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Chapter 4.1 Plankton

MohaMMeD a. Qurban1, MohiDeen Wafar1, Moritz heinle1, KaruppasaMy p. ManiKanDan1,
toDD r. ClarDy1, and KhaleD a. al-abDulKaDer2
The term “plankton” (derived from the Greek meaning “drifters”) is applied to a group of organisms in
seawater that lack (or have very feeble) capacity for independent locomotion, the distribution of which is
thereby determined by physical processes such as circulation and stratication. Based on mode of nutrition,
they are classied into two major groups of phytoplankton, which are autotrophic and zooplankton, which
are heterotrophic. They are further subdivided based on size (phytoplankton) or mode of life (zooplankton),
an approach that is essential to understand the patterns of biological production in sea and ecosystem
responses to external forcing.
Studies of plankton are important in four respects. The rst is that the phytoplankton, thanks to their
ability to synthesize organic matter, sustain their biological production in the sea. In fact, they account
for up to half of the global primary production (Field, et al., 1998). Second, life histories of almost all of
the marine shes pass through a planktonic phase and understanding, or even predicting, the success of a
shery is conditional on a good understanding of the (ichthyo) plankton dynamics. Third, the planktonic
phases of the life histories enable a wider distribution of biodiversity and colonization of new areas, and in
the current scenarios of intense coastal development, of even recolonization of aected areas. Finally, again
in the context of global changes, responses of dierent groups of short-lived plankton to environmental
conditions and changes in them provide a better insight into the future of the marine ecosystems.
Previous studies on plankton of the Arabian Gulf can be sorted into two groups, based on the extent
of coverage. The rst includes studies that are restricted to specic groups or geographically localized
(Bohm, 1931; Weigmann, 1970; Fenaux, 1973; Furnestin and Codaccioni, 1968), and considered along
with a few others (Yamazi, 1974; Al-Kaisi, 1976; Gibson, et al., 1980; Hendey, 1970; Enomoto, 1971; Kimor,
1973; Kuronuma, 1974; Al-Kaisi, 1976; Jacob, et al., 1979; Dorgham, et al., 1987; Al-Abdulkader, 1991; Al-
Abdulkader and El-Sayed, 1992), constitute the baseline studies before the 1990 oil spill in the Gulf.
While some of the post-spill studies were meant to assess the impact of oil spill on phytoplankton
biomass, productivity and community (El-Gindy and Dorgham, 1992; Habbashi, et al., 1992), two recent
studies stand out in terms of wide geographical coverage. The rst is the Oceanographic Survey for
Damage Assessment (OSDA) program wherein data on plankton were obtained in the entire spread of
the Saudi Arabian waters of the Arabian Gulf in ve cruises between 2002 and 2003. The second is the
Center for Environment & Water, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran, Kingdom of Saudi Arabia.
Email address:
2 Environmental Protection Department, Saudi Aramco, Dhahran, Saudi Arabia.
Sustaining Research Program (2010-2015) of King Fahd University of Petroleum and Minerals (KFUPM),
wherein data on phytoplankton biomass, composition and productivity, along with a set of environmental
factors and nutrients, were obtained at eight nearshore stations from the northern end to the southern end
of the Saudi Arabian waters of the Gulf. As these two constitute the largest data sets, they have been taken
to form the basis of this chapter.
Sampling stations were located between 26° 40’ N and 28° 40’ N, and between 48° 40’ E and 50°
45’ E, covering an spread from Al-Khafji to Ras Tanura (Figure 4.1). The ve cruises under OSDA were
undertaken in November-December 2002 (late fall), January 2003 (winter), April-May 2003 (spring),
June-July 2003 (onset of summer) and August 2003 (summer). A total of 272 samples were collected
for analyses of phytoplankton, zooplankton and ichthyoplankton. While the nets used for these groups
were of similar length (2 m) and mouth openings (50 cm dia), the mesh sizes of the nets were 53 µm for
phytoplankton, 250 µm for zooplankton and 330 µm for ichthyoplankton.
Sustaining Research
In the Sustaining Research surveys, six locations: Manifa (Mn), Ras al-Khair (Rk), Abu ‘Ali (AA), Tarut
Bay (Tb), Dammam (Dm) and Salwa (Sl), were sampled (Figure 4.2). At all locations, two inshore stations
– one close to the shore and one 3 km to 4 km away – were sampled. At both stations in a given location,
measurements of primary production were made at the surface and the bottom. In the Salwa sector, six
stations were sampled in every sampling period and sampling was either only on the surface or at two
depths (surface and bottom) depending on the depth of the water column at the station.
The temporal coverage was initially designed for sampling in winter and summer of every year for a
period of 3 years, from summer 2010 to winter 2013. Accordingly, the rst sampling was done in the summer
of 2010, the second in the winter of 2011 and the third in summer of 2011. Consequently, to cover all of the
seasons, the fourth and fth surveys in 2012 were conducted in spring and autumn, respectively. Therefore, it
was possible to have data sets for all the four seasons. The last set of measurements was done in winter 2013.
Field Methods
Primary production was measured by the use of a radioactive tracer of carbon (14C) and the standing
crop phytoplankton was measured as Chl a. Aqueous sodium bicarbonate of 5 µCi ml-1 was used as a tracer.
Incubation of the samples with 14C (5 µCi of labeled sodium bicarbonate) were performed in situ for 2
hours and at the end of the incubation periods, the samples were ltered onto Millipore lters of 0.45 µm
pore size. The number of samples incubated at any one given station varied from two light bottles and one
dark bottle to only light bottles depending upon the availability of the tracer.
Figure 4.1. Sampling stations for phytoplankton, zooplankton and ichthyoplankton during the OSDA cruises.
Figure 4.2. Map showing the locations of sampling stations in the Saudi coastal waters of the Arabian Gulf. Mn: Manifa,
Rk: Ras al-Khair, AA: Abu ‘Ali , Tb: Tarut Bay, Dm: Dammam, Sl: Salwa.
Water samples for measurements of concentrations of Chl a and nutrients were obtained from the
same location and depths as those for determination of primary production. Relevant physico-chemical
parameters (temperature, salinity, dissolved oxygen and pH) that inuence primary productivity were
measured with a portable water quality analyzer (YSI 55 Water Quality Meter), which was regularly
calibrated following the procedures recommended by the manufacturer.
Analytical Methods
The lters with 14C labeled particulate matter were dried, exposed briey to fumes of hydrochloric acid
and the radioactivity was counted in a Beckman LS6000 model liquid scintillation counter. The water samples
meant for determination of concentrations of Chl a were ltered onto GF/F (0.45 μm nominal porosity)
lter pads. The Chl a was then extracted in 10 ml of 90% acetone, its uorescence was measured in a Turner
Designs Trilogy Fluorometer and its concentration was calculated using the equations of Lorenzen (1966).
Concentrations of nutrients (nitrate, nitrite, phosphate and silicon) were measured using a Skalar Auto-Analyzer.
