Thailand Quantification of Macrofauna

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    Quantification of variability in marcofauna

    of pre-tsunami sedimentary tropical shores

    of SW Thailand

    By James Fay

    MSci Marine Biology

    2012

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    Abstract

    This report aimed to assess the variability of macrofaunal species at the sites: LSon = Laem

    Son; TND = Thung Nang Dam; KRa = Ko Ra; Kb = Krabi. Off of the coast of SW Thailand

    where it then quantified this variability by analysing the data using MDS plots, CLUSTER

    plots of abundances of the macrofauna at each station first with singleton results and then

    without singleton results. This showed that the removal of singletons decreased the similarity

    between the sites most likely due to the removal of a species that was common at another site.

    It also showed that from the MDS plots the site Kb was particularly dissimilar to the other

    three sites TND, LSon and KRa. The results then looked at the feeding mechanisms of the

    species to find a small variation between the sites which was attributed to each site having a

    different habitat. This was also seen in the last result which showed the sites were variable

    with regards to having vegetation present as only some sites had vegetation present. This was

    identified to be sea grass. However further analysis showed that the habitats varied even more

    due to physical factors where internal waves were present and the possibility of patchiness of

    the vegetation. Furthermore different levels of nutrient inputs influenced the productivity of

    each site causing more variation. These contributing factors lead to unique habitats at each

    site which was found to be the main cause in the variation as the habitat influences the

    species present at the site.

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    Introduction

    The importance of quantifying variability of an ecological system is an important study

    which is needed to understand processes which are occurring that cause various patterns to

    arise. By quantifying this variability it is possible to construct models which can predict

    patterns and responses of various anthropogenic and natural inputs to a system. From these

    models it is also therefore possible to form new hypotheses (Ysebaert & Herman, 2002). By

    quantifying variations it is possible to construct food webs by looking at the interactions

    between different sites. This also makes it possible to implement management protocols in

    order to maintain and sustain ecosystemsbiodiversitys which are of growing interest with

    the potential to discover new patterns (Landres et al. 1999 & Barrio Frojan et al. 2005).

    Within this study the area to be studied is a series of sites located off of the coast of SW-

    Thailand within the Andaman Sea shown by (figure 1). The reason for choosing this site for

    quantifying variability is because there is minimal previous work been carried out on this area

    before (Barrio Frojan et al. 2006). Where understanding the variability of a system is

    important in understanding its processes and makes it a scientifically important site (Ysebaert

    & Herman 2002). Furthermore it is an important location for this study to be carried out

    seeing as it is an important fishing ground and undergoes a biannual monsoon season creating

    a unique ecosystem through large seasonal variations (Buranapratheprat et al. 2002 &

    Nielsen et al. 2004). Other reasons for studying the SW Thailand coast is due to its strong

    tidal actions which makes suspended particulate matter available causing high productivity

    and a site of biological interest (Umezawa et al. 2009).

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    Figure 1. Map to show study area where data was collected at the stations, LSon, KRa, TND

    and Kb where LSon = Laem Son; TND = Thung Nang Dam; KRa = Ko Ra; Kb = Krabi

    (Barrio Frojan et al. 2006).

    From (figure 1) you can see the locations of the sites where the data was collected the sites

    are spread over 200km of coastline and are geographically separated as a result of this. Along

    the coastline mangroves and sea grass are present which provide sediment stability and help

    dampen the effect of tsunamis. All of the sites within the study have a semi-diurnal tidal

    cycle (Barrio Frojan et al. 2006).

    The reason for quantifying macrofauna off of the coast of Thailand is because they are a very

    important part of marine food webs. Where monitoring them is important for monitoring a

    system (Ysebaert & Herman, 2002). Macrofauna also make good indicator species of changes

    to a system due to their constant presence within the system due to various macrofaunal

    species having sedentary lifestyles. Therefore by studying the macrofauna of Thailand it is a

    good indicator towards changes occurring such as pollution and will also give an idea what

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    will be happening to the ecosystem as a whole which will aid in management (Ababio et al.

