The Pearl oyster Pinctada radiata forms enormous beds in the western
side of Arabian Gulf extending from the Kuwaiti coast in the north to
the coast of the United Arab Emirates and Oman in the south (Somer, 2003).
Qatar and other Arabian Gulf countries were endowed with a pearl oyster
resource which had been exploited for natural pearls from time immemorial
and had depended on its main economic resources.
The pearl oyster fishing industry in the Arabian Gulf declined with the
development of cultured pearls in Japan during the 1930 and with the discovery
of oil in the Gulf countries (Al-Matar et al., 1993; Somer, 2003;
Mohammed, 1994; Al-Khayat and Al-Maslamani, 2001; Kimani and Mavuti, 2002;
Mohammed and Yassien, 2003) have contributed much to our knowledge of
the pearl oyster fishing industry and fouling in the pearl oyster beds,
besides some valuable information on the anatomy, reproduction biology
and growth of P. radiata in the Arabian Gulf. However, observations
on the associated biota, their distributional abundance, the topographical
features and general ecology as well as community structure of the pearl
oysters and their habitat conditions of the oyster beds were either rarely
considered or remain unknown. However, the genetics and taxonomy (Khamdan,
1988) and the morphometric characters (Al-Sayed et al., 1993; Al-Sayed,
1995; Mohammed, 1994, 1995) were studied in Kuwait, Bahrain and Qatari
The fundamental objectives of this study were to determine the pearl
oyster associated biota, abundance, distribution and compare the physical
and chemical conditions within oyster beds.
MATERIALS AND METHODS
Pearl oyster beds were sampled from 18 locations by R/V Mukhtaber Al-Bihar
of the University of Qatar (Fig. 1, Table
1). Each site was visited once during the period August 2002-December
Seawater temperatures, salinity and pH measurements were carried out using
a pre-calibrated water quality logging system (Model 3800 and 6690 sonde from
YSI Incorporation). The Dissolved Oxygen concentration (DO) was determined by
the classical Winkler method. Determinations of chlorophyll-a (phytoplankton
biomass indicator) was carried out spectrophotometrically based on the acetone
extraction method described by Parsons et al. (1984). Quantitative surveys
for community assessment were carried out using SCUBA diving. A quadrate of
one meter square was used to collect macro-benthic fauna from each station.
The quadrate area was scooped using a hand shovel to a depth of 10 cm, sample
transferred into a polythene bag and stored in ice box on board the research
vessel. Samples were collected in triplicates and averaged. Additionally, dredge
was used for more than 18 min on each location. Macrobenthos samples were obtained
from pearl beds sites along the eastern, south eastern coast of Qatar.
||Map shows the main pearl oyster beds studied in Qtari waters
stations: East; 1: Al-ad Algharibi, 2: Um Khart, 3: Um Aljeteb, 4: Hadet
Migbel, 5: Um Alotteam, 6: Khrayes; South: 7: Alhadid, 8: Tunob, 9: Botheal,
10: Bokombarah, 11: Halat Delma, 12: Um Alshwahin; North: 13: Belhwnbar,
14: Um Shaif, 15: Alhawad, 16: Alria, 17: Niwat Adam, 18: Um Aljesh
||Hydro-chemical parameters of the pearl oyster beds in Qatari
Samples were sieved through 0.5 mm mesh sieve and retained specimens swere
preserved in 5% buffered formalin in seawater. In the laboratory, the macrofauna
and Algae were sorted according to their taxonomic rank and identified to the
genus level. On each site, under water video and close up photographs were taken
for the oyster beds and their associated living organisms.
Species diversity was determined following Shannon and Weaver Diversity
Index (1963). Principal Component Analysis (PCA) was performed for all
of the obtained data (depth, temperature, salinity, pH, dissolved oxygen,
chlorophyll-a, Algae, Porifera, Corals, Polychaeta, Crustacea, Mollusca,
Ascidiacea, Echinodermata and total species number) using SYSTAT®
10.2 for Windows. It was carried out to evaluate the effect of some physical/chemical
parameters of sea water at different stations of oysters beds on the
benthic fauna and Algae abundance and the inter-relationship among benthic
fauna and Algae species along the Qatari coast (Table 1).