Zooplankton sampling and biomass estimation were done following the procedures described in
UNESCO (1968) and ICES (2000) zooplankton methodology manuals. After the estimation of biomass (as
displacement volume and wet weight), the species composition of the sample was determined. In samples
with low concentration, subsamples of 50% were removed using a Folsom plankton splitter, whereas
in samples with higher concentrations of small-sized animals (e.g., copepods), aliquots were taken from
diluted samples, using a stemple pipette (12.5 ml). In both cases, subsamplings were extracted only after
removing large-sized zooplankton. Final identication was done on one-half to one-third of the total
sample. While a minimum 50% of each sample was analyzed for low-abundance species, the entire sample
was analyzed for medusae and crustacean larvae (especially decapod larvae). The counts and identication
were made using either stereomicroscopes (Olympus, model SZ 11) or research microscopes (Olympus,
model CX 41, and Nikon, model Eclipse E600).
As with the zooplankton samples, the ichtyoplankton (sh eggs and larvae) were sorted under stereo-
zoom microscopes and their biomass (as displacement volume) and density (numbers/100 m3) were
recorded. The samples further sorted species-wise or group-wise, to the extent possible.
This section deals with environmental and biological data. Environmental data includes parameters
such as irradiance and nutrients while biological data includes primary production, planktonic biomass and
species composition of phytoplankton.
Surface incident solar radiation is the major controlling factor of primary production and seasonality in
the former, which determines the seasonality in the latter. Figure 4.3 shows the photosynthetic active radiation
(PAR) in the Gulf during the winter, spring, summer and autumn of 2015 obtained from the ocean color
website ( PAR in winter was lower along the Northwest, adjacent to
Al-Arab waterway, probably due to sedimentation. In the summer, it was very high in some isolated pockets
in the north and in the inner bays. The lowest PAR among the four seasons was recorded in the autumn.
Measurements of concentrations of nutrients in the Arabian Gulf are few and far between and these
suggest that these waters are oligotrophic, a condition that is readily explainable by the absence of any
freshwater advection into the Gulf except at Shatt el Arab. In one of the earlier papers, El-Samra (1988)
reported a range of 0.12 to 0.23 µmol L-1 for phosphate and 0.26 to 0.30 µmol L-1 for nitrate, which were
signicantly lower than those measured outside the Gulf: 0.36 to 0.47 µmol L-1 of phosphate and 0.41
µmol L-1 of nitrate in the Strait of Hormuz and Gulf of Oman.
Figure 4.3. Photosynthetic active radiation (PAR) in the Gulf during the winter, spring, summer and autumn of 2015
obtained from ocean color website (
It was not until recently that more complete sets of data on nutrients, with a large spatial and seasonal
coverage, became available for the Saudi Arabian waters (KFUPM/RI, 2015). The range and average
concentrations (in parentheses) reported were: Nitrate – 0 to 0.83 µmol L-1 (0.17 µmol L-1); nitrite – 0
to 0.22 µmol L-1 (0.10 µmol L-1); phosphate – 0 to 0.67 µmol L-1 (0.14 µmol L-1); and silicon – 0 to 1.73
µmol L-1 (0.71 µmol L-1). These are remarkably similar to the concentrations measured elsewhere in the
Gulf (El-Samra, 1988). When a few high values are excluded, concentrations of nitrate and phosphate were
lower than 0.2 µmol L-1 at all stations, without any north-south gradients. Likewise, concentrations of
silicon were also uniformly lower than 1 µmol L-1. The dierences between concentrations of nutrients at
the surface and the bottom were not signicant.
Figure 4.4 shows, as an example, the concentrations of nutrients (nitrate, nitrite, phosphate and silicon)
measured in the spring at the stations occupied during the Sustaining Research Program (KFUPM/RI,
2015). What is remarkable here is the persistence of low concentrations at all stations and also the absence of
any inshore-oshore gradient. Only at stations near Dammam did the concentrations increase signicantly, a
situation owing to the fact that the site receives a large amount of wastewater from the Dammam municipality.
Phytoplankton Biomass
Figure 4.5 shows the patterns of distribution of Chl a in the nearshore and oshore stations during
the OSDA cruise, and Figure 4.6 shows the patterns in the coastal waters obtained during the Sustaining
Figure 4.4. Concentrations of nutrients (mean ± SE) during the spring of 2012.
Figure 4.5. Concentrations of Chl a (in µg L-1) in Saudi Arabian waters of the Arabian Gulf based on data obtained during
the OSDA cruises.
Figure 4.6. Concentrations of Chl a (in µg L-1) in Saudi Arabian waters based on data obtained during the Sustaining
Research Program.
Figure 4.7. Mean Chl a concentrations (with ranges) in the entire Saudi Arabian waters of the Arabian Gulf based
on data from OSDA cruises.
Research Program. Four major features become remarkable in these distributions. The rst is that most of
the concentrations measured were less than 2 µg L-1, indicating an oligotrophic status that agrees with the
concentrations of nutrients. The second is the gradient between inshore and oshore stations visible in the
OSDA data: In spring and summer, the coastal waters sustained a higher biomass, which became gradually
reversed in the autumn, culminating in a denite pattern of higher concentrations oshore in the winter
than in the inshore area. The third is the seasonality, even within these low concentrations, seen in both
data sets, which shows the low concentrations in the spring and the summer giving way to an increase in
the autumn to peak values in the winter (Figure 4.7). The fourth is the exceptionally higher values of Chl a
at stations located near sites of metropolitan cities: Concentrations at Dammam and Tarut Bay were several
times higher than elsewhere at any time of the year (Figure 4.6).
The data collected during the OSDA cruises were also helpful in describing the vertical distribution
of Chl a. The presence of subsurface Chl a maxima at depths between 25 m and 30 m was prominent
in oshore waters during the spring through summer, Figure 4.8. These subsurface Chl a maxima were
associated with the thermocline. Subsurface water of the coastal region oshore of Manifa to Jubail showed
relatively high Chl a concentrations in all seasons, Figure 4.9.
Primary Production
An earlier study in the Saudi Arabian waters (Al-Abdulkader and El-Sayed, 1992), covering a period
of three years from 1985 to 1988, showed that the rates of primary production were low, not greater than
5.12 µg C L-1 h-1 in the summer. Rates of production were still less in the autumn (average of 4.71 µg C L-1
h-1) and lowest in the spring (2.1 µg C L-1 h-1). The annual primary production estimated for the Arabian
Gulf with these data was of the order of 136 x 106 tons of carbon.
Data from the Sustaining Research Program showed that carbon uptake rates ranged from <1 to
>20 µg C L-1 h-1 (Figure 4.10). A comparison of the seasonal averages (Table 4.1) showed that the
Figure 4.8. Vertical distribution of Chl a along offshore waters.
Figure 4.9. Vertical distribution of Chl a in coastal waters.
