International Journal of Oceans and Oceanography
ISSN 0973-2667 Volume 8, Number 2 (2014), pp. 137-152
© Research India Publications
http://www.ripublication.com
Variability of dinoflagellates and diatoms in the
surface waters of Muscat, Sea of Oman: comparison
between enclosed and open ecosystem
Khalid A Al-Hashmi(1)*, Joaquim Goes(2), Michael Claereboudt (1), Sergey A.
Piontkovski (1), Adnan Al-Azri (1) Sharon L Smith (3)
1-Khalid A Al-Hashmi* (Corresponding author); College of Agricultural and Marine
Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of
[email protected]
2-Joaquim Goes; Lamont Doherty Earth Observatory, Columbia University,
Palisades, NY 10964, USA [email protected]
1-Michael Claereboudt; College of Agricultural and Marine Sciences, Sultan Qaboos
University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman. [email protected]
1-Sergey A. Piontkovski; College of Agricultural and Marine Sciences, Sultan Qaboos
University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman. [email protected]
1-Adnan Al-AzriCollege of Agricultural and Marine Sciences, Sultan Qaboos
University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman. [email protected]
3-Sharon L Smith;The Rosenstiel School, University of Miami, 4600 Rickenbacker
Causeway, Miami, FL 33149 USA. [email protected]
ABSTRACT
We investigated the distribution patterns of phytoplankton species over a one
year period (from April 2010 to February 2011) at an open ocean location off
the coast of Muscat, Sea of Oman (OFF) and the other at Bandar Khayran
(BK), a semi enclosed bay located downstream of the southeastward Sea of
Oman coastal current. Although these two locations come under the influence
of the semi-annually reversing monsoons, and experience nutrient influxes
associated with the southwest (SWM, June-Sept.) and the northeast monsoons
(NEM, Nov.-Feb.), they are hydrographically distinct. At both stations, a total
of 133 phytoplankton taxa were identified and quantified over the sampling
period. The two stations showed higher phytoplankton abundance, higher
diversity and higher chlorophyll concentrations during the SWM and NEM
seasons, a reflection of phytoplankton populations responding to injection of
nutrients during these two seasons. Phytoplankton communities at both at BK
and OFF were dominated by dinoflagellates and showed no significant
differences in dinoflagellate community composition. In addition, no clear
Paper Code: 27767 IJOO
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Khalid A Al-Hashmi et al
trend of dinoflagellate or diatom species succession was observed during the
study period. Among the dinoflagellate population, Prorocentrum minimum,
Gymnodinium sp., Scrippsiella trochoidea, Gymnodinium simplex and the
mixotroph Noctiluca scintillans. On the other hand, Lauderia punctata,
Bacteriastrum elongatum and Paralia moniliformis, Chaetoceros spp.
Guinardia striata and Thalassiosira spp. were the most dominant diatoms.
Key words: Dinoflagellate, diatoms, monsoon, upwelling, Sea of Oman,
Arabian Sea, coastal environments
Introduction
The distribution of marine organisms, including phytoplankton, in coastal areas is
greatly influenced by physical, biological and chemical processes that operate over a
range of spatial and temporal scales [1, 2]. In general, coastal environments can be
categorized into two main ecosystems based on their physical and hydrographic
attributes [3, 4]; open water and semi-enclosed ecosystems. Semi-enclosed
ecosystems include lagoons, estuaries and embayment and are characterized by
restricted depths, higher inputs of nutrients and fresh water and higher turbidity due to
tidal flushing and bottom sediment resuspension. Offshore open-water ecosystems are
much deeper and hence less impacted by sediment resuspension and are generally not
light restricted. In shallow semi-enclosed coastal embayments such as these,
phytoplankton biomass, and species composition are largely controlled by light,
temperature and nutrient availability [5, 6], which are not only highly variable but can
have a huge impact on phytoplankton biomass production [7]. At certain times of the
year especially during the inter-monsoon periods, stratification can exert a major
control on light and nutrient availability [8,9] with potentially large consequences for
cycle of phytoplankton abundance and biomass variability [10]. Phytoplankton
species composition for Bhandar-Khayran (BK) and the offshore region of the Sea of
Oman (OFF) over an interannual cycle have never been reported and neither
compared before. In this study we investigate in the spatial and temporal variability of
phytoplankton in these two environments, focusing on diatoms and dinoflagellates.