The hydrochemical data obtained during the period of sampling covered
the following parameters, water temperature, salinity (psu), pH, Dissolved
Oxygen (DO) and chlorophyll-a.
Water temperatures recorded at different stations are shown in Table
1. The water temperature varied slightly from 33.03 to 35.30°C
in August-September and from 27.95 to 29.90°C in November. The local
variations in the water temperature was observed in each station has been
attributed to the different time of the day during which the measurements
were carried out (Table 1).
Salinity values showed little variations between northern, eastern and
southern stations in August and September (Table 1).
Values varied slightly from 39.50-41.15 psu in September at the northern
stations and from 42.90 to 44.53 psu for the same period at the southern
stations, whereas the salinity values were slightly lower (40.83-41.60
psu) in August at the eastern stations. In general, salinity values in
the southern stations were usually high. This is mainly attributed to
the shallowness of the area.
The pH of the study area falls on the Alkaline side. The average pH calculated
for the northern stations was 8.4, as compared to 8.3 in the southern
and eastern stations with no significant differences between different
oyster beds or between sampling time.
The dissolved oxygen concentrations varied from 4.28-4.61 mg L-1
in September at the northern stations, from 3.59 to 4.33 mg L-1
in September at the southern stations and from 3.73 to 4.29 mg L-1
in August at eastern stations.
As shown from Table 1, Chlorophyll-a concentration
which were mainly responsible for the increase of decrease in productivity
fluctuating between 0.09 to 0.12μg L-1 in the northern
stations, 0.09 to 0.23 in southern stations in September and between 0.03
to 0.07μg L-1 at eastern stations in August.
The pearl oyster beds were encountered at depths ranging from 2 to
36 m. The investigated oyster beds in the east of Qatar are representing
about 42.9% of a mean depth of 16.42±0.8 m. The pearl oyster beds
located in the north of Qatar coast represent about 38.6% with a mean
depth of 13.7±0.9 m, while the oyster beds of the southern Qatari
coast represent about 18.57% having a mean depth of 14.7±2.7 m
In Qatari waters the pearl oyster Pinctada radiata were found
usually attached to the hard substratum such as rocks, dead Coral outcrops
or sand grit encrusted with marine organisms. In few of the investigated
stations, the seabed was sandy. Such substrates with no fragments do not
encourage the settlement and establishment of pearl oyster communities.
The abundance of pearl oysters in Qatari waters varied widely according
to their locations (northern, southern and eastern beds) and the different
substrates within the same bed. The abundance was highest (mean value
of 50.0±15.4 individuals m-2) at the eastern stations
(Al-ad Algharibi and Um Khart), followed by the northern stations (Belhanbar
and Um Aljesh) (mean values 45.0±15.4 individuals m-2)
and the lowest mean values of 21.7±9.0 individuals m-2
was observed at the southern stations (Halt Delma).
In total 2443 specimens of benthic biota were collected comprising
189 species. Molluscs comprised the most abundant group with 104 species,
followed by echinodermata with 25 species, Crustacea with 20 species,
Coral with 12 species, Algae with 7 species, Polycheates with 7 species,
Sipuncula, Actiniaria and Branchipoda with 1 species each.
The overall percentage distribution of the different biota collected
from all stations indicated that the mollusks and especially gastropods
and bivalves were more abundant than other fauna and the Algae groups
(Fig. 2). Lower species diversity and lower number of
individuals are indicative of the macrobenthos fauna and habitats response
to stressful environmental conditions.
The details of the distribution and percentage of the different taxa
groups and their representation at the investigated stations are summarized
in three sites namely: the eastern location which consists of Station
1-6, the eastern stations which consist of station 7-12 and the northern
stations which consist of stations 13-18.
