Study of some species of mollusks living clung, perforated on the tree mangrove and management capabilities in reducing their harm

MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND AND TRAINING RURAL DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURAL SCIENCES  HOANG THI THUY DUONG Study of some species of mollusks living clung, perforated on the tree mangrove and management capabilities in reducing their harm Specialization: Plant Protection Code: 62.62.01.12 SUMMARY OF Ph.D THESIS HA NOI - 2016 The research work was conducted at: VIETNAM ACADEMY OF AGRICULTURAL SCIENCES Supervisiors: Prof.Dr Nguyen Van Tuat – Vietnam Academy of Agriculture Sciences Assoc.Prof.Dr Nguyen Dang Hoi – Vietnam- Russian Tropical Center - Critic 1: - Critic 2: - Critic 3: The thesis was presented in the PhD dissertation commitees of Vietnam Academy of Agricultural Sciences at … in… th 2016 This thesis an be referred to at: - Vietnam National Library - The Library of Vietnam Academy of Agricultural Sciences INTRODUCTION The urgency of research The great role of mangrove forestfor nature and man been known as prevent soil erosion, limit the impact of natural disasters, where the livelihood of the people, the breeding ground and the habitat of many marine species There are many reasons degrade mangrovesin the world and our country, including the cause of global climate change, human abilities deforestation, pollution Very early on, the Party and state have plans to develop mangrove area nationwide, reforestation work is done in the coastal localities Some difficultiesinplanting mangrovesis detected,e.g.: locals not fully understand the role of mangroves, plants are not adapted for growing conditions, environment pollution.Actual investigation lasted several years, focusing on the 2009 - 2015 show that the influence of mollusks for the life of the mangroves is that needs close attention and is one of the elements impair the development of mangroves in both acreage and quality Mollusks mangroves are diverse and plentiful, they include species of bivalve layer, a shell plate, gastropods, cephalopods, Due to the wide distribution, has an important role in nature and in human life, were very much scientists worldwide research interest in various aspects such as research on taxonomy, biology, ecology, In Vietnam, mollusks also been interested in research and have remarkable results in the fields of investigation classification, species composition; biology, ecology; Biodiversity research and resources; food and nutrition; breeding and rearing However, until now, research the harmful mollusks mangroves is very limited and there is no adequate research has been published Derived from the practical requirements above, the consent of the Ministry of Education and Training, Institute of Agricultural Sciences Vietnam, thesis " Study of some species of mollusks living clung, perforated on the tree mangrove and management capabilities in reducing their harm " has been made The aim and requirements 2.1 Aim Identification of species harmful mollusks on mangroves: study the characteristics of biology, ecologyand proposed management measures to reduce the harmful effects of mollusks for mangrove trees 2.2 Requirement - Investigate to determine the composition mollusk species in some typical areas of mangroves in Vietnam - Identify mollusk species have caused damage to the mangroves - Study biological characteristics, ecology of some harmful mollusks - Studyandevaluate the impact of mollusksonmangrove trees - Proposed management measures to minimize the harmful effects of mollusks on mangroves The scientific and practical significances of subject 3.1 Scientific significance - Identify the major species in mangrove areas Cat Ba National Park, Con Dao National Park, Biosphere Reserve of Can Gio - Provide data on some biological characteristics, ecology of mollusks in the mangrove sand their harmful ways 3.2 Practical significance - The results of the study help to build integrated management measures for species at risk of harm to the protection and development of mangroves efficient and sustainable - To preserve and exploit the beneficial mollusks serve economic development of mangroves, risk prevention, damage in the development of mangroves, especially in new growing areas Objects and scope of the research 4.1 Objects - Mollusks (Mollusca), with primitive mouth (Protostomia), Delimitating multicellular animals (Metazoa) and belong to the invertebrates (Invertebrate) - The mangrove species of mangroves Cat Ba National Park, Con Dao National Park and Biosphere Reserve of Can Gio 4.2 Scope of the research + Scope of the study: The study of species harmful mollusk in mangrove area Cat Ba National Park, Con Dao National Park and Biosphere Reserve of Can Gio; study the characteristics of biology, ecology of mollusks; recommended management measures to minimize harm caused mollusks for mangrove trees New contributions of the thesis - Develop a list of species of mollusks mangrove area Cat Ba National Park, Con Dao National Park, the Biosphere Reserve of Can Gio - Detect mollusk species harmful mangrove areas in Cat Ba National Park, Con Dao National Park, the Biosphere Reserve of Can Gio and study the characteristics of biology, ecology live mollusks clinging, harmful to mangroves - Proposed measures to reduce the harmful effects of mollusks in mangroves and building synthetic process their harm reduction The thesis structure The thesis has 163 pages, including the opening pages Chapter is introductry and defines scientific basic and documents use in research (28 pages) Chapter illustrates the materials, content and methodology (17 pages); Chapter shows the results of research and discussion (82 pages); Conclusions and recommendations (2 pages) include 22 tables, 42 figure Reference Documents including 110 items, which 64 Vietnamese documents, 43 England documents and Russian documents CHAPTER I: BASIS OF SCIENCE AND OVERVIEW OF DOCUMENT 1.1 The scientific basis of the research The harmful mollusks to mangrove trees had been dentified in the field and researchers mention in their study as Phan Nguyen Hong(2004), Nguyen Quang Hung(2008) However, until now, there are no studies completed on the composition of harmful animals The general situation of our country's mangrove forests and the world are in decline, while natural disasters, environmental pollution, climate change and increasingly complex threats to human