Winter species composition, diversity and abundance of macrozoobenthos in Kuwait’s waters, Arabian Gulf

Abstract Th e paper describes the structure of macrozoobenthos inhabiting Kuwait’s waters (northwestern Arabian Gulf). Material for the study was collected from 17 stations in December 2004. A total of 270 species of macrozoobenthos and representatives of higher taxonomic groups belonging to 10 phyla were recorded and identifi ed. Species diversity was highest in polychaetes, gastropods, bivalved molluscs and crustaceans (83, 51, 52 and 38 species, respectively). Quantitative estimates of macrozoobenthos was studied in this geographic region for the fi rst time. In the depth of 2–20 m the abundance of macrozoobenthos averaged 795 ind./m2. Polychaetes, gastropods and crustaceans prevailed in the sublittoral zone. In assessing species diversity the ecological indices of Shannon-Wiener, Simpson, Pielou and Margaleff were used. Th e obtained results point out that in Kuwait’s waters the diversity of macrozoobenthos is relatively high while the level of dominance is low. It was also found that in Kuwait Bay macrozoobenthos is less diverse than in other locations of the region.

Winter species composition, diversity and abundance of macrozoobenthos in Kuwait's waters, Arabian Gulf Introduction Faunistic investigations in the Arabian Gulf began in the late 19 th century; since then many researchers have paid tribute to the area.During the fi shery investigations which H. Blegvad carried out for the Iranian Government in 1937-1938, G. Th orson andB.Loppenthin had conducted the fi rst large-scale studies of macrozoobenthos in the Arabian Gulf.Th eir collections of benthic invertebrates of diff erent groups contributed to a series of important publicatons on the taxonomy and faunistics of these groups (Stephensen 1945;Wesenberg-Lund 1949).However, these studies did not cover the northwestern waters, off Kuwait's coast.During the 1960s, a team of experts headed by D. A. Jones studied biota of the intertidal zone (Jones 1986).In his study of annelids M. B. M. Mohammad also focused on this specifi c zone (Mohammad 1970(Mohammad , 1971(Mohammad , 1973(Mohammad , 1980)).Knowledge of the distribution of macrozoobenthos in the sublittoral zone of Kuwait's waters in the northwestern Gulf is needed due to the lack of scientifi c documentation about the diversity and the quantitative distribution of bottom fauna.A couple of studies were conducted in Kuwait but the information is locked up in reports which are not accessible to scientists.Our investigation concentrated on the taxonomic composition, diversity and quantitative estimates of macrozoobenthos during winter in Kuwait's marine environment.

Material and methods
Samples for the study were collected during 5-19 December 2004 from 17 stations, out of which 14 stations were located in the sublittoral zone (from 2 to 20 m depths), and 3 stations were located in the littoral zone.Sublittoral samples were collected from three sections: near Failaka Island, in Kuwait Bay, off Kuwait Bay and near Bubiyan Island (stations 2-5; 6-9; 1; 10-13 and 17, respectively; Fig. 1).Littoral samples were collected from three sites: station 14 in Kuwait Bay, in the vicinity of the Kuwait Institute for Scientifi c Research in Shuwaikh; station 16 in the littoral zone off the Mariculture and Fisheries Department (MFD) at Ras Salmiyah, and station 15 was located about 75 km to the south of Kuwait city, at Ras-Al-Zor, which is close to the border with Saudi Arabia.
Samples of sublittoral macrozoobenthos were collected with a Van Veen grab sampler with capturing area of 0.05 m 2 , and littoral samples with a bottom dredge with an opening of 0.09 m 2 .For some stations, oceanographic variables such as the seawater temperature of near-bottom layer, salinity, dissolved oxygen (DO) concentration, pH and turbidity were measured (Table 1).At each station, 2 samples were obtained, washed through a sieve of 0.5 mm mesh size and fi xed with 4% formaldehyde.In the laboratory, benthic organisms were sorted, identifi ed to species level when possible and counted.At station 17 one qualitative sample was taken, and at littoral stations samples of large organisms were additionally collected.Results obtained from qualitative sample processing were added to the list of species encountered for the sampled area, but were not used in the analysis of biodiversity.
In assessing macrozoobenthos diversity, the biodiversity indices of Shannon-Weiner (Shannon and Weaver 1963) and Simpson (Simpson, 1949) (H` and 1-λ`, respectively), as well as Margaleff index (D) (Margalef 1958) for species richness were used.Dominance was assessed by means of Simpson index (λ`) (Simpson 1949), and evenness by Pielou index (J`) (Pielou 1966).spines and shells debris.Bottom ground at the littoral station 14 is muddy-silt with a strong smell of hydrogen sulphide, as it is under considerable anthropogenic load owing to municipal sewage discharge.

