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You have full access to this open access chapter. Seaweeds, Cyanobacteria, seagrasses and mangroves are the principal inshore primary producers in the southern basin of the Arabian Gulf. Of these the seaweeds are by far the most diverse with about species recorded from those Emirates bordering the region. Little is still known of the seaweed floras of the two Emirates within the Gulf of Oman Fujairah, Sharjah. Briefly discussed are the very extensive cyanobacterial mats association with inshore sedimentary environments. Described are the bands of seaweeds, cyanobacteria and sessile animals that are a feature of the intertidal of rocky shores. Much consideration is given to the striking forest-like community that develops seasonally on shallow and often seaward sloping rocky platforms. The ecological significance of the large biomass of dead and decaying seaweed produced in early summer is discussed. Briefly mentioned are seaweeds as providers of ecosystem services. You have full access to this open access chapter, Download chapter PDF. Conditions are particularly harsh in its southern basin and accounts for the relatively low number of seaweeds about species recorded so far from those Emirates that border it. Until the end of the twentieth century the seaweed flora of the UAE was virtually unknown, with a catalogue of the benthic marine algae of the Indian Ocean region Silva et al. Often the seaweeds of the Arabian Gulf are considered as representing a depauperate subset of those in the Indian Ocean due to the environmental extremes. Still little is known of the seaweeds of those other emirates bordering the Arabian Gulf whose coastlines are considerably shorter and possess few hard-bottom seaweed habitats. Very few seaweeds grow on sand and fine sediments with information still lacking on the inconspicuous forms usually associated with many coastal developments, including rough stone or concrete block breakwaters, sea walls, piers and revetments surrounding new or enlarged islands. Still scarcely studied are the seaweeds of those eastern emirates lying within the Gulf of Oman, namely Fujairah and Sharjah, where environmental conditions are less extreme and marine biodiversity might be expected to be significantly higher than within the Arabian Gulf. The seaweeds of Fujairah are mainly confined to the wave-beaten rocky shores lying to the north of the enclave of Khor Fakkan since to the south the wave-exposed coast consists mainly of sand beaches Chap. Just over 20 seaweeds have so far been reported from Fujairah John with even fewer known from the internationally important wetland conservation reserve of Khor Kalba in Sharjah D. John, unpubl. It consists of an extensive system of mangrove-fringed tidal lagoons, where the seaweeds are mostly confined to the rocky channel connecting them to the open sea see Chap. Also belonging to Sharjah is an island of considerable conservation importance, Sir Bu Nair, within the Arabian Gulf and lying some 65 km from the Dubai-Abu Dhabi border. The conservations importance of the island relates to the unique composition of its corals that until recently remained in a healthy state in contrast to the increasingly degraded inshore reefs Bejarano et al. Unfortunately, there is no published information on its seaweed flora, although it is likely that seaweeds will be inconspicuous and few in number because of the complete dominance of table corals Acropora although the situation might change following a warm water event that took place in summer Seaweeds are one of the principal primary producers in the southern basin of the Arabian Gulf along with seagrasses, mangroves, Cyanobacteria, vascular plants in salt marshes, and the symbiotic dinoflagellate associated with corals. Seaweeds are benthic i. Some smaller seaweeds do commonly grow as so-called epiphytes on some of the larger species. One of the few seaweeds colonising the surface of the soft mud of intertidal flats are the dark-green, felted masses of the coarse, tubular, branching filaments of Vaucheria piloboloides , a member of the yellow-green group of seaweeds. An important group of photosynthetic organisms frequently considered along with seaweeds are the Cyanobacteria, formerly referred to as the blue-green algae Cyanophyta. It has long been recognised that these organisms are more closely related to bacteria, hence now termed blue-green bacteria or Cyanobacteria. The Cyanobacteria and seaweeds sometimes occur together in fully marine situations although the Cyanobacteria are usually most abundant and conspicuous in some of the most inhospitable environments. In the UAE the Cyanobacteria form very extensive intertidal crusts or mats on sandy or muddy shores, and even above the normal high-tide level within coastal salt marshes or sabkhas where the sediments are often a mixture of sand, silt or clay and are sometimes associated with a crust of salt and other minerals. Seaweeds are a common feature of natural rocky shores throughout the UAE and often become most evident to the general public along parts of the Abu Dhabi coast in the spring and early summer when masses of dead and decaying seaweeds accumulate in bays and become deposited onto beaches. Otherwise for much of the year seaweeds are not usually very noticeable unless visiting a rocky shore at low tide or venturing below the waves with mask and snorkel. Seaweeds or benthic macroalgae are oxygen-producing marine organisms that are usually attached to hard surfaces and all members have somewhat similar ecological requirements. Like seagrasses and other vascular plants, seaweeds all possess chlorophyll a and b , although the green colour is frequently masked by accessory pigments except in the group commonly known as the green seaweeds Chlorophyta. As a character colour can be misleading, although it does link to a suite of other characters enabling the recognition of the following major seaweed group: Chlorophyta green seaweeds , Ochrophyta, Phaeophyceae brown seaweeds , Rhodophyta red seaweeds and Xanthophyta yellow-green seaweeds Box The red seaweeds contain the red pigment phycoerythrin and the blue pigment phycocyanin and commonly range in colour from bright red to dark purplish. Sometimes seaweeds belonging to the red group Rhodophyta become bleached by bright