safety Consequently, the plantation and protection of mangroves are a matter of urgency However, in fact, mangrove planting not achieve good results for many reasons, but one of the most important cause is the destruction and killing trees by live mollusks and perforated on the tree caused According to Phan Nguyen Hong (1999), along with the investigation, the study from 2005, in which the focus from 2009 to present, up to 30% of young trees die due to causes mollusks Determining the composition of species harmful mollusks and their characteristics are the basis of the proposed mitigation measures, improve the efficiency of crops, expanding the area of mangroves, Determining the composition of species harmful mollusks and their characteristics are the basis of the proposed mitigation measures, improve the efficiency of crops, expanding the area of mangroves, meet forestationtargets in the coastal localities 1.2 The recently status of mangrove forests in the world and Vietnam 1.2.1 The recently status of the world's mangroves The world has about 18 million hectares of mangrove forests, the Southeast Asian countries accounted for 35% of the area, which, in the Indian Ocean are the most diverse mangrove forest with 50 species (Spalding, 2010) Mangroves have been faced with many challenges such as mangrove forests in the world continuously declining 1.2.2 The recently status of mangroves in Vietnam In the report of biodiversity in Vietnam 5th by the Ministry of Natural Resources and Environment shall, (2014), has statistics: in 2012, 56% of the total areas of mangrove forests in Vietnam are considered "plantation"with the variety of species is very low The natural mangrove forests have almost completely disappeared Mangrove forest degradation is evident through the rapid decline in both area and quality of forests In 1943, there are over 408 500 hectares of mangroves, in 1990, the area of mangroves to about 255,000 hectares, 209,741 hectares reduced to in 2006, and 140,000 in 2010, only 131, 520 hecta of forest rest by the end of 2012 1.3 Research situation mollusks 1.3.1 Research situation mollusksworldwide 1.3.1.1 Classify Mollusksareinvertebrate - mollusks, with features such as body puree, can have limestone crust to protect and support, depending on the environment that the crust and body composition subject to change Research classify mollusks were conducted very early From ancient Greece (322-384 years BC), the philosopher Aristode has many studies on mollusks classification.He was the first founder of the discipline of mollusks and given classification method, he divided them into two big groups are groups with no crust and crust groups However, his method of classification is mainly based on external morphological characteristics of them By the mid 18th century, Linne and his colleagues have inherited, developed a method of Aristode classification and construction of "Systema Nature, 1758" The second half of the 19th century to the early 20th century, scientists like Deshayer (1853), Tryon (1884) studied and classified many species of mollusks distributed in many seas of the world, especially in regions Indian Ocean and the Pacific To 1939, Shintaro described, identifiedis 359 species of mollusks and distribution characteristics outlined in the Sea of Japan, Pacific In Southeast Asia, Zhang Billion (1960) studied and described the morphological characteristics, structure, distribution of more than 200 species of mollusks in the East Sea, of which many species are discovered in Vietnam 1.3.1.2 Biology, ecology Due to the wide distribution in most of the world's seas and importance in the fields of economic, biological, ecological and environmental protection, should mollusks were so many scientists on the world of research interest, typically such studies Barnes & Hughes (1999) on ecological characteristics of the class Bivalve In his research, Barnes & Hughes has described mollusk has parts: head, body and legs, the body of most species have bilateral symmetry These characteristics continue to be studied and used in the descriptionof mollusksinthe recent Brand's research (1972) on the mechanism of blood circulation Anodonta anatina species showed an open circulatory system of species including the atrium and ventricle, circulation cycle: heart - gaping slit system - the kidneys –gills - heart; According Coe (1943), mollusk is gender division as: male and female clear or bisexual, male and female in one individua Between these two categories, there are intermediate forms The vast majority of primitive mollusks are clear gender division The distinction maybe based on the male genitalia or copulatory organs, shapes and different sizes of males and females; Research of Comfort (1957) about the life cycle and reproductive characteristics, the growth of many species of mollusks, reproductive method of mollusks are plentiful There are self-fertilized species, there are species which have both male and female However, generally there is coordination between the male and female elements The phenomenon of mating between the male element can be fertilized in or external fertilization 1.3.1.3 Research on the harm of mollusks and control measures harmful mollusks Studies of harm and prevent harmful mollusks almost exclusively focused on the yellow snail species live on land and harm agricultural crops There are also some studies on mollusks published mentioned the pests, but these studies have not addressed specifically about harmful influence of mollusks On the other hand, subject to harmful mollusks are not host plants, such astypical: Studies of harm and prevent harmful mollusks almost exclusively focused on the yellow snail species live on land and harm agricultural crops Also, there are some studies on mollusks published mentioned the pests, but these studies have not addressed specifically about harmful influence of mollusks On the other hand, subject to harmful mollusks are not host plants, such as typical: Hunt &Scheibling studied (1998) on ecological distribute in space and time of the green mussel on the stone reefs in coastal zones The researchs by Hunt & Schilling (1998) about the distribution of spatial ecology and time of green mussel on the stone reef in the coastal zones published Researchs had shown the distribution of green mussel in the stone reefs zones, although not rated harm that study the distribution of green mussel but this study has shown the influence of this