Download Abundance and diversity of surface zooplankton in the Gulf of Aqaba

Journal of Plankton Research Vol.19 no.7 pp.927-936, 1997
Abundance and diversity of surface zooplankton in the Gulf of
Aqaba, Red Sea, Egypt
Magdy T.Khalil and Nasser S.Abd El-Rahman1
Zoology Department, Faculty of Science, Ain Shams University, Cairo and
1
National Institute of Fisheries & Oceanography, Egypt
Abstract. Surface zooplankton were studied in Egyptian coastal waters of the Gulf of Aqaba, from
bimonthly samples from July 1994 to May 1995. Species diversity, numerical abundance and dynamics were analysed for each taxon, at six sites, inside three Protectorates. A total of 62 taxa and species
were identified. At all sites, copepods were predominant in the standing crop with an average of 1945
ind. m~3 and formed -75.5%, numerically, of the total zooplankton community. The meroplanktonic
larvae occupied the second rank and they constituted -19.7% of the total zooplankton. Seasonally,
the main peak of zooplankton abundance was recorded in winter (January) with an average of 3510
ind. m~3, while September was characterized by the lowest density (1906 ind. m~3). The relatively
higher diversity values were recorded at Ras Mohammed Protectorate and a progressive decline in
diversity was observed northward.
Introduction
In view of the significant contribution of coral reef ecosystems to the productivity
of the coastal waters of the Gulf of Aqaba, Red Sea, the Egyptian government
declared three protected areas, during the period 1983-1992: Ras Mohammed,
Nabq and Abu Galoum.
Knowledge of the function of coral reefs and pelagic ecosystems in the Red Sea,
and their stability, is urgently needed before they are disturbed by man. The offshore exploitation of oil and gas fields is increasing in this region, and rapid urbanization and industrialization in the coastal zones has already produced local effects
on the susceptible reef ecosystem. To protect the Red Sea biota, an evaluation of
the intact ecosystem has to be made before the onset of a disturbance. Therefore,
through a project aiming to study the species biodiversity of different biota in
these reserves, the structure and diversity of zooplankton have been investigated.
Despite the importance of zooplankton in many marine food chains, relatively
few systematic seasonal studies have been conducted in the Gulf of Aqaba. Most
studies have been localized in the northernmost region (Eilat) and they focused
on isolated taxonomic groups, e.g. planktonic Tunicata and Chaetognatha
(Furnestin, 1958; Godeaux, 1960, 1986), Appendicularia (Fenaux, 1960), and
microplankton, planktonic decapods and stomatopods (Kimor and Golandsky,
1977; Halim, 1990; Kimor, 1990) and Copepoda (Almeida Prado-Por, 1983,1990).
Only a few multitaxonomic zooplankton studies have been conducted, including
those by Schmidt (1973), Reiss et al (1977), Vaissiere and Seguin (1982, 1984),
Echelman and Fishelson (1990) and Dowidar (1994).
In the present work, abundance characteristics of the distribution and species
diversity of surface zooplankton at the three different Protectorates in the Gulf
of Aqaba were examined seasonally for about 1 year.
© Oxford University Press
927
M.T.Khalfl and N.&AM El-Rahman
Method
Area of study
The Gulf of Aqaba lies between the Sinai Peninsula and the Arabian coast, and
is a part of the great Syrian-East African Rift (Gregory, 1921). It extends for 180
km from the straits of Tiran to the port of Eilat. At its northernmost point, it is
5 km wide and reaches a maximum width of 28 km opposite Dahab (Figure 1).
There are two major marine basins: the northern one extending south to Nuweiba
with a maximum depth of 1000 m, and the southern one which extends to the
Straits of Tiran and sounds 1800 m. The climate in this area is hot and dry. Rainfall is scarce (average 22 mm per year). The mean annual temperature of the
water is 23.0°C. Evaporation is exceptionally intense (average 200 cm per year)
(Godeaux, 1986). The water is hypersaline (41.0-42.0%o). Surface salinity
increases progressively from south to north. The Gulf of Aqaba can be described
as highly oligotrophic on the basis of data on the chlorophyll a values (0.024-0.522
mg nr 3 ) and primary productivity measurements (36 eg m~2 year 1 ) carried out
by several investigators (Oren, 1970; Azov, 1986; Berman et ai, 1986; Kimor,
1990).