Since the biota of the pearl oyster beds comprised thousands of small
and large animals and plants, the study of the interrelationship among
these was further complicated by the nature and density of such an assemblage.
The nature of these factors have profound effects on the well being of
the stock of oysters in the beds. Molluscs (gastropods and bivalves particularly),
crustaceans, star fish, annelids, coelenterates and Sponges were among
the dominant fauna. A luxuriant growth of different species of Algae belonging
to phaeophyta and rhodophyta dominated the pearls oyster beds (Table
||Checklist of the examined stations biota on the principal
of presence and absence densities
The Biota is Described under the Following Groups
Throughout the density of Algae on the rocky expanse and other hard
substrate studied seemed to be moderate especially at the eastern stations.
Sargassum sp. dominated most stations. Other brown Algae of the
genera Hormophysa and Padina were most common at eastern
stations. Among the red Algae the genus Hypnae was common at some
of eastern stations whereas the species Acarthophora sp. Liagora
distenta and Eucheum denticulatum were recorded at some stations
The class Calcarea was represented by only one species Callyspongia
sp. at station 7. The bread crumb sponge (Halichondria sp. and
Haliclona sp.) were observed attached to rock or hard surface of
dead shells and Coral at some stations, but boring Sponges (Cliona
sp.) were rarely recorded on pearl oyster shells. Other sponge species
encountered with limited distribution include Gellius cf. fibulatus
and Hyrtios sp.
Hydroids mostly settle on the outer surface of lift and dead oyster
shells and dead corals as well as hard surfaces. Hydroids were represented
by only two species: Obelia thecata and Obelia sp., the
former occurred at station 2 only and the latter was confined to stations
12, 13 and 17.
The small anemone Sagartianthus sp. was recorded in eight stations
of the oyster beds. This species usually lives on the surfaces of hard
rocks or may be attached to the rock underside.
There are two classes of Coral Alcyonaria and Anthozoa represented
in oyster beds. Very small colonies of the octacoral Dendronephthia
sp. occurred only at Station 12. The whip Coral Cirrhipathia sp.
and the sea fan Coral Gorgonia sp. were recorded in different oyster
beds. The Gorgonian sea fan (Gorgonia sp.) was found in high density
at Station 2 (Umm Khart).
Reef building Coral s such as the genera Acropora, Porites
and Montipora were found (alive or dead) in small colonies, widely
dispersed in the oyster beds. Dead forms act as a good surface for settlement
of the pearl oyster spat and other biofauling organisms. Other Corals
Reef species of the genera Favites, Platygyra, Fungia,
Tubastraea and Turbinaria, were found at several stations.
Polycheates are common on pearl shells, dead Coral and large boulders
and in substrata of oyster beds. Unidentified tube worms were found in
several stations. Among the polycheates Neries sp., was recorded
in several stations. Eunice antennata and Eunice sp. were
present in 7 and 10 stations respectively. Hydroides sp. was represented
in 8 stations and Janua kayi was present in 8 stations and Syllis
sp. was only present in Stations 2 and 17.
The number of crustacean species was low in most stations and ranked
third species in abundance (11%) in the oyster beds. However, the sample
contained a considerable number of taxa belonging to the subclass Cirripidia
and the orders Cumacea, Isopoda, Amphipoda and Decapoda (Caridea, Anomura
and Brachyura). Amphipoda species was highly abundance at Station
1 and Station 17. The most dominant crustaceans species were Peterolisthes
sp., Spider crab and Alpheus sp. and they were represented by 8,
5 and 9 species respectively. The barnacles Balanus amphitrite
were also found highly abundant in the most stations of oyster beds. Other
crustaceans known as fouling species were encountered in varying quantities.