mollusks species for stone reef and stone works Quayle's study (1988) on the Pacific oyster in waters Columbia This oyster species are bred for commercial, however, the Ministry of Natural Resources and Environment said the Pacific oyster species that affect survival of many species of zooplankton and larger animals It is easy to see that the research works on harmful mollusks are rarely The mollusks are studied and perceived to be harmful primarily for the hosts as the reef, ships, boats and other construction work Studies onthe effects of harmful mollusks and control measures harmful mollusks should be supplemented and further strong interest 1.3.2 The situation of domestic research 1.3.2.1 Investigation of species composition Vietnam is a country located in the tropics, the East and South are landlocked, many bays, there are hundreds estuary empties into the sea, creating diverse mollusk fauna is rich in species composition , including many species of high economic value, many rare species characteristic for the waters of Vietnam (Nguyen Huu Phung and cs.1996) Since 1905-1906, Dautzenberg and Fisher (1906) was the first to conduct investigations, fundamental research on species composition, structure, distribution of mollusks Vietnam Until 1906, the two authors have collected 97 species in the coastal areas of Thanh Hoa The general survey of Vietnam-China cooperation in the North Bay (from year 1959 to 1960), has identified 336 species of mollusks, for the years 1974 to 1980, the authors conducted a test, determined all kinds of mollusks form The results have identified 369 species belonging to 174 genera and 87 families in the same layers In particular, the class of bivalve (Bivalvia) has 160 species, 74 varieties of 36 of them (Nguyen XuanDuc, 2003) In 1978, Nguyen Van Chung et al also announced 190 species of mollusks investigation BinhCang Bay - NhaTrang, where animals classes Bivalvia includes 70 species, common species is common Mitram elegera, Vexillum cruentata, cerithium kochi, Turitella terebra, Meretrix tribulus (Nguyen Van Chung et al, 1997) Nguyen Chinh (1996) summarized the research and introduction of 88 species of mollusks have economic value in Vietnam Sea, bivalve class includes 24 species, each specie is described on characterized morphology, geographical distribution and economic value, this is one of the important documents for reference and distinguish the types of fauna quickly Bivalvia in Vietnam 1.3.2.2 Biology, ecology Nguyen Huu Phung (1999) investigated the biological characteristics and resources Blood cockle (Anadara granosa) in the coastal region of Vietnam has described, in the natural, blood cockle distribution mainly in the small and medium bay tidal Besides, Nguyen Huu Phung et al (2001) also studied and described some of the biological characteristics of species of brown shell (Modiolus philippinarum Hanley, 1843) in the waters of NinhThuan By 2003, this author continues to research and describe some of the biological characteristics of species of brown shell (Modiolus philippinarum Hanley, 1943) in the waters of BinhThuan Nguyen Thi Xuan Thu (1998), have studied in some detail and full of reproductive characteristics, growth and production techniques of species Scallops (Chlamys nobilis Reeve, 1952) have described, Scallops large shells, nearly round, length and height are equal, diverse in color casing, the growth plates closely together 1.3.2.3 Research on the damage and control measures From the old days till now, the most mollusks are studied with the purpose of assessing the value of diversity and resources, only a handful of which are soft-bodied research and assess damage on some crops shallow planting as slugs, snails and yellow snail Năm 1967 - 1969, Nguyen Xuan Duc et al thematic survey they Ha wood (Teredinidae) in coastal waters from Mong Cai (QuangNinh) to Door Day (Ninh Binh) obtained multiple animal samples Bialvia Result analysis has identified 22 specimens of their species Teredinidae (including 10 species sp) Existing specimens stored at the Institute of Marine Environment and Natural Resources However, this study limited at the level of investigation of their species composition (Nguyen XuanDuc, 2003) In our country, since the 1960s the harmful mollusks began to be interested in, research Derived from the ships, rafts, wooden materials at sea was the attack of a damaged mollusks The researchers sought to understand, classify and identify some of their species Teredinidae Then, the method toprotecg vessels and rafts and marine equipment made of wood materials have been proposed in two directions is the use of high temperature fire and used chemicals destroy Chapter II: RESEARCH CONTENT, MATERIALS AND METHODOLOGY 2.1 Materials research Use of equipment, chemicals and laboratory instruments, laboratory chemicals field 2.2 Research content Study on characteristics of mangrove area of Cat Ba, Con Dao, Gio Study on mollusk species studied area Identify pests and characteristics of the pests Study the effect of the pests to the mangroves Recommend measures to reduce the harmful effects of the mollusks to mangroves 2.3 Research methods 2.3.1 Study methodology natural features mangrove area Cat Ba National Park, Con Dao National Park and Biosphere Reserve of Can Gio • Investigation of mangrove plant research areas: according to section, online surveys ensure passing define habitat of mangrove trees Classification is based on the classification system of Pham Hoang Ho combined evaluation and classification of experts • Distribution of the intertidal zone, based on the principle of division of Stephenson tidal area (1949) • Measure the water environment indicators: using portable measuring equipment Hanna Establish measuring stations in the study area and measured seasonally Classification of countries according to the scale of distribution of Zernop (1934) 2.3.2 Research methods for components of mollusk species Survey methods, data collection in the field, analyze, evaluate biodiversity and resources mollusks shall comply with the instructions in the documentation of the WWF (2003) Classification Model: Using the latest classification system now Author Beesley et al (1998) 2.3.3 Method of determining the pests and their characteristics: Identifying pests based on their behavior 2.3.4 Research Methodology effects of the pests to mangroves Count mortality (CC) and mollusks live clinging plants (TMSB) using the formula: CC or plant