Five sites were chosen for this study in the three protected areas; two at Ras
Mohammed (#2 and #3), two at Nabq (#4 and #5) and one (#6) at Abu Galoum
(Figure 1). Site #1 represents the Gulf of Suez side which has more nutrients than
the Gulf of Aqaba; its euphotic zone is much shallower (Morcos, 1970; Weikert,
1987). Sites #2 and #3 are within Ras Mohammed Protectorate, although the
former one is affected by wastes from fishing and diving boats, and is crowded by
snorkellers and divers all the year round. Sites #4 and #5 are within Nabq Protectorate waters, but the latter site is bordered by mangroves and is affected by
discharges of shrimp fish farm drainage waters.
Sampling and laboratory techniques
Bimonthly sampling of zooplankton was performed for 11 months, during the
period from July 1994 to May 1995, using a conical standard plankton net of 55
um mesh size, with an opening diameter of 50 cm and 1 m length. The net was
towed horizontally just beneath the surface for 10 min (speed of boat 1.5 knots).
A flowmeter was fitted onto the opening of the net to calculate the filtration rate
and efficiency. Sampling was carried out in the vicinity of the coral reef area,
between 18:00 and 20:00 h each sampling period.
In the laboratory, zooplankton species were identified and taxon abundance
(per cubic metre) was estimated from a 3 ml subsample, taken after thorough
mixing of the entire sample (100 ml). Many publications and taxonomic references were used for identification, such as Dussart (1967,1969), Jorgensen (1933),
Newell and Newell (1967) and Wimpenny (1966).
Measurement of diversity
The choice of an index to measure species diversity is complicated by the fact that
it comprises two components—species richness and species evenness or
928
Surface zooptanktoo of the Gulf of Aqaba
29 c
SOUTH
SINAI
28°
Mohammed
' •
Red Sea
340
35°
Fig. L Index map showing the location of the Gulf of Aqaba and the study sites. Shaded areas represent the three Protectorates.
equitability—and although some indices combine both components, this can
obscure potentially useful information (Death and Winterboum, 1995). Thus,
929
M.T.Khalfl and N ^ A b d El-Rahman
several indices, using the taxa and species in Table I, have been used, each of
which measures a slightly different aspect of diversity. These are: (i) species
number; (ii) Margalef's index (Margalef, 1968; Clifford and Stephenson, 1975), a
simple measure of species richness; and (iii) Heip's index (Heip, 1974) to measure
evenness or equitability.
Ouster analysis was also performed to put similar stations into classes according to their plankton characteristics using the Sorensen Similarity Index for
quantitative data as modified by Bray and Curtis (1957). The complete linkage
clustering method (the farthest neighbour) was used to draw a dendrogram (De
Ghet, 1978).
Results and discussion
Community composition
A total of 62 taxa and species of zooplankton were recorded during the present
study in the Gulf of Aqaba and its entrance (Table I). Copepods and nauplii
appeared as the most abundant group. Their average standing crop (whole
seasons and sites) was 1945 ind. m~3 and occupied -75.5% of the total zooplankton community. The meroplanktonic larvae occupied the second rank and constituted -19.7% of the total zooplankton with an average of 508 ind. rrr3.
Protozoa, then Tunicata groups, came next with an average of 2 and 1.7%, respectively. The other components, which comprised the Chaetognatha, Cladocera,
Ostracoda, Siphonophora and other taxa, were rarely encountered and they contributed collectively -1.1% of the total zooplankton.
Copepods were represented by 27 species (Table I). Five of them, i.e. Calanus
vulgaris Dana, Centropages ponticus Karawiew, Candacia pectinata Dana,
C.simplex Giesbrecht and Corycaeus gracilis Dana are new records for the Gulf
of Aqaba. Almeida Prado-Por (1983,1990) recorded 31 copepod species during
the survey in the Northern Gulf of Aqaba in 1975 and 1990, respectively.
Site and seasonal dynamics
The magnitude of the standing crop of zooplankton attained its highest density
at site #1, which sustained an average annual number of 4138 ind. nr 3 (Table II).