The molluscan fauna are numerous and contributed about 55% of the
recorded fauna (104 species). The most abundant groups were gastropods
(41 species) and bivalves (60 species). The gastropods Cerathium scabridum,
Hexaplex kuesterianus, Thais tissoti, Mitrella blanda,
Nassarius (Niotha) jatabunus were dominant at station 6,
The oyster Pinctada radiata were the most dominant and present
in 15 stations. Other bivalves such as Glycymeris pectunculus maskatensis,
Malleus malleus, Malleus sp., Malvufundus regulla,
Chama asparella, Chama refexa and Chama sp. were
commonly found either on pearl oyster shells or vigorously attached to
rock surfaces or Coral crevices or no Coral boulders. In areas with soft
substratum, the pen shell (Pinna sp.) were found in few stations
and with low numbers. These were rooted deeply with their siphones protruding
above the bottom surface filtering water. Amphineura was represented by
1 species (Chiton sp.) at station 17. In the present investigation
only two species of Scaphineura (Dentalium octangulatum and Laevidentalium
longitrorsum) were encountered at station 4 and station 2 respectively.
Among the echinoderms, the brittle stars Opithrix sp. and Opiothela
venusta were the most common in rocky crevices and on Sponges. The
stars Pentaceraster mamillatus and Pentaceraster sp. were
frequent. These starfish are considered as enemies of pearl oysters because
they feed on them. Other starfishs species were present in small numbers
at selected stations.
By far the sea urchin, the sea sand-dollar Echinometra mathaei
was the most common at 9 different stations. The other sea stars Clypeaster
humilis and Clypeaster sp. were rarely seen. In general, although
the echinoderms found were of 25 species, yet they were never in abundance
as a whole.
The black ascidian Phallusia nigra and Styela canopus were
occasionally found under rocks or in crevices. The former was common at
7 stations and the latter in only 3 stations. The colonial ascidians Didemnum
sp. were common and always found spreading over dead corals or on hard
substratum and covering a wide area of the rocky surfaces.
The branchiopods were represented by only one species namely Gonodactylus
cf. demanil which was dominate at only different 4 stations (Table
Details of the Dominance for All Stations
The Eastern Area (Stations 1-6)
Six stations (stations 1-6) represent the eastern location. Biota
found at this area belongs to 12 groups. Of the 104 moullscs species encountered
(71%), 41 species were recorded at station 6 and between 10-18 species
were found at stations 1-5 (Fig. 2).
Of the 25 echinoderms, 9 species (representing 18%) were found in this
area of which 7 different species were present at station 2 and station
5 and the lowest number (1) was found at station 1.
The highest number of Crustaceans species was found at station 3 (10
species), followed by 9 species at station 7 and 7 species at stations
1 and 2.
Of 7 Algae species, 6 were recorded at station 2 and one species was
recorded at stations 5-6 Polycheates were represented by 6 species at
stations 1 and 2.
Four of the 12 Coral species were found at stations 1, 3-4 and 6. The
lowest number of Coral species was recorded at station 5. Some fauna groups
were represented by up to 3 species (Table 2).
The Southern Area (Stations 7-12)
Six stations (stations 7-12) are located within this area. Biota found
at this area belongs to 11 groups. Molluscs are usual, were highly abundance
73% particularly at station 7 (40 species) followed by 22, 20 and 19 species
at stations 8, 9 and 11 respectively. The lowest number of molluscs was
recorded at station 10 (41 species) and station 12 (17 species).
||Percentage distribution of different taxa collected from different
Echinoderms were represented by 5 species at stations 8 and 12 and with
4 for each of stations 9 and 10. The lowest number of echinoderms were
recorded at station 7 (2 species) and station 11 (1 species).
Coral species were represented with 8 species at station 8 and by only
2 at station 12. They were equally represented by 5 species at stations
9 and 10. Some fauna groups were represented by 1-4 species (Table
The Northern Area (Station 13-18)
Six stations (station 13-18) are located within this area. Biota found
at his area belongs to 12 groups. Molluscs were represented by 11 species
at stations 13-15 and 10 species at stations 17 and 18. The lowest number
of molluscs were recorded at stations 16 (3 species).