sunlight and then range from yellow-brown to orange when growing in the intertidal or in shallow water. The brown seaweeds contain the accessory brown pigment fucoxanthin and vary from dark brown to a yellow-brown or straw colour. Besides differences in pigmentation, seaweed groups are separated upon many structural and biochemical features. Some seaweeds exhibit the phenomenon of iridescence and are either completely iridescent, only iridescent at the branch tips or it is in the form of bands and spots. Seaweeds are an unnatural grouping of organisms, since they fall within different kingdoms on the biological classification system. The green and red seaweeds are in the Kingdom Plantae, whereas the brown and yellow-green seaweeds belong to a separate kingdom, the Chromista. Frequently considered along with the seaweeds are the Cyanobacteria whose cellular and biochemical characteristics are more closely related to the bacteria, hence they are no longer referred to as the blue-green algae. The Cyanobacteria are all microscopic and so only visible when cells, colonies or filaments grow together to form blue-green, black, brownish or red tufts, mats or crusts. Differences in colour relate to the different proportions of a red phycoerythrin and a blue phycocyanin pigment in the cells as well as to a brown scytonemin pigment produced within the sheath of filamentous forms. The Cyanobacteria are placed in the Kingdom Eubacteria and are only briefly considered here since have been scarcely studied in the region, are very difficult to identify and there is much disagreement even amongst specialists concerning their taxonomy and naming of species. Seaweed show considerably variation in form, size and complexity as well as in the nature of their reproduction. Some consist of simple or branched filaments of one to several rows of cells whereas others have a much greater morphological complexity ranging from cylindrical, compressed or flattened branches through to membrane-like forms. As none of the seaweeds have vascular tissues or roots, all gas and nutrient exchange occurs by diffusion through their tissues from the surrounding water, and hence typically they have thin, laminar surfaces. Occasionally the crusts bear surface projects such as nodules or non-articulated branches as is the case in Lithothophyllum kotschyanum , the most widely distributed and common crustose form within the Arabian Gulf. These crustose corallines play an important role as ecosystem engineers since involved in the growth and maintenance of coral reefs by stabilising coral rubble and dislodged coral colonies and are known to induce the settlement of the larvae of corals and other benthic animals. Green Seaweeds Phylum Chlorophyta : Characteristically a bright green since no secondary pigments mask the chlorophyll colour. Range from single cells, simple or branched filaments of cells aligned in a single series through to compact spongy forms to flattened membrane-like fronds or tubes. A few are lime-impregnated. Brown Seaweeds Ochrophyta, Phaeophyceae : Characteristically range from olive-brown to various shaded of brown due the pigment fucoxanthin masking the green chlorophyll. Varying from filaments of cells in a single series through to strap-like forms or those with leaf-like appendages foliose forms and sometimes having a distinct holdfast, stem stipe and frond s. Red Seaweeds Rhodophyta : Characteristically red in colour since the green chlorophyll pigment is masked by a combination of the red pigment phycoerythrin and the blue pigment phycocyanin. Often under high light conditions individuals become bleached to a brownish or straw colour. Varying from filaments of a single series of cells through to compact tissues in the form of cylindrical or flattened branches, sometimes membrane-like. Reproduction and life history is often very complex and is not considered here in any detail. Yellow-Green Seaweeds Ochrophyta, Xanthophyceae : Cells usually yellow-green due to predominance of a secondary pigment diatoxanthin in the chloroplasts two or more chloroplasts per cell ; unicellular, filamentous, colonial or coenocytic and motile forms with two subapical flagella; walls often with overlapping parts; storage material oil, fat or leucosin never starch. Blue-Green Bacteria Cyanobacteria : Single-celled, colonies of large numbers of cells embedded in mucilage or of single filaments or grouped together to sometimes form distinctive filamentous colonies. Some filamentous forms contain larger colourless cells known as heterocysts having one or two refractive polar nodes and are sources of nitrogen fixation in some species. Reproduce by large, thick-walled cells known as akinetes and by fragmentation to produce short lengths of trichome hormogonia. Seaweeds have complex life histories, with some species having stages showing so little resemblance to one another as to have once been considered separate species or genera. Some seaweeds reproduce vegetatively by fragmentation, although the majority have asexual reproduction by spores produced by a spore-producing stage known as the sporophyte. The males and female gametes are produced by the sexual stage gametophyte and fuse to form a zygote. For a discussion of the details of reproduction and complexity of the different life cycles in the algae, see general works on seaweeds and relevant websites. The terminology used to describe biologically defined bands or zones on rocky shores throughout the world by Lewis and Stephenson and Stephenson has been applied to shores in the UAE John and George Sometimes the Cyanobacteria form a blackish zone in and just below the littoral fringe and this is especially evident on limestone shores Fig. There is little information on the composition of the Cyanobacteria within this zone except for the often most common and conspicuous species Chroococcus varius Fig. Shore profile showing position of the tides in relation to the terminology used to describe the different zones based upon dominant plants and animal groups. Image credit: Oliver Farrell. Photo credits: David George a , e , f and David John b , c , d. Photo credits: David George a , c and David John b , d. A greyish band of barnacles often defines the upper part of the eulittoral zone and these typically occur immediately below or are mixed with the zone dominated by