This site lies at the Gulf of Suez side, which is characterized by the nutrient-rich
water with high concentrations of phosphate and nitrate (Weikert, 1987). Abd ElRahman (1993), in his study on zooplankton of the Gulf of Suez, reported that
the species densities are relatively higher than that of the Gulf of Aqaba, due to
increased nutrients and organic matter discharged in Suez Gulf waters.
On the other hand, a marked decline in the zooplankton densities from southern sites towards northern ones was noticed (Figure 2). The average annual
number of individuals at site #2 decreased to 3645 ind. nr 3 , then to 2065 ind. nr 3
at site #3, and to 1484 and 1736 ind. nr 3 at sites #4 and #6, respectively. However,
the zooplankton density at site #5 was relatively high (2389 ind. nr 3 ). This is probably due to increased nutrients and detritus from mangrove trees, which dominate this region. Almeida Prado-Por (1983,1985,1990) also observed a decrease
930
Surface zooplankton of the Gulf of Aqaba
TaWe L list of planktonic taxa and species collected from July 1994 to May 1995, in the coastal water
of the Gulf of Aqaba, Red Sea
Tintinnidae
1. Codonellopsis lusitanica Jorg.
2. donga Kof & Camp.
3. Codonella aspera Kof & Camp.
4. Cmorchella cleve
5. Favella brevis cleve
6. F.azorica (cleve) Jorg.
Foraminifera
7. Globigerina inflata (d'Orb.)
8. Spiroloculina depressa
9. India lucida
10. Bolirina sp.
Hydrozoa
Trachymedusae
11. Aglaura hemistoma Per. & Les.
Siphonophora
12. Diphyes dispar Chamisso & Eysenh
13. Lensia subtilis (Chun)
Chactognatha
14. Sagitta enflata Grassi
15. S.neglecta Aida
16. Krohnitta subtilis Grassi
Annelida
17. Ftolychaete larvae
Cladocera
18. Evadne nordmanni Loven
19. E.tergestina Claus
Ostracoda
20. Cypridina mediterrianea Costa
21. Loxocanche lanwnndus
Copepoda
Calanoida
22. Paracalanus crassirostris Dahi
23. P.parvus Claus
24. Acrocalanus gibber Giesbrecht
25. Ccntropages elongatus Giesbrecht
26. C.ponticus Karawiew (N.G.R.)
27. Ctenocalarws vanus Giesbrecht
28. Temora stylifera Dana
29. Acartia negligent Dana
30. A.centrura Giesbrecht
31. Calanus minor Claus
32 Cvulgaris Dana (N.G.R.)
33. Clausocalanus furcatus Brady
34. Candacia pectinata Dana (N.G.R.)
35. Csimplex Giesbrecht (N.G.R.)
36. Ctruncata Dana
Cyclopoida
37. Oncaea media Giesbrecht
38. Oithona nana Giesbrecht
39. O.plumifera Baird
40. Copilia mirabilis Dana
41. Corycaeus erythraeus Cleve
42. Cgracilis Dana (N.G.R.)
43. Cspeciosus Dana
44. Lubbockia squillimana Claus
45. Sapphirina angusta Dana
Harpacticoida
46. Microsetclla norvegica Boeck
47. Macrosetella gracilis Dana
48. Clylemnestra scutellata Dana
Amphipoda
49. Gammarus sp.
Cirripedia
50. Cirripede larvae
Decapoda
51. Decapod larvae
Nematoda
52. Nematode larvae and adults
Mollusca
53. Creseis virgula Rang
54. Gastropod larvae
55. Bivalve larvae
Echinodermata
56. Echinoderm larvae
Urochordata CRinicata)
Thaliacea
57. Thalia democratica Forskal
58. Doliolum denticulatum Quoy & Gaim.
Appendicularia
59. Oikopleura longicauda Vogt
60. O.fusiformis Fol.
61. O.dioicaFol.
Vertebrata
62. Fish eggs and larvae
N.G.R., new geographic record.
