Cells are high cylindrical connected in chains. The shell is very thin, structureless with numerous intercalary rims. Valves are slightly convex with a short thin spine in the centre. There is a hollow at the base of the spine into which a small spine of a neighboring cell of the colony goes. It joins cells into an unstable (brittle) colony. Chromatophores are lamellar, small, rather numerous.
Intraspecific forms. None
Related forms. Rhizosolenia delicatula Cleve, Rh. stolterfothii
Perag are widely distributed in the Baltic Sea (Pankov, 1976). Cells are scattered or otherwise when connected by extended valvular appendages form rather long, sometimes diversely curved chains. Rh. acuminata
Gran, Rh. calcar-avis M. Schultze, Rh. alata Brightw, Rh. minima Lev.,
Rh. setigera Brightw., Rh. styliformis Brightw., Rh. hebetata f. semispina Gran. (the Baltic, Black, Azov, Caspian, Japan Seas),
Rh. eriensis H. Sm. (European part of Russia), Rh. stagnalis Zacharias (lakes of Karelia),
Rh. longiseta Zach. (northern European regions of Russia) look like high cylinders with dome-shaped or conoidal valves at their ends. Apices of these valves are elongated in the form of straight or curved appendages..
Distribution of species within the Caspian Sea
Before Rh. calcar-avis appeared in the Caspian Sea, Rh. fragilissima was one of the most abundant species there
(Henckel, 1909; Ussachev, 1948) and occurred in the water column from 0 to 100 m (Proshkina-Lavrenko, Makarova, 1968). At present the species occurs in the Caspian Sea in small quantities and its number has never been observed to increase appreciably.
Status as per International Red Data Book. Not defined
Status as per National Red Data Books. Not defined
First Record for the Caspian Sea. A.G. Henckel, 1909
Redescription of Species. A.I. Proshkina-Lavrenko and I.V. Makarova, 1968;
H. Pankov, 1976; G.V. Konovalova, T.Yu.Orlova, L.A. Pautova, 1989.
General characteristics of species
Ecological-taxonomic group. Phytoplankton
Origin. Autochthonous Caspian species
World distribution. The species is widely distributed in all the European seas from Arctic to the Black and Azov Seas.
It is recorded for the Far East Seas of Russia, at Pacific and Atlantic coasts of North America. It is specificalle abundant in the temperate boreal zone. As a result of wide distribution of this species, its size structure in separate water body is somewhat different. In the coastal areas of the Caspian Sea, the chains of
Rhyzosolenia fragilissima are short, the longest ones do not contain more than nine cells, while in deep waters the chains consist of 2-5 cells, isolated cells occur frequently (Proshkina-Lavrenko, Makarova, 1968).
Dimensional characteristics of Rhizosolenia fragilissima Bergon
| Habitat |
Length, � |
Width, � |
Minimum |
Maximum |
Minimum |
Maximum |
| Caspian Sea |
34.4 |
112.7 |
4.2 |
16.8 |
| Black Sea |
30.0 |
115.0 |
6.25 |
20.0 |
| Sea of Azov |
50.0 |
110.0 |
4.5 |
10.0 |
| Japan Sea |
30.0 |
100.0 |
10.0 |
50.0 |
| Baltic Sea |
10.0 |
70.0 |
1.0 |
5.0 |
Note: data on the Caspian Sea � A.I. Proshkina-Lavrenko and I.V. Makarova (1968); the Black Sea -
A.I. Proshkina-Lavrenko (1955), D.A.Nesterova, L.S. Vasilenko (1986); the Sea of Azov -
A.I. Proshkina-Lavrenko (1963); the Japan Sea � G.V. Konovalova, T.Yu. Orlova, L.A. Pautova (1989); the Baltic Sea �
H. Pankov (1976).
Habitat. Water column of the Caspian Sea to 200 m depth line
Migrations. Information is not available
Relation to abiotic environmental factors
Relation to salinity. Marine and brackish water euryhaline species
It occurs in the Caspian Sea at a salinity 9-13o/oo (Proshkina-Lavrenko,
Makarova, 1968; autor's original data), in the Black Sea - up to
17-18o/oo (Proshkina-Lavrenko, 1955), in the Sea of Azov
(Kerch Strait) � up to
13o/oo (Proshkina-Lavrenko, 1963).
Relation to temperature. Eurythermic species
found in the Northern Caspian during the whole vegetative period (April-October) at a temperature from 4 to
260C (Levshakova, 1971, author�s original data), in the Middle and Southern Caspian - throughout the year at a temperature
5-260C (Proshkina-Lavrenko, 1968; original data).
Vertical distribution. Eurybathic species
It is most abundant in the Northern Caspian in its deeper and more saline part at depths 10-30 m. In the Middle and Southern Caspian, the species occurs in the water column from 0 to 200 m depth line, the major densities of
Rhizosolenia fragilissima occur in the photic (0-50 m) layer (Proshkina-Lavrenko, 1968; author�s
original data ).
Relation to oxygen condition. Information is not available
Relation to fluctuations of the sea level. During the period of low seawater level (1956-1978), the biomass of
Rhizosolenia fragilissima varied from 1.1 to 1.6 mg/m3.
In the period of sea level rise, the species density increased to 169.2 mg/m3 in the 1990-s.
Long-term changes in the biomass and number of Rhizosolenia fragilissima population in the Northern Caspian (April)
Period
Years |
I |
II |
| 1960-s |
1970-s |
1980-s |
1990-s |
| Biomass, mg/ m3 |
1.6 |
1.1 |
1.3 |
169.2 |
| Number, thou. Sp./ m3 |
318 |
53 |
60 |
19817 |
Feeding
Feeding type. Autotrophic
Feeding behavior. Utilization of solar energy and mineral substances in the process of photosynthesis.
