its present master channel and shift to a position a hundred kilometers north from its present position. A large volume of sediment has been transferred to the floodbasin, with progradation of crevasse splay deposits over fine overbank sediments. Many geomorphic features, recognizable in satellite and radar images, clearly show that avulsion has occurred many times before in the Taquari River. Avulsion belt deposits and former diverted channels testify to ancient avulsion events within the fan lobe and show that progradation of splays onto the floodbasin is the most important infilling process within the Taquari distributary fan lobe. The avulsion process in the lower Taquari River has accelerated in the last 30 years, along with the magnitude of flooding. Pasture and intensive agriculture in the catchment area has increased the sediment supply to the wetland, but larger floods are also a consequence of higher rainfall since 1973. Avulsion and floods have been a cause of great concern among the local population and landowners. Before human intervention in attempting to control floods, however, a better understanding of the avulsive river system is needed, especially because a major navigation project including the channelization of the Paraguay River was recently proposed.

Multiscale control of vegetation patterns: the case of Doñana (SW Spain)

The early studies about the plant ecology of Donana carried out at a small scale showed that the main process controlling vegetation composition of the stabilized dunes was soil water availability. However, the extrapolation of this model to larger spatial scales failed to explain observed vegetation patterns. In this work, the vegetation patterns and the processes causing them are studied at a larger scale. Data of topography, soil pH, electrical conductivity, and available iron allowed to distinguish three large geomorphologic zones on the stabilized dunes of the Donana Biological Reserve which correspond to different dune building episodes. Different dune episodes showed differences in both water table depth and dynamics, which are due to groundwater flow systems of different scale. It is further manifested by differences in shrub composition. The results show that geomorphology controls the vegetation pattern at different scales mediated through water availability. Differences in water availability are due to the connection to groundwater flow systems of contrasted scale. On a small scale (10−102 m), along dune slopes, there is a gradient from dune ridges to slacks, from xerophyte to hygrophyte vegetation types. On a mesoscale (102−103 m), there are several dune episodes with variable topographic altitude, dominated by different types of xerophytes. On a regional scale (>103 m), the discharges of the regional aquifer produce strong environmental and biotic stresses resulting in a mixed community.

Spatial variability in macroinvertebrate assemblages: comparing regional and multivariate approaches for classifying reference sites in South Africa

Spatial variability in macroinvertebrate assemblages was examined with the aim of evaluating the utility of regional classification systems in aquatic bioassessment. Sampling was undertaken at reference sites in the Western Cape and Mpumalanga, South Africa, using the rapid bioassessment method SASS4 (South African Scoring System Version 4). Multivariate analysis of macroinvertebrate assemblages showed that assemblages varied regionally with differences most apparent in upland areas, i.e. mountain streams and foothill-cobble beds, with lowland areas less regionally distinct. Within regions, longitudinal zonation into upland and lowland areas was important, with sites grouping on the basis of broad geomorphological zones or subregions. Of the upland sites, differentiation into mountain streams and foothill-cobble beds was not evident, although overall variability of assemblages within upland areas, in particular the Western Cape, was very high. In general, a priori regional classification of sites using the hierarchical spatial framework developed in South Africa provided a useful framework for preliminary classification of reference sites. Groups of sites based on a posteriori analysis of macroinvertebrate data, however, provided a more robust classification than any regional classification. Spatial classifications therefore offer geographic partitions within which to expect somewhat similar conditions, and regional reference sites selected within the context of the spatial framework are likely to be more representative of specific river types than those selected without using the framework. Classification of sites needs to be an iterative process that allows for subjective a priori regional classifications to be modified on the basis of independent, objective a posteriori classification of biological assemblages.