Table II. Average values of diversity indices of zooplankton in the Gulf of Aqaba at different sites
Diversity index
No. of species
Equitability
Richness
Site
#1
#2
#3
#4
#5
#6
50
036
3.5
46
0.41
2.9
56
032
4.1
45
0.45
28
38
0.48
2.7
39
0.41
2.6
931
M.T.Khali] and N-S.AM El-Rahman
xlO 3
<• Copepoda
• Tunicata
Meroplankton
Chaetognatha
Protozoa
Otheres
Fig. 2. Site variations of total zooplankton at the Gulf of Aqaba (July 1994-May 1995).
in calanoid density from south to north in the Gulf of Aqaba. However, these
observations agree with the traditional concept of increasing oligotrophy of Red
Sea water to the north (Halim, 1969; Kimor, 1973; Almogi-Labin, 1984).
Regarding the seasonal variations, the main peak of zooplankton abundance
was recorded in winter (average 3510 ind. m~3), whereas September and May
harboured the lowest densities (1906 and 1917 ind. m~3, respectively). The
Jan.
1995
' Copepoda
'Tunicata
March
1995
May
1995
Meroplankton D Protozoa
Chaetognatha • Otheres
Fig. 3. Bimonthly variation of total zooplankton at the Gulf of Aqaba (July 1994-May 1995).
932
Surface zooplankton of the Golf of Aqaba
abundances of January and March were due to increased numbers of meroplanktonic larvae (Figure 3), including polychaete, cirriped, decapod, mollusc
and echinoderm larvae. Moreover, it is worth mentioning that Beckmann (1984)
attributed the winter peak of zooplankton in the Indian Ocean and the Persian
Gulf which are imported into the Red Sea through Bab El Mandab during winter,
to the water exchange pattern prevailing toward the Red Sea. As summer
approaches, the plankton density in the Red Sea decreases as the surface habitat
becomes more hostile due to increasing temperature, and the recruitment from
the Gulf diminishes with decreasing rate of water exchange (Beckmann, 1984).
Species diversity
The zooplankton community in the Gulf of Aqaba is characterized by high
species diversity (Tables II and III), compared to that of the Gulf of Suez (Abd
El-Rahman, 1993), indicating higher nutrients, instability or pollution of the latter
(Huston, 1994). Relatively higher diversity values were recorded at site #3, in the
Ras Mohammed protected area, where 56 species were recorded. A high proportion of these species was made up of meroplanktonic forms of larvae of the
diverse array of organisms that comprise the reef benthos.
On the other hand, site #5 exhibited the lowest species diversity, which may be
due to increasing organic pollution caused by discharges of shrimp fish-farm
water and mangrove detritus. The diversity progressively declined from south to
north. Weikert (1987) indicated that the habitat becomes more hostile to planktonic life as depth increases and with distance from the Gulf of Aden, which is
the source of plankton, and thus the number of species decreases with depth and
towards the Gulfs of Suez and Aqaba. For example, in calanoid copepods that
form the most abundant group in the mesozooplankton, >300 species are known
from the Arabian Sea, whereas only 60 have been reported in the southern Red
Sea proper, 46 in its northern part and about 35 in the Gulfs of Suez and Aqaba
(Delalo, 1966; Almeida Prado-Por, 1983).
An inverse relationship was observed between equitability and the magnitude
of the standing crop of zooplankton, as indicated at sites #3 and #5 which harboured the relatively low densities, but they exhibited high evenness values. On
the other hand, the lowest equitability value was recorded at site #1, which
showed a moderate density of zooplankton. Such an inverse relationship is attributed to the increase in density of only one group, the Copepoda, which comprised
-80% of the whole population, as shown in Figure 2.
Regarding the similarity of species diversity between the different sites, the
cluster analyses indicated a relatively high degree of homogeneity in the
Table DL Average values of diversity indices of zooplankton in the Gulf of Aqaba in different seasons
Diversity index
July
1994
September
1994
November
1994
January
1995
March
1995
May
1995
Equitability
Richness
0.40
3.1
0.49
3.7
0.55
33
0.42
3.2
0.34
2.7
038
3.1
933
M.T.KhaHl and N-S.AM El-Rahman
1.6
#3 #1 #5
#6 #4 #2
1.4
1.2
1.0
i
0.6
c/5
0.4
0.2
0.0
Fig. 4. A classification (dendrogram) showing site similarity of zooplankton composition in the Gulf
of Aqaba, based on average seasonal Sorensen Similarity Index (for sites, refer to Figure 1).
zooplankton composition between the northern sites (#5 and #6; Figure 4). Such
similarity was less clear between southern sites (#2 and #3), which may be attributed to the high densities of zooplankton at these sites and also because site #2
is nearer to the Gulf of Suez side.
