Ecology and distribution of ostracods in Kuwait Bay

Few ostracods live in the central part of Kuwait Bay due to the effect of ebb and flow currents in the central channel. The number increases gradually towards the nearshore areas and then decreases rapidly near the tidal flat areas due to turbidity in the northeastern zone and pollution in Sulaibikhat Bay. Different ostracod assemblages inhabit the subenvironments of the bay. The tidal-flat assemblage differs from that of the nearshore area and from the assemblage living in the restricted area in the western corner of the bay. Ostracods in the bay are mostly found living on clayey silt sediments and sandy mud. Forty-nine species belonging to 39 genera were recognised in the bay, of which 28 were found living there. The dominant living species in the bay include Hemicytheridea paiki Jain, 1978; Keijella nealei Jain, 1978; Jainella karwarensis Bhatia & Kumar, 1979; Propontocypris sp.; Chrysocythere keiji Jain, 1978; Aglaiocypris sp.; Alocopocythere reticulata indoaustralica (Hartmann, 1978); Carinocythereis batei Jain, 1978; Cytherella pulchra Brady, 1868; Hemikrithe peterseini Jain, 1978 and Neomonoceratina sp. cf. N. delicata Ishizaki & Kato, 1976.


INTRODUCTION
Bay is a small, V-shaped embayment in the northwestern part of the Arabian Gulf. T h e gulf is a marginal sea measuring about 1000 km in length and 200 to 300 km in1 width. 'The average depth is 35 m, and the maximum depth near its entrance at the Strait of Hormuz is 1 0 0 m . The Strait of Hormuz is 6 0 k m wide, connecting the gulf with the Gulf of Oman and the Indian Ocean. The long axis of the gulf bas8in separates two distinct morphological provinces whose character is related closely to contrasting tectonic styles on each side. The floor on the more stable Arabian side d o p e s gently towards the bathymetric axis, while the tectonically unstable Iranian side of the basin is relaltively steep (Purser 6 ' Seibold, 1973).
T h e present study is part of the Marine Pollution Environmental Assessment Program (MPEA) carried out at Kuwait Institute for Scientific Research (KISR). This paper intends t o fill thc gap in ecological works i n Kuwaiti waters and throw light on the ecology and distribution of ostracods in Kuwait Bay.

METHODS
The Kuwait Bay survey was carried out by staff members of M P E A Programme using the ship R.V. A B A T H and a small boat. Ninety bottom sediment samples were collected from the bay (Fig. 1) using a Van Veen grab. Samples were collected o n six cruises from 3: 12:79 t o 5:S:XO.
I n the laboratory, living ostracods were picked from wet samples or stored frozen (in 70% ethanol solution) and later studied after the addition of Sudan Black B . The samples were washed under a jet of fresh water in a 200 mesh sieve and dried in an oven at 80°C. The dried residue was then sieved into five fractions and stored in vials. Ostracod specimens were separated from the sediments by flotation and hand picking. The latter procedure was necessary for separated valves.