The second highest groups are echinoderms. They were represented equally
with 6 species at stations 13 and 14. The highest numbers of echinoderms
were found at station 18 (7 species).
||Species diversity indicates of biota at 18 sampling stations
of pearl oyster beds (Shannon index analysis)
Coral reef species were represented with 3 species at stations 13, 14
and 16. The lowest number of Coral species were recorded at stations 15
and 17 (1 species). Some fauna groups were represented with only 1-4 species,
or they were absent at some stations.
The species diversity indices differ slightly between 18 stations
(Table 3). The overall species diversity (H) was greater
at station 6 (H = 3.542), Station 7 (H = 3.722) and the lowest species
diversity index was recorded at station 16 (H = 0.949). The difference
unevenness followed those in species diversity (H) for all stations.
The overall evenness based on number of individual was at station 15 (J
= 0.949) and station 7 (J = 0.929). The lowest value of species evenness
occurred at Station 16 (J = 0.456).
The pearl oysters belong to the genus Pinctada (Röding)
under the family Pteriidae, enjoys a world wide distribution occurring
in almost all the seas of the tropical belt and also in the subtropical
regions. Seven species of the family Petriidae belong to 3 genera occur
in the Arabian Gulf viz., Pteria macroptera (Lamarck, 1819), Pteria
tortirostris (Dunker, 1848), Pteria penguin (Röding, 1798),
Electroma (Pterelectroma) zebra (Reeve, 1857), Pinctada
margaritifera (Linnaeus, 1758), Pinctada radiata (Leach, 1814))
and Pinctada cf. nigra (Gould, 1850), of which Pinctada
radiata (from 95% of the pearl oyster beds), Pinctada margaritifera
and Pteria marmorata (from 5% of the pearl oyster beds) have contributed
to the pearl fisheries in Qatari waters and the Arabian Gulf in general.
Pinctada radiata is found in the Arabian Gulf, Red Sea and the
Indian Ocean. Pinctada margarififera is distributed in the Arabian
Gulf, Red Sea and the Indo-Pacific and is cultured in the Pacific. In
Qatari waters, the black-lip pearl oysters Pinctada margaritifera
is mostly confined to the deeper waters around Halul Island. Most settlements
of spat of P. radiata and P. margaritifera are usually found
on the ridges of rocks and corals.
The pearl oyster beds highly dominate Al-ed Al-Gharbi, Umm Al-Jesh, Balhambar
and Tunob where the sea bottom is formed from hard and rocky substrate,
dead Coral blocks, sand with highly shell fragments, Algae and other solid
objects. Few of the oyster beds investigated were found in areas that
have sandy bottoms such as Halat Dalma, Kherees, Halat Mejaeble, Newhat
Adams and Al-Hawad where the sandy substrate does not encourage the settlement
and establishment of the pearl oyster communities.
Oyster beds investigated were with depth ranges of 6 to 25 m. These varied
widely even within the same bed.
The hydrographic data obtained during the period of study does not
show a significant differences in the temperature readings between the
different oyster beds. The summer-winter differences in water temperature
in the Arabian Gulf are remarkably high (Hunter, 1986; Sheppard et
al., 1992). Salinity reading varied with a range of 39.5 psu to 44.6
psu in the oyster beds between summer and autumn. Pearl oysters are truly
a marine form in its entire life cycle and can tolerate great variation
in salinity (Alagarswami and Victor, 1976). Salinity readings indicate
a normal pattern of variation acceptable for the normal life in the pearl
oyster beds. As a matter of fact, detailed assessment of salinity effects
may be increased, decreased or masked by other simultaneously effective
environmental factors such as light, temperature, water movement and interactions
between co-existing organisms (Nayar and Mahadevan, 1987). Dissolved oxygen
values obtained ranging from 3.35 to 4.72 mg L-1 in the oyster
beds between summer and autumn and it appears to be common in the pearl
oyster beds of Qatari waters. The oyster is not stressed much due to the
limited range of high and low oxygen concentration. It is a known fact
that the metabolism of many molluscs is independent of the ambient oxygen
tension until some low oxygen tension is reached (Nayar and Mahadevan,
Chlorophyll-a concentration fluctuated between 0.01 to 0.28 μm L-1.