Cyanobacteria. Discovered at this level on rocks and cement blocks associated with an artificial island on Hail Shoal in Abu Dhabi were low growing light brown mats of the filamentous cyanobacterium Gardnerula fasciculata Fig. Below the barnacle zone there is often a noticeable increase in biological diversity with the dominant organisms present often dependent on such factors as wave-exposure, nature of shore, slope and aspect. Sometimes on more steeply sloping rocks in Abu Dhabi were low growing turfs or mats of seaweeds that were frequently accompanied by clusters of calcareous tubes belonging to the serpulid polychaete worm Pomatoleios kraussii Fig. Low growing mats were often particularly noticeable growing over crustose corallines on steeply-sloping, wave-battered rocks Fig. Photo credits: David George a , b and David John c , d , e. The lower littoral zone along much of the more sheltered parts of the coastline of Abu Dhabi and emirates to the east is normally characterised by low clumps of Palisada perforata Figs. These seaweeds persist throughout the year, whereas some of the mat-forming seaweeds are only evident during the winter months; often these seaweeds are most conspicuous along the seaward margin of those rocky platforms constantly wave splashed at low water. During the spring and early summer seasonally present seaweeds disappear, leaving some of the perennial forms mentioned above and these are often accompanied by pinkish or bleached crusts of crustose corallines. Sometimes there develop in early summer dense spongy, cushion-like growths of the green seaweed Cladophoropsis fasciculata on rocks in the lower littoral and shallow sublittoral zones Fig. These have been observed covering extensive areas in the west of Abu Dhabi and sometimes become detached to accumulate in vast quantities in sheltered bays early in summer. The uppermost limit of the infrequently exposed sublittoral fringe is usually defined by organisms normally growing in the shallow sublittoral zone. The black sea-urchin Echinometra and the oyster Pinctada radiata frequently define the fringe since are commonly present on the seaward margin of intertidal platforms along with mats of filamentous red seaweeds. During the winter months a few larger seaweeds sometimes grow within the fringe along with Dictyosphaeria cavernosa Fig. Some brown seaweeds similarly occur within the sublittoral fringe but are also more common in the subtidal zone, including the peacock tail weed Padina boergesenii Fig. The attractive but often bleached filamentous red seaweed Spyridia filamentosa Fig. Conditions for marine life are extremely harsh in these rocky pools, with some mostly supplied with water by wave splash and spray. Often Cyanobacteria are the only photosynthesising organisms surviving in such pools that are subject to exceptionally high salinities and water temperatures. These are usually filamentous Cyanobacteria forming brownish mats and are most common in nutrient-enriched pools associated with bird colonies. During low water some shore platforms are partly covered by wide expanses of shallow water, as is the case at Shuweihat in Abu Dhabi see Fig. The environmental conditions are much more hospitable within lower shore pools compared to smaller ones at higher shore levels. Sometimes subtidal seaweeds are to be discovered in larger and deeper lower shore pools and frequently grow on the sometimes steeply sloping sides as well as on stones, shells and other debris lying on the bottom of those that are sandy floored. Some of those growing on the steep sides of pools are perennial forms that also occur on adjacent rock. Many seaweeds become bleached straw-coloured or brownish and this applies to Polyides myrica, a rhodiophyte that is sometimes heavily epiphytised by the small crustose coralline Hydrolithon Fig. If sand is absent then lower shore rock pools might become lined by the pinkish crusts of coralline seaweeds, most commonly Lithophyllum kotschyanum Fig. In Fujairah very small pools or depressions in the sublittoral fringe are typically lined by such crustose corallines and these are often occupied by the black sea urchin Echinometra. Easily overlooked is the beautiful umbrella-shaped green seaweed Acetabularia calyculus Fig. Photo credits: Chris Teasdale a , b and David John c — e. Sandy beaches range from steep, wave-exposed beaches of coarse sand through to those that are low to moderately wave-exposed, gently sloping and of fine-grained sand. Seaweeds are normally absent from such beaches unless sufficiently sheltered to enable hard sand-embedded sediments to be stable enough to allow colonisation by often fast-growing seaweeds. If partially sand-buried rocks, coral fragments, shells, cables or other artificial surfaces are present then these may be colonised by various seaweeds over the winter months. Most common are green seaweeds such as the much branched filamentous Cladophora nitellopsis Fig. The latter commonly forms a low carpet-like mat on wave-exposed rocky platforms along the northern coast of Fujairah Fig. The grey mangrove Avicennia marina is the only true mangrove tree to survive the temperature and salinity extremes encountered within the Arabian Gulf see Chap. The trees often form well-developed stands on the compacted muddy shores of creeks, channels, lagoon systems Fig. Dark-coloured cyanobacterial mats commonly cover the frequently compacted mud associated with the trees. Also associated with the mangroves are some of the same seaweeds growing on partially buried hard surfaces on sandy shores. Occasionally the unbranched threads of the green seaweed Chaetomorpha linum become entangled with the breathing roots pneumatophores of the mangroves to form a curtain-like shroud Fig. Sometimes associated with the mangroves are bushy clumps of the filamentous green seaweed Cladophora nitellopsis Fig. Sometimes such green seaweeds as Ulva are commonly association with dredged navigation channels close to industrial areas. Unsurprisingly the seaweeds on the uppermost margins of the calcareous limestone platforms through which these channels are cut are similar to those growing around and below the sublittoral fringe. Photo credits: David George a , b and David John c. Fine sediments and decomposing organic material tend to accumulate in inner harbour basins, sheltered