    1999). Macrofauna are also have important ecological effects on the environment through

    their sediment interactions due to some species having burrowing lifestyles as burrows

    increase microbial productivity (Kristensen and Kostka 2004). Furthermore macrofauna can

    also be classified into bio-turbators and bio-stabilisers where they either weaken or strengthen

    the sediment respectively via burrowing or foraging motions, this has a major impact

    ecologically as it influences the habitat they live in (Volkenborn et al. 2009). For these

    reasons this study will concentrate on the variability of macrofauna as they are of important

    ecological significance.

    The aims of this study is therefore to look at the variability of macrofaunal species between

    the sites Kb, LSon, KRa and TND with an emphasis on polychaete species where it is then to

    identify any variabilitys and differences found between these sites using statistical analysis.

    The aim is to then quantify the variability in order to understand why these sites differ from

    each other in order to understand any patterns that may occur. To hypothesis the sites will be

    varied from one another as they are located within different areas and will have different

    processes acting upon them. On the other hand the stations within the sites will be less varied

    as they will have the same processes acting upon them.

    Methods

    The data was collected from the methods of (Barrio Frojan et al. 2006).

    This data was then analysed using Primer where MDS plots and CLUSTER plots were

    constructed to look at the similarities between each station of the study area. The data was

    also re-analysed after removing species that only appeared once at a station so the more

    abundant species could be compared more closely. Furthermore as polychaetes were the

    primary subject of the study and also most abundantly found the results were also analysed

    without the other species found so the stations variability can be compared with respect to

    just polychaetes. Whilst constructing graphs for where singleton species had been removed

    for polychaete and crustacean species the stress level of the graphs were too high and

    therefore not reliable enough to be used as a result. In addition to looking at the variability of

    species found. The feeding mechanisms of each species found were identified and compared

    using MDS and CLUSTER plots and a stacked bar graph to look at breakdown of feeding

    types at each station which would reveal variations attributed to feeding. Lastly the seabed

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    habitat was identified for each station and compared comparatively within a table in order to

    identify variation at a habitat level.

    Results

    After analysing the results collected off the coast of Thailand the graphs showed the

    following variations between the different sites of macrofaunal species:

    Figure 2. MDS plot of polychaete and crustacean species abundances at each site including

    singleton species with similarity rings in (%) to show how similar each site are from each

    other.

    From (figure 2) the variation between different sites is very high as they are only 24% similar

    and there is a larger variation between Kb and the other sites TND, LSon and KRa, therefore

    a larger difference between them. However the stations at each site were more closely related

    as they have a higher similarity shown by the 40% similarity ring. This shows that there is

    still a high amount of variation within each site of the study area. As a result when

    quantifying the variation there are site specific and station specific variables that need to be

    explained.

    Speci es_Ab undance

    Transform: Log(X+1)

    Resemblance: S17 Bray Curtis similarity

    SiteTND(N)

    TND(S)

    KRa(N)

