Gammarus pauxillus, Grimm

Taxonomic description of species

The body is laterally compressed, smooth, without spines, keels or tubercles. Cephalon ( 2) is without rostrum, eyes are oval. The peduncle of antenna I (3) is somewhat thicker than joints of flagellum that is longer than antenna II; additional flagellum consists of 3-4 joints. Joints of antenna II peduncle are cylindrical without bottom lobes. Pairs I and II of pereiopods (gnathopods) ( 4) are of the same size with pseudo-chelas, they are bigger in males than in females; the palmar edge of chelas is even. The second joint of pereiopod VII (5) is linear without a widened posterior lobe. Uropod III (6) is two-branched, exopodite is 2.5-3 times longer than protopodite. On each side of exopodite there are 3 groups of spines. Telson (7) is cleft to the base, its lobes are round at tips and have not more than 1-2 spines, lateral spines are absent.
The first, very brief incomplete description of this species almost inaccessible now was made by O.A.Grimm (1880, quoted by Sovinsky, 1904). A more detailed description based on the same material with remarkable drawings was provided by G.O.Sars (1886). As a result, both scientists are called authors, though Sars regards Grimm as author.
Intraspecific forms. The subspecies Gammarus (Chaetogammarus) pauxillus hyrcanus Pjatakova, 1962 that differs by more intensive arming of all the segments of uropod III and telson was described Pjatakova, 1962). The separation of the subspecies has to be verified (Birshtein, Romanova, 1968).
Related forms. It is represented in the Ponto-Caspian basin by the only subgenus Chaetogammarus (Martynov, 1924; Shellenberg, 1942; Birshtein, 1945) which includes beside G.(Ch.) pauxillus five more species. G.(Ch.) placidus Grimm occurs in the Middle and Southern Caspian mostly on soft sediments at depths 5-200 m (Birshtein, Romanova, 1968). It is widespread in estuarial systems of the Danube, Dnepr and Bug Rivers.
G.(Ch.) macrocerus (Derzh.) is known as an endemic to the Southern Caspian. It was encountered not far from Ogurchinsky Island at a depth of 73 m on lime mud (Birshtein, Romanova, 1968).
G.(Ch.)behningi (Mart.) is rather rare and occurs in the Azov-Black Sea basin, in the middle and lower reaches of the Volga River, in the Middle Caspian (Birshtein, Romanova, 1968).
G.(Ch.) ischnus Stebbing is distributed in the Middle and Southern Caspian, in the middle and lower reaches of the Volga River, in estuarial systems of the Danube, Dnestr, Dnepr-Bug, Don, Kuban Rivers. It entered the rivers of the Baltic Sea basin through these river systems (Mordukhay-Boltovskoy, 1960; Orlova, 2000).
G.(Ch.) warpachowskyi G.O. Sars is common to freshened (less than 10 PSU) areas of the Caspian and Azov-Black Sea basins, in the lower reach and delta of the Volga, Kura and Denube Rivers(Birshtein, Romanov, 1968; Dedyu, 1967).

Distribution of species within the Caspian Sea

G.(Ch.) pauxillus is one of the most abundant species. Its largest densities were recorded in the north-eastern part of the Middle Caspian, in the upwelling zone. It occurs in the entire Middle Caspian except for the areas with soft sediments in the Agrakhan shallow water region, north of the Apsheron Peninsular and at depths 10-15 m. It is rare in the Southern Caspian, mainly in its northern part. It was seen only at Kulaly Island in the Northern Caspian (Birshtein, Romanova, 1968; Romanova, 1956, 1973; Israpov, 1981).
Status as per International Red Data Book. Not included
Status as per National Red Data Books. Not included
First record for the Caspian Sea. Grimm, 1880
Redescription of species. Sars, 1986; Martynov, 1924; Schetllenberg, 1942; Birshtein, 1945; Mordukhay-Boltovskoy, 1960.