ECOLOGY
Kuwait Bay is a small emhayment with an average length of 35 km and average width o f 2 0 kin ( gradually slopes towards its centre and out towards Ral Al-Ard where the bay is deepest (28 km). Khalaf (1979, Fig. 7) considered the bay, with the exception of the deeper parts which lie within Kuwait Bay trough, to be part of the submerged estuarine flat, a shallow, muddy area extending from the northern part of the Arabian Gulf south of Faylakkah Island and west in the bay. Physical and chemical oceanographic data on the bay were collected through the Oceanographic Project of the MPEA Programme (Jacob et al., 1981). All data used in this study are from this project unless stated otherwise.
The sediment distribution in the bay is as follows: the tidal zone extending from Ras As Subbiyah to Ras Kathma, as well as the tidal flat area of Sulaibikhat Bay, has a silt substrata. The area extending from Ras Al-Ard to Ras Ajuza westward to around Al-Akaz tidal flat and Umm An-Name1 Island as well as Doha headland to Khuwaisat contains a mixture of sand, muddy sand, and sandy mud sediments. Rocky-bottom surfaces occur near Ras Al-Ardh at a depth of 25 to 28 metres, as well as near the coastline of Ras Ajuza, near the Shuwaikh port, around Al-Qurain (Al-Akaz) and Umm-An-Name1 islands and the Doha coastline. The centre of the bay contains silty clay which is surrounded by clayey silt covering more than 50% of the bay (Fig. 3).
Living ostracods in Kuwait Bay occur in different types of bottom sediments. They are most abundant in clayey silt and sandy mud; their numbers decrease in silty clay, sand, silt and muddy sand respectively. In the sandy bottom areas the ratio of carapaces to valves is more than 1; usually between about 2.1 and 7.1. The ratio decreases in sandy silt, silt, and sandy mud samples, where it lies between 0.1 and 0.9.
The surface water temperature of the bay ranges between 14.7"C during January and 27.4"C during May. Little difference was recorded between surface and bottom temperature, about 0.5 to 1.5"C due to the shallowness of the bay. The highest temperatures are during August (30-37°C) (Enomoto, 1971). Jacob et al. (1981) recorded an average salinity of 3 1.8"/00 during December, whereas Moharnmad (1 978) found that salinity increased rapidly from the northwestern ( 40°/oo) t o the southern and southwestern parts Dissolved oxygen in the bay waters ranges between 7 and 7.9rngil in most localities, except near Ras As-Sublbiyahi where it increases t o 8.2 and 8.3 mg/l. These values, however, decrease near Sulaibikhat Bay (4 t o 5 mgil), probably due t o the increase of the Iota1 organic carbon (T. O.C.) in this area making the consumption of oxygen higher. T h e highest dissolved oxygen content in the bay is at its entrance (8.7 mg/l) at station 62A. Khalaf et tzl. (1981) showed that T. O.C. in the bay ranged between 0.46% to 2.0%, with the highest percentages near the southern coast of the bay, especially in Sulaibikhat Bay and decreasing northwards.
PIH values in the bay remain almost constant with an average of 8.3 during the months of December and May, although the southern part (Sulaibikhat Bay) has higher of the Bay (52"/00). values (8.5 to 8.6). Andrewsetaf. (1972) indicated that a p H range of 6.7 t o 8.6 will support a good fish population, and very few species tolerate a p H beyond this range. The extreme p H values in Sulaibikhat Bay are not as expected since the high organic content and high rate of organic decomposition generally result in acid waters. Extreme p H values are therefore taken to represent pollution ; in Sulaibikhat Bay this takes the form of the dumping of alkaline materials and release of constructional wastes into the bay (see Al-Abdul-Razzaq et ul., 1982).
Turbidity o f the water is affected by the northwestern (shamal) winds and the monsoon winds, as well as water depth and currents. In general, turbidity is 6.8ppm with the exception of the northern coastal area, where t h e turbidity increases t o an average of 25ppm due to the effects of extreme shallowness and the currents in this area.
Living ostracods in Kuwait Bay were abundant except in the tidal flat areas and the central channel (Fig. 2).

big. 2 . A biofacies map
showing the abundance of living ostracods (as a whole) in Kuwait Bay. Few ostracods live in the central part of the bay, although the area is covered with silty clay and the physical and oceanographic parameters have average values, due to the effect of tidal currents through the central channel of the bay. The number of living ostracods increases gradually towards the ncarshore areas, which are covered with silty clay sediments. The distribution is also true of dead ostracod specimens (Fig. 3). All the physical and oceanographic controlling factors in the nearshore areas are average compared to the rest of the bay.
Living ostracod numbers decrease towards the tidal flats of the bay, where turbidity seems to be the most important controlling factor in the northeastern tidal flat zone while high salinity, temperature, T.O.C. and pH, low dissolved oxygen content and pollution are the controlling factors in Sulaibikhat Bay area (see Al-Abdul-Razzaq, el ul. 1982). The number of dead specimens continues to increase both towards the north and the south and reaches a maximum near Ras As-Subbiyah due to the effect of currents in the bay. The low number of ostracods in Sulaibikhat Bay is influenced by tidal currents within this small bay.

Loxoconcha (L.) i n d i c d
The dominant species of the tidal flat zone of Sulaibikhat Bay ( H . paiki; Loxoconcha ( L . ) indica Jain, 1978; Xestoleberis rotunda Hartmann, 1964;X . rhomboideu Hartmann, 1964;and Tanella grucillis Kingma, 1948, see Al-Abdul-Razzaq, et al., 1982 are not found in Kuwait Bay with the exception ofH. paiki. This species shows no special preference for a particular environment and lhas a wide range of tolerance t o salinity and temperature. Living specimens of H . paiki were repor,ted i n almost all the: samples studied in the bay; thesc were the only living specimens found in the tidal flat zone of Ras As-Subbiyah. Individuals of H . paiki were found living after storage in a refrigerator at a temperature of about 4 t o 5°C for 20 days.
Loxoconcha (L.) indica, X . rotundu, and X . rhomboidea are restricted to the tidal flat zone of Sulaibikhat Bay, the only area in Kuwaiti waters where these species are found living. Bate & Gurney (1 98 1) indicated that Loxoconcha (L.) indica is restricted solely to a lagoon environment in the Abu Dhabi area in the Arabian Gulf.

DISTRIBUTION
Most of the dominant ostracods living in Kuwait Bay also occur in the Arabian Sea along the western coast of India; H . paiki, A . reticulata indouustralica, C. keiji, H . peterseni, C. batei, J . kurwarensis, K . nealei, N . cf. delicata, C. guhai, and C . jlavidofusca itricatoides. I t is considered that these species migrated to the gulf from the Indian Ocean. H . puiki has been found not only in the tidal-flat zone, the lagoonal areas, and nearshore areas of Kuwait Bay,