Presence of the Ctenophore Mnemiopsis leidyi in south Caspian Sea
Background
Recent findings show that the invasive Comb Jelly Mnemiopsis leidyi has appeared in the Caspian Sea in considerable numbers. The jellyfish Aurelia aurita also is observed in the Caspian. Presence of these species stresses that there is still the possibility of invasion by other species.
Presence of the Comb Jelly Mnemiopsis leidyi in the Caspian Sea was recognized for the first time by Iranian Fisheries Research Organization in 1995 and warning letters were issued in this regard. Researchers from Tarbiat Modarres University also reported occurrence of this species in large numbers (Esmaili et al, 1999). Today after almost 6 years this species has increased in numbers and a reduction in the catch of Kilka has been linked with the presence of this Comb Jelly. However more investigation is needed to prove the impact of Mnemiopsis on Kilka stocks in South Caspian Sea. It is also reported that Mnemiopsis has been found in Funnel nets in large numbers.
Following observation of Aurelia aurita in the Caspian IFRO and Tarbiat Modarres University are running a combined research on biomass and distribution and biology of this species.
Parallel to this Iranian Fisheries Research Organization is conducting a research study on abundance, distribution and possible control of Mnemiopsis populations in southern Caspian Sea.
Present information on Mnemiopsis in South Caspian Sea
Two pilot studies were conducted in southern Caspian and the results of which showed that in winter 2000 maximum biomass of Ctenophore in south Caspian Sea, was 125 g/m2 in Khazarabad region and a minimum of 0 was observed in surface waters of Amirabad (Table 1).
Meanwhile in summer 2000, there were an increase with depth in most sites with a maximum of 470 g/m2 in 20metre depth. However, Gorgan showed a maximum in 5 meter depth.(93.7 g/m2) (Table 2).
This data indicates that Ctenophore biomass in different sampling sites tends to increase from surface to bottom.
Possible effects on the Caspian
The follow up of invasive effects of M. on Black Sea, considering the same situation in the Caspian Sea (there are about 400 endemic species in the Caspian), would lead us to postulate that a similar thing is most likely to happen in this area. It seems that this has already started, bearing in mind that this is a different environment these effects could be categorized as follows:
-
A decline in the population of endemic mostly pelagic, benthic or semi-benthic species such as crustaceans of the orders Amphipoda, Mysidacea, Cumacea, Copepoda and Onychopoda (Zaittsev and Mameav 1997 sited in Ivanov et al. 2000).
-
A reduction in pelagic fish larvae and eggs (as in Black Sea). The main stock of pelagic fish in the Caspian is Kilka (small Clupeids) with 3 species constituting the main fishery in southern Caspian. Kilka feeds exclusively on zooplankton, mostly copepods(55-77% by weight), cladocerans and meroplankton. A reduction in zooplankton and fish eggs and larvae has most probably resulted to a 18000 tons decline in Kilka fisheries of Iran in a course of one year (Table 3).
-
A possible impact on top predators of the Caspian, sturgeon fishes and the Caspian seal as a result of a reduction in their food (Kilka).
-
The presence of Mnemiopsis in the Caspian may produce a great change in the food chain and influence the entire fish populations.
Recommendations
It is obvious that the invasion problem in the Caspian Sea is a regional problem and all neighboring countries should be involved when proposing any action plan or policy. It is proposed that a working committee consisting of a group of scientists from all member states of CEP should be established and concentrate on the followings:
-
assess abundance, distribution and impacts of Mnemiopsis in the Caspian Sea.
-
investigate means by which this species has been introduced to the Caspian and evaluate extent of damages caused.
-
conduct experimental studies on effective control mechanisms, possibly using endemic predators (GESAMP 1997).
-
develop a strategy and recommend measures to overcome the outbreak of this invading species.
-
enhance co-operation among national research centers and stakeholders.
-
improve co-ordination among institutions, national and international programs in the areas of scientific research, monitoring and control measures.
Table.1.Biomass of Ctenophore (g/m2) in winter 2000
|
Site |
Depths(m) |
Surface |
5(m) |
10(m) |
20(m) |
|
Khazarabad |
5 |
9.30 |
11.35 |
0 |
0 |
|
10 |
15.55 |
30.20 |
124.85 |
0 |
|
|
20 |
12.35 |
15.30 |
6.60 |
16.95 |
|
|
Amirabad |
5 |
0 |
24.25 |
0 |
0 |
|
10 |
15.25 |
65.75 |
105.45 |
0 |
|
|
20 |
25.35 |
17.85 |
25.85 |
35.45 |
|
|
Babolsar |
5 |
0 |
0.50 |
0 |
0 |
|
10 |
0.67 |
3.65 |
55.45 |
0 |
|
|
20 |
0 |
0.70 |
9.86 |
4.50 |
Table.2.Biomass of Ctenophore (g/m2) in Summer 2000
|
Site |
Depth(m) |
Surface |
5m |
10m |
20m |
|
Khazarabad |
5 |
0 |
26.7 |
0 |
0 |
|
10 |
51.90 |
203.1 |
237.7 |
0 |
|
|
20 |
55.90 |
59.1 |
180.8 |
62.8 |
|
|
Amirabad |
5 |
0 |
10.5 |
0 |
0 |
|
10 |
0 |
7.2 |
1.5 |
0 |
|
|
20 |
0 |
5 |
50 |
10.5 |
|
|
Turkmen |
5 |
75.24 |
11.3 |
0 |
0 |
|
10 |
231.96 |
134 |
129.9 |
0 |
|
|
20 |
30.60 |
70.1 |
112.5 |
470.3 |
|
|
Gomishan |
5 |
60 |
20 |
0 |
0 |
|
10 |
10 |
240.4 |
280.5 |
0 |
|
|
20 |
30.50 |
240.2 |
245.1 |
470.4 |
|
|
Gorgan |
5 |
4.60 |
93.7 |
0 |
0 |
Table.3. Kilka landings at Iranian Ports of the Caspian Sea
|
Fishing season |
Catch (Tons) |
|
1998/1999 |
82100 |
|
1999/2000 |
83000 |
|
2000/2001 |
65000 |
References
Ivanov, V. P. et al., 2000. Invasion of the Caspian Sea by the Comb Jellyfish Mnemiopsis leidyi (Ctenephora). Biological Invasion 2: 255-258, 2000.
Esmaeili Sari, B. et al., 1999. First report on occurrence of a combjelly in the Caspian Sea. Journal of Environmental Sciences and Technology, No.3, Islamic Azad University.
GESAMP, 1997. Opportunistic settlers and the problem of ctenophores Mnemiopsis leidyi invasion in the Black Sea, GESAMP Report and Studies No. 58.
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