[ { "id": 210233, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1984", "page_number": 204, "title": "RAS-1984", "content_text": "183\n\nmarsh, which has been enclosed by bunds to form kei wais, (iv) a shallow channel running parallel to the outer bund; (v) a zone of mangrove plants some 15-25 m. wide with Kandelia candel, Avicennia marina and Aegiceras corniculatum as the commonest species, (vi) Deep Bay, which forms part of the estuary of the Pearl River and also receives water from the Sham Chun River and smaller streams. At intervals channels run through the mangrove zone to join channel (iv) beside the outer bund to Deep Bay; water moves along these channels during the rise and fall of the tide and thus the kei wais are filled.\n\nWithin the kei wais are small, irregularly shaped, muddy islands. Essentially all of our results were obtained from Mai Po kei wai No. 7 (total area ca 9.3 ha, area of islands 5.6 ha, area of open water 3.7 ha). This kei wai is 820 × 120 metres with its shorter sides parallel to the shoreline. It is surrounded by a bund which, on the seaward side, is pierced by a sluicegate with a concrete frame. The frame is about 2 m. wide and is usually closed by a gate consisting of heavy wooden planks, placed horizontally, which can be raised or lowered in slots in the concrete frame (Plates 7-9). The sluicegate is essential to the operation of the kei wai because it enables the operator to control exchange of water between the kei wai and the adjoining estuary. The kei wai, like others in the neighbourhood, was held on lease renewable every seven years.\n\nSource of Future Produce\n\nAs already mentioned, an important source of future produce is the adjoining estuary: fry and larvae are carried on the high tide through the open sluicegate into the kei wai where they are \"trapped\" when the gate is closed. Species entering in this way include marine fish, shrimps and crabs. In addition, the source of produce is supplemented and diversified by the operator, who may add fry of tilapia (Sarotherodon mossambicus, syn. Tilapia mossambica) and the brackish-water striped mullet (or grey mullet, Mugil cephalus). Small oysters (Crassostrea gigas) are bought from local fishermen and used to stock oyster beds set up in the vicinity of the sluicegate; their growth period is 1.5 to 3 years.\n\nThe basis of production of the kei wai is the usual two food", "txt_file_path": "txt/dfo323lmgvd/RAS-1984.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/5h73wh572", "rank": 0 }, { "id": 213589, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 185, "title": "RAS-1995", "content_text": "156\n\ngrow in isolated patches around our coastline. Also, few species are present, and so a list for Hong Kong (Table 1) would contain only 8 species (Hodgkiss, 1986).\n\nHodgkiss, Thrower and Man (1981) give colour illustrations of these species together with some mangrove associates and they are described by Hodgkiss in a WWF (undated) pamphlet. Hodgkiss (1986) also provides a key for their identification.\n\nAdaptations of mangrove plants\n\nBecause of their location at the fringes of land and sea, mangrove plants face three major problems: an unstable substratum, anaerobic conditions and high salinity.\n\nMud is a shifting substrate and to overcome this problem some mangrove plants have root systems which either spread out horizontally just beneath the substrate surface (cable roots) as in Avicennia (Fig 1), or they produce supporting roots from the main stem (prop or stilt roots) as in Kandelia (Fig 1) and Bruguiera, or they produce upwardly projected ridges from their main lateral roots (buttress roots) as in Heritiera (Plate 1).\n\nSome mangroves (Kandelia, Aegiceras, Bruguiera, Avicennia) produce seeds which develop while the fruit is still attached to the plant and so do not undergo the normal period of seed dormancy before germination - a state known as vivipary. Kandelia (Fig 2a) and Bruguiera (Fig 2b) show true vivipary in that the developing hypocotyl ruptures the pericarp forming the so-called 'dropper', whereas the other 2 species, Aegiceras (Fig 2c) and Avicennia (Fig 2d), exhibit cryptovivipary since no rupture of the pericarp is involved during initial embryo development.\n\nVivipary allows rapid growth and establishment of the young plants when they are finally detached from the parent plant and come into contact with the substratum. In the case of those which produce 'droppers' this can be almost instant in that, as soon as the dropper touches the substrate, adventitious roots are produced from the tip of the hypocotyl and the plant becomes established before it can be washed away (Plate 2). Alternatively, if the dropper lands in water, it floats,", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213590, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 186, "title": "RAS-1995", "content_text": "157\n\nand can be dispersed some distance and will retain its viability for several months until reaching a suitable substrate. In the case of Avicennia and Heritiera (a non-viviparous form producing large, woody, one to several seeded keeled fruits - Plate 3) the fruits have spongy outer layers which afford extra buoyancy.\n\nThe other non-viviparous forms Excoecaria and Acanthus have an exploding capsule releasing numerous seeds, and Lumitzera produces an indehiscent single-seeded fruit. In these forms seed dispersal and development follow the normal pattern.