Figure 4.10. Primary production (in µg C L-1 h-1) in Saudi Arabian waters of the Arabian Gulf between 2010 and
2012. Data from Sustaining Research Project, Phase V.
Table 4.1. Ranges in and averages of carbon assimilation rates measured at the eight locations along the Saudi coast
of the Arabian Gulf.
Season Range in Carbon Assimilation
(µg C L-1 h-1)
Averages for all Stations
(µg C L-1 h-1)
Averages Excluding Stations
at Dammam and Tarut Bay
(µg C L-1 h-1)
Spring 2012 3.52–15.35 9.45 9.23
Summer 2010 0.31–22.67 6.51 3.51
Autumn 2012 0.17–19.10 6.14 3.58
Winter 2013 0.22–13.06 2.02 1.52
highest production rates were recorded in the spring, followed by near similar rates in the summer
and autumn, and lowest rates in the winter. What is interesting in these data is the fact that when the
data for Dammam and Tarut Bay are excluded, then the averages for summer, autumn and winter are
reduced by about a factor of 2 (last column in Table 4.1). Taken together with the high nutrient and
Chl a concentrations measured at these stations, this clearly shows that the production rates at these
two sites are inuenced by proximity to municipal and industrial euent sources. It was only in spring
that the rates of primary production were high all along the coast (Figure 4.10; Table 4.1). While the
averages deduced by excluding the data from Dammam and Tarut Bay are reminiscent of the data of
Al-Abdulkader and El-Sayed (1992), they also suggest that in the 30-year period between the two sets
of measurements, anthropogenic inuence on the coastal waters of Dammam and Tarut Bay must have
increased tremendously.
Spatial and Seasonal Patterns
To elucidate patterns of spatial changes, primary production, phytoplankton biomass and nutrient
concentrations at three locations Manifa in the north, Dammam in the middle, and Salwa in the south of
Saudi Arabian waters were compared (Figure 4.11). The average rates of primary production, phytoplankton
biomass and concentration of nitrate showed signicant variations between the three locations.
In the winter, levels of Chl a and rates of primary production were low, suggesting a limitation by light
and possibly by temperature. While the increase in biomass in the spring was not pronounced, there was a
rapid increase in primary production so that seasonal peak values were attained in Manifa and Salwa. After the
spring peak, levels of primary production decreased through the summer and autumn in Manifa and Salwa,
whereas it continued to increase in Dammam toward a summer peak value, followed by a decrease. Chl a
concentrations, on the other hand, continued to increase toward a summer peak before decreasing in autumn.
Changes in the concentrations of nitrate were not pronounced and in most of the seasons, they remained
less than 0.4 µmol L-1, except in the autumn when the average concentration rose to 1.15 µmol L-1 at Salwa.
Overall, concentrations of nutrients were low at any time, and therefore, they would have a signicant
inuence on controlling primary production. The low rates of primary production in the winter and
Figure 4.11. Seasonal changes of (a) primary production (in µg C L-1 h-1), (b) phytoplankton biomass (in µg chl a L-1) and
(c) concentrations of nitrate (in µmol N L-1) at three locations in the coastal waters.
the subsequent increase in the spring indicate that light has an important controlling eect on primary
production. The decrease in production in the summer is more likely as a result of low concentrations of
nutrients. The increase in Dammam could have been supported by regenerated nitrogen because this site
receives large amounts of wastewater (Sadiq, et al., 1982). The Chl a peak in the summer suggests that
the buildup of biomass is slow after the spring peak. Light has a more controlling inuence on primary
production than nutrients. Though a seasonality is evident, peak production values are not of sucient
strength to cause a bloom.
Phytoplankton Species Composition
The phytoplankton community in the Arabian Gulf is characterized by high species diversity. Two
reviews (Jacob and Al-Muzaini, 1990; Jacob and Al-Muzaini, 1995) list a total of 888 diatom species and
211 dinoagellate species for the complete area of the Arabian Gulf. In an earlier study in the Saudi
Arabian waters, Al-Abdulkader and El-Sayed (1992) identied 77 species of diatom and dinoagellates,
with the abundance of diatoms ranging from 59% to 100% of the total phytoplankton count. Table 4.2 lists
all the diatom and dinoagellate species recorded since then by KFUPM in various surveys in the last two
decades. Figure 4.12 illustrates the percentage distribution of various groups of phytoplankton in the Saudi
Arabian waters, showing that diatoms (68%) and dinoagellates (29%) dominate the community.
Species-wise, the dominance of the phytoplankton community is highly variable. In terms of cell densities,
the colonial cyanobacteria Trichodesmium erythraeum and Oscillatoria limosa were dominant at various times
(KFUPM/RI, 2015). Other species dominating the phytoplankton community by cell numbers at times
were the diatoms Rhizosolenia alata, Chaetoceros curvisetus, Thalassiosira subtilis, Lauderia annulata, Thalassiothrix
frauenfeldii, and the dinoagellate Gonyaulax monilata. Subsequently, cell numbers do not show the full picture.
While studying such dominance, it is equally important to take phytoplankton biomass (carbon content)
into account and dierentiate between small (low carbon content) and large (high carbon content) species.
Smaller species might occur at high numbers, but their role in the production of carbon biomass could be less
important. Often this biomass comparison is restricted to certain important species in the ecosystem because
it involves very laborious methods. Each species is assigned a certain geometrical shape and a number of size
measurements are taken to calculate cell volumes (Hillebrand, et al., 1999). At least 25 individuals of each species
are measured under the microscope and the volume is calculated from the medians of these measurements.
The computed volume can then be converted to carbon biomass using group specic conversion factors
(Menden-Deuer and Lessard, 2000), and when multiplied with cell numbers, gives the total biomass of each
species in the study area (Table 4.3). For example, Thalassionema nitzschoides which ranked second in terms
of cell numbers, occupied only a 12th position in terms of biomass. Other species that are less important in
biomass than they are in cell numbers are Scrippsiella trochoidea (from 5th rank to 10th), Prorocentrum micans
(from 3rd to 6th), Prorocentrum gracile (from 1st to 2nd), and Ceratium fusus (8th to 9th). In contrast, Akashiwo
sanguinea ranks 13th in cell number, but 8th in biomass, and Pyrodinium bahamense var. compressum rises from
rank 10 to four when biomass is considered. Other species that are more important by biomass than by cell
number are Ceratium furca (4th to 1st), Gyrodinium spirale (7th to 3rd), Protoperidinium minutum (9th to 7th), and
Protoperidinium steinii (6th to 5th). The fact that nine out of 10 species (abundance by cell number), and all 10
species (abundance by biomass) are dinoagellates agrees with Margalef s mandala (Margalef, 1978), which
states that dinoagellate species should dominate the phytoplankton community in environments with a
stable temperature, light, and nutrient regime.
Table 4.2. List of diatoms, dinoflagellates and cyanobacteria enlisted by KFUPM/RI (2015).