embayments, quiet areas of lagoons and on the lee side of islands. These areas of very soft, muddy deposits are high in organic matter and often black and anoxic just a few millimetres beneath the surface. Sometimes the mud surface on the lower shore is covered by a dark green, felty mat consisting of the finely branched filaments of Vaucheria piloboloides , the only yellow-green seaweed so far reported from the UAE Fig. Photo credits: David John a and David George b. Where lagoons have no through-flow or only flood during the highest tides spring tides conditions are hypersaline, especially in their innermost reaches see Chap. Commonly on the sand or muddy shores of such lagoons there are cyanobacterial crusts or mats Box These are usually most extensive along the seaward margins of low-lying areas of the coastal plain that only flood during very high spring tides and periods of strong onshore wind. The seaward margins of these coastal plains are subjected to very high rates of evaporation and are often referred to as evaporative coastal salt flats, called sabkha pl. The sabkha plain extends well beyond the cyanobacterial mats and is influenced by changes in the groundwater level and the sediments are associated with surface deposits of gypsum and anhydrite see Chap. Cyanobacterial mats have distinctive surface features relating to a number of factors, including frequency of immersion by the tides, seawater salinity, drainage, water flow and what species of cyanobacteria are present Golubic and Abed Two of the main mat-forming cyanobacteria, Microcoleus chthonoplastes and species of Schizothrix principally S. Schizothriz splendida is common along the banks of creeks and the sandy floors of well-drained lagoons where it forms pinnacle-shaped mounds Fig. The Microcoleus frequently forms flat mats in ponds and variously sized waterlogged depressions and is sometimes accompanied in the middle and upper shore by Lyngbya aestuarii, another filamentous cyanobacterium. In the mid-tidal zone the Cyanobacteria are rearranged at a finer scale in response to changes in the length of time surfaces are exposure to air and therefore to water loss. This zone extends from about the lower to mid-shore level and is so-called because the surface is covered by minute blisters pustular or nipple-like projections see Abed et al. Immediately above this zone lies a so-called polygonal zone where desiccation results in the surface mat cracking into polygons whose upturned edges enclose dark green, leathery, layers of cyanobacteria. These polygons tend to form in shallow pools and channels, especially those frequently flooded by the sea, with cracking of the surface resulting in the formation of different microhabitats. Different Cyanobacteria are dominant in the water-retaining depressed centre of the polygons compared to the upturned margins and cracks. In the littoral fringe there is often a thin, crinkled, crenulated or convoluted, leathery, blackened cyanobacterial mat that often dries out and crumbles. Usually very flat is the landscape in areas dominated by cyanobacterial mats and crusts due to sediment accumulation and poor drainage, with the mats developing initially on what becomes soft, swampy ground when flooded by the tide. The sabkha plain extends well beyond these mats and is influenced by changes in the groundwater level and associated with the sediments are surface deposits of gypsum and anhydrite. Golubic and Abed , p. Many shallow water platforms have low physical relief and are partially sand-buried, often much fissured and have creviced hard surfaces. Periodic sand-burial of hard surfaces is especially common in shoal areas where there are strong tidal streams as well as considerable wave action. There is a diverse faunal assemblage associated with these surfaces, including the pearl oyster Pinctida radiata , the mussel Brachydontes variabilis , and the snail Cerithium scabridium to name a few. Also present are many annual and perennial seaweeds that are frequently attached to surfaces that are sometimes buried beneath a thin layer of sediment or sand. Often in winter this shallow water community is spatially dominated by foliose brown seaweeds and these extend into deeper water where growing on loose lying rocks and dead sand-embedded coral fragments that are sometimes on the bed of dredged channels. The most conspicuous brown seaweeds present are the distinctively flattened branches of Sargassopsis decurrens Figs. Photo credits: David George a — d and Chris Teasdale e. On occasion orange-coloured clumps of Chondria dasyphyllum , with its irregularly divided and distinctively club-shaped laterals, form extensive beds on low sand-embedded rocks and lithified hard-grounds Fig. It is often accompanied by other bleached red seaweeds such as Laurencia obtusa Fig. The mosaic of seaweed communities reflects the instability of these hard surfaces that are available for colonisation for varying lengths of time and at different times during the year. Of the submarine seaweed communities, the most diverse and complex is the forest-like one in which brown foliose seaweeds are the canopy dominants Fig. These submarine forest usually occur on gently seaward sloping rocky platforms that fringe the mainland coast of Abu Dhabi as well as some of its offshore barrier islands and shoals. Many of these fringing slopes in the central and eastern region of this Emirate, somewhat sheltered from the north-westerly shamal winds, were probably once spatially dominated from about 1 to 4 m depth by table corals Acropora along with an understorey of mound and brain corals such as Porites, Platygyra and many other smaller merulinids George and John Photo credits: David George a — e and Chris Teasdale f. The first of such warm water episode was in the summer of and its impact was particularly severe on shallow water stands of Acropora table corals. A second and even more severe episode took place 2 years later and this now impacted many of other shallow water corals, especially the frame-building mound and pillar coral Porites colonies together with various corals that historically flourished in the understorey of the shallower Acropora George and John , , ; Riegl Since the s there have been further warm water episodes, with these becoming more frequent and sometimes more intense. It has been estimated by Burt