    KRa(S)LSon1

    LSon2

    Kb1a

    Kb1b

    Kb2a

    Kb2b

    Similarity24

    40

    60

    TND(N)_A3TND(N)_B1

    TND(N)_B3TND(N)_B4

    TND(N)_C1

    TND(N)_C3

    TND(S)_A1

    TND(S)_A2

    TND(S)_B1

    TND(S)_B3TND(S)_B4

    TND(S)_C2

    KRa(N)_A1

    KRa(N)_A3

    KRa(N)_B1KRa(N)_C1

    KRa(N)_C3KRa(N)_C4

    KRa(S)_A2KRa(S)_A3KRa(S)_B2

    KRa(S)_B3

    KRa(S)_C1KRa(S)_C4

    LSon1_A4

    LSon1_B2LSon1)_B3

    LSon1_C1

    LSon1_C3

    LSon1_C4

    LSon2_A1

    LSon2_B1LSon2_B4

    LSon2_C1

    LSon2_C2

    LSon2_C3

    Kb1a_A1

    Kb1a_A2Kb1a_B1

    Kb1a_B2

    Kb1a_C1Kb1a_C2

    Kb1b_A3

    Kb1b_A4Kb1b_B3

    Kb1b_B4

    Kb1b_C3

    Kb1b_C4

    Kb2a_A1

    Kb2a_A2

    Kb2a_B1

    Kb2a_B2Kb2a_C1

    Kb2a_C2Kb2b_A3

    Kb2b_A4

    Kb2b_B3

    Kb2b_B4

    Kb2b_C3

    Kb2b_C4

    2D Stress: 0.24

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    Figure 3. MDS plot of just polychaetes at each station including singleton species with

    similarity rings in (%) to show how similar each site are from each other.

    Within (figure 3) where crustacean species have been removed when comparing to (figure 2)

    it shows a similar pattern of variation between sites at 24% similarity and also between

    stations at 40% similarity. However it has also increased similarity between some stations for

    example station LSon2_A1 is now more similar to its surrounding stations, yet it has also

    decreased similarity between other LSon stations. This indicates that there is a strong

    crustacean presence at LSon which is causing variation between the sites and stations.

    Speci es_Ab undance

    Transform: Log(X+1)

    Resemblance: S17 Bray Curtis similarity

    SiteTND(N)

    TND(S)

    KRa(N)KRa(S)

    LSon1

    LSon2

    Kb1a

    Kb1b

    Kb2a

    Kb2b

    Similarity24

    40

    60

    TND(N)_A3TND(N)_B1

    TND(N)_B3TND(N)_B4

    TND(N)_C1

    TND(N)_C3

    TND(S)_A1

    TND(S)_A2

    TND(S)_B1

    TND(S)_B3TND(S)_B4

    TND(S)_C2

    KRa(N)_A1

    KRa(N)_A3

    KRa(N)_B1

    KRa(N)_C1

    KRa(N)_C3KRa(N)_C4

    KRa(S)_A2KRa(S)_A3KRa(S)_B2

    KRa(S)_B3

    KRa(S)_C1KRa(S)_C4

    LSon1_A4

    LSon1_B2LSon1)_B3

    LSon1_C1

    LSon1_C3LSon1_C4

    LSon2_A1

    LSon2_B1LSon2_B4

    LSon2_C1

    LSon2_C2

    LSon2_C3

    Kb1a_A1

    Kb1a_A2

    Kb1a_B1

    Kb1a_B2Kb1a_C1

    Kb1a_C2

    Kb1b_A3

    Kb1b_A4

    Kb1b_B3

    Kb1b_B4

    Kb1b_C3

    Kb1b_C4

    Kb2a_A1

    Kb2a_A2Kb2a_B1

    Kb2a_B2Kb2a_C1

    Kb2a_C2

    Kb2b_A3Kb2b_A4

    Kb2b_B3

    Kb2b_B4

    Kb2b_C3

    Kb2b_C4

    2D Stress: 0.23

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    Figure 5. CLUSTER plot of site total abundances of polychaetes with singleton species with

    a 50% slice.

    The similarity between each site shown in (figure 5) also shows the differences between the

    Northern, Central and Southern sites as shown in (figure 4). The TND and KRa Central sites

    are more closely related together, the Southern Krabi sites are more closely related to each

    other and the Northern LSon sites. From the above figures it shows that there are clear site

    specific variables causing variation.

    Adundance

    Group average

    Kb1b

    Kb1a

    Kb2a

    Kb2b

    KRa(N)

    KRa(S)

    KRa

    TND(N)

    TND(S)

    TND

    LSon2

    LSon1

    Samples

    100 80 60 40 20

    Similarity

    Transform: Log(X+1)

    Resemblance: S17 Bray Curtis similarity

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    Figure 6. MDS plot of polychaete abundances at each station without singleton species with

    similarity rings in (%) to show how similar each site are from each other.