number TMSB Rate% CC or TMSB = - x 100 The total number of trees to be monitored 2.3.5 Construction propose measures to reduce the harmful effects of mollusks to mangroves: Effectiveness of plant protection products on mollusks formula Henderson – Tilton 2.3.6 Data processing methodology: To Use Excel and Primer 6.0 software to process and analyze the data 2.4 Research location and time: 2.4.1 Research location: - Laboratory of Tropical Ecology Institute (Vietnam-Russia Tropical Centre); Plant Protection Institute, Fisheries Research Institute, 11 3.3.2 Characteristics of harmful mollusks on mangroves 3.3.2.1 Characteristics of Saccostrea cucullata(Born, 1778) ClassisBivalvia OrdoOstreoida FamiliaOstreidea Genus Saccostrea • Morphological characteristics and structure of the body Crust thick, heavy, abdomen edges curved Crust shape significant changes, usually oval shaped or triangular, height and length of the shell is not stable, opaque white, outside shaggy, rough Oysters have uneven shell piece, a large shell containing introspective piece, small is piece lids Deep concave surface of milky white crust, stain adductor muscle behind his back near the edge of the shell, light brown The two crusts are closed in, opened by two front adductor muscle and the rear muscle Simple digestive system, intestine before mouth, the two sides have two lobes mouth, long midgut section, are rolled into song in the body, into the hindgut in the back position There siphon drainage and suction Unisexual reproductive system Gonads are in the body, surrounded by intestines Respiratory system included gill plates, two outer plates thinner than mitral in Gill's surface have natatory hair, always active causing the water enters, bring food and dissolved oxygen Structure characteristics of gills, their shaped is plates, including gill filaments arrangement the two parties Water goes into gills, bring food The food selection to follow physical properties These lightweight beads, small, finely taken to the mouth, the grained, heavy falling edge of the mantle and was taken out • Characteristics of distribution: Oysters live mainly on the mangrove trees, rocks and other substrates in the intertidal zone • Nutritional characteristics: Saccostrea cucullata is powerful filter feeders group, favorite food is algae and detritus small size Thus, they act as biological filters, water purification • Growth characteristics: Individual size Oysters grown at about 9-10cm shell length, 150250g weight The growth rate of Oyster crusts vary by region and are affected by environmental conditions Water temperature is the most influential factor Low winter water temperatures influence on the growth of the crust 12 • Reproductive Characteristics: Oysters can be transgendered species between breeding seasons Breeding season from April to October Near the breeding season, gonads flourish, white milk Fertilized eggs, hatch into larvae swimming in the water, then look for trees to cling and live there The time from when the fertilized egg to larvae cling 2-3 weeks Fecundity of huge oysters and depending on the size of the individual, eg Oysters parents type 40-80 mm will give 39 million eggs / individual, type of 80-100 mm to 81 million eggs / individual 3.3.2.2 Characteristics of Brachyodontes emarginatus (Reeve, 1858) Class Bivalvia OrdoMytiloida FamiliaMytilidae GenusBrachyodontes • Morphological characteristics and structure of the body Thick crusts, hard, egg-shaped, the top tip, rounded rear section The majority of them two equal crusts but two sides are not equal Growth rings on the small crust, thick, clear Black-blue crust face, the inside is white, silver, smooth, outer edge of a light green color Adductor muscle scars in the rear the quadrilateral shape Its outer surface of the ball, not rough, their size is smaller than Oysters Its legs brown or yellow violet purple as a short stick is located in the abdomen The underside of the foot has a byssiferous gland to a exudate, it is able to cut the silk and silk secreted by new legs, so, they could cling to change their position However, this process only occurs in young body, adult body is very sturdy cling to trees • Characteristics of distribution Brachyodontes emarginatulives in shallow waters, salinity stable, moderate water flow rates We cling to hard objects, such as poles, trees, bridges, and cages, reefs and mangroves They often stick together and form a large crowd However, when conditions are unfavorable (bad environment, lack of food, shelter, cramped, more enemies ) they can move to other places in the leg sticking out and silk They grow in seawater salinities around 18 ‰ - 32 ‰, preferably 20 ‰ - 30 ‰ Focus on trees clinging to the large crowd to ensure the safety of the individual against threats from enemies, unfavorable environment, as well as take advantage of the power of a collection of individuals • Nutritional characteristics: Brachyodontes emarginatusis following filter feeding group, favorite food is phytoplankton and suspended organic matter It is 13 nutrition constantly, even at high tide, shallow tide, however, the declining nutritional when shallow tide • Growth characteristics In the shallow waters , individuals are often under developed due to less nutrition Brachyodontes emarginatus is the slow-growing species Mature individual with 2-3 cm shell length The growth of Brachyodontes emarginatuson is the thickness of the crsust and add on the extra length of the crust If the crust thickness increases, then the length of delay And reverse, if the crust length increased then the crust thickness of delay In addition, the growth rate of crust and meat also uneven, depending on the growth stage Growth between individuals of the same species are very different • Reproductive Characteristics Most of them are analyzed (male - female separately), but in the course of life due to the change of the weather conditions, temperature, salinity, food should be bisexual phenomenon or denaturation Thus, in terms of sexual, can includes: male, female, bisexual The proportion between these categories are not fixed and vary with the size of them They can breed all year round In the North, they have main breed seasons: The beginning of the year from March to May, late service from September to October In the breed season, females gonads is the brick red, male gonads is fawn colour 3.3.2.3 Characteristics of Anomia cytaeum (Gray, 1850) Class Bivalvia OrdoPectionoida