*Mnemiopsis leidyi* **Invasion and Biodiversity Changes in the Caspian Sea**

Aboulghasem Roohi1 and Ameneh Sajjadi2

*1Caspian Sea Research Institute of Ecology, Khazarabad Boolvar, Sari, 2Meteorology Dept, Islamic Azad University Rasht Branch, Rasht, Guilan Iran*

## **1. Introduction**

170 Ecosystems Biodiversity

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#### **1.1 Caspian Sea**

The complex history of the Caspian Sea formation has lead to a variety of different habitats. Like Australia, the Caspian Sea became isolated thousands of years ago (Plate 1). This isolation led to the speciation of many rare animals in particular the sturgeon.

The Caspian Sea is the biggest enclosed body of water on Earth, having an even larger area than that of the American Great Lakes or that of Lake Victoria in East Africa. It is situated where the South-Eastern Europe meets the Asian continent, between latitudes 47.07́N and 36.33́N and longitudes 45.43́E and 54.20́E. It is approximately 1,030 km long and its width ranges from 435 km to a minimum of 196 km. It has no connection to the world's oceans and its surface level at the moment is around \_26.5 m below MSL. At this level, its total coastline is some 7,000 km in length and its surface area is 386,400 km2. The water volume of the lake is about 78,700 km3.

Plate 1. Caspian Sea area

*Mnemiopsis leidyi* Invasion and Biodiversity Changes in the Caspian Sea 173

The Volga Delta is situated in the Prikaspiisk lowlands covering around 10,000 km2 and the delta has a width of about 200 km. A feature of the delta region are the so-called Baer knolls which are hillocks, between 3m and 20m in height, formed by the action of onshore winds on the river sediments. These sediments are discharged into the delta at a rate of 8 million tones per year. Numerous small lakes can be found between the knolls and there is a complex system of channels with many islets. The Volga-Caspian shipping canal traverses the delta and is dredged to maintain a depth of no less than 2m (Aladin and

The biodiversity of the Caspian aquatic environment is a product of thousands of years of isolation from the world's oceans, allowing ample time for speciation. The biological diversity of the Caspian and its coastal zone makes the region one of the most valuable ecosystems in the world. The Caspian harbors some 147 species of fish, 450 species, varieties, or forms of phytoplankton, 87 species of algae, and 315 species of zooplankton. One of the most important features of the Caspian's biodiversity is the relatively high level of endemism among its fauna. Recent studies suggest the actual endemism may be even higher than what is already known. To date, there are 331 known endemic species in the Caspian. They are represented by the following: UNDP, www.caspianenvironment.org/

Tran boundary Diagnostic Analysis for the Caspian Sea, Caspian Environment Programme. September

The decline in bioresources and biodiversity are closely linked through food chains and feeding patterns. A disturbance in the phytoplankton-zooplankton and benthic communities caused by invasive species for instance may impact species at higher trophic levels, such as sturgeon or seals. With the invasion of ML (*Mnemiopsis leidyi*) as well as introductions of other species the naturally occurring food web may have undergone or be undergoing

The sturgeon species existed 200 million years ago at the same time as dinosaurs and can therefore be called living fossils. At that time sturgeon inhabited many ancient seas. Later on in the process of evolution, possibly due to competition with bony fish species, the

Plotnikov, 2004).

**2. Biodiversity in the Caspian** 

newsite/Data-MajorDocuments.htm.

Twenty (20) species of *Mysidacea*

Four (4) species of *Spongia* One (1) species of *Isopoda*

Twenty-three (23) species of *Copepoda* One (1) species of *Isopoda*

Table 1. Known endemic species in the Caspian Sea.

2002. Baku. www.caspianenvironment.org/newsite/Data-MajorDocuments.htm.

potentially significant disruptions particular when under concurrent stresses.

Two (2) species of *Coelenterata* Sixty-eight (68) species of *Amphipoda* Twenty-nine (29) species of *Turbellaria* Nineteen (19) species of *Cumacea* Three (3) species of *Nematoda* One (1) species of *Decapoda* Two (2) species of *Rotatoria* Two (2) species of *Hydracarina* Two (2) species of *Oligochaeta* Fifty-three (53) species of *Mollusca* Four (4) species of *Polychaeta* Fifty-four (54) species of fish Nineteen (19) species of *Cladocera* One (1) species of marine mammal Three (3) species of *Ostracoda* Twenty (20) species of *Mysidacea*

The Caspian can be considered as divided into three parts, the northern, middle and southern parts. The border between the northern and middle parts runs along the edge of the North Caspian shelf (the Mangyshlak threshold), between Chechen Island (near the Terrace River mouth) and Cape Tiub-Karagan (at Fort Shevchenko). The border between the middle and southern parts runs from the Apsheron threshold connecting Zhiloi Island in the west to Cape Kuuli in the east (north of Turkmenbashi). The northern part covers about 25% of the total surface area, while the middle and southern parts cover around 37% each. However, the water volume in the northern part accounts for a mere 0.5%, while the volume in the middle part make up 33.9%, and in the southern part 65.6% of Caspian waters. These volumes are a reflection of the bathymetry of the Caspian. The northern part is very shallow, with average depths of less than 5m. In the middle part, the main feature is the Derbent Depression with depths of over 500m. The southern part includes the South Caspian Depression with its deepest point being 1025m below the surface (plate 2).

Plate 2. Caspian Sea riparian countries

Approximately 130 large and small rivers flow into the Caspian, nearly all of which flow into the north or west coasts. The largest of these is the Volga River that drains an area of 1,400,000 sq. km and runs into the northern part of the Caspian. Over 90% of the inflowing freshwater is supplied by the 5 largest rivers: Volga – 241 km3, Kura – 13 km3, Terek – 8.5 km3, Ural – 8.1 km3 and Sulak 4 km3. The Iranian rivers and the smaller streams on the western shores supply the rest, since there are no permanent inflows on the eastern side. Apart from the extensive shallows of the northern part, the other two physical features that characterize the Caspian are the Volga and the Kara Bogaz Gol gulf.

The Volga Delta is situated in the Prikaspiisk lowlands covering around 10,000 km2 and the delta has a width of about 200 km. A feature of the delta region are the so-called Baer knolls which are hillocks, between 3m and 20m in height, formed by the action of onshore winds on the river sediments. These sediments are discharged into the delta at a rate of 8 million tones per year. Numerous small lakes can be found between the knolls and there is a complex system of channels with many islets. The Volga-Caspian shipping canal traverses the delta and is dredged to maintain a depth of no less than 2m (Aladin and Plotnikov, 2004).
