Psevdosolenia calcar-avis, M. Schultze

Rhizosolenia cal�ar-avis referring to large diatoms is aciform in shape with a strong silicic shell. Cells are single. They have a shape of long thin sticks, round in cross-section. Their diameter varies from 3 to 50 μ, usually 5-12 μ. The length (height) of cells of small diameter reaches 1000 μ, those of large diameter varies from 238 to 417 μ. The length of the former exceeds the diameter by a factor of 70-77, that of the latter by a factor of 15-17. The shell is thin, intercalary rims are numerous, squami-form-rhombic, arranged in two dorsal-ventral rows. Valves are elongated-conic, somewhat off-center, end in a rough, hollow, nail-shaped curved spine. The structure of valves (cap) consists of very small dots arranged in oblique intersecting rows. Chromatophores are fine, abundant, spread throughout the cell and usually accumulate at the nucleus.
Long cells 5-12 μ in diameter usually occur in the Caspian Sea. Only during the spring and winter 1956 extensive populations of cells 33-50μ in diameter vegetated in the zone of the lighthouse Kuli. Cells of  large diameter (up to 100μ) never occurred in the Caspian Sea. Deformed caps and spines of abnormal shape were observed, solitary individuals had two and even three spines. Spores rarely occurred in autumn (Proshkina-Lavrenko, 1968).
The diameter of cells in the Sea of Azov is 4.5-17.5 �, but cells 5-8 � in diameter are more common. The diameter of cells in the Black Sea is 5-57.5 �. The length of wide cells is 300-900 �, that of narrow ones is 1310 �. The diameter of cells in the Japan Sea is 35-70 �, the length is 250-500 � (Proshkina-Lavrenko, 1955; Konovalova et al., 1989).
Intraspecific forms. Unknown
Related forms. 1. Rhizosolenia fragilissima Bergon (1903)
The neritic boreal-temperate wide-spread species is distributed in the Barents, Bering, Chukotski, Japan, Caspian and Azov Seas, well known to all the European seas from the Arctic Ocean to Mediterranean Sea and at Californian coast of North America. It occurs throughout the Middle and Southern Caspian, in the Northern Caspian - only in its deep, more saline waters at the border with the Middle Caspian (Proshkina-Lavrenko, 1968).
2. Rhizosolenia delicatula Cleve (1990)
The neritic species inhabits temperate warm waters and is distributed in the Black, Baltic, Barents, Kara and Japan Seas, Amur Firth, in temperate latitudes of the Atlantic Ocean and in the Mediterranean Sea.
3. Rhizosolenia acuminata (Perag.) Gran. (1905)
The oceanic, warm-water species distributed in the limited area occurs sporadically in the Black Sea near Karadag (Crimea) (Stroikina, 1940, 1950). Registered for the tropic and subtropic Atlantic up to latitude 630 North, in the Mediterranean Sea and at the Californian coast.
4. Rhizosolenia alata Brightw (1858)
The oceanic neritic species often occurs at shores presumably within the temperate latitudes. General distribution: the Barents, White, Kara, Chukotski, Okhotsk, Bering, Japan Seas and all the European seas of the Arctic Ocean including the Bosphorus Strait. The Pacific, Indian Oceans and Antarctica.
5. Rhizosolenia longiseta Zacharias
This freshwater species is frequently found in the plankton of eutrophic lentic and slowly flowing waters from the Kolsk Peninsular to the lower Volga River, in the Middle Asia and in all Western Europe.
6. Rhizosolenia eriensis H.L. Sm.
Freshwater species, wide-spread in the plankton of lentic waters, especially in subalpine lakes, less frequently in rivers and freshened areas of the sea (Zabelina, Kiselev et al., 1951; Proshkina-Lavrenko, 1968).

Distribution of species within the Caspian Sea

Rhizosolenia calcar avis is widely distributed throughout the Caspian Sea, though located mostly in the surface area reaching there mass development from spring till autumn. It also occurs at a depth more than 100 m. This species vegetates year-round; it dominates in the Middle and Southern Caspian and occurring in great quantities causes water bloom in spring and autumn. In the Northern Caspian it occurs as far as the estuary of the Volga and Ural Rivers and when developed abundantly replaces other planktonic algae. Its maximum development in the Northern Caspian is recorded during summer, spring and autumn.
Status as per International Red Data Book. Not defined
Status as per National Red Data Books. Not defined
First record for the Caspian Sea. Rhizosolenia calcar-avis was first found by P.I. Ussachev (1948) in the southern area of the central part of the Southern Caspian (solitary specimens) and at the Krasnovodsk Bay in September 1934.
In October 1934 water bloom caused by this alga was noted in the area of the Astrabad Bay. During the autumn 1935 Rhizosolenia calcar-avis spread all over the Caspian Sea as far as the eastern zone of the Northern Caspian.
Redescription of species. Information is not available.