FamiliaAnomiidae Genus Anomia • Morphological characteristics and structure of the body Crusts of Anomia cytaeum, they are round or oval light The body flat, symmetrical two sides No front adductor muscle, the behind adductor muscle is degeneration Anomia cytaeumis clinging to the host Because sedentary lifestyle, adapted to the water filter life, clinging on in the process of life, so reduce the head, legs bottom is blade shape, sticking out when they move The mantle cavity is development than other mollusks The shell consists of 2-piece contains the whole body Species Anomia cytanium is reducted legs, they move by abruptly closed by mode crusts, creating water jets unto two hinges to swim toward the opposite behind, the leg is secreting silk gland to clinging on the tree 14 The crust consists of two pieces, covering sides, attached to each other on the back thanks to ligaments and joints A externodorsodorsal link together by closed teeth, they are similar in size • Characteristics of distribution They are distributedin the mangroves, onthereef, coraldebris They live in the water sector is slow,less opaque • Nutritional characteristics: They feed on organic debris deposited residue, small animals and phytoplankton Digestive system including the mouth, esophagus, stomach, midgut, hindgut and hepatopancreas The esophagus is a large tube connected to the front of the stomach Followed by a long midgut, roll into pieces Siphon drainage near the anus, in the pallial sinus Plates mouth and stomach have a muscles strong, acts as a grinding plate for grinding food • Reproductive Characteristics Their eggs develop in the gill plate, forming larvae which structure adapted to clinging and called larvae glochidium Glochidium have two pieces crust, have cling thorny and cling gland, but feet, mouth, anus and digestive tract undeveloped Larvae under water through the drain line and then hit the bottom or sticking to animals (fish, shrimp ) Often we cling to fins, gills of fish as parasites, and after about 20 days to leave the hosts hit the bottom to grow to the adult form Based on the ability of ectoparasitic on other animals to mollusks larvae may use to expand food and dispersal ability of species distribution 3.3.3 The invation and symptomatic on trees when mollusks clung and damaging to trees 3.3.3.1 The invation of mollusks on the trees Two mollusc species are nourished, those are mollusks which clinging with high levels on the mangrove trees in the mature stage to observe and study the cycle of the invation as follows: • Saccostrea cucullata Investigations, sampling and anatomical observations that: Oyster’sbreeding season ranges from April to October every year The individual big size, crust intact, shell length average size of 9-10 cm, height shell about 12.5 to 14.5 cm and the average body weight of about 600 - 1400g that individuals with high fertility In conditions of temperature 28 - 300C, salinity 18-30 ‰, after 20 days of larval oysters appear foot-move and to be ablity cling • Brachyodontes emarginatus 15 Through field investigation and observation, anatomy shows that the size Brachyodontes emarginatus is around 6.5 to cm, which is already on the 1-year-old from the larval stage, this is the stages genital gland mature After 20 days of larval appear, it have footmove and to be ablity cling Thus, studying the invation of mollusks on mangrove have given the cycle is as follows: As individuals mature parents, eggs and sperm come together to form gametes develop self due in water, approximately 2-3 weeks after start forming clinging silk will find hosts clung on mangrove trees After clinging fixed to the host, where they will continue to grow and develop, continue to the next generation In the course of life, the process of catching prey, toxic waste and their activities affect the growth and development of the host cause stunting, even lethal tree 3.3.3.2 Symptoms is showned when mollusks live clinging harm on mangrove trees - Scape, roots, leaves are rough - The tree is retardation and stunted when mollusks clinging dense - Dead tree 3.4 Effect of harmful mollusks to mangrove forests In mollusk species found harmful, there are common species widely distributed across all study sites are: Hau (Saccostrea cucullata), Diep (Anomia cytaeum), Queo (Brachyodontes emarginatus) So, mollusks species are continues to be selected in the study of the level of mollusks clinging on mangroves It is investigated in the nature that, the period from planting seedlings to months is the period the tree vulnerable under the impact of the environment and the creatures around This phase was easy attacked by cling and harmful mollusks species When mollusks harm to mangroves, it will be stunted and retarded Thus, it would affect the productivity and efficiency of mangrove According to observers, the plants affected by harmful mollusks include Duoc, Vet, Su, To clarify on this, experiments on the effects of mollusks for mangrove trees have been deployed 3.4.1 Assess the level of mollusks clinging damage on mangroves 3.4.1 Assess to the damage level of cling mollusks on mangroves According to the preliminary investigation in the field, the frequency appear of Queo and Hau is high in three areas studied Cat Ba, Con Dao and Can Gio Two species of mollusks cling mainly on stems and roots, they are gather into large clumps form rough, so affect to respiratory activity of forest trees mangrove is done through the vents (the little open space on the stem or roots) 16 Table 3.11 Assess the level of cling of mollusk species harmful for mangrove trees (Van Don, -10 / 2013) Species Formula Su Duoc Vet Other species (individuals / trees) Hàu 74 - 75 40 - 41 46 - 47 10-11 Quéo 123 - 124 52 - 53 - 73 15-16 Điệp - 10 3-4 0-1 StatisticalAnalysis: Table 3.12.The abilities to cling of Hautomangrove Formula Value Su 74,67 ± 25,14 a Duoc 43,67 ± 15,00 a Vet 46,34 ± 16,86 a Other species 10,34 ±03,05 b CV = 19,26% Table 3.12.The abilitiesto cling of Queotomangrove Formula Value Su 123,67 ± 22,30 a Duoc 52,67 ± 30,30 ab Vet 15,34 ± 16,25 b Other species 19,00± 08,54 b CV = 28,40% Table 3.12.The abilitiestocling of Dieptomangrove Formula Value Su 9,67 ± 8,32 a Duoc 3,67 ± 0,60 ab Vet 0,67± 0,60 bc Other species 0,00 ±0,00 c CV = 53,30% The table of results (3:11 to 3:14) showed the cling strongest is Queo on all the formulas (Su, Vet, Duoc and other species) and the number of individuals achieve the highest cling on Queo Diep species