Our investigation was driven by two working hypotheses: 1) the differences in
physical properties and their annual cycle between the semi-enclosed and open
ecosystem could result in large variations in phytoplankton dynamics between the two
locations, and 2) the composition of native phytoplankton communities is different
between the two locations, largely as a result of differences in environmental
conditions.
Methods
This study was carried out in coastal waters of Muscat near the embayment of Bandar
Khayran, the largest semi-enclosed bay on the southern coast of the sea of Oman with
an approximate surface area of 4 km2 and an average depth of 10 m. Two stations
were sampled; one inside the Bay (BK, 23°31′454″ N, 58°43′614″ E); the other
Variability of dinoflagellates and diatoms in the surface waters of Muscat
139
offshore (OFF, 23°35′342″ N, 58°38′123″ E) located in the open water represented
conditions occurring outside of the direct influence of the embayment (bottom depth =
100 m) (Fig.1). The investigation was carried out from April 2010 until February
2011. Sampling was carried out twice a month, during which, seawater temperature,
conductivity and depth were measured with an Idronaut-Ocean Seven 316 CTD probe
fitted with an additional sensor for Chlorophyll a (Fluorescence). Surface values for
temperature (SST) and in-situ fluorescence were averaged over the depth of the mixed
layer (maximum gradient in temperature) for comparison with seawater chlorophyll a
concentrations measured in water samples obtained from discrete depths. Seawater
samples were also collected for nitrate, nitrate, phosphate, ammonia and silicate in
acid-washed 50ml polyethylene bottles, frozen and analyzed later using a 5-channels
SKALAR® Flow Access auto-analyzer according to methods in Strickland and
Parsons, [11] as modified by the manufacturer of the analyzer [12].
Water samples (500 ml) for phytoplankton species identification and cell count
determination were collected and preserved with 1% Lugol’s iodine solution. In the
laboratory samples were allowed to settle in 20-mm diameter tubes. In order to
concentrate the phytoplankton samples a reverse filtration cone fitted with a 1 µm
pore size, Nucleopore filter® size was used to prevent loss of phytoplankton during
the concentration process [13]. Whenever possible microscopy based taxonomic
analysis of the concentrated material was undertaken to species level. The
identification and taxonomic studies are based on the following references: [14, 15,
16].
Phytoplankton community structure recorded at the two stations was analyzed
with nonparametric multivariate methods using Primer v.5® [16]. Prior to analysis the
data were Root 4 transformed to reduce the effect of a very abundant species to the
pattern. Bray-Curtis similarity index, which reflects changes in relative abundance as
well as species composition, was used to obtain multi-dimensional scaling (MDS)
ordinations. Community relationships were examined with two-dimensional plots.
The similarity/permutation test ANOSIM [17] was used to establish statistical
differences between stations, based on the Bray-Curtis similarities measure. Simper
test (in Primer 5) was used to find similarities in phytoplankton community between
stations. Simpson’s biodiversity index (in Primer 5) was used as a measure of
biodiversity of phytoplankton. BIOENV procedure (in Primer 5) and principle
component analysis (PCA) were used to correlate phytoplankton community structure
with environmental variables (Temperature, salinity, oxygen nitrate, nitrite, silicate
and phosphate). Paired t-tests were used to test significance in variables
(dinoflagellate and diatoms) between linked data sets. Seasons were determined
according to the strong seasonal signal created by the monsoons. Spring Intermonsoon
(SIM) (April-June); South-West summer Monsoon (SWM) (July-September); Fall
Inter-monsoon (FIM) (October-December); North-East winter Monsoon (NEM)
(January-March).
Results
Sea surface temperature (SST) varied from ~23 to 31oC and showed a bi-modal
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distribution with a primary summer SST peak in June and a secondary peak in
October (Fig.2). The first 2-3oC drop in SST was recorded during the SWM months of
July-August followed by the second steady drop from a high of ~31oC in the first
week of Nov. (FIM) to ~23oC by mid Feb (NEM). At both OFF and BK, the salinity
showed a slight decline during the late SWM upwelling period (July-August) (Fig.2).