Actinocyclus octonarius
Actinocyclus octonarius var.
Amphora egregia
Amphora obtuse
Amphora ostrearia
Amphora proteus
Amphora sulcate
Amphora turgida
Auricula amphitritis
Bacillaria paxillifera
Bacillaria socialis
Bacteriastrum delicatulum
Bacteriastrum elongatum
Bacteriastrum hyalinum
Bacteriastrum sp.
Bellerochea malleus
Carinasigma rectum
Cerataulina dentate
Chaetoceros atlanticus
Chaetoceros coarctatus
Chaetoceros compressus
Chaetoceros costatus
Chaetoceros curvisetus
Chaetoceros danicus
Chaetoceros decipiens
Chaetoceros diadema
Chaetoceros diversus
Chaetoceros laciniosus
Chaetoceros laevis
Chaetoceros lauderi
Chaetoceros lorenzianus
Chaetoceros messanensis
Chaetoceros peruvianus
Chaetoceros teres
Chaetoceros tortissimus
Climacosphenia moniligera
Cocconeis guttata
Coscinodiscus granii
Coscinodiscus sp.
Coscinodiscus marginatus
Coscinodiscus radiatus
Coscinodiscus wailesii
Cylindrotheca closterium
Dactyliosolen fragilissimus
Diploneis didyma
Diploneis smithii
Diploneis suborbicularis
Diploneis weissflogii
Donkinia recta
Entomoneis sulcata
Fragilaria synegrotesca
Fragilariopsis cylindrus
Fragilariopsis oceanic
Grammatophora marina
Grammatophora oceanica
Guinardia delicatula
Guinardia flaccida
Guinardia striata
Haslea balearica
Haslea ostrearia
Hemiaulus membranaceus
Hemiaulus sinensis
Lauderia sp.
Leptocylindrus danicus
Leptocylindrus minimus
Licmophora splendid
Licmophora sp.
Lithosdesmium undulatum
Lyrella hennedyi
Lyrella praetexta
Mastogloia arabica
Mastogloia erythraea
Mastogloia grunowi
Mastogloia linearis
Mastogloia smithii
Navicula directa var. remota
Navicula peregrina
Navicula ramosissima
Navicula transitans
Neocalyptrella robusta
Nitzschia acicularis
Nitzschia amphibia rostrata
Nitzschia coarctata
Nitzschia constricta
Nitzschia distans
Nitzschia fluminensis
Nitzschia lorenziana
Nitzschia lorenziana Grunow
var. subtilis
Nitzschia palea
Nitzschia panduriformis
Nitzschia recta
Nitzschia sigma
Nitzschia sp.
Pinnuavis elegans
Plagiogrammopsis vanheurckii
Plagiotropis lepidoptera
Plagiotropis gaussii
Pleurosigma angulatum
Pleurosigma elongatum
Pleurosigma formosum
Pleurosigma strigosum
Proboscia alata
Pseudo-nitzschia delicatissima
Pseudo-nitzschia pungens
Pseudo-nitzschia seriata
Pseudo-nitzschia turgidula
Rhizosolenia cochlea
Rhizosolenia imbricate
Rhizosolenia pungens
Rhizosolenia styliformis
Rhoicosigma compactum
Striatella unipunctata
zSurirella fastuosa
Surirella sp.
Thalassionema bacillare
Thalassionema frauenfeldii
Thalassionema nitzschioides
Thalassiosira eccentric
Trachyneis antillarum
Trachyneis aspera
Triceratium cf. broeckii
Akashiwo sanguinea
Alexandrium minutum
Alexandrium insuetum
Alexandrium sp.
Ceratium carriense
Ceratium furca
Ceratium fusus
Ceratium inflatum
Ceratium lineatum
Ceratium trichoceros
Ceratium tripos
Cochlodinium sp.
Dinophysis caudata
Dinophysis miles
Dinophysis norvegica
Gymnodinium sp.
Gyrodinium spirale
Gyrodinium undulans
Karenia brevis
Katodinium glaucum
Lingulodinium polyedrum
Ornithocercus magnificus
Oxytoxum sceptrum
Phalacroma rotundatum
Preperidinium meunierii
Prorocentrum balticum
Prorocentrum gracile
Prorocentrum micans
Prorocentrum redfieldii
Prorocentrum rhathymum
Prorocentrum triestinum
Protoceratium reticulatum
Protoperidinium brevipes
Protoperidinium cerasus
Protoperidinium claudicans
Protoperidinium conicum
Protoperidinium crassipes
Protoperidinium depressum
Protoperidinium divergens
Protoperidinium minutum
Protoperidinium murrayi
Protoperidinium stenii
Protoperidinium sp.
Pseudophalacroma nasutum
Pyrodinium bahamense var.
Pyrocystis obtusa
Pyrophacus steinii
Scrippsiella trochoidea
Nostoc sp. Oscillatoria limosa Spirulina sp Trichodesmium erythraeum
Figure 4.12. Contribution of important phytoplankton groups to species diversity in the Arabian Gulf.
Based on data collected during research cruises conducted in 2003 by KFUPM/RI, cell concentrations
(Fraction = mesh size ≥ 53 µm) showed seasonal and spatial variations. Cell concentrations were the lowest
during late fall and spring (Figure 4.13), corresponding with low concentrations of chlorophyll. This is a
further indication that small phytoplankton, with a cell size less than 53 µm, dominates the community during
this time and is responsible for the high rates of primary production that were observed. In the southern
sector, the coastal waters had high cell densities from late fall to the onset of summer and the oshore waters
Table 4.3. Abundant phytoplankton species in the Arabian Gulf, in terms of cell number and carbon content.
S. No Species Cell number
(cells L-1)Species Carbon
(µg L-1)
1. Prorocentrum gracile 82,000 Ceratium furca 128.8
2. Thalassionema nitzschioides 53,000 Prorocentrum gracile 122.2
3. Prorocentrum micans 35,250 Gyrodinium spirale 118.2
4. Ceratium furca 27,750 Pyrodinium bahamense var. compressum 94.1
5. Scrippsiella trochoidea 21,250 Protoperidinium stenii 88.4
6. Protoperidinium stenii 20,750 Prorocentrum micans 66.3
7. Gyrodinium spirale 20,000 Protoperidinium minutum 48.7
8. Ceratium fusus 16,250 Akashiwo sanguinea 45.6
9. Protoperidinium minutum 14,750 Ceratium fusus 35.4
10. Pyrodinium bahamense var. compressum 12,750 Scrippsiella trochoidea 28.1
Figure 4.13. Seasonal changes in phytoplankton cell density (cells/m3).
Figure 4.14. SEM pictures of common phytoplankton from the Arabian Gulf. (a) Ceratium furca, (b) Pyrodinium bahamense, (c)
Thalassionema nitzschoides, (d) Prorocentrum micans, (e) Licmophora sp., and (f) Nitzschia Lorenziana.
had two peaks of relatively high densities, one during the winter and the other during the summer. The cell
density was relatively low in the spring when there was a strong stratication of water column.