Food spectrum. Biogenic elements: phosphorus, nitrogen, silicon, sulfur, calcium, magnesium, potassium, iron, manganese, and other elements.
Phosphorus is assimilated as a compound of the phosphoric acid (Harvey 1940; Goldberg et al., 1951; Mackereth, 1953). In the light and in the darkness, diatoms can assimilate orthophosphates, pyrophosphates (Chu, 1946), glycerophosphate, inositol etc. (Lewin, Guillard, 1963). Nitrogen is
utilized by diatoms as inorganic and organic compounds: nitrates, nitrites and ammonia (Harvey, 1940). Silicon is assimilated
as silicic acid, organic and inorganic compounds of silicon (Vinogradov, Boichenko, 1942).
Supply of food. Biogenic elements
Quantitative characteristics of feeding. Information is not available
Reproduction
Reproduction type. Vegetative division.
Reproduction areas. There are no specific areas of reproduction in the Caspian Sea.
Terms of reproduction. Year�round.
Division usually occurs at night and at dawn, in active forms � at static state of a cell as well as during its movement.
Division is most active in spring and in early summer. It decreases gradually by autumn reaching a minimum in winter (Diatoms of the USSR, 1974).
Fecundity. Information is not available.
Limiting factors. Salinity, biogenic elements, solar activity.
Life history and development
Life-history stages. Information is not available.
Relation to environmental factors. Rhizosolenia fragilissima develops in the Caspian Sea at a salinity of
9-13o/oo and water temperature 4-260C in the photic layer of water (0-50 m).
Age of maturity. Information is not available.
Thermal conditions of development. Rhizosolenia fragilissima reaches the best development in the Northern Caspian in spring. The size of its population decreases by 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. Before the rise in the seawater level (1956-1978),
Rh. fragilissima occurred in the Northern Caspian only in spring (April). Its biomass varied from 0.2 to 4.5
mg/m3 and the densities were 17,000-775,000 sp./m3. During the summer period (June)
Rh. fragilissima was not traced. At the present time, Rh. fragilissima is observed throughout the vegetative period, but specimens are rare and occur sporadically. In the spring 1986, the biomass of
Rh. fragilissima was maximum and amounted to 336.9 mg/m3 while its density reached
59,432,000
sp./m3. In June its biomass did not exceed 4.5 mg/m3. Rh. fragilissima is dispersed in deep waters of the western part of the Northern Caspian. Maximum biomass throughout the studied period constituted 1.4
g/m3 (the area of Bolshaya Zhemchuzhnaya Bank). The biomass in the Middle and Southern Caspian varied from 0.02 to 0.7
mg/m3.
Population trends. Since 1970s the size of Rh. fragilissima population has gradually increased.
Interspecific relation
Information is not available
Impact on the Ecosystem
Information is not available
Importance of species to bioresources production of the Caspian Sea
Economic significance of species. None
Human impact/Threats. A decline in the Rh. fragilissima population was recorded after the introduction of
Rh.calcar-avis.
Conservation measures. Information is not available.
References
Chu, S.P. 1946 The utilization of organic phosphorus by phytoplankton. J. Mar. Biol. Assoc. U.K. 26, 3: 285-295 (in English).
Diatoms of the USSR (fossil and extant). 1974. Leningrad. Nauka. 403p.(in Russian).
Goldberg, E.D., T.J. Walker, A. Whisenard, 1951. Phosphate utilization by diatoms. Biol. Bull., 101: 274-284 (in English)
Harvey, H.W. 1940. Nitrogen and phosphorus required for the growth of phytoplankton. J. Mar. Biol. Assoc. U.K. 24, 1: 115-123 (in English).
Konovalova, G.V., T.Yu. Orlova, L.A. Pautova, 1989. Atlas of the phytoplankton of the Japan Sea. Leningrad. Nauka. 185 p.(in Rusian).
Lewin, J.C., R.R. Guillard, 1963. Diatoms. Ann. Rev. Microbiol. 17: 373-414.
Levshakova, V.D. 1971. Some ecological characteristics of the phytoplankton of the Northern Caspian. CaspNIRKH Proceedings, 26: 67-82 (in Russian).
Mackereth, F.J. 1953. Phosphorus utilization by Asterionella formosa Hass. J. Exptl. Bot. 4: 296-313 (in English).
Nesterova, D.A., L.S. Vasilenko, 1986. Size characteristics of the mass species of the phytoplankton in the western part of the Black Sea. Hydrobiol. J. Vol. 22, 3: 16-21.
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. 1955. Plankton diatoms of the Black Sea. Moscow. USSR AS. 222 p.(in Russian).
Proshkina-Lavrenko, A.I. 1963. Plankton diatoms of the Sea of Azov. Moscow. USSR AS. 191 p.(in Russian).
Pankow, H. 1976. Algenflora der Ostsee. II. Plankton. Veb Gustav Fisscher Verlag. Jena. 493 p.
Studenikina, E.I., A.Ya. Aldakimova, G.S. Gubina, 1999. Phytoplankton of the Sea of Azov under anthropogenic impact. Rostob-Don. 176 p.(in Russian).
Vinogradov, A.P., E.A. Boichenko, 1942. Break down of kaolin in diatoms. Proceedings of USSR AS. 37, 4: 158-162 (in Russian).
Compiled by:
A.G. Ardabiyeva (Caspian Fisheries Research Institute, Astrakhan, Russia)
Acknowledgements:
The author is grateful to senior research workers T.A. Tatarintseva and
O.V. Terletskaya for furnishing data on the distribution of Rhizosolenia fragilissima in the Middle and Southern Caspian.