These conservative physical variables exhibited similar trends at both the locations in
2010-2011.
Dissolved oxygen (DO) were highest (>7 ml l-1) during the peak SWM and during
the NEM seasons dipping to values <4 ml l-1 in May and in November. Patterns of
DO fluctuation were similar inside and outside the embayment (paired t-test, n=22,
p>0.05) (Fig.2).
Patterns of nutrient changes at the two stations revealed two peaks in inorganic
nitrate and phosphate concentrations during the SWM and NEM. Concentrations of
these two nutrients did not differ appreciably between the two stations throughout the
year, except during the SWM and NEM) when the concentrations were lower at OFF
than at BK. (Fig.3). Patterns of ammonia and silicate fluctuations were not systematic
and appeared to be independent of changes in physical processes and/or hydrographic
conditions associated with the SWM or the NEM unlike changes observed for nitrate
and for phosphate. Furthermore the concentrations of both ammonia and silicate
differed appreciably between the two stations (paired t-test, n=22, p<0.05).
In situ Chlorophyll a values varied between 0.3-2.7 µg/L and between 0.2-1.26
µg/L at BK and OFF stations respectively (Fig.2). Two Chlorophyll maxima during
July-August and January-February were observed in this study. Chlorophyll-a
concentrations were significantly different between stations (paired t-test, n=24, t =
2.5, p<0.05). Concentration, in general, was higher in the embayment in comparison
to that at offshore.
A total of 133 phytoplankton taxes were identified and quantified throughout the
sampling period at both stations. Dinoflagellates accounted for 60.7% of the total taxa
identified followed by diatoms which account for ~39.3% of the species detected by
microscopy. Station “BK” had larger populations of both diatoms and dinoflagellate
taxa (37, 61) than “OFF” station (25, 52). Simpson’s (S) diversity index, calculated
from the species count data revealed that September-October (Late SWM) and
January-March (NEM) periods were the two periods of greatest phytoplankton
diversity. April-May (SIM) and November-December (FIM) were periods of lowest
phytoplankton diversity.
Population abundances varied 100 fold over the study period, with a minimum
abundance of 426 cells L-1 in May and a maximum of 53890 cells L-1 in February
(Fig.4). A paired t-test of the species counts revealed no significant differences
between the two stations (paired t-test, t29=1.7, p=0.39
A total of 55 diatom taxa were identified and quantified in BK and OFF during the
study period. Of these, 26 species were found only at the “BK” station and 14 were
found only at the “OFF” station. Chaetoceros was the most abundant genus
represented by 12 species (11 were only found in “BK” station) followed by the
genera Thalassiosira, Nitzschia and Rhizosolenia with 8 species each. Most of the
diatom community consisted of centric diatoms as compared to pennate diatoms. BK
Variability of dinoflagellates and diatoms in the surface waters of Muscat
141
station had a more diverse pennate population than that recorded OFF (26 Vs 15 at
BK; 11 Vs 9 at OFF station). The highest diversity of diatoms in “BK” was 0.87 in
the month of October (late SWM), while it was 0.79 in March (late NE winter
Monsoon) in “OFF” station. However, the average diversities were 0.5 and 0.57 for
station BK and OFF respectively.
A total of 85 dinoflagellate taxa were identified in both stations of which 31 taxa
were only found in BK and 22 were only observed in OFF station. The majority of the
recorded species belonged to the genera Protoperidinium (18 species), Gonyaulax,
Prorocentrum and Gymnodinium (7 species). The diversity of dinoflagellates was
conspicuously high through most of the year (0.81, 0.4-0.9) and (0.72, 0.35-83) at
“BK” and “OFF” respectively. The highest diversity of dinoflagellate in both stations
was observed during the NEM and the lowest during the SIM. There were no
significant difference between dinoflagellate abundances at both stations (paired ttest, n=24, p=0.09).
Diatoms at both stations were mostly composed by centric diatoms mainly
Lauderia punctata, Bacteriastrum elongatum and Paralia moniliformis, Chaetoceros
spp Guinardia striata and Thalassiosira spp. The overall contribution of diatoms to
the total phytoplankton counts was smaller than dinoflagellates. At the OFF station, L.
punctata, B.elongatum and P. moniliformis contributed 6.7 %, 20% and 6.1 % of the
total phytoplankton production, during SIM, SWM and NEM seasons respectively.