Figures 4.14 to 4.16 show scanning electron micrographic (SEM) images of some phytoplankton from
the Saudi Arabian waters of the Gulf.
Harmful Algal Blooms
There are no reports of algal blooms in the Saudi Arabian waters of the Arabian Gulf until
now. Reports from Kuwaiti waters suggest that algal blooms periodically occur in the Arabian Gulf
(Al-Kandari, et al., 2009) and there have been several reports of harmful algal blooms (HAB) in
Figure 4.15. SEM pictures of common phytoplankton from the Arabian Gulf. (a) Amphora decussate, (b) Cocconeis scutellum,
(c) Cyclotella striata, (d) Gonyaulax spinifera, (e) Scrippsiella trochoidea, and (f) Prorocentrum balticum.
Figure 4.16. SEM pictures of common phytoplankton from the Arabian Gulf. (a) Mastogloia erythraea, (b) Surirella fastuosa,
(c) Nitzschia coarctata, (d) Corythodinium tesselatum, (e) Thalassiosira eccentric, and (f) Haslea crucigera.
the Arabian Gulf and the adjacent Gulf of Oman (Al Shehhi, et al., 2014). The rst recorded event
was from the Gulf of Oman in 1976, caused by the dinoagellate genus Gonyaulax. Further HABs
in this region were reported in 1988, 1995, 1996, 2000 and 2005 (Al Shehhi, et al., 2014). In most
of these, Noctiluca scintillans was the major species. Three HABs (1988, 1999 and 2001) were reported
in Kuwaiti waters, three (1996, 2003 and 2008) in waters near the UAE, two (1996 and 1998) close
to Qatar, and two (2008 and 2009) in Iranian waters (Al Shehhi, et al., 2014). The main drivers
of these events were Prorocentrum arabianum, Noctiluca scintillans, Phaeocystis globosa, Agloboseium sp.,
Pseudo-Nitzschia sp., Gymnodinium breve, Dinophysis sp. Karenia sp., Pyrodinium bahamense, and
Cochlodinium polykrikoides (Al Shehhi, et al., 2014). Other harmful algae, mainly dinoagellates, were
observed in Kuwaiti waters but no blooms have been reported for them so far (Al-Kandari, et al.,
Zooplankton occupies a key position in the pelagic food web because it transfers the organic energy
produced by unicellular algae through photosynthesis to higher trophic levels such as pelagic sh stocks
exploitable by man (Lenz, 2000). As grazers, zooplankton not only regulates the phytoplankton productivity,
but also fuels the benthic community via vertical particle ux.
Studies of zooplankton in the Arabian Gulf date back to the early 20th century when Pesta (1911)
described a new copepod species, Acartia pietschmanni, from samples collected near the coast of Iran.
Pesta (1912) then provided the rst records of 29 copepod species in the Arabian Gulf and reviewed
their distribution from a cruise that sampled 13 stations in October 1910 along a transect in the
northern Arabian Gulf, stretching from the Shatt al Arab estuary in the northwestern Arabian Gulf
to the Strait of Hormuz. In addition to copepods, Pesta (1912) noted an abundance of cladocerans,
chaetognaths, gastropod larvae, and decapod larvae from these plankton samples, but did not elaborate
on their diversity, distribution, or abundance. After Pesta’s (1911, 1912) reports, no zooplankton
research from the Arabian Gulf was published during the next 50 years.
Interest in global biological oceanographic patterns and processes during the 1960s resulted
in several exploratory expeditions in the Indian Ocean, some of which investigated zooplankton of
the Arabian Gulf (Frontier, 1963; Nellen, 1973; Kimor, 1973). These studies were quite helpful for
framing the diversity and production of zooplankton communities of the Arabian Gulf relative to the
rest of the Indian Ocean. Consequently, they each relied on single cruises with 20 to 40 sampling
stations, limiting their utility for understanding the spatial and seasonal processes that structure
zooplankton communities within the Arabian Gulf. Additionally, they generally lacked taxonomic
resolution, choosing to focus on individual groups of organisms or on measures of total zooplankton
Research on Arabian Gulf zooplankton has increased steadily since the 1970s. The formation of the
Regional Organization of the Marine Environment (ROPME) in 1979 was a milestone that united
many of the nations surrounding the Arabian Gulf in an eort to understand the eects of anthropogenic
factors, such as coastal development and pollution, and natural factors, such as global climate change, on
the marine wildlife of the Arabian Gulf. ROPME conducted a comprehensive survey in the Arabian Gulf
in the winter of 2006, which included documenting the composition and abundance of zooplankton at
115 stations throughout the Arabian Gulf (Dorgham, et al., 2008; Dorgham, 2013). From this survey, 231
taxa of zooplankton were recorded with the highest diversity and abundance near the opening of the
Arabian Gulf. Regionally, there have been several studies of zooplankton within national waters, such
as Saudi Arabia (KFUPM/RI, 1988 and 1990a; Abdul Azis, et al., 2003; Baker and Hosny, 2006), Kuwait
(Jacob, et al., 1979; Michel, et al., 1981, 1986a and 1986b; Al-Yamani, et al., 1993; Al-Yamani, et al.,
1995; Al-Yamani and Prusolva, 2003), Qatar (Ghobashy, et al., 1994; Nour El-Din and Ghobashy, 1999),
UAE (Sharaf and Al-Ghais, 1997; El-Serehy, 1999), Bahrain (Grabe, et al., 2004), and Iran (Eftekhar, et
al., 2011).
Species Composition
A total of 181 species of zooplankton belonging to 92 families have been reported by
KFUPM/RI (2003). The zooplankton abundance ranged from 1,395 to 3,494 ind./m3, with a mean
numerical abundance of 2,307 ind./m3. The major zooplankton groups identied were Copepoda,
Cladocera, Appendicularia, Ostracoda and Chaetognatha (Table 4.4), together contributing up to
84% of the total zooplankton population. Copepods (46.8%) dominated the zooplankton population.
Among copepods, calanoids and cyclopoids were the most abundant forms. The most dominant
copepods were Parvocalanus crassirostris, Clausocalanus sp., Temora turbinata, Corycaeus spp., Oithona
plumifera and Oncaea coniferra. Cladocerans formed the second dominant group (14.5%) and the most
important species was Penilia avirostris. Appendicularians formed the third group (9.9%) and the most
important species observed was Oikopleura spp. Ostracods (8.7%) ranked fourth with Euconchoecia
aculeate as the most encountered species. Chaetognaths ranked fth (4%) followed by meroplanktonic
Biomass and Abundance
The standing stock of zooplankton exhibited wide spatial and temporal variations in the study area.
The minimum and maximum values of total zooplankton biomass were found during the onset of summer
with values ranging from 200.7 mg/m3 (southern waters) to 1,042.4 mg/m3 (northern waters) (Figure
4.17 and Table 4.5). The mean biomass estimated was 513.9 mg/m3.