\n\nBecause of the reduced supply of oxygen in the mud, the mangroves require an additional air supply. Forms such as Avicennia produce lots of upright root branches called pneumatophores from their cable roots (Plate 4). These pneumatophores contain aerenchyma (Fig 3) (specialized cells with large air spaces between) so that air transfer can readily take place. Bruguiera (Fig 4) and Kandelia produce bends in their roots which push up above the substrate surface (knee joints). These knee joints are again rich in aerenchyma to facilitate the transfer of air. Both pneumatophores and knee joints have special areas of thin-walled cells at their surface (lenticels) for gaseous exchange.\n\nAt high tide, the water within the substrate is highly saline, and mangrove plants are adapted in several ways to overcome the problems of high salt concentrations in their internal tissues. Like halophytes in general (plants which grow where salt concentration is high), mangroves can tolerate relatively high internal salt concentrations (Table 2). In addition, however, some are “salt excluders” (e.g. Kandelia) and physiologically prevent the entry of salts into the root tissues by a special ultrafiltration method. Any excess salt in the tissues is removed by an active pump mechanism. These forms thus maintain a salt concentration in their tissues which is only about 10% of that found in the non-excluders.\n\nOther (e.g. Avicennia (Fig 5) and Acanthus) are \"salt excreters\" and continually remove salt from their tissues via salt glands in their leaves; others (e.g. Bruguiera and Lumnitzera (Fig 8)) store salt in vacuoles or even in crystalline form in their leaves so that it is physiologically inactive and will be lost at leaf fall; while others use more than one method (e.g. Excoecaria stores salt crystals and is a...", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213591, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 187, "title": "RAS-1995", "content_text": "158\n\n“salt excluder”, and Aegiceras has salt glands and is a “salt excluder”).\n\nMangroves also show morphological characteristics related to their \"physiologically xerophytic\" habitat (where water must be conserved to reduce the intake of high salinity water). Thus, many have water storage tissues in their leaves (Avicennia, Aegiceras, Lumnitzera (Fig 6), Kandelia). Many have a waxy thick cuticle and epidermis, and have stomata restricted to the lower leaf surface (Avicennia, Aegiceras, Kandelia, Excoecaria). In Avicennia the stomata are sunken and this species also has the undersurface of its leaves covered by blunt hairs (trichomes) to prevent water loss (Fig 7). Heritiera has its lower leaf surfaces covered with scales for the same purpose.\n\nIn summary, this plant community is one of the most remarkable aggregations of unrelated families of plants in the world, which have developed in common a number of special characteristics such as modified roots for support and gaseous exchange, water conservation mechanisms, 'salt balance' mechanisms and a viviparous seedling habit.\n\nWhy are mangrove plants important?\n\nBecause of their relatively high natural productivity which may be more than twenty times that of the plankton of open ocean waters and five times that of the plankton of rich coastal waters, mangrove plants are able to support a large number and a wide variety of consumer animals. The falling leaves and other plant debris from the mangroves may either be eaten directly or (and this refers to the greater part) it is colonized by bacteria and fungi and partially decomposed before it becomes available to most marine animals. The leaf particles with their associated rich colonies of microorganisms are then eaten by small fish. Much of the leaf material itself is not digested but is passed back into the water where recolonization by microorganisms begins the cycle again. Eventually the very smallest particles (detritus) will be consumed by detritus feeding animals such as molluscs and crustaceans. At the same time algae will be feeding on the dissolved nutrients released, and they in turn form the diet for more consumers.\n\nThus, fish, shrimps and oysters all depend on the mangroves for their basic food supply. Man has learned to exploit this fact and the commercial rearing of all three groups of animals is common in", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213592, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 188, "title": "RAS-1995", "content_text": "159\n\nmangrove areas (See Irving & Morton, 1988).\n\nIf we choose as our example the Mai Po Marshes in Deep Bay we see that the mangroves, and the mudflats in front of them, support a unique flora and fauna (Morton & Morton 1983) and, together with the tidally operated shrimp ponds (geiwais), have been exploited by man for commercial gain for many centuries. It is the mangrove litter which supports all of these activities. The geiwais are perhaps the best example of commercial use and at Mai Po yield 1500-4000 kg of fish (mainly Tilapia) and shrimps (Gei Wai Ha) per pond per annum.\n\nThe mangrove stands also serve as the nursery ground for both shrimp and fish fry, which again accumulate there because of the abundance of food. The fish fingerlings of grey and other mullets are netted by local fishermen and then raised in nearby ponds for about one year when they reach marketable size.