Chaetoceros spp comprised 7.1 % and G.striata comprised 20 % of total counts
during SWM and NEM seasons in BK station respectively. Even though there were
more centric diatoms than pennate diatoms, there were no significant difference in
terms of abundance between the two groups at BK station (paired t-test, t22=1.21,
p=0.23;), however, a significant difference was observed at the OFF station ( paired ttest, t22=2.1, p=0.04). Overall diatom abundance was not significantly different at the
“BK” station from that at the “OFF” stations (paired t-test, n=24, p=0.41. On the
average, diatoms were 5 times less abundant than dinoflagellates at both stations (Fig.
4).
Phytoplankton community structure, illustrated by the MDS plot, did not differ
appreciably among samples collected at the “BK” and “OFF” station. A 1-way
ANOVA analysis of similarity (ANOSIM) also showed no significant differences in
the species composition in phytoplankton communities between the two locations
(ANOSIM R= 0.007; p = 0.33). A similar analysis on the seasonality, failed to detect
any significant seasonal differences between BK and OFF stations in overall
community structure (Stress=0.24; ANOSIM R= 0.063; p = 0.10). Also there was no
detection of significant seasonality in phytoplankton populations within BK and OFF
station (BK: R= 0.078; p= 0.11) (OFF: R=0.108; p= 0.11). The BIOENV analysis
(Primer v.5), carried out to identify possible linkages between community structure
and environment variables, showed that overall phytoplankton community in BK was
significantly correlated to changes in the measured environment variables, in
particular salinity, dissolved oxygen, nitrite, and phosphate (Rho =0.385) whereas
OFF, phytoplankton assemblages were best correlated with silicate and phosphate
(Rho =0.38).
Principal component analysis of the major phytoplankton groups and biomass
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changes in the context of the environment (Fig.5) showed that dinoflagellate at both
stations were the major contributors to Chl a and that diatoms were dependent on
silicate. Also the increase in nitrate was associated primarily with drops in surface
temperature.
Prorocentrum minimum, Gymnodinium sp., Scrippsiella trochoidea,
Gymnodinium simplex, Noctiluca scintillans were more frequently present at both
OFF and BK contributing highly to the average similarities between the two stations
(SIMPER TEST). Even though there is no significance difference in total abundance
between the two stations (paired t-test, n=22, p>0.05), these species were relatively
greater in their abundance during their maxima at BK than OFF (Fig.6). Maximum
abundance of these species was observed during the NE Monsoon, followed by SW
Monsoon season at both stations. Blooms of N. scintillans were observed over the
course of this study at the end of July 2010 during the SWM and in early January
2011 (NEM). N. scintillans counts within bloom were higher OFF station than BK
station during both the seasons (Fig. 7)
Discussion
Monthly changes in SST, dissolved oxygen, nutrients and chlorophyll-a at BK and at
(OFF) provided strong indication of the two ecosystems responding to upwelling
during the SWM and to winter cooling towards the end of the FIM into the NEM. The
sharp drop in SST during July-August for instance was clearly forced by coastal
upwelling which is typical along the coast of Oman during this period [18]. This drop
in SST coincided with a similar drop in salinity, indicating that the upwelled water
was fresher as compared to the surface waters, which are characterized by higher
salinities because of the high evaporation rates in this region. The SIM prior to onset
of the SWM soon, is also a period when rain fall is absent in the region.
During July-August, when a drop in SST and salinity were noticed, dissolved
oxygen concentrations declined due to upwelling, which also results in the shoaling of
subsurface hypoxic waters. The increase in dissolved oxygen concentrations observed
after the initial decline were associated with the increase in chlorophyll-a
concentration an indication of oxygen production by actively photosynthesizing
phytoplankton cells.
Chlorophyll a concentrations of 0.2 to 1.0 μgl-1observed in the surface waters of
BK and OFF-shore station during the SIM and the FIM are typical for oligotrophic
tropical waters [19]. The larger values (1.1-2.7 μgl-1) observed during SWM and
NEM are associated with nutrient enrichment and phytoplankton growth resulting
from shoaling of subsurface waters under the influence of local and regional winds
[20]. Our observations are consistent with that of Smith and Hollibaug (1993) who
also reported that phytoplankton biomass is generally higher in sheltered coastal
embayments than offshore.