    By removing species that only appeared once at a site or station the species that form themajority of a sites population can be compared and as a result can be more closely compared.

    from (figure 6) looking at polychaete species by removing the singletons it has decreased the

    similarity between sites as the Northern, Central and Southern sites have decreased similarity

    between each other. Furthermore comparing between stations at each site their similarity has

    also decreased. This shows that the addition of singleton species causes less variation

    between sites and stations, but also that the majority of the population present at each site is

    more varied between each other which by removing the singleton results have revealed this

    result.

    AbundanceTransform: Log(X+1)

    Resemblance: S17 Bray Curtis similarity

    Site

    TND(N)

    TND(S)

    KRa(N)

    KRa(S)

    LSon1

    LSon2

    Krabi 1a

    Krabi 1b

    Krabi 2a

    Krabi 2b

    Similarity

    20

    50

    2D Stress: 0.22

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    Figure 7. The percentage of each feeding type found at each site shown comparatively

    against other stations (Fauchald & Jumars, 1979).

    Analysing the feeding type (figure 7) shows that there is some variation with feeding type at

    each site as the Central cites TND and KRa have a higher percentage of deposit feeders than

    the other stations. However they vary from each other as TND has a larger percentage of

    carnivores than KRa. Yet KRa has a higher percentage of surface deposit feeders than TND.

    When looking at the LSon Northern sites has the largest percentage of carnivores present and

    has low percentages of other feeding type species. It also has a small percentage of filter

    feeders present as well. And lastly the Krabi Southern sites have a consistent carnivore

    percentage but have a high percentage of surface deposit feeders and deposit feeders. From

    these variations in feeding type between each site this could explain some of the variation

    between the sites. However as they are still very similar as shown by (figure 8) it cannot

    account for all of the variation and there are other factors causing the variation between the

    sites.

    0%

    10%

    20%

    30%

    40%

    50%

    60%

    70%

    80%

    90%

    100%

    TND(N) TND(S) TND KRa(N) KRa(S) KRa LSon2 LSon1 Kb1a Kb1b Kb2a Kb2b

    surface deposit feeder carnivore deposit feeder filter feeder carrion feeder

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    Figure 8. MDS plot to show how similar the variation in feeding types between stations is

    using similarity rings in (%) to show how similar each site are from each other (Fauchald &

    Jumars, 1979).

    Within (figure 8) it shows the similarity of each site with regards to each feeding type found

    at each site for polychaete species which shows that the sites are very similar with similarity

    between all sites above 80% as shown by (figure 9). It also shows there is still a larger

    difference between the Southern Krabi sites and the other Northern LSon and Central TND

    and KRa sites. This could account for some of the large species variations between Kb and

    the other three sites TND, KRa and LSon.

    Abundance

    Transform: Log(X+1)

    Resemblance: S17 Bray Curtis similarity

    TND(N)

    TND(S)

    TND

    KRa(N)KRa(S)

    KRa

    LSon2

    LSon1

    Kb1a

    Kb1b

    Kb2a

    Kb2b

    Similarity85

    9095

    TND(N)

    TND(S)

    TNDKRa(N)

    KRa(S)

    KRa

    LSon2

    LSon1

    Kb1a

    Kb1b

    Kb2a

    Kb2b

    2D Stress: 0.11

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    Figure 9. CLUSTER plot showing the similarity of different feeding types at each station

    (Fauchald & Jumars, 1979).

    From (figure 9) it further reinforces the high similarity shown by (figure 8) and that there is a

    site variation with regards to feeding type which could account for some of the variation of

    the study area of Thailand. It also shows that the variation between the Northern, Central,Southern site is the greatest. Also as the similarity of the feeding types is very high it means

    that the feeding type does not explain all of the variation between the sites and is therefore

    only a contributing factor.