An important feature was the presence of a larger zooplankton biomass (about 57% greater)
in the oshore waters (mean: 478.4 mg/m3) compared to the coastal waters (mean: 303.4 mg/m3).
There was also a clear latitudinal trend. The northern waters showed the highest zooplankton biomass
(667.2 mg/m3), followed by central (447.4 mg/m3), and southern (425.5 mg/m3) waters (Figure
4.18). Again, the zooplankton biomass in the northern waters was 57% greater than that of the
southern waters. The dierences observed between the oshore and coastal areas, and the latitudinal
trends were statistically signicant (P < 0.05). Marked temporal variations were also observed in the
biomass. In general, the biomass, which was low in the late fall (mean: 274.8 mg/m3), increased rapidly
to a peak in the winter (mean: 742.9 mg/m3), then decreased through the spring and the onset of
summer before attaining a low value during the summer (mean: 349.4 mg/m3). Spatial dierence in
density was maximum during the winter and the onset of summer, then minimum during the spring
(Figure 4.19).
The biomass in the northern waters was higher than that in the other regions during most
part of the year; however, low values were observed in the late fall. Since the gelatinous zooplankton
had larger individual body mass than the other zooplankton, the total zooplankton biomass was
greatly inuenced by the seasonal abundance of gelatinous zooplankton. In the northern transect, for
instance, the zooplankton biomass was very high in the winter and the onset of summer due to an
increase in the biomass of gelatinous forms, which contributed to about 75% of the total zooplankton
Because the coastal waters o Manifa and Abu ‘Ali are proven shelters for the meroplanktonic forms
like larvae of penaeid shrimps (Poonian, 2003), an attempt was made to investigate the distribution of
zooplankton biomass in these areas.
In the coastal waters o Manifa, zooplankton biomass was higher during the summer (445.6 mg/m3)
and lower during the winter (50.7 mg/m3). The contribution of the gelatinous zooplankton varied from
19.0% in the winter to 87.3% in the summer, while Abu ‘Ali coastal waters had low values (56.8 mg/
m3) during late fall, and high (408.1 mg/m3) values during the spring (Figure 4.20). During the summer,
gelatinous forms contributed to 64% of the total biomass.
Spatial and Seasonal Patterns
Zooplankton diversity (H’) and evenness (J’) indices showed seasonal uctuations. Subsequently,
maximum values for both indices were seen during the late fall. The H’ values uctuated between 3.10
(onset of summer) and 4.09 (fall), and the J’, between 0.64 (spring) and 0.74 (fall) (Table 4.6, Figures 4.21
and 4.22).
Table 4.4. Mean abundance of major groups of zooplankton in the Gulf (KFUPM/RI, 2003).
Region Season
Dominant Group (ind./m3)
Copepoda Cladocera Ostracoda Appendi-
Northern waters Late Fall 408 46 97 39 57
Winter 1,221 183 160 156 38
Spring 906 973 320 170 105
Onset of Summer 948 111 170 359 63
Summer 1,491 260 101 332 204
Central waters Late Fall 963 75 224 96 64
Winter 2,298 1,326 160 578 35
Spring 778 767 241 162 90
Onset of Summer 672 156 288 121 71
Summer 858 290 36 275 102
Southern waters Late Fall 838 85 184 27 43
Winter 1,747 1,126 196 225 63
Spring 1,493 204 275 314 154
Onset of Summer 591 127 202 228 79
Summer 782 200 57 310 107
Figure 4.17. Seasonal fluctuations in biomass of total zooplankton, herbivores-carnivorous gelatinous plankton and
zooplankton other than gelatinous forms in the Gulf.
Table 4.5. Zooplankton biomass (mg/m3) distribution in the Saudi territorial waters of the Arabian Gulf, from late
fall 2002 to summer 2003.
Region Late Fall Winter Spring Onset of Summer Summer
Total Zooplankton Biomass (mg/m3)
Coastal 89.01 328.34 451.03 236.95 411.65
Offshore 432.53 1,176.30 683.35 807.88 292.15
Northern 223.53 892.18 642.42 1,042.35 535.66
Central 264.46 594.33 629.92 481.80 266.77
Southern 336.42 742.14 602.87 200.72 245.82
Gelatinous Zooplankton Biomass (mg/m3)
Coastal 6.12 92.76 149.53 145.28 296.71
Offshore 214.80 802.56 401.96 539.21 52.04
Northern 75.84 656.93 389.85 807.91 359.25
Central 94.96 329.58 364.07 263.65 84.59
Southern 184.96 195.43 228.05 22.57 47.27
Other Zooplankton Biomass (mg/m3)
Coastal 82.85 235.57 301.5 91.64 114.95
Offshore 217.73 373.74 281.39 268.68 240.11
Northern 147.69 235.25 252.57 234.44 176.41
Central 169.51 264.75 264.08 218.15 182.17
Southern 151.46 546.71 374.82 178.15 198.55
Figure 4.18. Distribution of zooplankton biomass (mean ± 95% CI), in the northern, central, and southern waters.
Figure 4.19. Temporal variation in zooplankton biomass distribution.
The distribution of the zooplankton species showed signicant latitudinal dierences during the period
of study. The maximum dierence was observed between the northern and southern waters. In general,
a coastal oshore trend was also evident throughout the study period. Two main clusters, characterizing
coastal and oshore waters, were observed during the late fall and summer (Figures 4.23 to 4.27).
During the late fall, two clusters were formed at a similarity level of 35%: Cluster I, characterizing
the coastal waters with a similarity of 41.7% and cluster II, the oshore waters, with a similarity of 58.3%.
The dierence in zooplankton community structure, investigated using the ANOSIM subroutine, revealed
signicant dierences between these two clusters (Global R = 0.779, P < 0.05). The patterns observed
with NMDS (stress = 0.16) were in accordance with cluster analysis. It was observed that species diversity
(low dominance) was higher in cluster I compared to cluster II. While 21 species contributed to 80% of
the population in cluster I, only 14 species made that proportion in cluster II. Analysis using SIMPER
(Similarity Percentage), revealed the characterizing/discriminating species in cluster II (mainly responsible
for its separation from cluster I). The species were Euconchoecia aculeata, Parvocalanus crassirostris, Oithona
plumifera and Canthocalanus pauper.
Figure 4.20. Seasonal variation in zooplankton biomass distribution (mean ± SD): (a) off Manifa, and (b) off Abu ‘Ali.
Table 4.6. Characteristics of zooplankton diversity indices in the Gulf through the seasons.
Diversity Indices Late Fall Winter Spring Onset
of Summer Summer
Shannon-Weiner (H’) 4.09 3.26 3.20 3.10 3.85
Pielou’s Evenness (J’) 0.74 0.65 0.64 0.72 0.72
Figure 4.21. Shannon-Wiener diversity index (H’) showing the difference in zooplankton distribution patterns
in the Gulf through the seasons.