Both stations showed higher phytoplankton abundance and thus higher diversity
during the SWM and NEM seasons, an indication of phytoplankton populations
responding to either increased nutrients influxes and/or possibly to optimal
temperature and light conditions [18, 21]. Higher chlorophyll a concentrations and
Variability of dinoflagellates and diatoms in the surface waters of Muscat
143
phytoplankton abundance were observed inside BK the in the OFF station during
these seasons. While in part, the greater growth of phytoplankton in BK may be
related to its unique hydrographic conditions and possibly due to the reduced grazing
pressure. As can be seen in Fig.8, [22] copepods, were one of major grazers of
phytoplankton and were much higher in number in OFF as compared to BK. Corals
abound in BK and their presence, could have led to a decline in zooplankton numbers
thus reducing grazing pressure in the embayment [23]. Corals are also known to
produce exudates can also cause nutrient enrichment [24]. In addition, because BK is
a shallow embayment, enhanced wind activity during the SWM in particular can
cause sediment resuspension and nutrient enhancement [25].
Phytoplankton communities at both locations were dominated by dinoflagellates
that appeared to be the major contributor to Chl a biomass (Fig.5). These findings are
consistent with previous reports which indicate the dominance of dinoflagellates in
the coastal water of Muscat during most of the year [7,26] and in the Sea of Oman
during FIM [27]. At our two sampling sites, dinoflagellate numbers did not differ
significantly and both stations showed increases during the SWM and the NEM, an
indication of the positive response of this group of organisms to nutrient enrichment
of the water column.
Our observations suggest no clear indication of dinoflagellate species succession
over the course of the year at both the stations. Dinoflagellate assemblages at the two
stations were largely made up of cells of P. minimum, Gymnodinium sp., S.
trochoidea, G. simplex, N. scintillans. The relative contributions of these five species
to overall abundance differed both spatially and temporally (Figure.6). The highest
contribution to overall abundance of P. minimum was during SIM in OFF station
(34%), while it was during SWM in BK (37%). P. minimum was responsible for 40%
and 32 % of the total contribution of phytoplankton counts during the study periods in
OFF and BK stations respectively. P. minimum could be considered as the key species
in controlling the population’s abundance in these waters. Gymnodinium sp.
contribution was almost constant in all seasons in BK station making about 15 % of
the total counts, but it dominated the FIM assemblages in OFF station, contributing
about 30% of the total abundance, and less than 10 % in SIM and SW Monsoon
seasons. Gymnodinium sp. ranked second in overall contribution to total counts in
both stations. The maximum contribution of S. trochoidea to phytoplankton
assemblage was observed during the NEM season at BK station and during the SWM
at OFF station. S. trochoidea appeared to be more important species in BK than in
OFF station, while N. scintillans is more important in OFF than in BK Station. G.
simplex showed higher contribution during fall in both stations but more abundance in
BK station than OFF station.
During our study we observed, bloom of N. scintillans at the end of July 2010 and
in early January 2011 coincident with the shoaling of nutrient and hypoxic waters.
The occurrence of N. scintillans blooms twice a year (August-October) and
(December-February) is a common phenomenon in the Sea of Oman (26, 28]. The
cell concentrations of this species were found to be higher OFF station than at BK
during both periods (Figure.6). These differences in cell densities are probably due to
hydrographic differences between an open and an enclosed ecosystem and to the
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different conditions prevailing at both locations [26]. The Noctiluca bloom in BK
appeared to be the result of concentration and accumulation of cells caused by tidal
inflow and currents along the mountain side of the bay. Blooms of N. scintillans
appeared to occur when water temperatures ranged from 24 to 27 0C. This
temperature values are reported to be among the optimum ranges for N. scintillans
bloom formation [29,30,31].