    Abundance

    Group average

    Kb1a

    Kb1b

    Kb2b

    TND(N)

    TND(S)

    TND

    KRa(S)

    Kb2a

    LSon2

    LSon1

    KRa(N)

    KRa

    Samples

    100 95 90 85 80

    Similarity

    Transform: Log(X+1)

    Resemblance: S17 Bray Curtis similarity

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    Station Habitat Sand (%)

    TND (N) Vegetated 71

    TND (S) Vegetated 62

    KRa (N) Non-Vegetated 60KRa (S) Non-Vegetated 64

    LSon1 Non-Vegetated 55

    LSon2 Vegetated 41

    Kb1a Vegetated 60

    Kb1b Non-Vegetated 93

    Kb2a Vegetated 60

    Kb2b Non-Vegetated 56Table 1. Habitat state and sand coverage at each station (Barrio Frojan et al. 2006).

    Within (Table 1) it shows what type of habitat is present at each site and the sand coverage of

    the seabed. From which you can see that the habitat state is variable as Vegetative state is

    regardless of sand coverage for example KRa (N) is not vegetated but Kb2a is vegetated

    where both have a sand coverage of 60%. However as the habitat state is variable between

    sites this could explain some variation in species found. The habitat state variation is most

    likely due to some other variable acting upon the system. Also when comparing the

    vegetative state against feeding type. Sites that have vegetation have a larger percentage of

    the more dominant feeding type and seem to account for a larger percentage of the feeding

    types present at a station.

    To summarise the results there is a large difference between the sites particularly between Kb

    and the other three sites TND, KRa and LSon. Also by removing the crustaceans it decreasesthe variation as and the sites become more similar. But removing the singletons increases

    variation between the sites. The stations within each site are also more similar to each other

    than compared to other station from other sites. There is also a variation of feeding type

    between the sites but are still very similar. And lastly the vegetative state varies from site to

    site with different coverages of sand. Furthermore the most common species of polychaetes

    to be found are from the families: Nereididae, Spionidae, Capitellidae and Paraonidae (Barrio

    Frojan et al. 2006).

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    Discussion

    Analysing the results there are many different potential causes to the large variation between

    each site seen within the results which could be attributed to physical, chemical or biological

    factors. Furthermore there may be some anthropogenic influences that could cause these

    variations. In addition interactions between all these may produce further variations.

    Firstly possible variations that may be quantified by physical processes could be the presence

    of solitons caused when the waves hit the Nicobar Islands causing internal waves which

    allow the potential for high productivity. This causes turbulence and shear which has a

    potential of mixing and exposure to strong wave action which is documented on nearby

    beaches of Phuket Island (Dexter, 1996). However due being on the other side of Phuket

    island Krabi is sheltered from this and therefore is not exposed to these unlike LSon, TND

    and KRa. This therefore allows for some potential variation between these stations.

    Furthermore LSon is more exposed as it is not as sheltered as TND or KRa which are more

    sheltered by the island Ko Phra Thong (Nielsen et al. 2004). Furthermore Krabi is within a

    mangrove area which reduces water currents making it a sheltered area which is also similar

    for TND which has allowed the growth of sea grass and vegetation which may quantify for

    variation between the sites (Chansang and Poovachiranon 1994 & Cochard et al. 2008). Due

    to the sheltered nature of Krabi compared to the other stations which are more exposed via

    the internal waves this has implications towards larval dispersal as the larvae will not disperse

    as well compared to the other stations and therefore species at Krabi may be different

    compared to the other stations as they become more isolated (Beu and Kitamura, 1998). This

    could explain why the other sites are more similar compared to Krabi.