General Characteristics of Species

Ecological-taxonomic group. Macrozoobenthos
Origin. Caspian autochthon.
World distribution. Caspian endemic.
The species occurs only in the Middle and Southern Caspian, sometimes it is carried out into the Northern Caspian by sea current (Romanova, 1956).
Habitat. Bottom of the Caspian Sea. G.(Ch.) pauxillus reaches the greatest biomass in the Middle Caspian on shell sediment with sand and mud at depths 25-100 m although it may be encountered in deeper waters as well as on softer sediments.

It inhabits mud and clay grounds of the Southern Caspian (Pjatakova, 1964).
Migrations. G.(Ch.) pauxillus does not migrate.

Relation to abiotic environmental factors

Relation to salinity. Gammarus (Ch.) pauxillus refers to brackish water stenohaline species. These organisms inhabit the south-western part of the Northern Caspian adjoining the Middle Caspian with water salinity 10-12 PSU (Birshtein, 1945).
Relation to temperature. Gammarus (Ch.) pauxillus prefers temperatures below 13⁰C.

Vertical distribution. Eurybathic species
It occurs at depths from 7 to 538 m though its highest densities were recorded at a depth of 25-100 m (Romanova, 1973; Israpov, 1981). In recent years small numbers of the organism have been recorded in the area of Kurinsky Kamen Cape at a depth of 600 m (original data obtained by Kochneva, 1993).
Relation to oxygen conditions. Oxyphilous species
Gammarus (Ch.) pauxillus inhabits hard grounds in the routes of rapid current under the conditions of good aeration (Birshtein, 1945).
Relation to fluctuations of the sea level. Indifferent, as it inhabits the depths of 17-600 m.

Feeding

Feeding type. Heterotrophic
Feeding behavior. Mobile collectors of epyfauna
Moving on the bottom, they collect detritus from sediment surface (Yablonskaya, 1976).
Food spectrum. Gammarus (Ch.) pauxillus consumes small food fractions: fine-grained detritus, rounded dinoflagellatae, small diatoms, green and blue-green algae. The diameter of food fractions does not usually exceed 20 μκμ rarely reaching 40-50 μκμ. Of great importance are plankton algae and plankton detritus which is filtered by these organisms from bottom suspension or collected from sediment surface (Yablonskaya, 1971).
G. pauxillus intestines contained Coscinodiscus granii Gough, Rhizosolenia calcar-avis M. Schultze, Exuviaella cordata Ostf. var.cordata, Prorocentrum obtusum Ostf., Prorocentrum scutellum Schroder, Gonyaulax polyedra Stein (Babayev, 1965).
Supply of food. Phytoplankton and phytoplankton detritus
Quantitative characteristics of feeding. During spring and summer the content of light fine-grained detritus in the alimentary canal of G. pauxillus increases from 78.3 to 89% while the consumption of large plankton algae decreases from 19.3 to 2.6%.

Composition of the alimentary canal content. %
(Yablonskaya, 1971)

Reproduction

Reproduction type. Gamogenesis
Reproduction areas. The same as the species range
Terms of reproduction. From April to September
Egg bearing females range from 3 to 7 mm in length and are on average 5 mm (Pjatakova, 1973)
Fecundity. Direct correlation was established between the size of Amphipodae and their fecundity (correlation coefficient is 0.85). The smallest organisms 4-6 mm in length display the minimum fecundity of average 2-3 eggs (Pjatakova, 1973).
Limiting factors. Temperature, salinity, oxygen content, sediments, fish predation.