Description of the study area
Th e waters off Bubiyan are highly turbid (43.66 mg/l) and has lower salinity (35.26 PSU) than the rest of Kuwait's waters.Th e sea bed is predominantly silty, with sandy patches in the immediate vicinity of the Island.
Samples collected from the deeper station (station 1, 20 m depth) displayed lower concentration of dissoved oxygen (1.46 mg/l), and lower turbidity (3.83 mg/l) than in Kuwait Bay and near Bubiyan Island.At the southern littoral station (station 15) off the city of Al-Zor, the seawater transparency was the highest for the examined area, with nearby coral reefs.Strong tides aff ect the littoral stations 14 and 15, especially station 15.Station 16 is located between piers and therefore is relatively sheltered from wave activity.

Sublittoral (subtidal zone)
Th e number of species found at stations situated in the sublittoral zone varied between 14 and 46, with an average of 30 species.Maximum number of species per station was registered at station 3 off Failaka Island (depth 2 m; salinity of 40.5 PSU; turbidity of 3.32 mg/l) and minimum at station 13 in Khor Al-Sabiyah off Bubiyan Island (depth 7m; salinity of 35.26 PSU; turbidity of 43.66 mg/l).Th e abundance of macrozoobenthos varied in the range of 340-1800 ind./m 2 , with an average of 795 ind./m 2 .In general, the sublittoral bottom grounds in the studied area are composed of silts.Th e ratio between the abundances of the diff erent taxonomic groups reliably shows how the benthic organisms distribute on the silty beds (Fig. 3a).Most abundant are polychaetes, gastropods and crustaceans.Only at the station positioned at a sandy patch (5 m depth), where crustaceans, bivalved molluscs and echinoderms prevailed, the ratio was slightly diff erent (Fig. 3b).Maximum numbers of macrozoobenthos was registered at station 8 (3 m depth) in Kuwait Bay; small gastropods, Tornatina inconspicua and Chrysallida sp.contributed 50 and 14%, respectively, to the total abundance of benthic organisms.Quantitative characteristics of macrozoobenthos diff ered among Failaka, Bubiyan and Kuwait Bay.In Kuwait Bay, the average abundance of benthic organisms was greater and the number of species were lower than near Failaka and Bubiyan Islands.Th e polychaete Magelona cornuta, crustaceans Periculodes sp., Eocuma sp., and Cyclaspis sp. were absent from the sampled Kuwait Bay stations.Th e percentage composition of the abundances of the diff erent taxonomic groups inhabiting the Bay was diff erent than that of the other sampled areas.Th e overwhelming majority in Kuwait Bay were bivalves (62%), followed by polychaetes (20%) and crustaceans (7%).Polychaetes and crustaceans prevailed at the other two areas of Bubiyan and Failaka islands (Fig. 4).
Analysis of macrozoobenthos distribution in relation to sampled station depth has revealed several interesting tendencies.In the examined depth range of 2-20 m, the abundance of macrozoobenthos decreased with increasing depth while the number of registered species increased (Fig. 5).Th erefore, in analyzing species diversity indices for the above three areas the depth factor was taken into consideration (Table 3).Species richness (D) and diversity (H') were highest (5.158 ± 0.812; 3.293 ± 1.528; 2.39 ± 0.64) in Kuwait Bay (Fig. 6).In the area near Failaka Island Pielou index ( J') also yielded very high estimates (0.933 ± 0.028) approximating 1, which indicates high evenness level of the community.For Kuwait Bay, the corresponding estimates decreased to (0.769 ± 0.125) (Fig. 7a).Dominance index (λ') fl uctuated from 0.03 to 0.28, the maximum was registered at station 8 (Kuwait Bay), where about half of the total macrozoobenthos abundance was due to the abundance of the small gastropod Tornatina incospicua.In general, the level of dominance was high (0.184 ± 0.98) in the benthic community of Kuwait Bay and very low (0.046 ± 0.009) near Failaka Island (Fig. 7b) that conforms with the statement that the higher the dominance, the less biodiversity in the area.Th us, the obtained results of the study suggest that the benthic community in Kuwait Bay is less diverse than that off Failaka Island.
For stations sampled near Bubiyan Island, all the studied indices varied in a broader range.Th e obtained averages point out that, based on the entire set of measured biodiversity parameters, benthic community of this area should be regarded as intermediate between the communities of Failaka Island and Kuwait Bay (Fig. 8).
Table 3. Th e estimates obtained using Margalef index for species richness, Shannon-Wiener and Simpson indices for the diversity, Simpson index for the dominance and Pielou index for evenness (D, H`, l-λ`, λ`, and J`, respectively).S -total number of species.N -total number of individuals (abundance, ind./m 2 ).

Station
No.