    Chemical processes could also quantify some of the variation between the sites as Thailand

    has a large amount of pig, poultry farm, fish ponds and paddy fields which causes a high

    amount of nutrients to run-off into the estuaries of Thailand which pollute the surrounding

    areas (Buranapratheprat et al. 2002). Where also industrialisation and use of pesticides has

    caused an increase in mercury contamination within the Andaman sea (Cheevaporn and

    Menasveta, 2003). Through different levels of nutrient inputs from different estuaries can

    cause variation between the sites through different levels of productivity. The different levels

    of nutrients available to the sites are also different if vegetation is present as the bioavailable

    carbon is much higher where vegetation is present compared to sites where no vegetation is

    present. As a result of sites with vegetation present more nutrients are available and therefore

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    have a higher productivity allowing a larger carrying capacity for that site which will allow

    more species to exist and as a result have a higher diversity. This higher diversity will cause

    variation between the sites and could be a possible reason for the large difference seen

    between the sites (Duarte et al. 2005). Furthermore because Krabi is more sheltered it could

    cause eutrophication through high residence times and poor tidal flushing (Cheevaporn and

    Menasveta, 2003). In addition to that there is also a large amount of sewage discharge from

    Phuket which would fuel eutrophication (Reopanichkul et al. 2010). In addition due to the

    other sites being more exposed to wave action and in a tsunami vulnerable area they are

    prone to backwash where sediment is transported via tsunamis and causes large amounts of

    Suspended particulate matter to become available (Sugawara et al. 2009).

    In addition potential biological influences that could cause the large variations observed

    could be due to different predators present at different site which would cause different food

    webs to emerge and as a result cause different species to occur at different sites causing

    variation between the sites. This would arise through a variation of habitat caused by the

    above physical and chemical factors which cause different habitats to occur. For example the

    sheltered nature of Krabi surrounded by mangroves and some of the stations vegetated by sea

    grass provide a more complex habitat allowing prey items to hide more efficiently as a result

    predators adapted to hunting in vegetation would arise here. This would also be similar atTND but because it is more exposed a different predator adapted to hunting in more exposed

    conditions would arise here. Then compared to the sites like LSon and KRa which are

    exposed and low in vegetation predators adapted to catching prey items that dont have the

    option of hiding in vegetation would be found here as the habitat complexity would be lower.

    Through different levels of habitat complexity i.e. vegetated with sea grasses or non-

    vegetated will cause different predators which causes variations between the sites (Beukers &

    Jones, 1997).

    In addition the variation in habitat makes different niche environments available where

    different species will arise suited to their surrounding environment for example the presence

    of vegetation at the sites which is known to be sea grass (Barrio Frojan et al. 2006). The

    presence of sea grass provides a three dimensional habitat for macrofauna as they can feed

    amongst the sea grass and not just on the sediment as a result it provides a larger habitable

    environment for species to live in which will increase the diversity of the site containing sea

    grass. On the other hand the sites without sea grass will be restricted to feeding on the

    sediment and therefore be less diverse as the habitable environment is less without sea grass

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    (Ansari etal. 1991). Which as shown within the results there are sites with sea grass and

    without sea grass present. Through the presence of different habitats this therefore causes

    variation between the sites. Furthermore from the seabed coverage of sand all sites had sand

    present which would indicate that the sea grass is most likely patchy which could explain the

    variation between the stations of sites that contained sea grass (Wiens, 1997). Furthermore

    patchiness also creates two habitats within the same area which would increase diversity

    further and allow new species that can utilise both the sea grass habitat and the exposed

    seabed environment which would cause greater variation between the sites depending on the

    patchiness of sea grass (Wiens, 1997). This could account for the differences between the

    Northern, Central and Southern areas. Where the Northern site is non-vegetated and exposed.

    The Central sites are both vegetated and non-vegetated and semi-exposed and the Southern

    Krabi site is both non-vegetated and vegetated but sheltered. With different habitats present at

    each location different species will occur and cause variation between the sites and could be

    the reason why the sites are so different from each other.