Life history and development

Life-history stages. Information is not available
Relation to environmental factors. Not defined
Age of maturity. Information is not available
Thermal conditions of development. The cycle of development begins at a water temperature more than 5⁰C. The maximum development is recorded at a temperature 8-9⁰C.
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. In the 1950s G. pauxillus formed considerable densities along the eastern coast especially in the zone of Sagyndyk Cape (the biomass is 6 g/m², density is 1700 ind./m²), Kenderly Bay (3g/m² and 2700 ind./m²), Bektash Cape (9.4 g/m² and 11630 ind./m², respectively). Some quantities of G. pauxillus were recorded in the area of the Krasnovodsk Bay and at the western coast of the Southern Caspian. The species also occurs in the deep water zone of Kulaly Island.
In the 1960s Gammarus pauxillus constituted 0.48 g/m² in the western part of the Middle Caspian, 1.98 g/m² in the eastern part. In the 1970s this species dominated Gammaridae and amounted to 0.7 g/m² in the western area and 2.6 g/m² in the eastern one (Osadchikh, 1978).
In the 1980s in summer Gammarus pauxillus formed densities of 2-5 g/m² mostly along the eastern coast of the Middle Caspian while in autumn its biomass increased from 5 to 10 g/m² at Sagyndyk Cape and in the area from Peschanyi Cape to Rakushechnyi Cape. In winter the main densities of 2-5 g/m² occurred at the western coast north of Derbent City.

Gammarus pauxillus has been currently encountered in the Northern Caspian south of Kulaly Island (1.4 g/m²) at a depth of 28 m. In certain years its density reached 18.0 g/m² and 6200 ind./m² in the area of Bautino and Sagyndyk Island. Gammarus pauxillus occurs in the Middle Caspian along the western coast of the Agrakhan Peninsular as far as Izberga and Derbent Cities at depths varying from 17 to 45 m. Its biomass ranges within 0.1-1.4 g/m² while its density is 300-2200 ind./m². G. pauxillus biomass and density increase to 3.7 g/m² and 3550 ind./m² in the area of Derbent City whereas the biomass of sand hoppers does not exceed 1.1 g/m² southerly in the area of Kilyazi City and 0.5 g/m² at depths 45-142 m not far from Zhiloi Island. The biomass and density of G. pauxillus along the eastern coast varies from 0.1 to 3.4 g/m² and from 75 to 3300 ind./m², respectively.
The species was seen in small numbers (0.01-0.5 g/m²) in the Southern Caspian in the zone of Kurinsky Kamen Cape at a depth of 600 m, 0.2 g/m² at Ogurchinsky Island (original data obtained by Kochneva).

Population trends. Between 1956 and 1993 the abundance of G. pauxillus in the Northern Caspian increased considerably: from several cases of sampling in the area of Kulaly Island (Romanova, 1973) to 6200 ind./m² in 1993. On the whole, the biomass of sand hopper increased in the sea from 0.23 g/m² (Romanova, 1973) in the 1950s to 0.7 g/m² in the 1990s (original data obtained by Kochneva).

Interspecific relations

It forms part of food resources of stellate sturgeon, Russian sturgeon, young beluga, ship sturgeon and gobies (Tarverdiyeva, 1965, 1982; Stepanova, 1985).

Importance of species to bioresources production of the Caspian Sea

Economic significance of species. G. pauxillus is a food organism of commercially important fish species.
Commercial characteristics of species, catches. It is not used commercially.
Fishing gears and fishing zones. None