\n\nFarmers also cultivate oysters in this area, the oysters filter feeding on very fine organic detritus and plankton, based again on mangrove productivity (the total Deep Bay oyster crop is some 250 tonnes per annum). Many oyster farmers also trap mudskippers in woven bamboo baskets and, again, these fish are very dependent on mangrove productivity for their survival.\n\nTo the farmers living on the shores of Deep Bay the mangroves also offer a source of firewood and other useful products. Thus, the tallest Kandelia provide timber, fishing stakes, firewood and charcoal, and from the bark can be obtained various tannins; Acanthus fruits are used medicinally as a blood purifier and boil dressing while their leaves are used to cure rheumatism and their dried roots are used in the treatment of hepatitis, cancer and asthma; Avicennia seeds yield a resin used to treat ulcers and tumours, and an infusion of the bark is a medicine against parasites and a balm for gangrenous wounds; Excoecaria sap is used as a purgative, and finally Derris roots contain rotenone, a powerful fish poison, used in fish culture to harvest the fish.\n\nThe modern availability of fuel resources and other materials and of western medicine has led to a decrease in utilization of mangroves for these purposes. Now their major value lies in their role in", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213594, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 190, "title": "RAS-1995", "content_text": "161\n\nhighly productive area for fish and shrimps and, as a result, will cease to be the venue for the enormous variety of wading birds that congregate there as they overwinter or merely rest on their migratory flight.\n\nREFERENCES\n\nHodgkiss, IJ, Thrower, S L & Man, S M (1981). An introduction to the Ecology of Hong Kong (2 volumes) Federal Publications, Hong Kong\n\nHodgkiss, I. J. (1986) Aspects of Mangrove Ecology in Hong Kong Memoirs of the Hong Kong Natural History Society 17 107-116\n\nLiving, R & Morton, B. (1988) A Geography of the Mai Po Marshes. Hong Kong University Press.\n\nMorton, B. & Morton, J (1983) The Sea Shore Ecology of Hong Kong Hong Kong University Press\n\nWWF HK (Not dated) Mangroves. Mai Po Nature Reserve Pamphlet issued by Worldwide Fund for Nature, Hong Kong\n\nPLATES\n\nPlate 1 Buttress roots in Heritiera\n\nPlate 2 Kandelia plantlet developing from 'dropper'\n\nPlate 3 Heritiera fruit\n\nPlate 4 Avicennia tree plus pneumatophores\n\n[These will be published in a later Journal - Editor]", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213595, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 191, "title": "RAS-1995", "content_text": "162\n\nTable 1. Mangrove species in Hong Kong\n\nAcanthus ilicifolius L.\n\n(Acanthaceae)\n\nAegiceras corniculatum (L.) Blanco\n\n(Aegicerataceae)\n\nAvicennia marina (Forsk.) Vierh.\n\n(Verbenaceae)\n\nBruguiera conjugata (L.) Merr.\n\n(Rhizophoraceae)\n\nExcoecaria agallocha L.\n\n(Euphorbiaceae)\n\nHeritiera littoralis Dryand. ex. W. Ait.\n\n(Sterculiaceae)\n\nKandelia candel (L.) Druce\n\n(Rhizophoraceae)\n\nLumnitzera racemosa Willd.\n\n(Combretaceae)\n\nTable 2. Salt concentration and salt exclusion/secretion/deposition in the various mangrove species.\n\n \n Species\n Salt cone\n Salt excluders\n Salt glands\n Salt crystals\n g/L in leaf\n \n \n Kandelia\n \n X\n \n X\n 0.08-0.9\n \n \n Excoecaria\n \n \n X\n X\n 0.8-3.4\n \n \n Aegiceras\n \n \n X\n X\n 0.9-1.8\n \n \n Bruguiera\n \n X\n \n X\n 4-11.4\n \n \n Avicennia\n \n \n X\n X\n 6.7-11\n \n \n Acanthus\n no data\n X\n \n \n \n \n \n Lumnitzera\n no data\n X\n \n X\n \n \n \n Heritiera\n no data\n X\n \n X", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213596, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 192, "title": "RAS-1995", "content_text": "Fig 1 Cable roots (e) and pneumatophores (p) in Avicennia (upper) and prop roots (r) in Kandelia (lower).\n\nt = trunk; n = nutritive roots; s = support roots,\n\nPage 163", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213597, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 193, "title": "RAS-1995", "content_text": "164\n\nX\n\nFig 2. Viviparous fruits: a - Kandelia; b - Bruguiera; c - Aegiceras and d - Avicennia.\n\nT", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213598, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 194, "title": "RAS-1995", "content_text": "Fig 3 Section through a pneumatophore of Avicennia A = aerenchyma, C = cortex; L = lenticel; X = xylem\n\n165", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213600, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 196, "title": "RAS-1995", "content_text": "167\n\nFig 5. Salt gland of Avicennia. Left in section; \n\nright in surface view.", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213602, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1995", "page_number": 198, "title": "RAS-1995", "content_text": "Fig 7. Sunken stomata (S) and trichomes (T) in Avicennia.\n\n169", "txt_file_path": "txt/dfo323lmgvd/RAS-1995.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/95941j25g", "rank": 0 }, { "id": 213930, "series_id": 26, "series_slug": "histsyn-rashkb-journal-engine", "series_title": "RASHKB Journal 皇家亞洲學會香港分會學刊", "series_use_hku_proxy": false, "document_key": "RAS-1996", "page_number": 282, "title": "RAS-1996", "content_text": "260\n\nAvicennia tree plus pneumatophores", "txt_file_path": "txt/dfo323lmgvd/RAS-1996.txt", "external_url": "https://digitalrepository.lib.hku.hk/catalog/3n209j641", "rank": 0 } ]