Biological and ecological characteristics of Pterocuma pectinata (Malacostraca, Cumacea) in Sasyk Reservoir

Abstract

Sasyk (Kunduk) – estuary in the North-Western Black Sea region, is located 120 kmsouth-west of Odessa. In 1979–1980 Sasyk was separated from the sea by a dam, connected by a canal with the Danube and transformed into a reservoir. The fauna of Sasyk underwent significant changes and continues to adapt to the new conditions. This process is of great theoretical and practical interest. Cumacea – a small order, numbering about 600 species; is represented in the Black Sea-Azov basin by 23 species, 11 of them belong to the Caspian complex. Due to their high quantity indicators, they play a significant role in the diet of many species of fish. Pterocuma pectinata (Sowinski, 1893) is the most abundant species of cumacean not only in the Sasyk Reservoir, but also in many bodies of water in the region. However, the biology and ecology of this group of animals has been very inadequately studied. The material for these studies was provided by 120 benthic samples collected from 41 stations in the Sasyk Reservoir in the vegetation period 2013–2014. In this study we also used the material collected by means of H. Hungerford underwater light traps. In total 4,000 specimens of cumaceans were processed. This article shows the results of the studyof the post-embryonic development, fertility and size-mass characteristic of P. pectinata in Sasyk Reservoir. For both sexes for age stages have been distinguished and described for cumaceans: «manca», youth, prebreeding and breeding. Between breeding cycles, females live through one more preparatory (intermediate) stage; the males die. This article provides a detailed morphological and morphometric description of all the stages of the ontogeny of cumaceans. The ratio of number of cumaceans at different stages of ontogeny varies considerably with the seasons. In the summer sexual development of cumacean occurs earlier than in the less warm seasons. A directly proportional relationship was found between body length and fertility of P. pectinata. With decrease in water temperature fertility increases. The corresponding regression equations were obtained. The maximum number of eggs observed in the spring of 2014 – 160 ind. in a female 8.0 mm in length (including the uropod length – 10.2 mm). Mean fecundity was 22 ± 1 and 21 ± 1 ind. in the summer of 2013 and 2014, 40 ± 2 and 32 ± 2 ind. in the autumn of 2013 and 2014, 72 ± 4 ind. in the spring of 2014; during the vegetation season 2014 – 42 ± 2 ind. The smallest oviparous female cumaceans (4–6 mm) were observed in the summer in both years of research with domination of the size group of 4–5 mm. The largest oviparous females (6.1–9.0 mm) were observed in the spring with domination of 6.1–7.0 mm size group. P. pectinata produces at least two generations per year in Sasyk Reservoir. P. pectinata reproduction occurs from March to the beginning of November. The peak of breeding is in early spring (March – April), which contributes to the restoration of population numbers after hibernation. The second stage of reproduction (October – November) is less intense. The lifespan of P. pectinata in the Sasyk Reservoir is about one year. Dependence of individual weight of the body is directly proportional to the length of P. pectinata and varies with the seasons. This article provides a table of the average "size – weight" of cumaceans. The data in this table can be used in ichthyological studies, namely the calculation of the reconstructed weight of the food item – P. pectinata, by size of its undigested chitin skeleton. The maximal length of P. pectinata in Sasyk is 8.5 mm (including uropod length – 10.7 mm), weight – 5 mg, significantly greater than the values specified for the populations of the upper reaches of the Kuibyshev Reservoir and the Caspian Sea. The results of the study significantly complement the existing knowledge of biology and ecology of P. pectinata, and expands our idea of the state of the ecosystem of the Sasyk Reservoir.