Sheppard (1993) and Basson et al. (1977) stated that the chlorophyll-a
concentration fluctuated between 0.2 and 0.86 mg L-1 and showed
a wide seasonal variation. Also densities of total plankton in Arabian
Gulf waters, between the Saudi Arabia and Karan Island were 100-150x10
m3 in summer and up to 250x10m3 in winters
(Basson et al., 1977).
The very fact that the biota of the pearl oyster beds comprises the
whole assemblage of more than 189 species is considered an important ecological
parameters affecting oyster communities. They can compete with oyster
spot for space, getting food and for growth (Nayar and Mahadevan, 1987).
Al-Khayat and Al-Maslamani (2001) reported that a total of 111 fouling
organisms from 12 different pearl oyster beds occur in the Qatari waters
of the Arabian Gulf.
The Algae flora found in pearl oyster beds consists mainly of the same
types as those found on the Coral beds of rocky regions in tropical seas.
This is in accordance of Verma (1960) observation in Indian pearl banks.
In this study is has been noticed that the Coral reefs were found in
some stations, no Coral existed, while in others 1 to 4 Coral species
were found. The occurrences of Coral in the oyster beds enhance the diversity
of taxa. Most of the biota found in the pearl oyster beds consisted mainly
of the same types as those found on the Coral beds in Qatar (Al-Ansi and
Principal Component Analysis (PCA)
The raw data of depth, corals and polychaetes have normal distribution;
therefore the raw data for them were used for PCA application. Whereas,
log-transformed values were used for test application of temperature,
dissolved oxygen, chlorophyll-a, Mollusca, Ascidiacea and total species
number. Square root-transformed values were used for test application
of salinity, pH, Porifera, Crustacea and echinodermata; and second square
root-transformed values were used for test application of Algae. However,
hydrozoa, Actiniaria (Sea anemon), Sipuncula (trumpet worms) and Branchiopoda
were absent in most of the studied sites, so there data gave error when
trying to compute PCA for those species separately, therefore their records
were included only in the total species number.
In considering the assessed community structure of benthic fauna and
Algae, the following three PCA were computed:
Bottom Fauna Species-Abundance
This analysis was done to illustrate inter-relationship among benthic
fauna and Algae along the Qatari waters. It was done on data of Algae,
Porifera, Corals, Polychaetes, Crustacea, Mollusca, Ascidiacea, Echinodermata
and total species number.
Mollusca-Physical/Chemical Analysis of Sea Water
This test was made to assess the importance of depth, temperature,
salinity, pH, dissolved oxygen, chlorophyll-a, in controlling Mollusca
abundance along the Qatari waters.
The obtained results from application of factor analysis (PCA) indicated
that the analysis Bottom fauna species-Abundance yielded three
main components retained with eigenvalues greater than 1.0 (Table
4, Fig. 3). They accounted for 91.621% of the total
variance. The first and second extracted components accounted for the
largest part of the total variance (74.108%), while the third component
added 17.513%. The eigenvalue for the first component is the highest (3.822)
followed by component-2 (2.847), then component-3 (1.576). The eigenvalues
for the rest of the components were lower than 1.0 with a significant
level at 0.5.
The number of loaded species decreased from PC1 to PC3 (Table
5). Six species were loaded highly on PC1 (Algae, Corals, Polychaetes,
Crustacea, Mollusca and Total Species number). The PC2 retained with five
highly loaded species (Porifera, Corals, Polychaetes, Crustacean and Mollusca),
whereas, two species were loaded highly on PC3 (Ascidiacea and Echinodermata).
||Produced components from the Principle Component Analysis
(PCA) of bottom fauna species-abundance at different stations of oyster
beds during the present study
||Correlation level loading of considered variables in the first
two principle components in bottom fauna species-abundance at different
stations of oyster beds during the present work
|The bold values indicate correlation coefficient higher
than |0.5|; Raw data were used for test application of corals and
polychaeta; Log transformed values were used for test application
of mollusca, Ascidiacea and total species No; Square root transformed
values were used for test application of Porifera, Crustacea and Echinodermata;
Second square root transformed values were used for test application
||Produced scree plot of computed eigenvalues in different components
in bottom fauna species-abundance at different stations of oyster beds during
the present study
Plotting PC1 against PC2 (Fig. 4A) revealed that the most
dominant species on PC1 were total species number, followed by Crustacea and
Algae then Corals and Polychaetes after that Mollusca. An indirect relation
between Ascidiacea and previously mentioned species is obvious from their negative
loading on PC1. On PC2 there was indirect relation between two groups of species.