Figure 4.22. Pielou’s evenness index (J’) showing the difference in distributional patterns of zooplankton in the Gulf.
Figure 4.23. MDS showing the characteristic distribution of
coastal and offshore stations of the northern,
central, and southern waters, during the late
fall 2002.
Figure 4.24. MDS showing the characteristic distribution of
coastal and offshore stations of the northern,
central, and southern waters, during the winter
Figure 4.25. MDS showing characteristic distribution of
zooplankton in the coastal and offshore stations
of the northern, central, and southern waters,
during the spring 2003.
Figure 4.26. MDS showing the characteristic distribution of
coastal and offshore stations of the northern,
central, and southern waters, during the onset of
summer 2003.
Figure 4.27. MDS showing the characteristic distribution of
coastal and offshore stations of the northern,
central, and southern waters, during the
summer 2003.
During the winter, two main clusters were formed at a similarity level of 35%. Cluster I, composed
of coastal northern and central waters, showed an average similarity of 44.6%. Cluster II divided into
two subclusters, IIA and IIB, at a similarity level of 45%. Subcluster IIA (average similarity, 58.1%)
characterized the oshore waters, while subcluster IIB (average similarity, 67.0%) mainly characterized
the southern coastal waters. The pattern observed with NMDS was in accordance with cluster analysis
(stress = 0.14). The ANOSIM subroutine revealed a maximum dierence between cluster I and cluster
IIA (Global R = 0.811, P < 0.05) followed by clusters IIB and IIA (Global R = 0.730, P < 0.05), and
cluster I and cluster IIB (Global R = 0.578, P < 0.05). Oikopleura spp. showed consistent abundance
in cluster I. Cluster IIA was discriminated by ve species (Parvocalanus crassirostris, Euconchoecia aculeata,
Oithona plumifera, Clausocalanus spp. Oncaea conifer) and bivalve veligers, while cluster IIB was mainly
characterized by dierent species (Penilia avirostris, Corycaeus spp., P. crassirostris, Temora turbinata and O.
For the spring, cluster analysis revealed two main assemblages at a similarity level of 42%. Cluster I was
formed at an average similarity of 57% (characterizing the coastal northern and central waters). Cluster
II was divided in to two subclusters, IIA (average similarity, 66.8%) and IIB (average similarity, 68.5%). A
small cluster of three stations was found at a lower similarity level of 25% at the southernmost part of the
coastal waters. The pattern observed with NMDS was in accordance with cluster analysis (stress = 0.13).
The dierence in the zooplankton community structure was at maximum between cluster I and cluster
IIB (Global R = 0.964, P < 0.05) followed by cluster I and cluster IIA (Global R = 0.840, P < 0.05),
and cluster IIA and cluster IIB (Global R = 0.643, P < 0.05). The third cluster showed a big dierence
with the main clusters. Cluster I was mainly characterized by Acartia sp.1, polychaete larvae, Oikopleura
spp., Parvocalanus crassirostris, Paracalanus aculeatus, and Corycaeus spp. The characterizing species for cluster
IIA were P. crassirostris, Euconchoecia aculeata, Clausocalanus spp. Oncaea conifera, Oikopleura spp., Corycaeus
spp., Sagitta neglecta, Canthocalanus pauper, P. aculeatus, Temora turbinata, Sagitta enata, and Hyalocylis striata,
whereas Penilia avirostris, Corycaeus spp., P. crassirostris, O. conifera, Oikopleura spp., S. enata, Clausocalanus spp.
and E. aculeata were the discriminating species for cluster IIB.
During the onset of summer, the patterns observed were very similar to those that prevailed in the
spring, with zooplankton forming two main clusters, cluster I (36.6%), and cluster II (cluster IIA, at an
average similarity of 52.8%, and cluster IIB at a similarity of 61.9%). The pattern observed with NMDS
was in accordance with cluster analysis (stress = 0.13). The maximum dierence between the clusters
was observed between cluster I and cluster IIB (Global R = 0.917, P < 0.05) followed by cluster IIB and
cluster IIA (Global R = 0.872, P < 0.05), and cluster I and cluster IIA (Global R = 0.305, P < 0.05). The
characterizing species for cluster I were polychaete larvae, Oikopleura spp. and gastropod veligers. Parvocalanus
crassirostris, Corycaeus spp., Sagitta enata, Oithona spp. and Penilia avirostris were the discriminating species in
cluster IIA, whereas Euconchoecia aculeata, Corycaeus spp., P. avirostris, S. enata, Clausocalanus spp., Oikopleura
spp., Oithona plumifera, Temora longicornis, P. crassirostris, Paracalanus aculeatus and bivalve veligers were the
discriminating species for cluster IIB.
In the summer, the existence of two main zooplankton assemblages was evident in the study area.
Cluster I was formed at an average similarity of 46.8%, characterizing the coastal waters and cluster II
(at a similarity of 63.7%), the oshore waters. The ANOSIM subroutine revealed a signicant dierence
between the clusters (Global R = 0.911, P < 0.05). The pattern of sample distribution observed in
the NMDS conrmed the above analysis (stress = 0.13). The abundance and inter-relationships of the
species, Oithona plumifera, Penilia avirostris, Oncaea coniferra, Evadne tergestina, Oikopleura sp., Centropages
yamadai, Euconchoecia aculeata, Sagitta enata and Oncaea sp., characterized the oshore zooplankton
Maximum numbers of penaeid eggs (9,726 ind./100 m3) were observed during the onset of summer
with a mean of 216 ind./100 m3. O Abu ‘Ali, the highest abundance (4,780 ind./100 m3) was observed
during the onset of summer. The mean was 597 ind./100 m3. In general, maximum abundance was found
in the coastal regions of the northern and central waters. The highest numerical abundance of penaeid
nauplii was observed during the onset of summer (1,761 ind./100 m3) with a mean of 39 ind./100 m3. The
maximum number (994 ind./100 m3) of nauplii was observed o Manifa with a mean of 142 ind./100
m3 during the spring. Overall, nauplii followed a pattern very similar to the distribution of eggs. Penaeus
semisulcatus larvae were recorded in maximum numbers (958 ind./100 m3) during the spring. The mean
was 21 ind./100 m3. O Manifa, a high abundance (778 ind./100 m3) was observed during the summer
with a mean of 111 ind./100 m3. When protozoeal stages were found in the coastal and oshore regions
of the northern and central waters, mysis stages were more abundant in oshore waters. Post-larval stages
were observed in the oshore central waters only (Figure 4.28).
Maximum numbers of M. anis larvae were observed during the onset of summer (4,214 ind./100
m3) with a mean of 93 ind./100 m3. Regionally, a higher abundance (1,633 ind./100 m3) was observed
o Abu ‘Ali with a mean of 204 ind./100 m3 during the same season. Protozoeal stages were abundant in
coastal waters, while mysis and post-larval stages were found more in number in oshore waters of the
central and northern regions.