General characteristics of species

Ecological-taxonomic group. Phytoplankton
Origin. Mediterranean Sea invader
World distribution. It occurs currently in the Caspian, Azov, Black, Japan Seas as well as in the temperate latitude of the Atlantic, at the coasts of Europe and America, in the Mediterranean Sea. The species is known to inhabit the Indian and Pacific (at the coast of California ) Oceans.
Habitat. Oceanic neritic species inhabits the water column of the Caspian Sea.
Migrations. Daily vertical migrations are known. The biomass of this algae undergoes abrupt diurnal fluctuations. A sharp reduction in the nocturnal biomass may be caused both by predation of plankton-feeding crustaceans and natural mortality (Kondratieva, 1963).

Relation to abiotic environmental factors

Relation to salinity. Marine and brackishwater species
It lives in the Caspian Sea at a salinity range 1.33-13^o/_oo (Proshkina �Lavrenko, 1968), in the Black and Azov Seas at a salinity of 10-13^o/_oo (Proshkina-Lavrenko, 1963; Studenikina et al., 1999).
Relation to temperature. Eurythermic species
Rhizosolenia calcar-avis dominates the Caspian phytoplankton throughout the year at a water temperature of 2-28⁰C . In the Northern Caspian, Rhizosolenia calcar-avis first appears in the phytoplankton in spring at a water temperature from 2 to 4⁰C. The quantity of Rh. calcar-avis cells is observed to fluctuate at a higher temperature (from 5 to 28⁰C). In the Middle and Southern Caspian Rh. calcar-avis is responsible for water bloom in summer and autumn at a temperature more than 24⁰C (Levshakova, 1967; original author�s data). 
Vertical distribution. Eurybathic species
Rhizosolenia calcar-avis is mostly confined to the surface layer where it reaches mass development. The vertical distribution of Rh. calcar-avis in the Caspian sea is usually limited to the depth of 100m where it shows a good vegetative state (Kisselev, 1950). The highest abundance in the Middle and Southern Caspian is recorded in the upper photosynthetic layer from 0 to 25 m (up to 90%). It is rare (occurs sporadically) at depths from 200 to 800 m (Kisselev, 1938; original author�s data).
Relation to oxygen conditions. Information is not available
Relation to fluctuations of the sea level. Unstable water regime and sea level fluctuations affect abundance of this species. In the low-water years (reduced riverine discharges) increased water salinity was due to intensified water inflow from the Middle Caspian into the Northern Caspian, which facilitated the wide distribution of Rh. calcar-avis throughout northern areasand contributed to the increase in its biomass. In low-water years (1984, 1988) predominant southern winds provided for large quantities of Rh. calcar-avis (500-864 mg/m3) in the eastern zone of the sea and south-eastern part of the western area. During the high-water years the increase in freshened areas resulted in sharp reduction of its range - usually to the boundary between the Northern and the Middle Caspian. The maximum biomass of Rh. calcar-avis (1015-1328 mg/m³) was observed in the area of Chechen Island (Tatarintseva et al., 2001). The rise in seawater level and extension of freshened areas leads to a decline in Rh. calcar-avis quantities, especially in the Northern Caspian where water/salt balance is more unstable than in the Middle and Southern Caspian. The rise in sea water level positively affected this alga development. In the 1970-s, its biomass reached 152 mg/m³ in the Middle Caspian, 117mg/m³ in the Southern Caspian. By 1993, it increased 4 times and twice, respectively, and reached 603 and 242 mg/m³, though in recent years its abundance has declined because of a sharp decrease in silicon content in water (Katunin et al., 2000).