S. trochoidea and P. minimum are frequent observed species in BK [25]. These
species had relatively higher abundances during their maxima (Fig.10). The maximum
abundance S. trochoidea was during the SWM and NEM, while P. minimum peaked
during the SWM in BK and during the SIM OFF. However, Gymnodinium sp. showed
maximum abundance during NEM OFF and during the SWM and NEM at BK. G.
simplex was more frequently part of the phytoplankton assemblages in BK rather than
OFF station.
It has been described previously that phytoplankton assemblages selected under
regular patterns of environmental conditions tend to share similar characteristics and
adaptation strategies [32]. S. trochoidea for instance is known to tolerate broad range
of temperature variability [33] whereas P. minimum can grow better under high light
conditions or warm temperatures [34]. P. minimum and S. trochoidea are known to
acquire energy by phagotrophic mode of nutrition [35, 36]. Moreover, these species
are very small and similar in size; G. simplex: 15-20 μm; P. minimum: 14-22 μm; S.
trochoidea: 20-23 μm, which allow them to take up nutrients even at very low
concentration [35] and compete other phytoplankton species. These dinoflagellates
species were frequent components of phytoplankton assemblages found at BK where
conditions of low turbulence, relatively higher temperatures and light regimes and
nutrient extremes would have favored their growth.. Also species like S. trochoidea
are known to form cysts [37]. Cysts supply seed to the water column, thus enhancing
the ability of this organism to survive and proliferate [38]. We suggest that shallow
embayments like BK along the coast of Oman, could function as sedimentary basins
serving to supply the water column with this species.
Despite the fact that diatom abundance was not significantly different between BK
and OFF, it was found that certain taxa dominating each station are spatially and
temporary different.The diatom assemblages at OFF during the SIM were only
composed of L. punctata, being dominant, Thalassiosira eccentric and Nitzschia sp.
The increase in nutrient supply during the SWM saw an increase in the of diatoms
whose populations were dominated by chain forming species, B. elongatum and
Leptocylindrus danicus. On the other hand, diatom populations during the FIM at
OFF was composed of only 2 small-size species, Pseudo-nitzschia delicatissima and
T. eccentrica, due to the reduction in the supply of nutrients, causing phytoplankton
diversity during this season to be the lowest. The NEM diatom assemblages were
characterized by a mix of 13 different taxa dominated primarily by centric diatoms
Helicotheca tamesis, Paralia moniliformis. The diatoms Climacodium
frauenfeldianum, Guinardia flaccida, L. danicus, Chaetoceros cinctus and the pennate
diatom P. delicatissima were dominant during this period as a result of nutrient
influxes.
The composition of the diatom assemblages at BK was driven by the nutrient
Variability of dinoflagellates and diatoms in the surface waters of Muscat
145
availability especially silicate and regenerated nutrients from within the Bay
(Ammonia). This was evident when a shift from small and very low abundant diatoms
P. delicatissima and T. eccentrica during the SIM was followed by the chain-forming
diatoms Chaetoceros species mainly Chaetoceros compressus (18.5%) and
Chaetoceros pseudocurvisetus (20%) during the SWM. Eleven Chaetoceros species
dominated the phytoplankton assemblages at BK station, making more than 60% of
the total phytoplankton abundance. The small centric diatoms of T. eccentrica and
Thalassiosira subsalina, were the major contributors to the diatom assemblages of the
FIM. The NEM assemblage of diatoms at BK were characterized by a mix of 52
different taxa chiefly dominated by Guinardia striata that composed more than 20 %
of total phytoplankton population. The other contributors were centric diatoms
Thalassiosira subtilis and Paralia moniliformis.
T. eccenrica is the only diatoms that frequently occurs representing a noticeable
contribution (20%) to total phytoplankton during the study period at BK alone.
Diatoms were a negligible component of the assemblages of OFF contributing to the
very low diversity of diatoms for most part of the year at OFF. The highest diversity
of diatoms at BK was in the month of October (late fall), while OFF, it was in March.
There are some species, during this study which were only found at only one
stations. These species can be regarded as rare species and could have either been
missed during sampling or during identification. For example, B. elongatum which
was only found at OFF was reported earlier to be part of BK diatoms assemblages
[26]. Similarly, Chaetoceros species and many Thalassiosira species were more
common in BK than in OFF. Most of these species produce resting spores during
unfavourable environmental conditions and nutrition limitation, especially nitrogen
[39, 40, 41]. These spores then germinate and migrate from the shallow bed of BK
into the water column allowing them to be more common in BK station than OFF
station. Spore formation could be a major factor determining planktonic dynamics in
marine environment [42].