In conclusion, the Gulf of Aqaba is regarded as being among the most oligotrophic marine habitats when considering the magnitude of the standing crop of
zooplankton, and diversity is relatively high compared to the Gulf of Suez, which
has been disturbed by pollution. Higher diversity of zooplankton at Ras
Mohammed Protectorate reflects the diversity of the reef environment as a
whole, and indicates the importance of marine reserves in the protection of biodiversity and providing areas in a natural balance free from direct human disturbance, acting as reference areas for the study of natural processes in the
environment.
Acknowledgement
The authors wish to express sincere appreciation to Prof. Helmy M.Bishai, Cairo
University, for his kind support of this study and for providing valuable comments
on the earlier version of the manuscript.
934
Surface zooptankton of the Golf of Aqaba
References
Abd El-Rahman,N.S. (1993) Ecological studies on the distribution of zooplankton communities in the
northern part of the Suez Gulf 'Suez Bay'. MSc Thesis, Faculty of Science, Suez Canal University,
Egypt, 316 pp.
Almeida Prado-Por,M.S. (1983) The diversity and dynamics of Calanoida (Copepoda) in the northern Gulf of Elat (Aqaba). Oceanologica, 6,139-145.
Almeida Prado-Por,M.S. (1985) Distribution of Calanoida Copepoda along the Gulf of Elat (Aqaba).
Rapp. Cowan. Int. Mer MediL, 29, 9.
Almeida Prado-Por,M.S. (1990) A diel cycle of vertical distribution of the Calanoidea (Crustacea:
Copepoda) in the northern Gulf of Aqaba (Elat). Bull Inst Ocianogr. Monaco, 7,109-116.
Almogi-Labin,A. (1984) Population dynamics of planktonic Foraminifera and Pteropoda—Gulf of
Aqaba, Red Sea. PalaeontoL Proc. B, 87, 481-511.
Azov,Y. (1986) Seasonal patterns of phytoplankton productivity and abundance in near shore oligotrophic waters of the Levant Basin (Mediterranean). J. Plankton Res., 8,41-53.
Beckmann.W. (1984) Mesozooplankton distribution on a transect from the Gulf of Aden to the
central Red Sea during the winter monsoon. OceanoL Ada, 7, 87-102.
Berman.T., Azov,Y., Schneller^A., Walline,P. and TownsendJJ.W. (1986) Extent, transparency, and
phytoplankton distribution of the neritic waters overlying the Israeli coastal shelf. OceanoL Ada,
9,439-447.
BrayJ.R. and Curtis.C.T. (1957) An ordination of the upland forest communities of southern Wisconsin. Ecol Monogr., 27, 325-349.
Clifford J t T . and Stephenson,W. (1975) An Introduction to Numerical Classification. Academic Press,
London.
Death^R.G. and Winterbourn^O. (1995) Diversity patterns in stream benthic invertebrate communities: the influence of habitat stability. Ecology, 76,1446-1460.
De Ghet.VJ. (1978) Hierarchical cluster analysis. In Colgan.W. (ed.), Quantitative Ethology. London,
pp. 115-144.
Delalo^EJ. (1966) Distribution of the zooplankton biomass in the Red Sea and the Gulf of Aden,
winter 1961/62. OkeanoL Issled., 15,131-139 (in Russian).
Dowidar^N.M. (1994) Biodiversity of the Marine Plankton in the Egyptian Waters. Egypt. Env. Aff.
Agen., Reports I, II, i n and IV.
Dussart,B. (1967) Les Copepodes des eaus continentales d'Europe Occidentale. In Boubee,N. (ed.),
Tome I Calanoides et Harpacticoides. Acad. Sci., Paris, pp. 1-500.
Dussart,B. (1969) Les Copepodes des eaus continentales d'Europe Occidentale. In Boubee,N. (ed.),
Tome II Cyclopoides et Biologic. Acad. Sci., Paris, pp. 1-292.
Echehnan,T. and FishelsonJ- (1990) Surface zooplankton dynamics in the northern Gulf of Aqaba
(Elat), Red Sea. Bull Inst. Ocianogr. Monaco, 7, 67-77.