Quantitative characteristics of Rhizosolenia calcar-avis development during summer period at different seawater level (original data)

Feeding

Feeding type. Autotrophic
Feeding behavior. Utilization of solar energy (photosynthesis)
Food spectrum. Biogenic elements, of which the main is silicon.
Supply of food. Information is not available
Quantitative characteristics of feeding. Information is not available

Reproduction

Reproduction type. Agamogenesis, the vegetative division of cells occurs day and night
Reproduction areas. There are no specific areas of reproduction in the Caspian Sea.
Terms of reproduction. . In the daytime the number of Rh. calcar avis cells is 1.5-2 times more than at night. There is a certain trend observed: a reduction in the number of cells from midnight to sunrise and increase in their number from dawn to noon. The day light is used for photosynthesis while the night for reproduction. Rhizosolenia calcar-avis in the Middle and Southern Caspian vegetates day and night and the same trend is observed in the Black Sea (Morozova-Vodyanitskaya, 1954).
Fecundity. Information is not available.
Limiting factors. Temperature, salinity, biogenic elements.

Life history and development

Life-history stages. Information is not available.
Relation to environmental factors. Salinity factor is determinant to Rh. calcar-avis development. This species vegetates at water salinity 1.33-13^o/oo. Its maximum development occurs within 6.1-7^o/_oo.
Age of maturity. Information is not available.
Thermal conditions of development. The temperature range of the species is between +2 and +28⁰C. The maximum development of Rhizosolenia calcar-avis occurs in spring and summer.
Quantitative characteristics of growth. Information is not available.

Structural and functional population characteristics

Sex ratio. Information is not available.
Age-size structure. Information is not available.
Quantitative characteristics.

Rhizosolenia calcar-avis is randomly distributed throughout the Caspian Sea. In 1990 its distribution pattern was similar to that in 1981. In 1990 increased densities were recorded in the shallow water zones at the western and eastern coasts of the sea. Small areas with biomass exceeding 1000 mg/m³ occurred in the Northern Caspian in the zone of steep slopes of Ukatny and Chechen Islands and in the Southern Caspian at Ogurchinsky Island. In 1986 the alga biomass in the entire Caspian Sea was significantly lower than in 1981 and 1990. Large densities of Rhizosolenia calcar-avis occurred almost in all eastern shallow water area of the Northern Caspian, in deep waters of the eastern part of the Middle Caspian from Sagyndyk to Melovoy Cape. In the Southern Caspian, high biomass of Rh. calcar-avis was recorded in a narrow strip from Ogurchinsky Island to the border of Iran.
Population trends. After the introduction of Rhizosolenia calcar-avis into the Caspian Sea in 1934, its biomass during the 1930-s reached 2.7 g/m³, i.e. 20-45% of the total phytoplankton biomass. The maximum biomass 3.7 g/m³ was recorded in 1936 (Ussachev, 1948). In the 1960-s, Rh. calcar-avis amounted to 4.3 million cells per 1m³ or about 7% of the total number of cells and 21-30% of the total biomass (Levshakova, Sanina, 1973; Levshakova, 1985). During the period of the lowest seawater level (in the 1970-s) the summer biomass of Rhizosolenia calcar-avis in the southern part of the Middle and Southern Caspian was 81-86% and 75-79%, respectively. At present, Rhizosolenia calcar-avis occupies the entire area of the Middle and Southern Caspian and amounts to 50-60% of the total biomass of the phytoplankton (Tatarintseva et al., 2000).

Interspecific relations

Mollusks Hypanis angusticostata, Didacna trigonoides, Cerastoderma lamarcki, Dreissena polymorpha, Mytilaster lineatus partially filter small cells (from 190 to 300μ) of Rh. calcar-avis . Nevertheless, the food value of Rhizosolenia calcar-avis is uncertain as mollusks do not develop enzymes to split up cellulose and the silica shell of diatoms (Romanova, 1963).

Impact on the Ecosystem

The explosive development of Rh. calcar- avis is responsible for the reduction in the useful production of phytoplankton (Levshakova, 1967). At the same time, live and dead cells of Rh. calcar-avis are used not only by bacteria, but also by benthic animals (Yablonskaya, 1952). Because of the morphological structure of the cells of Rh. calcar-avis, invertebrates can not use them directly as food. This large alga is used as detritus thus contributing to the food supply of plankton animals in the Caspian Sea (Alfimov, Proshkina-Lavrenko, 1966).

Importance of species to bioresources production of the Caspian Sea

Economic significance of species. None
Human impact/Threats. Pollution. The problem is not thoroughly studied yet.
Conservation measures. Information is not available.