et al. Smaller brown seaweeds commonly form an understorey and include the somewhat rigid and distinctively shaped Polycladia myrica Fig. Often seen between about March and April are the distinctive, spherical or somewhat convoluted bladders of the brown seaweed Colpomenia sinuosa Fig. The on-going decay of the canopy dominant seaweeds leads to the eventual loss of the Jania which sometimes washes ashore in vast numbers along parts of the coast of Abu Dhabi as whitish balls. Occasionally large accumulations of these balls have been observed lying on the seabed in the shallows and remain pinkish in colour and seem still to be growing. Photo credits: David George a , c , d and David John b , e , f. The on-going decay of the canopy dominants seaweeds leads to the eventual loss of the Jania which sometimes washes ashore in vast numbers along parts of the coast of Abu Dhabi and appear as whitish balls. Some of the canopy dominants survive into the following growing season despite losing many of their side branches and become reduced in summer to sometimes a perennial holdfast bearing a few almost naked main axes. The greatly reduced cover of these canopy-dominants during summer results in the submarine seascape becoming transformed, since now the most conspicuous seaweeds present are those forming turf-like mats, crustose corallines and various sessile animals Fig. One of the more common of these low growing forms is Gelidium pusillum Fig. Also evident during summer are semi-erect fronds of the brown seaweed Lobophora variegata Fig. Seaweeds were always an inconspicuous component of healthy coral carpets, but are now becoming increasingly significant due to the demise of the corals caused by recurrent episodes of their bleaching and death. The first such incidence in the UAE took place in George and John , , ; Riegl and only became apparent when the coral. Subsequently Cyanobacteria have been reported in Chap. By the spring of there was a succession of seaweeds on the still intact skeletons of the tabular coral Acropora with the crustose coralline the spatially dominant group Fig. There was a large reduction in physical complexity as the framework of Acropora skeletons began to collapse, leaving many shallow rocky platforms in Abu Dhabi covered by mounds of coral rubble Fig. Photo credit: David George. The island of Sir Bu Nair remains the only place of those emirates within the Arabian Gulf where relatively healthy stands of the tabular coral Acropora still exist, although even these have been damaged by recent severe warm water episodes Bejarano et al. Seaweeds are more commonly associated with rocky areas where the corals have become degraded and coral communities are becoming dominated by more stress-tolerant brain and mound corals Burt and Bauman One seaweed particularly associated with dead and living corals is Lobophora variegata Fig. Otherwise, turf-like mats are typically confined to dead or damaged areas on coral where they are occasionally accompanied by the green filamentous seaweeds Cladophora and Cladophoropsis. Most commonly associated with corals are crustose coralline seaweeds, with Lithophyllum kotschyanum the most conspicuous and varies from a crust bearing nodules and simple or divided, cylindrical branches Fig. Often crustose corallines develop on the steep sides of rock ledges and coral skeletons Fig. By far the most abundant seagrass is the narrow leaved Halodule uninervis and is accompanied in places by the two broader leaved species belonging to the genus Halopila , namely H. Sometimes there is a mosaic of seagrass vascular flowering plants and seaweed communities where the sea bed is of sand and also contains surfaces suitable for seaweed attachment. The only seaweeds growing directly on sand in the UAE are Caulerpa sertulariodes , Caulerpa racemosa and Avrainvillea amadelpha. The most common Caulerpa is Caulerpa sertularioides form farlowii Fig. Avrainvillea amadelpha is mostly encountered in very shallow sandy areas where its large holdfasts produce solitary or clusters of branches that often terminate in flattened blades Fig. Photo credits: David George a — c and Chris Teasdale d. Photo credits: Chris Teasdale a — c and David John d. Common on these hard surfaces are a mix of filamentous green seaweeds, such as Cladophora nitellopsis Fig. Some seaweeds and the surfaces to which they are attached occasionally become dislodged by strong tidal streams and sometimes leave a distinctive trail when dragged across the sandy seabed Fig. Smaller seaweeds grow epiphytically on the blades of the seagrass Halodule uninervis , including the crustose coralline Hydrolithon that often appears as small pink spots. Suitable seaweed habitats continue to be created as the coastal zone of the UAE is increasingly modified by the construction of new breakwaters, stone jetties, metal piers, floating marinas, harbours, channels, landfill, rock armoured islands and peninsulas e. Many islands and breakwaters have revetments of natural stone blocks usually of limestone or, less commonly, of concrete tetrapods or metal piles. Most of these surfaces become quickly colonised by fouling animals along with fast-growing seaweeds and sometimes are in areas where no such hard-bottom had existed previously. Suspension-feeding invertebrates frequently foul pier piles and floating pontoons whereas hard corals are recorded on the sediment-free seaward side of rough stone breakwaters and are accompanied by red seaweeds, such as the bushy seaweed Asparagopsis taxifolia Fig. Breakwaters and other shoreline developments might be thought of as large-scale artificial reefs capable of supporting abundant and diverse marine communities. Consideration has therefore been given to applying ecological engineering principles to such shoreline developments in order to enhance biodiversity, with the first step been to determine those best suited to enhance recruitment of desirable organisms Burt and Bartholomew ; Burt et al. Channel marker buoys and pontoons are frequently festooned by a diverse assemblage of seaweeds during the winter months, together with many invertebrates. Immediately at or just below the water surface Fig. Occasionally present are clumps of the form of the crustose coralline Lithophyllum kostchyanum whose branches are flattened Fig. These man-made structures are periodically