    One potential cause of variation between the sites could be due to the presence or absence of

    mangroves at a station as it is documented that mangroves are along the coast line (Barrio

    Frojan et al. 2006) which provide a different habitat for species to thrive in. however near

    Ranong the mangroves have been commercially exploited which is near the site LSon whichis an exposed area. The removal of the mangroves from this area may have caused variation

    of LSon from the other sites by removing a habitat for prey items to hide amongst. This could

    explain why LSon has a large proportion of carnivores present compared to the other sites

    (Macintosh et al. 2002).

    Another biological influence that could be a contributing factor towards the the large

    variation between the sites is the feeding type of the species found at the sites. Due to the

    different habitats different food sources are available and therefore different feeding methods

    are used in order to obtain that food which causes variation as shown in the results. These

    different feeding mechanisms arise as a result of the habitats being different which as a result

    mean different species are present (Fauchald and Jumars, 1979 & Gutierrez and Iribarne,

    2004).

    Looking at the results section other potential reasons for the large variability between stations

    could be due to the presence of crustaceans as well as polychaetes. As within the singleton

    section where crustaceans have been added the sites become more dissimilar from each other

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    but when removed become more similar to each other. This shows that basing the similarity

    of a site based on just polychaetes is not enough to quantify the full extent of variability at a

    site as when adding other classes of species the variation increases between the sites as

    interactions between different species becomes more noticeable as species that are usually

    associated with another species will occur near them. After taking into account all the species

    that appear at each site there will be even more variation as it cascades through different

    trophic levels (Southwood, 1977).

    When the singleton species were removed it showed that the sites became more dissimilar

    indicating that the singletons reduced variability. This is most likely due to the singletons

    being present at more than one site and therefore by removing them it removes a common

    factor between sites and therefore decreasing similarity. Also it was documented from

    previous studies using the same dataset that only one species occurred at all stations and that

    33% of the species found only occurred at one site therefore by removing singletons it would

    mean that there would not be the same species present at every station and unlikely that 1

    species would appear at multiple stations as a result removing singletons causes more

    variability between the sites (Barrio Frojan et al. 2006). The possibility why the removal of a

    singleton species may decrease similarity is because if at one site a species is abundant but at

    another site it is a singleton, the presence of that singleton makes it more similar to the sitewhere the same species is abundant. By removing it removes the link between the sites and

    makes them more dissimilar. On the other hand it would improve similarity if rare species

    were removed that only occurred at one site as it would remove a difference between sites.

    However as similarity decreased it would imply that singletons found and removed were

    most likely present in more abundance at other sites rather than being rare. This has most

    likely occurred due to larval dispersal where a few larvae have left the Krabi site and become

    singletons at other sites or vice versa where larvae have been carried into Krabi this would

    explain how you could have an abundant species at one site and then a singleton species at

    another site (Beu & Kitamura, 1998).

    Another source of potential variability is the genetics of species at each site. Where Krabi is

    more isolated there is the potential for limitation in the gene pool as conditions are more

    stable due to being sheltered. This would impact the site by reducing the fitness of individuals

    and whilst having a large species diversity there may be a low genetic diversity as a result of

    low larval dispersion. As a result at the other stations there may be smaller species diversity

    due to more exposed conditions but a greater genetic diversity and therefore a higher

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    individual fitness due to a greater larval dispersal potential (Bell and Okamura, 2005 &

    Bulleri and Chapman, 2010). However this has not been tested and would be ideal for future

    study in order to test this as a hypothesis. Another potential topic for future study would be to

    look at the larval dispersal from each site as this data would reinforce or disprove the gene

    pool limitation hypothesis. Furthermore it would also further investigate the presence of

    singletons and their implications on variation between the sites.

    To conclude the main variation between the sites can be attributed to different habitats at

    each site which allow different species to occur as they occupy different niches created by the

    habitat causing the variation. However the variation in habitats is caused by variation of

    various contributing factors such as physical, chemical and biological interactions and

    anthropogenic inputs which create these different habitats and allow the wide variation of

    macrofaunal species to occur.

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