Multi-site evaluation of IKONOS data for classification of tropical coral reef environments

Ten IKONOS images of different coral reef sites distributed around the world were processed to assess the potential of 4-m resolution multispectral data for coral reef habitat mapping. Complexity of reef environments, established by field observation, ranged from 3 to 15 classes of benthic habitats containing various combinations of sediments, carbonate pavement, seagrass, algae, and corals in different geomorphologic zones (forereef, lagoon, patch reef, reef flats). Processing included corrections for sea surface roughness and bathymetry, unsupervised or supervised classification, and accuracy assessment based on ground-truth data. IKONOS classification results were compared with classified Landsat 7 imagery for simple to moderate complexity of reef habitats (5–11 classes). For both sensors, overall accuracies of the classifications show a general linear trend of decreasing accuracy with increasing habitat complexity. The IKONOS sensor performed better, with a 15–20% improvement in accuracy compared to Landsat. For IKONOS, overall accuracy was 77% for 4–5 classes, 71% for 7–8 classes, 65% in 9–11 classes, and 53% for more than 13 classes. The Landsat classification accuracy was systematically lower, with an average of 56% for 5–10 classes. Within this general trend, inter-site comparisons and specificities demonstrate the benefits of different approaches. Pre-segmentation of the different geomorphologic zones and depth correction provided different advantages in different environments. Our results help guide scientists and managers in applying IKONOS-class data for coral reef mapping applications.

Geomorphological and sedimentological characteristics of coastal and inland sabkhas, Southern Kuwait

Sabkha deposits in the southern sector of Kuwait occur as scattered, irregular, and closed lowland areas of different sizes. On the basis of their field occurrence, and geographic setting two distinct types of sabkhas are recognized, coastal and inland. The coastal sabkhas extend along the elongated depression in Al-Jailaiaha and Al-Khiran areas. The inland sabkhas are formed in the irregular slopes in the western side of the desert area in Al-Maqwa, Urafjan, and Al-Gurain areas. Formation of sabkhas is related to pre-existing morphological features such as depressions and gentle slopes, and is distributed in the study area in different geomorphological zones. Both coastal and inland sabkhas are subjected to mobile sand invasion under the action of the northwesterly prevailing wind. Texturally, both groups of sabkhas may be classified within the gravelly to slightly gravelly muddy sand class. Their sediments are mostly unimodal with a modal class of medium sand, poorly sorted, nearly symmetrical and mesokurtic. The surface features of quartz grains show the mechanical and chemical action on their surfaces. Mineralogically, coastal and inland sabkhas are mainly composed of quartz, feldspars, gypsum and rock fragments, which are mostly of carbonate type. Skeletal fragments and oolites are present in the coastal sabkhas and are absent in the inland sabkhas. Based on the heavy-mineral suites, most of sabkha sediments are thought to be derived from Al-Dibdibbah deposits, which were derived from the Arabian Shield igneous and metamorphic rocks by wadi A1-Rimmah-Al-Batin valley system.

Biomass and distribution of herbivorous blennies in the southern Great Barrier Reef

At the small scale (<1 m2), a correlation between microhabitat availability and abundance of comb–toothed blennies was apparent at Heron Island. Investigation of medium scale (>20 m2) differences, showed that community structure and biomass of herbivorous blennies differed among the 14 geomorphological zones identified. Large scale differences (>10 km2), detected using comparisons between Heron, Lady Elliot and North West reefs, revealed that species composition and biomass, but not density, differed significantly. At Heron Reef, density and biomass of comb–toothed blennies exceeded published estimates for most groups of conspicuous herbivorous fish in equivalent zones. The influence of scale on interpretation of patterns of fish distribution and the role of inconspicuous grazers such as comb–toothed blennies, deserves closer attention.

Biomass and distribution of herbivorous blennies in the southern Great Barrier Reef

At the small scale (&lt;1 m2), a correlation between microhabitat availability and abundance of comb–toothed blennies was apparent at Heron Island. Investigation of medium scale (&gt;20 m2) differences, showed that community structure and biomass of herbivorous blennies differed among the 14 geomorphological zones identified. Large scale differences (&gt;10 km2), detected using comparisons between Heron, Lady Elliot and North West reefs, revealed that species composition and biomass, but not density, differed significantly. At Heron Reef, density and biomass of comb–toothed blennies exceeded published estimates for most groups of conspicuous herbivorous fish in equivalent zones. The influence of scale on interpretation of patterns of fish distribution and the role of inconspicuous grazers such as comb–toothed blennies, deserves closer attention.