The first group includes mollusca, porifera and corals loaded positively on
PC2. The second group includes polychaetes and Crustacea loaded negatively on
PC2. The both groups were loaded positively on PC1.
Plotting PC1 against PC3 (Fig. 4B) revealed a high positive
loading of both echinodermata and Ascidiacea on PC3, this indicate the indirect
relation between echinodermata and Ascidiacea and those species loaded positively
on PC1 (those species might feed on echinodermata and ascidiacea).
Plotting PC2 against PC3 (Fig. 4C) confirmed the inverse
relation between Mollusca and porifera (a high positive loading) from one side
and polychaetes and crustacean (a high negative loading) from the other side.
The second PCA Mollusca-physical/chemical analysis of sea water yielded
seven components. Two extracted components retained with eigenvalues greater
than 1.0 (Table 6, Fig. 5). They accounted
for the largest part of the total variance (77.83%). The eigenvalues for
these two components are 3.711 and 1.736, respectively. The eigenvalue
for the rest of the components were lower than 1.0.
Component loadings revealed that water depth, temperature, salinity,
pH, dissolved oxygen and chlorophyll-a were loaded highly on PC1 (Table
7). Chlorophyll-a and Mollusca have a high load on PC2. Plotting PC1
against PC2 (Fig. 6) revealed that, on PC1 there was
indirect relation between two groups of parameters. The first group includes
salinity, temperature and chlorophyll-a loaded positively on PC1. The
second group includes water pH, dissolved oxygen and depth loaded negatively
on PC1. On PC2, Mollusca loading was high and it had a positive relation
with chlorophyll-a, pH and dissolved oxygen. The inverse association is
indicated by depth and temperature which was loaded negatively on PC2
||Produced components from the Principle Component Analysis
(PCA) of Mollusca-physical/chemical analysis of sea water during the present
||Vector plot of component loadings from Bottom fauna
species-abundance at different stations of oyster beds during the present
||Produced scree plot of computed eigenvalues in different components
in mollusca-physical/chemical analysis of sea water during the present study
||Correlation level loading of considered variables in the first
two principle components in Mollusca-physical/chemical analysis of sea water
during the present study
|The bold values indicate correlation coefficient higher
than |0.5|; Raw data were used for test application of depth;
Log transformed values were used for test application of temperature,
dissolved oxygen, Chlorophyll-a and Mollusca; Square root transformed
values were used for test application of Salinity and pH
||Vector plot of component loadings from Mollusca-physical/chemical
analysis of sea water during the present study
Generally, the two most important parameters are water salinity followed
by water temperature. Rise in these two parameters affect negatively the
total species number and positively Mollusca abundance in Qatari waters.
Comparing with previous studies of biota occurrence and distribution
conducted in the region, demonstrates that the biota of Qatari waters
is most similar to that of Saudi Arabia and Bahrain, whilst also expressing
some similarity to the rest of the region.
The authors wish to express their thanks to all scientific staff and
crew on board R/V Mukhtaber Al-Bihar of the University of Qatar, for their
assistance, we are grateful to Professor Ekhlas M. Abdel Bari from Environmental
Studies Centre, who kindly read the first manuscript. Great thank to Professor
M.A. Abdel-Moati from Supreme Council for the Environment and Natural
Reserves, who kindly read the second manuscript. Thanks extended to Dr.
Nabiha Youssif for her assistance in Principal Component Analysis (PCA).