have the number of individuals clung on all mangrove species under investigation lowest All of three species Hau, Queo, Diep have the number of individuals clung on plant Su highest When statistical analysis showed, the cling of Hau have not the difference between 17 species of Su, Vet, Duoc but there is a discrepancy between the level of cling on the plants with other plants Queo the level of cling on the trees of no significant differences for Duoc but significant differences compared with the level of cling on Su and other species Diep the level of cling no difference between Su and Duoc, the Vet and Duoc, Vet and other trees, but there is significant differences between the level of cling between Su and Vet and other plants Thus, we can see that Su, Vet, Duoc are mainly hosts of harmful mollusks 3.4.2 Assessing the impact of the mollusks to develop mangrove tree height Table3.15.The impact of the mollusks to develop mangrove trees height ( 3-9/2013) Height increases (cm) After1month After2months After3months After4months After5months After6months Formula Trees have hamrful mollusks 1,36±0,10 2,83±0,20 1,81±0,41 1,48±0,41 1,57±0,29 1,06±0,07 Trees haven’t hamrful mollusks 1,70±0,15 3,17±0,39 2,39±0,28 2,16±0,17 1,40±0,37 152,00±0,36 Prob = 0,03 0,04 0,09 0,01 0,05 0,07 T tính = -3,74 -3,17 -2,02 -4,85 2,74 -2,203 Ttest There are many factors that affect the development of mangrove tree height, such as temperature, light, salinity, tidal regime, mollusks are also a factor affecting the development height through the mollusks clinging on a tree sealed air holes on the branches, the leaves, which affect the metabolism of the plant gas and salt waste Su is a species most affected by mollusks So, using object Su to research results more clearly about the impact of mollusks to develop plant height The growth rate over the first months of the tree is shown in the results table 3:15 Results of statistical analysis showed that the growth in Su height is not the same each month The first month, the 2nd and 4th month after planting has noted differences between the growth in height of trees between trees have hamrful mollusks and trees have not harmful mollusks But the difference in height growth in trees 18 unclear all months but the influence of mollusks for plant quality is the problem posed to growers The degree of influence of unclear mollusk in the results table to evaluate the effects of the mollusks to the growth of trees because there are many aspects of the study should be considered as plants cling but mollusks cling to what extent, density cling big enough or not is the question To solve this problem, the impact of harmful mollusks density be included in the follow-up study 3.4.3 Assessing the impact of harmful mollusks density to mangroves According to research on the biology and ecology of mollusks, cycle invasion of mangrove trees is as follows: As individuals mature parents, egg and sperm meet each other, formed larvae, they living of freedom in water, about 20 days after the start forming clinging silk will find hosts cling to wood, stone and mangrove trees After clinging fixed to the host, where they will continue to grow and develop, continue to the next generation In the course of life, the process of catching prey, toxic waste and their activities affect the growth and development of the host, it causes stunting, transfigure plant trees even death Results of monitoring the effects of density harmful mollusks to the mangrove trees are showned in Table 3:16 Table 3:16 The impact of harmful mollusksdensity on the mangrove trees (Van Đon, – 10/2013) Level Number ofmollusks (Individuals / a tree) (Control) x 1-5 x 6-10 x 11-15 x 16-20 x x >20 x x According to the experimental results are presented in the results table 3:16, the average density of mollusks from 1- individuals /a tree, plant under months of age are not affected to the growth of development, they are not differences compared to controls When the density of mollusks from 6-10 individuals /a tree, the plant is retardation phenomenon in young leaves than the control, the plant 19 develops in level When mollusks from to less than 20 individuals /a tree, the plant grows in level le3 and When density of up to 20 individuals /a tree, the plant develops in level and level 7, stunting, it is not grow and develop, even death Experiments with both of HauangQueo species on Su plant are the same results However, according to the survey, the investigation in nature as well as in the experimental, 15 Hau individuals on a tree is rarely occur 3.5 Measures to minimize the harmful effects of mollusks for mangroves 3.5.1 The measure hands This is the safest methods for nature and aquatic products This meausurement is appropriate by the local conditions abundant manpower, mangrove forests are managed by the military units The result applied measures hands removemollusks clinging on planting mangrove trees after months are shown in Table 3:18 Table 3.18.The applying result of measures hands to remove mollusks clinging on mangrove trees (Van Don, 8-11/2013) Element Quantity Species Weight (Individuals/ha) Rate( %) (kg/ha) Rate (%) Hau (Saccostrea 108 11,65 12 40,54 cucullata) Queo 754 81,34 14 47,30 (Brachyodontes emarginatus) Diep(Anomia 65 7,01 3,6 12,16 cytaeum) Total 927 29,6 The data table 3.18 shows, after months mollusks are removed the number of individuals of Queo the largest (754 individuals/ha, corresponding to 81.34% of the total of individuals collected), followed by Hau (108 individuals/ha, corresponding to 11.65% of the total) is lowest Diep (65 individuals/ha, corresponding to 7.01% of individuals collected), while the total volume of Queo also highest (14kg/ha, corresponding to 47.30% of the total), Hau (12kg/ha, corresponding to 40.54%), Diep lowest, total individual is 3,6kg/ha corresponding to 12.16% of the total The total number of individuals of mollusks collected after an individual is 927, achieved 29,6kg in 20 mangrove research 1ha Measures to collect harmful mollusks by hands, not pollute the water, to avoid harming other aquatic species in the region, mollusks are collected can be used in livestock (by interviewing indigenous people in Van Don in March 2013) 3.5.2 Measures used bamboo poles Measures used bamboo poles are taken to fake traps with purpose reduce the proportion of mollusks clinging on mangroves Table 3.19 The effects of bamboo poles on the abilities cling of mollusks to mangroves (Van