cleaned to remove fouling organisms so a stable animal-dominated assemblage is probably never attained. Small buoys in sheltered marinas and the hulls of small boats frequently have a covering of the green filaments of Cladophora nitellopsis Fig. The ability of some seaweeds to quickly colonise and become establish might impact on the successful colonization and re-establishment of corals following episodes of bleaching and death. It is known that turf-like mats very soon colonize coral skeletons following bleaching and yet Birrell et al. Some seaweeds are adapted to survive the ravages of herbivorous fish and sea urchin grazing through morphological and chemical defence mechanisms Duffy and Hay ; Hay and Fenical The heavy calcification of crustose corallines means they are not normally grazed by fish other than parrotfish and are well adapted to survive chronic grazing or scraping by sea urchins. These forms also survive in habitats where there is violent wave action hence are conspicuous on very wave-battered and often steeply sloping shores, including the seaward side of breakwaters. For example, the crustose corallines form a very distinctive band in the lowermost zone on rocky headlands along the northern coastline of Fujairah see Fig. The success of crustose corallines is not only due to their hardness but also their ability to continuously replace those surface cell layers lost through grazing, heavy wave-action and sand abrasion. Some of the larger seaweeds, such as the foliose browns, are known to be an important food source in the UAE for animals including green turtles and dugongs. It has been suggested by Fulton et al. Depending on the trophic diversity of these macroalgal-associated fishes, such overlaps in habitat occupation could help stabilise ecosystem structure and function in the face of disturbances affecting a particular habitat type e. Much of the large biomass of decaying seaweed often seen floating in the sea along parts of the western coast of Abu Dhabi in spring and early summer becomes deposited on beaches and probably contributes significantly to detrital food webs as well as to the microbial loop. Small turf-like mats of seaweeds are typically formed of short, tightly packed, highly branched filaments and consist of erect branches arising from a system of creeping or prostrate branches. Such growth forms are common and survive loss or damage to the apices of the erect portion by fish browing, desiccation, wave action and sand abrasion by having basally positioned growing points or meristems. These mats are conspicuous in the lower littoral zone of rocky shores or breakwaters including those subject to considerable heavy wave action. Still to be investigated in the UAE are such plant-animal interactions, including the impact of herbivory on the distribution and composition of the seaweeds in the littoral and shallow subtidal zone. The maximum summer sea temperature and seasonal temperature range in the southern basin of the Arabian Gulf is the greatest worldwide. Observations on seasonal changes to the seaweed flora have been confined to Abu Dhabi, where seaweeds undergo a dramatic transformation as the sea temperature rapidly rises in spring and early summer April-May. Many seaweeds begin to undergo decay and are lost during this period, and large floating masses have been observed in the western region of Abu Dhabi which frequently accumulate in sheltered bays before washing ashore Fig. Photo credits: David George. Most seaweeds appear to be moribund or dormant over the summer when sea conditions tend to be very calm and most submarine surfaces become coated in what is believed to be a film of sediment mixed with microalgae. Recovery of these seaweeds often takes the form of new branches from often persistent basal portions and of small juveniles arising from resting spores and microscopic life history stage. The winter period is the most appropriate time for studying this important group, since this is at the time when seaweeds are most abundant and diverse. The only seaweed believed to have been introduction in recent times is Caulerpa racemosa form requienii Fig. This green seaweed was first discovered in September in Palm Jebel Ali Dubai where it formed dense and extensive beds over the sandy and muddy seabed at depths ranging from 3 to 5 m Venneyre et al. It consists of creeping stoloniferous branches attached by clusters of rhizoids and giving rise at intervals to cylindrical or slightly compressed, regularly forked branches. Dense bed showing the cylindrical or slightly compressed erect branches of Caulerpa racemosa form requienii growing on the sandy floor of Palm Jebel Ali in Dubai. Image credit: Laurence Vanneyre. One possible vector responsible for its introduction are the suction dredgers employed for the construction of Palm Jebel Ali and the Dubai waterfront. These dredgers use sand as ballast in their hoppers and, just prior to travelling to Dubai, had been deployed extracting and transporting sand from near Jakarta in Indonesia for the construction of a harbour in Singapore. To determine whether this is the source of the introduction it will be necessary to carry out a genomic investigation to compare the Dubai population with that from Indonesia. This introduced species is a potential invasive species, since other members of the genus have become widely distributed and have brought about disastrous changes in shallow water environments in different parts of the world, especially in the Mediterranean. There is no recent information on these seaweeds within the Arabian Gulf so its current status is unknown. Seaweeds, along with seagrasses, are the key primary producers lying at the base of inshore food webs within the southern basin of the Arabian Gulf. Some seaweeds are a direct food source for fish, invertebrates, as well as turtles and dugongs, but much seaweed biomass enters the food web as detritus. They are therefore seasonally important to suspension and detrital feeders alike and, through decomposition, make a significant contribution to the microbial loop. Detrital feeders are important general consumers of organic material and along with microalgae probably account for the importance of inshore mud flats and offshore shoals and islands as feeding grounds for millions of migratory and resident water fowl see Chap. The