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:
1. Prof.Dr. Nguyen Van Tuat – Vietnam Academy of Agriculture Sciences
2. Assoc.Prof.Dr. Nguyen Dang Hoi – Vietnam- Russian Tropical Center

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Critic 1:

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Critic 2:

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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


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INTRODUCTION
1. 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.
2. 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


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- 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
3. The scientific and practical significances of subject
3.1. Scientific significance
- Identify the major species in mangrove 3 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.
4. 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.
5. 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 4 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.


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- Proposed measures to reduce the harmful effects of mollusks in
mangroves and building synthetic process their harm reduction.
6. The thesis structure
The thesis has 163 pages, including the opening 5 pages. Chapter 1 is
introductry and defines scientific basic and documents use in research.
(28 pages). Chapter 2 illustrates the materials, content and
methodology (17 pages); Chapter 3 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 3
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

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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
ha 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


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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 3 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


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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 5 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


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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
1. Study on characteristics of mangrove area of Cat Ba, Con
Dao, Gio.
2. Study on mollusk species studied area.
3. Identify pests and characteristics of the pests.
4. Study the effect of the pests to the mangroves.


8

5. 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, ...


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- Mangrove Area Cat Ba National Park, Con Dao National Park and
Biosphere Reserve of Can Gio. The following mainly research areas:
+ Cat Ba National Park (HaiPhong): mainly research area Gia Luan,
Ghenh Goi and Phu Long.
+ Con Dao National Park (Vung Tau): mainly research area in Dam
Tre
+ Can Gio Biosphere Reserve (Ho Chi Minh City):

2.4.3. Research time: From May 01/2009 to 9/2015
CHAPTER III: RESULTS AND DISCUSSION
3.1. Characteristics of mangrove research area
Investigation components mangrove species of mangrove forests
of Cat Ba, Con Dao, Gio shows, the mangrove species found mainly
in these areas is Su (Aegiceras corniculatum), Vet (Bruguiera
gymnorrhiza), Đươc(Rhizophora apiculata), Mam (Avicenia alba)
and some other species such as Cha la (Phoenix paludosa), Coc
(Lumnitzera littoralis), Gia(Excoecaria agallocha), .... In particular,
Su, Vet are two mangrove species frequently encountered in all 3
areas of study; Mangrove trees are regularly caught in the mangroves
and Gio Con Dao; Mam is frequently encountered tree in mangrove
forests of Cat Ba.
3.2. Diversity and distribution of species of mollusks research area
Results of species of mollusks collected through survey research
in three areas: mangroves Cat Ba Island and Con Gio mangrove forest
52 species, belonging to 20 families, focusing on Gastropoda and
Bivalve. In particular, the Can Gio mangrove forest with high levels
of species diversity, the number of species surveyed 40 species (=
77% of total species recorded) of 18 families (4 species of
Gastropoda, 36 species bivalve class), followed by the Cat Ba with 27
(= 52% of the recorded species) species belonging to 16 species of the
family of 4 and 23 Gastropoda class bivalve species. The lowest is the
region Con Dao with mangrove species number 17 (= 33% of total
species recorded)
3.3. Characteristics of harmful mollusks for mangroves
3.3.1. Species composition harmful mollusks
As mentioned in Part components mollusk species in three
research areas (mangroves Cat Ba, Con Dao, Gio), in addition to
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:


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+ Type 1: When mollusks clinging on a tree, the tree was sticking
section shaggy, stunted. This is a symptom caused by mollusks.
+ Type 2: 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 plots. From the 52 species investigated
mangrove area of Cat Ba, Con Dao, Gio identify pests 4 for
mangroves. Include:
- Live grip on the leaves, stems: 3 species identified as Diep (Anomia
cytaeum), Hau (Saccostrea cucullata) and Queo (Brachyodontes
emarginatus).Mollusk species cling on mangroves, individually or
into dense crowds on the trees causing stunted, deformed or dead
trees.
- Live perforated in the trunk: Identify species Bankia Sauli (Wright,
1866) in the area of Can Gio mangrove forest. This mollusk species
gradually carve into the trunk, live in the trunk and destroying trees.
In 4 mollusk species in the mangrove harmful,3 species in all
three study areas are: Diep (Anomia cytaeum), Queo (Brachyodontes
emarginatus) and Hau (Saccostrea cucullata); Ha (Bankia saulii) only

found only in the area of Can Gio mangrove forest. So, 3 species:
Anomia cytaeum, Brachyodontes emarginatusand Saccostrea
cucullata be brought into the next study.
Table 3.9.Species compositionof harmful mollusks to mangroves
(2/2011-6/2012)
Distribution
Namesof
№
Science name
Vietnam Cat Con Can
Ba Đao Giơ
I Anomiidae
1 Anomia cytaeum (Gray, 1850)
Diep
+
+
+
II Ostreidae
2 Saccostreacucullata(Born, 1778)
Hau
+
+
+
III Teredinidae
3 Bankiasaulii(Wright, 1866)
Ha
+
+
+
IV Mytilidae

4 Brachyodontesemarginatus(Reeve, Queo
+
1858)
Note: "+" Found
" - " Not found


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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 2 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 4 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.


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• 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


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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 2 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 2 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 2 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 8 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 4 mollusk species found harmful, there are 3 common species
widely distributed across all study sites are: Hau (Saccostrea
cucullata), Diep (Anomia cytaeum), Queo (Brachyodontes

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 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, 3 -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
7 2 - 73
15-16
Điệp
9 - 10
3-4
0-1
0
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 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 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, 3 – 10/2013)
Level
Number
0
1
3
5
7
ofmollusks
(Individuals / a tree)
0 (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- 5
individuals /a tree, plant under 3 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 1. When mollusks from 6 to less than 20 individuals
/a tree, the plant grows in level le3 and 5. When density of up to 20
individuals /a tree, the plant develops in level 5 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 3 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 3 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, do 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, 7 - 11/2014).
Time

1 day
5 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 1 day and 5 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 5 - 7/2014).


21

Time

0
(%)

1stweek
(%)

2nd week 3rd week
(%)
(%)

4th
week
(%)

Formula
Control
0
8
11
15
17
1
0
0
2
5
8
2

0
0
0
9
11
3
0
0
1
6
13
Table results show, for the first week in all 3 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 3 days, 7 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 3 days of chemical spraying, the rate of harm fulmollusks
in the formula 2 is the lowest 14.29%, down 85.71% compared to the

control. By day 14 after spraying, the rate of harmful mollusks
clinging formula 2 lowest belongs to 54.35% 2. The effect of the


22

chemical kind for mollusks in formula 3 after 3 days spraying higher
formula 1 but after 7 days and 14 days spraying results show the
validity of formula 1 is higher formula 3; Formula 2 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
1. Conclusions
1. 52 mollusk species are investigated in 3 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 2 species of
Gastropoda and 15 species of bivalve class.
2.

harmful species are identified, including Diep (Anomia
cytaeum), Hau (Saccostrea cucullata), Queo (Brachyodontes
emarginatus) and Ha (Bankia saulii). 3 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.
3. 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) 9 -10 individuals / 100
trees.
4. 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.
5. Control measures harmful mollusks on mangroves are as
follows:
- The collecting mollusks by hands: the case study showed that in
the mangrove forest of 3 months age the total number of individuals of
harmful mollusks were collected 927 individuals, which is equivalent
to 29.6kg mollusks per ha. 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 .