Don, - 11/2014) Time day days 10 days 15 days 20 days 30 days Formula 00,00±0 123,66±5 163,00±5 180,00±5 212,34±4 212,34±4 Control 0,00 7,7 1,02 8,38 3,61 3,61 Experim 00,00±0 134,66±4 152,67±3 162,67±4 187,00±2 187,00±2 ent 0,00 0,41 1,7 0,50 3,30 3,30 Pro 0,26 0,36 0,275 0,36 0,36 T- b = tes T t tính -0,75 0,39 0,71 0,39 0,39 = The result is showned in Table 3:19 that, there is no much difference between formula using bamboo poles and control formula Within 30 days of the experiment found that, after day and days using bamboo poles, the average density of mollusks clinging on a tree is not reduced, even higher than the control but to come 10th day, there is a difference between the two formulas experiments The average density of mollusks clinging on a tree from the 10th day to the end of 30 days of treatments with use of bamboo poles lower control formula.However,it is not statistically significant difference in the two formulas 3.5.3 The measure used leaves Xoan (Melia azedarach) Xoan is easy to find, easy to grow and can be found in the locality Xoan leaves have been used in the science and the folk to eradicate multiple objects harmful to people and animals, plants In this experiment, the Su (Aegiceras corniculatum) to be continue selected Results areshowned in Table3:20 Table 3:20 The effect of Xoan leaves to the rate of mollusks clinging on Mangrove trees (Van Don - 7/2014) 21 Time (%) 1stweek (%) 2nd week 3rd week (%) (%) 4th week (%) Formula Control 11 15 17 0 0 11 0 13 Table results show, for the first week in all formulas with Xoan leaves are not appear mollusks clinging on a tree, while the control had the appearance of mollusks In formula 1, mollusks began to appear on trees in 2nd week 2, in formula 2, mollusks began to appear on the trees in 3rd week, in formula 3, mollusks began appear on trees in 2nd week The results also showed that the rate of harmful mollusks on mangroves in the formulas in 4weeks rate is also lower than in the control Thus can be seen, Xoan leaves is affect to harmful mollusks 3.5.4 Chemical measure Three types of chemicals used in this study are: Deadline Bullets 4%, 100GB MILAX and PISANA 700WP Table 3:21 The effect of some chemical kinds on harmful mollusks to mangroves (Van Don, 5- 7/2014) Chemical kinds Rate of Rate of Rate of harmful after harmful after harmful after 3rd day 7th day 14th day (%) (%) (%)(%) Deadline Bullets 19,64 39,27 55,64 4% (CT 1) MILAX 14,29 33,85 54,35 100GB (CT 2) PISANA 18,69 43,94 60,1 700WP (CT 3) Notes: - The chemical kinds are used follow to the manufacturer's instructions - "CT": The formula After days, days, 14 days of using chemical kinds, valid test results of some chemical kinds to harmful mollusk on mangrove are showned in Table 3:21 After days of chemical spraying, the rate of harm fulmollusks in the formula is the lowest 14.29%, down 85.71% compared to the control By day 14 after spraying, the rate of harmful mollusks clinging formula lowest belongs to 54.35% The effect of the 22 chemical kind for mollusks in formula after days spraying higher formula but after days and 14 days spraying results show the validity of formula is higher formula 3; Formula for the highest effect with the rate appears harmful mollusks lowest in three formula treatments at all time track However, through monitoring experiment also found that, after spraying, in addition to the absence of harmful mollusks also entail the absence of common fish species in the region, such as shrimp, fish, 3.6 Synthetic recommends steps to minimize the harmful effects of mollusks for mangrove 3.6.1 For plantable mangroves Step 1: Planting mangroves should identify plant species suitable to the natural conditions, soil planting areas Step 2: Prepare the soil, fertilizing lining Step 3: Planting Step 4: After planting, care regimen depends on each species, each different region For harmful mollusks, need to take measures to reduce their impact on the mangrove trees Should be used to start planting by bamboo poles, it is help plants withstand the effects of wind, currents and other impacts Measures handsneed to manually perform regularly (should follow 2-3times/a week) because this is a safe measure to the aquatic environment and the product obtained (as mollusks) can be used livestock When the density of harmful mollusk is high, can use herbal remedies to limit the damage of the mollusks on mangroves The chemical measure apply only when all manual methods, measures fake trap and herbal remedies are not effective as desired by growers (or when harmful mollusks outbreak) because application of chemical measures creates the risk of environmental pollution 3.6.2 For natural mangroves Step 1: Managing mangroves Step 2: Care and protection of plants Step 3: The plant protection measures Seedlings are protected by mother plants and other plants should not need to bamboo poles, only applied the measure hands, herbal measure and the chemical measure to reduce the harmful effects of mollusks for trees 23 CONCLUSIONS AND PROPOSALS Conclusions 52 mollusk species are investigated in areas of mangrove forests In particular, the Can Gio mangrove forest has the highest levels of species diversity; the number of species surveyed are 40 species belonging to 18 families (4 species of Gastropoda, 36 species of bivalve class), followed by Cat Ba with 27 species belonging to 16 families (4 species of Gastropoda, 23 species of bivalve class) Lowest mollusks have been identified in mangrove areas of Con Dao with number 17 species belonging to 13 families, including species of Gastropoda and 15 species of bivalve class harmful species are identified, including Diep (Anomia cytaeum), Hau (Saccostrea cucullata), Queo (Brachyodontes emarginatus) and Ha (Bankia saulii) species: Diep (Anomia cytaeum), Hau (Saccostrea cucullata) and Queo (Brachyodontes emarginatus) are distributed in the all tree studied sites, including Cat Ba, Con Dao, Can Gio; only species of Ha (Bankia saulii) just found in the area of Can Gio mangrove forest Su (Aegiceras corniculatum) have the highest level of harmful symbios of mollusk species in Cat Ba, Con Dao, and Can Gio mangroves The parasitic level of harmful symbios of mollusk species on trees respectivey are as follow: Hau (Saccostrea cucullata) 75-75 individuals / 100 trees; Queo (Brachyodontes emarginatus) 123 -124 individuals / 100 trees, Diep (Anomia cytaeum) -10 individuals / 100 trees Mangrove trees under three months of age, when the density