Littoral (intertidal zone)
Abundance of macrozoobenthos substantially diff ered among stations.Station 16 (MFD/Ras Al-Salmiyah) displayed the largest diversity (38 species) and highest abun- dance (nearly 18,000 ind./m 2 ); most abundant are the polychaete Lumbrineris impatiens, and the gastropod Caecum sp., lancets (Branchiostoma sp.), small crustaceans, and juvenile bivalved molluscs of several species.It is noteworthy that the total macrozoobenthos abundance at station 16 is more than 75% higher than at the other stations owing to the high juvenile abundance of two bivalved molluscs of the genus Tellina (Tellina donacina and Tellina sp.).Th ese larval or juvenile forms were encountered in the collected benthic samples, probably soon after the larvae had settled on the bottom substrate.Th e settling larvae were about 0.3 mm in size; the majority of larvae in the collected samples were of 1 mm size.Th e unusually high abundance of macrozoobenthos at station 16, was probably due to its position in an area with less wave actions, unlike stations 14 and 15.
A total of 18 species of macrozoobenthos were found at station 15 (Al-Zor), with a total abundance of 260 ind./m 2 .Most numerous were the polychaete Glycera tridactyla, the gastropod Umbonium vestiarium and small crustaceans of 6 species.
Th e least diversity (7 species) was registered at station 14 (KISR/Shuwaikh).Th e gastropod Cerithidae sp.(38% of the total abundance), oligochaetes (18%) and large nematodes prevailed.Th ese organisms have well adapted to oxygen defi cient substrate.Th eir presence in the absence of crustaceans and the extraordinary strong smell of hydrogen sulphide indicate anoxic conditions in the bottom sediment.
Th ough the obtained data are insuffi cient to provide for a detailed analysis of macrozoobenthos diversity in the littoral zone, they allow us to conclude that it is not as large as in the sublittoral zone.Comparison between the three stations shows that in Kuwait Bay the species richness and diversity both in the littoral and sublittoral zones are the least.Probably, this could be due to special oceanographic conditions as well as pollution impact from sewage and industrial discharges into the Bay (Al-Yamani et al. 2001).
Comparing the abundance of macrozoobenthos in the Arabian Gulf and in some other seas (Table 4), it is interesting to note that the abundance of bottom-dwelling organisms in silty biotope of the Arabian Gulf is superior to the Aegean, Mediterranean and Red seas but second to the Adriatic Sea.

Conclusions
Th e main fi ndings of the study is summarized below:  A total of 270 species of macrozoobenthos and representatives of higher taxonomic groups belonging to 10 phyla have been identifi ed from Kuwait's marine environemnt.Species number is largest in polychaetes, gastropods and bivalved molluscs.High taxonomic diversity and the absence of mass forms are characteristic of the bottom fauna.
Th e abundance of macrozoobenthos varied from 260 to 18,400 ind./m 2 .At stations with 2 to 20 m depths, the average abundance of macrozoobenthos is 795 ind./ m 2 .Th e groups prevailing in the sublittoral zone are polychaetes, gastropods and crustaceans (32, 29 and 22%, respectively).
Generally, Kuwait macrozoobenthos has high species diversity and low dominance level though biodiversity estimates may markedly diff er depending upon the locality.Compared with other locations under the study, Kuwait Bay harbours less diverse benthic community.
Kuwait's waters are shallow and its northern waters (off Bubiyan Island) are infl uenced by the discharges from Shatt Al-Arab River and Shatt Al-Basrah Channel.Kuwait Bay is relatively vast and shallow (about 12 m deep).Seawater salinity (41.38 PSU) and turbidity (10.44 mg/l) are high.Th e bottom substrate of the Bay is mainly composed of silt or silty clay.During our survey we encountered sediments smelling of hydrogen sulphide.Sediments in the central part of the Bay contain a large fraction of urchin

Figure 2 .
Figure 2. Th e percentage composition of species number of the diff erent taxonomic groups.
Th e taxonomic composition and the abundance (ind./m 2 ) of macrozoobenthic species at each sampled station (* found in the qualitative samples;

Figure 3 .
Figure 3. Th e abundance (ind/m 2 ) of diff erent taxonomic groups of macrozoobenthos in the sublittoral zone: a Average distribution and b Distribution at station 12 in Khor Al-Sabiyah.

Figure 4 .
Figure 4. Percentage composition of the abundance of the main taxonomic groups in the sublittoral zone of the three sampled areas of Kuwait Bay, Bubiyan Island and Failaka Island.

Figure 5 .
Figure 5. Changes in the abundance A and the number of species B in relevance with depth.

Figure 6 .
Figure 6.Th e variation in Margalef and Shannon-Wiener indices (D and H`loge, respectively, denoted as a and b, respectively) evaluated for the three examined areas (Failaka, Kuwait Bay and Bubiyan).

Figure 7 .
Figure 7. Th e variation in a Pielou index of evenness (J`) and b Simpson index of dominance (λ`) for the three sampled areas of Failaka, Kuwait Bay and Bubiyan.

Figure 8 .
Figure 8. Averages of a the indices of diversity by Margalef, Shannon-Wiener and Simpson (D, H`loge and l-λ`, respectively), and b Pielou index of evenness and Simpson index of dominance (J` and λ`, respectively) for the benthic community in the three studied localities.

Table 1 .
Sampled stations and oceanographic variables measured at each station during December 2004 in Kuwait's marine environment.