Larvae of M. stebbingi showed the highest numerical abundance (996 ind./100 m3) during the summer
with a mean of 23 ind./100 m3. Regionally, Abu ‘Ali showed maximum abundance (231 ind./100 m3) with
a mean of 28 ind./100 m3 during late fall. Protozoea showed distribution both in the coastal and oshore
waters, while mysis were more abundant in the oshore waters.
The maximum number of P. stylifera larvae were recorded during the summer (1,161 ind./100 m3)
with a mean of 27 ind./100 m3. Larval forms were more abundant (689 ind./100 m3 with a mean of 172
ind./100 m3) in Safaniyah during the late fall. Protozoea and mysis stages were more abundant in oshore
waters than in coastal waters.
Higher protozoeal abundances was observed during the late fall (254 ind./100 m3) with a mean of 5
ind./100 m3. Regionally, maximum numbers were recorded o Ras Tanura (121 ind./100 m3) with a mean
of 24/100 m3 during the late fall. The distribution was restricted more or less to coastal waters.
During the spring, the onset of summer and during the summer (spawning seasons) penaeid eggs, nauplii
and larvae showed signicant positive correlation (P < 0.05) with temperature and salinity. Signicant
dierences were also observed in the distribution of penaeid eggs and larvae between stations and nauplii
and larvae among seasons (P < 0.05).
Figure 4.28. Abundance of Penaeus semisulcatus (ind./100 m3) larvae in the Gulf during 2002-2003 (data for late
fall not included due to low abundance).
Protozoea of penaeid shrimps were more abundant than mysis and post-larval stages in the collections.
Penaeid eggs, nauplii and larvae were more abundant in coastal waters than in oshore waters, indicating
that spawning occurs in shallow waters.
Three types of penaeid prawn eggs were observed in this study. These egg types are dierentiated
by their size and perivitelline space. Type A eggs showed a very narrow perivitelline space (about 15 µm
width), characteristic of the eggs of the genus Penaeus, probably P. semisulcatus (Muthu, 1978). These eggs
were recorded in maximum number during the late fall, spring and summer, especially in Manifa. The
eggs of type B have a perivitelline space of 20 µm to 30 µm width and these eggs showed similarities with
Metapenaeus species (Muthu, 1978). During the present study, maximum numbers of type B eggs were
encountered during the onset of summer, o Abu ‘Ali. Similar observations were noted by KFUPM/RI
(1990b) in the Saudi waters. Abdulqader (1999) identied these eggs to be most likely belonging to M.
stebbingi and M. anis, which spawn in the Tubli Bay (Bahrain) during early summer. Habib-Ul-Hassan
(1992) observed that M. stebbingi spawn in spring and early summer in the Kuwaiti waters. The type C
eggs possess a wide perivitelline space of 80 µm width. The diameter of the yolk mass was 220 µm to
270 µm. The eggs of the species Parapenaeopsis stylifera showed similarity with type C eggs (Muthu, 1978).
These eggs occurred in good numbers during the spring, the onset of summer and during the summer o
Safaniyah, Manifa and Abu ‘Ali.
Studies on the plankton dynamics and the factors controlling them are less numerous in the Arabian
Gulf waters and even among them, very few focus on larger spatial and wider seasonal coverages, with
measurements of plankton parameters along with environmental parameters. Nonetheless, some important
conclusions can be arrived at from this review.
The rst is that the Arabian Gulf waters are oligotrophic, a situation owing to a lack of freshwater
advection. The concentrations of nutrients measured at several locations along the Saudi Arabian coast over
a seasonal cycle attest to this. They were almost consistently less than a µmol L-1 of nitrate, phosphate and
silicon. Concentrations of Chl a and rates of primary production are reections of this oligotrophic status:
The former rarely exceeded one µg L-1 and the latter, even at the highest, were still less than 25 µg C L-1 h-1,
of the same order as measured in oceanic waters.
The second is the seasonality of changes in plankton. In the case of phytoplankton, it is marked by a
winter maximum, and in the case of primary production, it is marked by a spring peak. In the summer,
both decline to low levels. The likely explanation of this mismatch in peaks could be that while the winter
phytoplankton abundance is sustained by nutrients, the low lights are not conducive for higher primary
production. When the surface incident radiation becomes greater in the spring, the production rises rapidly
to be eventually limited by nutrients and possibly photo-inhibition. The changes in zooplankton biomass
also revealed signicant dierences through the seasons, with a decreasing trend from the winter to the late
fall. The elevated biomass values observed in some stations during the late fall and the winter could be due
to the higher phytoplankton concentration. Such trends were observed in earlier studies also (Price, 1979;
Michel, et al., 1986b). A maximum dierence in biomass distribution was observed between the spring
and summer. The higher biomass observed during the winter was in accordance with the observations
made by Michel, et al. (1986a) in Kuwaiti waters, and Banse and McCain (1986) and Madhupratap, et
al. (1996) in the northern waters of the Arabian Gulf, which was attributed mainly to the convective
overturning associated with winter cooling. In the winter, when the coastal waters experienced a decrease
in temperature (especially the northern and central waters) and an increase in density, the principal factors
controlling the biomass distribution were temperature and chlorophyll. A similar observation was made by
Kovalev (1988) in the coastal waters from the Mediterranean Sea to the Sea of Azov.
The distribution of zooplankton was also notable for spatial dierences. The biomass of zooplankton
exhibited a coastal oshore, and north-south trend throughout the seasons. A higher biomass (total biomass,
i.e., gelatinous + other zooplankton) was observed in the northern waters compared to other areas, especially
from the winter through the summer. Correlations with chlorophyll, explained to a great extent, trends in
zooplankton biomass distribution. The grazing pressure of the herbivores on phytoplankton was very clear
during the onset of summer (when thaliaceans, belonging to the genera Weelia and Thalia, dominated the
total biomass), especially in the northern waters. Overall, a higher contribution of gelatinous forms was
evident in the oshore regions of the northern waters, followed by the central and southern waters, a trend
opposite to that exhibited by other zooplankton.
The third is the response of plankton production to anthropogenic impacts. In sites close to industrial
and municipal development, concentrations of nutrients were remarkably high, entraining high Chl
biomass and primary production (Price, 1993). Though the conditions are nowhere near eutrophication or
causative of HABs as of now, sustained release of nutrients into coastal waters may cause these impacts in
the near future. Though the plankton diversity was only moderate compared with what is known for the
entire Gulf, there were no instances of pronounced mono-specic dominance.
The Arabian Gulf, like the Red Sea, is a sea area that is characterized by high temperatures and salinities,
conditions that have been predicted to occur elsewhere in other oceans only in the future. In-depth and
focused studies on plankton dynamics will help us to understand now how the trophic structures at the
base level respond to global changes and use this knowledge for designing strategies to mitigate impacts
from global changes in other sea areas.
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