Impact of fisheries on the population status

None
Human impact/Threats. Not defined
Conservation measures. Not required

References

Aliyev, A.D. and G.M. Pjatakova, 1969. Benthos of the eastern coast of the Middle Caspian and its seasonal dynamics. Hydrobiol.J., V.5, 3: 71-75 (in Russian).
Birshtein, Ya.A. 1945. Annual changes in the benthos of the Northern Caspian. Zool.J., V. XXIV, 3: 133-146 (in Russian).
Birshtein, Ya.A. and N.N. Romanova, 1968. The order Amphipoda. P.p. 241-289. In: Atlas of invertebrates of the Caspian Sea. Food Industry. Moscow (in Russian).
Babayev, G.B. 1965. The importance of phytoplankton for feeding some benthic invertebrates of the Southern Caspian. P.p. 54-58. Azerb SSR AS Press.
Dedyu, I.I. 1967. Amphipodae and mysidae of the Dnestr and Prut River basins. Nauka. Moscow (in Russian).
Grimm O. 1880. Beitrag zur Kenntniss einiger blinden Amphipoden des Kaspisees. Arch.F.Naturg/Bd. XVIV, p.119.
Israpov, I.M. 1981. Species composition and quantitative distribution of Amphipodae at the western coast of the Middle Caspian. Author�s Abstract. AS IO. Moscow. 24 p. (in Russian).
Mordukhay-Boltovskoy, F.A. 1960. Caspian fauna in the Azov-Black Sea basin. P.p. 158-163. USSR AS Press. Moscow-Leningrad.
Ossadchikh, V.F. 1978. Importance of certain species for the biomass of benthos in the Northern and Middle Caspian. Zool. J. V.LVII: 26-31 (in Russian).
Orlova, M.I. 2000. The Caspian basin as a region-donor and region-recipient of bioinvasions of benthic invertebrates. P.p.58-75. In: Species-colonizers in European seas of Russia. Apatity (in Russian).
Pjatakova, G.M. 1962. New forms of Gammaridae of the Caspian Sea. Azerb.SSR AS Reports. V.18: 49-51(in Russian).
Pjatakova, G.M. 1964. Amphipodae of littoral and sublittoral of the Southern Caspianfrom Apsheron to Astara. Author�s Abstract. Azerb. AS Press. Baku. 16 p. (in Russian).
Pjatakova, G.M. 1973. Some data on reproduction and fecundity of Caspian Amphipoda. Zool. J. Vol., 3:685-688.
Romanova, N.N. 1956. Distribution of Amphipoda and Cumacea in the Northern Caspian depending on salinity and sediments. Authors� Abstract. AS IO. Moscow. 14 p. (in Russian).
Romanova, N.N. 1973. Ecology and quantitative distribution of autochthon Gammaridae in the Caspian Sea. VNIRO Proceedings. Vol. 80, 3:73-103 (in Russian).
Sars, G.O. 1896. Amphipoda, Supplement. Crustacea Caspia. Bull.Acad.Sci.St-Pstb. Vol IV, 5: 421-489.
Sovinsky, V.K. 1904. Introduction into investigation of fauna of the Ponto-Caspian-Aral Sea basin considered as an independent zoo-geographical province. Notes of the Kiev Society of Naturalists. V.18. 497 p. (in Russian).
Stepanova, T.G. 1985. Fish feeding. Gobiidae. P.p. 214-220. In: The Caspian Sea. Fauna and biological productivity. Nauka. Moscow (in Russian).
Tarverdiyeva, M.I. 1965. Importance of acclimatized organisms for Russian and stellate sturgeon feeding in the Caspian Sea over the last few decades. Nauka. Moscow. P. 234-256 (in Russian).
Tarverdiyeva, M.I. 1982. Russian and stellate sturgeon feeding in the Caspian Sea. In: Feeding and food supply utilization by sturgeons of the Caspian Sea. VINITI, 375: 6-164. Moscow (in Russian).
Yablonskaya, E.A. 1971. Feeding of benthic invertebrates and trophic structure of the benthos of the Caspian, Azov and Aral Seas. Moscow. 146 p. (in Russian).
Yablonskaya, E.A. 1976. Studies of trophic relations between benthic communities of southern seas. P.p. 117-144. In: Biosphere resources: results of Soviet investigations based on the International Biological Program, 2. Nauka. Leningrad (in Russian).

Compiled by:

L.A. Kochneva, Caspian Fisheries Research Institute, Astrakhan, Russia
M.G. Karpinsky, Caspian Fisheries Research Institute, Astrakhan, Russia

Acknowledgements:

Authors are grateful to Dr. A.A. Polyaninova for valuable comments, L.V. Malinovskaya for providing data on the Northern Caspian.