spring and the early summer are when a large quantity of decaying seaweeds and seagrasses are cast up on some beaches with brown seaweeds and contributing to much of this biomass Fig. Decaying seaweeds deposited on beaches i. This justifies leaving them in situ rather than removing them simply because they are considered unsightly when on leisure beaches. The increase in abundance in rocky subtidal areas of crustose coralline seaweed following the mass bleaching and death of corals was first observed in Abu Dhabi in the late s George and John , , The increased importance of crustose corallines has been confirmed by a study of colonisation of tile surfaces in which these seaweeds were a major component of the settlement community and this led Bento et al. The crustose corallines play an important role in coral-dominated areas by reinforcing dead coral skeletons. Seaweeds are known to induce the settlement of coral larvae Ritson-Williams et al. This has important implications given the increasingly degraded nature of coral reefs around the UAE since such beneficial coral-algal interactions might aid their recovery. Crustose corallines are able to survive where wave-exposure is extreme, hence are conspicuous on wave-beaten shores such as the rocky headlands along the northern coast of Fujairah John These are predominant and sometimes the only conspicuous seaweeds to survive in submarine rocky areas where there is chronic grazing by large aggregations of the black sea urchin Echinometra Fig. Crustose seaweeds persist because they have a subsurface growth or meristematic layer that continually replenishes the outer surface cells removed by the scraping or rasping of urchins. One of the only threats to crustose corallines comes from parrotfish that feed by removing entire portions of crust along with any branches or surface nodules, although parrotfishes are relatively rare along the southern Gulf coast of the UAE Hoey et al. So far 16 species of crustose coralline seaweeds have been recorded in the UAE John and Al-Thani of which three are only known from Fujairah. All these corallines were originally described in three unpublished reports written in the late s by Dr Yvonne Chamberlain, a specialist in crustose corallines, and reproduced in a report prepared for what was then the Abu Dhabi Company for Onshore Oil Operations John and George There is an urgent need for a taxonomic revision of this increasingly important, and yet much neglected group of seaweeds, ideally involving combining the more traditional approach based on morpho-anatomical characters with modern DNA sequence analysis. There have been several studies in the southern Gulf focusing on chemical elements extracted from local seaweeds, and Al-Adilah et al. Less convincing is the suggestion by Farzanah et al. All such studies have focused on a few of the more readily recognised and relatively common seaweeds, including the green seaweed Ulva. A species of Ulva , referred to as Ulva intestinalis , has been discovered to have high concentrations of essential minerals such as potassium, magnesium, iron and zinc, so making it a promising novel food source in the UAE according to Farzanah et al. Other seaweeds investigated elsewhere in the southern Gulf include the seasonally common inflated brown seaweed Colpomenia sinuosa , the so-called peacock tail weed Padina boergesenii, various species of Sargassum and Sarcothalium trinodis. The degradation and decline in coral cover over the last two decades has been very significant and has resulted in new opportunities for seaweeds to colonise and replace them as the spatial dominants in some shallow rocky areas Fig. All indications are that environmental stressors such sea temperature will continue to favour seaweeds that are likely to continue to become an ever more significant component of benthic marine communities. Differences in the composition and abundance of seaweeds between the emirates reflects the availability of suitable substrates for seaweeds, extent of these hard substrates and the amount of collecting effort. Abu Dhabi has received, by far, the greatest amount of attention, in part due to many nearshore and offshore habitats suitable for the development of seaweeds and the presence of extensive rocky areas once completely dominated stony corals see Grizzle et al. Surveys are needed of the seaweeds of those emirates lying to the west of Abu Dhabi since few, if any, records exist for most of these areas see John and Al-Thani The seaweed flora has been scarcely studied in the emirates bordering the Gulf of Oman Fujairah, Sharjah , unlike in the neighbouring sultanate of Oman where they have been well researched and for which over species have been recorded see Wynne The exceptional high seaweed diversity in Oman compared to Fujairah and Sharjah is not just a reflection of greater research effort but, rather, the exceptional development of seaweeds that takes place where there is upwelling of colder, nutrient-rich water along its southern coast during the seasonal monsoon Savidge et al. The rockier parts of the coastline of Fujairah are more comparable to northernmost parts of the Omani coast where seaweed diversity is low due to high air temperatures, desiccation and low nutrient levels B. Jupp, pers. Since the s new coastal and offshore developments in the UAE will have benefitted seaweeds by providing hard surfaces suitable for colonisation, sometimes where none existed before. Although there is no evidence that increasing summer sea temperatures has had an adverse impacted upon the seaweed flora, it is impossible to know whether this will continue to be the case as the environment becomes more stressful. There are a multitude of environmental factors that impact seaweeds, corals and other marine organisms besides sea temperature, including sea water acidity that is increasing in the Arabian Gulf see Uddin et al. The decline in pH and carbonate levels combined with rising CO 2 and bicarbonate levels will be a threat to crustose coralline seaweeds, corals as well as marine invertebrates having shells of calcium carbonate. Uncertain surrounds the threat from acidification because the seawater in the Arabian Gulf is supersaturated with aragonite as a result of regional environmental conditions. One of the groups most likely to benefit from some of the