of mollusks 0-5 individuals/a tree, without a clear expression of affect tree growth rates, but the threshold 20 individuals /a tree, it is killed trees Control measures harmful mollusks on mangroves are as follows: - The collecting mollusks by hands: the case study showed that in the mangrove forest of months age the total number of individuals of harmful mollusks were collected 927 individuals, which is equivalent to 29.6kg mollusks per The ratio of the number of species of Hau, Queo, Diep is 11.65%; 81.34%; 7.01% and the rate weight is 40.54% , 47.30%, 12.16%, respectively - The use of bamboo poles have not showed the statistical difference between formulas used and unused 24 - The use of neem tree leaves (Melia azedarach) to control harmful mollusk has effective in the first week, in all formulas with Xoan leaves are not appear harmful mollusks, while the control had the appearance of harmful mollusks - The use of chemical pesticides showed that Deadline Bullets 4%, MILAX 100GB (containing metaldehyde), PISANA 700WP (containing niclosamide) are effective against harmful mollusks Proposals - Should be used the data from this thesis in the management of harmful mollusks and implement measures to limit their harmful effects on mangroves Vietnam - Continue to improve the process of prevention, harm reduction of mollusks for mangroves and implementing research and investigation in the new location on the different geographical areas in Vietnam PRINTED PAPERS Hoang Thi Thuy Duong, Tran Thanh Lan, Nguyen Hong Phuong, 2011, ” Prelimilary study result of characteristics of mangrove forest of Cat Ba island”, Proceedings of the 1st national scientific conference of Vietnam natural museum system, pages 222-227 Hoang Thuy Duong, Nguyen Van Tuat, Nguyen Dang Hoi, 2013, ”The characteristic of Oyster Saccostrea cuculata strike and grow up on mangrove trees in Con Dao island”, Science and Technology Journal of Agriculture & Rural Development, pages 89 – 92 Hoang Thuy Duong, Nguyen Van Tuat, Nguyen Dang Hoi, 2014, ”Mollusca species composition in Cat Ba, Con Dao, Can Gio mangroves”, Journal of Vietnam Agricultural Science and Technology, pages 96 -101 Hoang Thuy Duong, Nguyen Van Tuat, Nguyen Dang Hoi, 2015, ”Reseach some measures to reduce the harmful effects of molluscs clinging to mangrove trees in Van Don, Quang Ninh”, Journal of plant protection, pages 19 – 23 [...]... 700WP (containing niclosamide) are effective against harmful mollusks 2 Proposals - Should be used the data from this thesis in the management of harmful mollusks and implement measures to limit their harmful effects on mangroves Vietnam - Continue to improve the process of prevention, harm reduction of mollusks for mangroves and implementing research and investigation in the new location on the different... emarginatus) So, 3 mollusks species are continues to be selected in the study of the level of mollusks clinging on mangroves It is investigated in the nature that, the period from planting seedlings to 3 months is the period the tree vulnerable under the impact of the environment and the creatures around This phase was easy attacked by cling and harmful mollusks species When mollusks harm to mangroves, it... appear mollusks clinging on a tree, while the control had the appearance of mollusks In formula 1, mollusks began to appear on trees in 2nd week 2, in formula 2, mollusks began to appear on the trees in 3rd week, in formula 3, mollusks began appear on trees in 2nd week The results also showed that the rate of harmful mollusks on mangroves in the formulas in 4weeks rate is also lower than in the control... When molluskswere perforated in the trunk, the tree section is perforated, broken items, with the hole through the trunk This is the kind of symptoms caused by mollusks living in the trees According to preliminary investigations, with 15 random plots (10m x10m) and along the routes observed in every region of mangrove forests, the proportion of cells that live mollusks clinging trees up to 40-50% of. .. research on the biology and ecology of mollusks, cycle invasion of mangrove trees is as follows: As individuals mature parents, egg and sperm meet each other, formed larvae, they living of freedom in water, about 20 days after the start forming clinging silk will find hosts cling to wood, stone and mangrove trees After clinging fixed to the host, where they will continue to grow and develop, continue to the. .. next generation In the course of life, the process of catching prey, toxic waste and their activities affect the growth and development of the host, it causes stunting, transfigure plant trees even death Results of monitoring the effects of density harmful mollusks to the mangrove trees are showned in Table 3:16 Table 3:16 The impact of harmful mollusksdensity on the mangrove trees (Van on, 3 – 10/2013)... the level of cling on the 3 plants with other plants Queo the level of cling on the trees of no significant differences for Duoc but significant differences compared with the level of cling on Su and other species Diep the level of cling no difference between Su and Duoc, the Vet and Duoc, Vet and other trees, but there is significant differences between the level of cling between Su and Vet and other... distribution in the intertidal zone, the sand, mud, also recorded get some mollusk species distributed on the leaves, stems and live perforated in the trunk When mollusks clinging on a tree will cause damage to the mangroves.There are two main types of damage include: 10 + Type 1: When mollusks clinging on a tree, the tree was sticking section shaggy, stunted This is a symptom caused by mollusks +... trees when mollusks clung and damaging to trees 3.3.3.1 The invation of mollusks on the trees Two mollusc species are nourished, those are mollusks which clinging with high levels on the mangrove trees in the mature stage to observe and study the cycle of the invation as follows: • Saccostrea cucullata Investigations, sampling and anatomical observations that: Oyster’sbreeding season ranges from April to... develop self due in water, approximately 2-3 weeks after start forming clinging silk will find hosts clung on mangrove trees After clinging fixed to the host, where they will continue to grow and develop, continue to the next generation In the course of life, the process of catching prey, toxic waste and their activities affect the growth and development of the host cause stunting, even lethal tree 3.3.3.2