References

Alfimov, N.N., A.I. Proshkina-Lavrenko, 1966. On the biology and biochemistry of mass marine diatoms Coscinodiscuc jonesianus (Grev.) Ostf. and Rhizosolenia calcar-avis M.Schultze in the Azov and Caspian Seas. Bot. J. V.51, 9:1267-1283 (in Russian).
Fauna and biological productivity. 1985. P.p. 23-54. In: Caspian Sea. Moscow. Nauka (in Russian).
Katunin, D.N., N.P. Bespartochny, V.V. Sapozhnikov, N.M. Torgunova, Yu.A. Mikhailovsky, V.V. Bulanov, 2000. Complex oceanographic exploration of the Caspian Sea during a cruise of the research vessel �Issledovatel Kaspia� (August-September 1999). Oceanography. V.40, 1:156-158 (in Russian).
Kisselev, I.A. 1950. Dinoflagellata in the seas and fresh waters of the USSR. Moscow. USSR AS. 279 p. (in Russian).
Kisselev, I.A.1938. On the phytoplankton of the Caspian Sea. P.p. 229-254. In: Data on hydrology and lithology of the Caspian Sea. Moscow-Leningrad. USSR AS (in Russian).
Kondratyeva, T.M. 1963. Daily changes in the phytoplankton of the Black Sea. Proceedings of the USSR AS Sevastopol Biological Station of the USSR AS, 16: 53-70 (in Russian).
Levshakova, V.D. 1967. Long-term changes in the spring phytoplankton of the Northern Caspian. CaspNIRKH Proceedings, 23:25-57 (in Russian).
Levshakova, V.D. and L.V. Sanina, 1973. Summer phytoplankton of the Middle Caspian before and after the introduction of Rhizosolenia calcar-avis. VNIRO Proceedings, 80, 3:18-27 (in Russian).
Morozova-Vodyanitskaya, N.V. 1954. Phytoplankton of the Black Sea. Proceedings of the Sevastopol Biological Station. Part II, 8:11-99 (in Russian).
Proshkina-Lavrenko, A.I. and I.V. Makarova, 1968. Plankton algae of the Caspian Sea. Leningrad. Nauka. 291 p.(in Russian)
Proshkina-Lavrenko, A.I. 1963. Diatoms of the plankton in the Sea of Azov. Moscow-Leningrad. USSR AS. P.102 (in Russian).
Romanova, N.N. 1963. Feeding habits and feeding groups of benthic invertebrates of the Northern Caspian. USSR AS VGBO Proceedings, 13:146-177 (in Russian).
Stroikina, V.G. 1940. Dyaki dani pro sklad phytoplanktonu Karadagckogo rayonu Chernogo morya. Proceedings of the Karadag Biological Station, 6: 94-96 (in Ukrainian).
Stroikina, V.G. 1950. The phytoplankton of the Black Sea in Karadag area and its seasonal dynamics. Proceedings of the USSR AS Karadag Biological Station, 10:38-52. Kiev (in Russian).
Studenikina, E.I., A.A. Aldakimova, G.S.Gubina 1999. The phytoplankton of the Sea of Azov under anthropogenic impact. Rostov-Don. Everest. 175 p.
Tatarintseva, T.A., A.G. Ardabyeva, O.V. Terletskaya, D.Kh. Tinenkova, L.V. Malinovskaya, L.I. Tarasova, E.L. Petrenko, 2000. Invaders of the Mediterranean Sea in the plankton and benthic fauna of the Caspian Sea. P.p. 169-183. In: Species-invaders in European seas of Russia. RAS MMBI KNTS Proceedings. Apatity (in Russian).
Ussachev, P.I. 1948. Quantitative variations in phytoplankton of the Noethern Caspian. Proceedings of the Institute of Oceanography, 2:60-88 (in Russian).
Yablonskaya, E.A. 1952. Nereis succinea feeding in the Caspian Sea. P.p. 285-351. In: Nereis acclimatization in the Caspian Sea. Moscow (in Russian).
Zabelina, M.M., I.A. Kisselev, A.I. Proshkina-Lavrenko, V.S. Sheshukova. 1951. Diatoms. P. 108. In: Inventory of freshwater algae of the USSR. Moscow. Sov. Nauka.

Compiled by:

T. A. Tatarintseva (Caspian Fisheries Research Institute, Astrakhan, Russia)

Acknowledgements:

The author is grateful to the research worker Dr. A.G. Ardabyeva, senior research worker O.V. Terletskaya for data on the Northern and Southern Caspian supplied.