predicted longer-term changes in the marine environment will probably be the Cyanobacteria. These mats will be at risk from storm surges predicted to increase linked in response to rising temperatures in the region. Other risks include inundation resulting from land subsidence linked to oil and groundwater extraction and sea-level rise due to thermal expansion and melting of land-based ice elsewhere on the globe Melville-Rea et al. Seaweeds and Cyanobacteria remain some of the least-researched primary producers in the UAE, with very few genomic studies yet undertaken using DNA sequence data to identify seaweed floras. It is of crucial importance to ensure material is correctly identified and representative specimens suitably stored in national institutions e. For further information on the seaweeds of the Emirates, the following sources are recommended as accessible readings: Al Abdessalaam , John , , John and George , , George and John In: Seckbachm J, Oren A eds Microbial mats: modern and ancient microorganisms in stratified systems, cellular origin, life in extreme habitats and astrobiology. Springer, Dordrecht, pp — Chapter Google Scholar. Motivate, Dubai, pp 55— Google Scholar. Foods 10 10 Mar Pollut Bull — Front Mar Sci — Article Google Scholar. Mar Pollut Bull 51 1—2 — Munksgaard, Copenhagen, pp 42— Burt JA, Bartholomew A Towards more sustainable coastal development in the Arabian Gulf: Opportunities for ecological engineering in an urbanized seascape. Aquat Ecosyst Health Manag 23 2 :1—9. Burt J, Bartholomew A, Bauman A, Saif A, Sale P Coral recruitment and early benthic community development on several materials used in the construction of artificial reefs and breakwaters. J Exp Mar Biol Ecol — Coral Reefs — Chem, struct and morphological defences are often adjusted to spatial or temporal pattern of attack. Bioscience 40 5 — Adv Environ Waste Manag Res 3 1 :1—6. Phycology 2 1 — Springer, Dordrecht, pp 51— Fish Fish — Reef Encount — In: Anon ed Proceedings of the international symposium on the extent and impact of coral bleaching in the Arabian region. In: Anon ed Abstract volume. Marine Atlas Abu Dhabi. Trident, London, pp — In: Seckbach J, Oren A eds Microbial mats: modern and ancient microorganisms in stratified systems, cellular origin, life in extreme habitats and astrobiology Systematics Association Special Volume. Clarendon, Oxford, pp — John DM Marine plants. John DM Marine algae seaweeds associated with coral reefs in the Gulf. Coral reefs of the world 3. John DM Seaweeds and microalgae. Motivate, Dubai, pp — Nova Hedwigia 98 3—4 — Nat Hist Museum, London, pp. Oxford University Press, Oxfordshire, pp — Emirates Heritage Club, Abu Dhabi, pp 95— Lewis JR British rocky shores: the ecology of rocky shores. English Universities Press, London. Front Mar Sci 8. Mar Pollut Bull 62 2 — Coral Reefs 18 1 — Glob Chang Biol 24 6 — Article PubMed Google Scholar. Cont Shelf Res — Academic, Toronto. Univ Calif Publ Bot — Freeman WH, New York. Sci Rep J Environ Monit — In: Sheppard C ed World seas: an environmental evaluation, vol. Academic, Cambridge, pp 1— Phycologist 86 spring — Bot Mar — Download references. Thanks go to the Abu Dhabi Company for Onshore Oil Operations now ADNOC Onshore for providing grant funding to the Natural History Museum in London in order to carry out the marine environmental survey of Abu Dhabi upon which much of this chapter is based, and to the following: the late Peter Hellyer for much invaluable advice and support over many years, Veryan Pappin and Richard Hornby of Nautica Environmental Associates Abu Dhabi who were involved in all phases of my research, Gareth John, Graham Hornby and Chris Teasdale of Nautica Environmental Associates who accompanied me on fieldwork, very special thanks go to David George for his scholarly advice, friendship and providing many of the photos in this chapter. Finally, thanks to the Natural History Museum in London for providing facilities to enable me to undertake the research necessary to complete this chapter. You can also search for this author in PubMed Google Scholar. Correspondence to David M. The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. Reprints and permissions. John, D. Seaweeds of the Emirates. In: Burt, J. Springer, Cham. Published : 01 November Publisher Name : Springer, Cham. Print ISBN : Online ISBN : Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Policies and ethics. Skip to main content. Download book EPUB. A Natural History of the Emirates. Download book PDF. Abstract Seaweeds, Cyanobacteria, seagrasses and mangroves are the principal inshore primary producers in the southern basin of the Arabian Gulf. Fleshy red algae mats act as temporary reservoirs for sessile invertebrate biodiversity Article Open access 13 June Box Yellow-Green Seaweeds Ochrophyta, Xanthophyceae : Cells usually yellow-green due to predominance of a secondary pigment diatoxanthin in the chloroplasts two or more chloroplasts per cell ; unicellular, filamentous, colonial or coenocytic and motile forms with two subapical flagella; walls often with overlapping parts; storage material oil, fat or leucosin never starch Blue-Green Bacteria Cyanobacteria : Single-celled, colonies of large numbers of cells embedded in mucilage or of single filaments or grouped together to sometimes form distinctive filamentous colonies. Full size image. Acknowledgements Thanks go to the Abu Dhabi Company for Onshore Oil Operations now ADNOC Onshore for providing grant funding to the Natural History Museum in London in order to carry out the marine environmental survey of Abu Dhabi upon which much of this chapter is based, and to the following: the late Peter Hellyer for much invaluable advice and support over many years, Veryan Pappin and Richard Hornby of Nautica Environmental Associates Abu Dhabi who were involved in all phases of my research, Gareth John, Graham Hornby and Chris Teasdale of Nautica Environmental Associates who accompanied me on fieldwork, very special thanks go to David George for his scholarly advice, friendship and providing many of the photos in this chapter. John Authors David M. John View author publications. About this chapter. Cite this chapter John, D. Copy to clipboard. Publish with us Policies and ethics. Search Search by keyword or author Search. 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