Fenaux,R. (1960) Sur quelques Appendiculaires d'Israel—Contrib. to the knowl. of the Red Sea, 17.
Bull Sea Fish. Res. Stn Haifa, 29, 3-7.
Furnestin,M. (1958) Quelques echantillons de zooplancton du Golfe d'Eylath—Contrib. to the knowl.
of the Red Sea, 6. Bull Sea Fish. Res. Stn Haifa, 16, 6-14.
Godeaux J. (1960) Tuniciers Pelagiques du Golfe d'Eylatli—Contrib. to the knowl. of the Red Sea,
18. Bull Sea Fish. Res. Stn Haifa, 29, 9-14.
GodeauxJ. (1986) The Gulf of Aqaba, a zone of great biological interest Unesco Tech. Pap. Mar. Set,
49,104-106.
GregoryJ.W. (1921) The Rift Valleys and Geology of East Africa. Seely, Service and Co., London, 479
pp.
Halim,Y. (1969) Plankton of the Red Sea. Barnes,H. (ed.), Oceanogr. Mar. BiolAnnu. Rev., 7,231-275.
Halim.Y. (1990) On the potential migration of Indo-Pacific plankton through the Suez Canal. Bull
Inst. Ocianogr. Monaco, 7,11-27.
Heip.C. (1974) A new index measuring evenness. / Mar. BioL Assoc UK, 54,555-557.
HustonJvI.A. (1994) Biological Diversity. Cambridge University Press, Cambridge, UK, 681 pp.
Jorgensen,O.M. (1933) On the marine dadocera of the Northumbrian plankton. /. Mar. BioL Assoc
UK, 19,177-226.
Kimor3- (1973) Plankton relations in the Red Sea, Persian Gulf and Arabian Sea. In ZeitzscheLBand Gerlach,S. A. (eds), 77ie Biology of the Indian Ocean. Ecological Studies 3. Springer, Berlin,
pp. 221-232.
Kimor3. (1990) Microplankton of the Red Sea, the Gulf of Suez and the Levantine Basin of the
Mediterranean. BulL Inst Ocianogr. Monaco, 7,29-38.
935
M.TJOianl and N.&AM El-Rahman
Kimor,B- and Golandsky.B. (19T7) The microplankton of the Gulf of Eilat: aspects of seasonal and
bathymetric distribution. Mar. BioL,A2, 55-76.
Margalef.R. (1968) Perspectives in Ecological Theory. University of Chicago Press, Chicago, IL, 111
pp.
Morcos.S.A. (1970) Physical and chemical oceanography of the Red Sea. Oceanogr. Mar. BioL, 8,
73-202.
Newell,G.E. and NewelLR-C. (1967) Marine Plankton, A Practical Guide. London, Hutchinson Educational, 221 pp.
Oren,O.H. (1970) Seasonal changes in the physical and chemical characteristics and the production
in the low trophic level of the Mediterranean waters off Israel. Spec PubL Sea Fish. Res. Stn Haifa,
238 pp.
Reiss,Z., LevanonJ., Raz,G., Harpaz,H., Ben Avraham,Z. and Padan,E. (1977) DCPE data collecting program in the Gulf of Eilat. The H. Steinitz Biology Laboratory Report No. 6, pp. 31-54
(unpublished).
Schmidt Ji. (1973) Vertical distribution and diurnal migration of some zooplankton in the Bay of Eilat
(Red Sea). HelgoL Wiss. Meeresunters., 24,333-340.
Vaissiere^R. and Seguin.G. (1982) Preliminary study of the zooplankton from the coral reef and opensea areas of Jordan in the Gulf of Aqaba, Red Sea. Vie Mar., 4,1-6.
Vaissiere^R- and Seguin.G. (1984) Initial observations of the zooplankton microdistribution on the
fringing reef at Aqaba (Jordan). Mar. BioL, 83,1-11.
Weikerttf. (1987) Plankton and the pelagic environment. In Edwards.AJ. and Head.S.M. (eds), Key
Environments, Red Sea. Pergamon Press, Oxford, pp. 90-111.
Wimpenny,R.S. (1966) The Plankton of the Sea. Faber and Faber Ltd, London, 426 pp.
Received on June 8, 1996; accepted on March 4, 1997
936