Conclusions
Physical and biological properties exhibited similar trends in their seasonal variability
at BK and at OFF during 2010-2011. The two stations showed higher phytoplankton
abundance, higher diversity and higher chlorophyll concentrations during the SWM
and NEM seasons. This increase in abundance was related to injection of nutrients
during these two seasons. Phytoplankton communities at both stations were mostly
dominated by dinoflagellates. There were no appreciable differences in phytoplankton
communities between the two stations. Despite these similarities, variations were
observed in succession and abundance of some species. Higher phytoplankton
abundance of the dominant species were observed BK station. This was probably the
result of the higher nutrients supply either from upwelled water or from regenerated
nutrients from within the bay at BK. Also BK is very calm environment as compared
to OFF.
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Figure1. Map of Oman (A) and sampling sites (B)
32
T-BK
A
T-OFF
28
psu
SST(C)
30
26
24
22
A M J
A S O N D
J
37.4
37.2
37.0
36.8
36.6
36.4
36.2
36.0
F
A M J A S O N D
Months(2010-2011)
A S
O N D J
F
Months(2010-2011)
Ox-OFF
Ox-BK
J
F
microgram/L
mg/L
C
S-OFF
A M J
Months(2010-2011)
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B
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1.5
1.0
0.5
0.0
D
Chl-BK
Chl-OFF
A M J
J A S O N D J
Months(2010-2011)
F
Figure 2. Distributions of surface water temperature (A), Salinity (B), dissolved
oxygen (C) and Ch a (D) in BK and OFF stations
Variability of dinoflagellates and diatoms in the surface waters of Muscat
4.0
Si-BK
A
Si-off
3.0
2.0
1.0
2.5
Micromole/L
Micromole/L
5.0
0.0
2.0
PO4-off
1.5
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J A S O N D J F
A M J J A S O N D J F
Months(2010-2011)
Months(2010-2011)
NH4-BK
NH4-off
C
No2+No3 BK
8.0
Micromole/L
Micromole/L
PO4-BK
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A M J
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147
6.0
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2.0
0.0
A M J J A S O N D J F
Months(2010-2011)
A M J J A S O N D J F
Months(2010-2011)
Figure 3. Micronutrients (μM/L) distribution in BK and OFF stations
Figure 4. Diatoms and dinoflagellates abundances (Cells/L) in BK and OFF
stations
148
Khalid A Al-Hashmi et al
BK
OFF
Figure 5. PCA analysis showing the grouping of the 2 major phytoplankton
groups (diatoms and dinoflagellates) and their relationship to environmental
variables at OFF and at BK.
4000
3500
A BK
Cells/L
3000
N.scintillans
G.simplex
S. trochoidea
Gymnodinium sp.
P.minimum
2500
2000
1500
1000
500
0
SIM
2500
B
SWM
OFF
FIM
NEM
FIM
NEM
Seasons
Celss/L
2000
1500
1000
500
0
SIM
SWM
Seasons-2010
Figure6. Average seasonal abundances of most frequent dinoflagellates (Cells/L)
in BK and OFF stations
Variability of dinoflagellates and diatoms in the surface waters of Muscat
2500
149
Noctiluca scintillans-off
Noctiluca scintillans-bk
2000
Cells/L
1500
1000
500
0
A
M
J
J
A
S
O
D
J
F
Months(2010-2011)
Figure 7. Monthly abundances of Noctiluca scintillans in BK and OFF stations.
BK-Cop
700
OFF-Cop
Indv.Copepod/m3
600
500
400
300
200
100
0
A
M
J
J
A
S
O
Months(2010)
Figure8: Copepods abundance (m3) in BK and OFF stations. Modified after
Piontkovski et al., 2013, [22].
Acknowledgements
We acknowledge the support of the Department of Marine Science and Fisheries,
150
Khalid A Al-Hashmi et al
Sultan Qaboos University for the work reported here. This research is supported by
the grants under the projects RC/AGR/FISH/10/1 and U.S National Science
Foundation grant number 0825598
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