ISSN 1063-0740, Russian Journal of Marine Biology, 2008, Vol. 34, No. 5, pp. 263–269. © Pleiades Publishing, Ltd., 2008. Original Russian Text © Zh.P. Selifonova, 2008, published in Biologiya Morya.
PLANKTONOLOGY
Taxonomic Composition and Interannual Variations in Numerical Density of Meroplankton in the Sea of Azov Zh. P. Selifonova Murmansk Marine Biological Institute, Kola Scientific Center, Russian Academy of Sciences, Murmansk, 183010 Russia e-mail:
[email protected] Accepted May 16, 2008
Abstract—This paper presents data on the taxonomic composition and dynamics of numerical density of meroplankton in the Sea of Azov. Studies performed in June 2003–2005 revealed benthic invertebrate larvae of 26 taxa: Polychaeta, 7; Cirripedia, 1; Decapoda, 5; Gastropoda, 5; and Bivalvia, 8. Meroplankton was dominated by larvae of species that are able to endure considerable concentrations of pollution by labile sulfides in bottom sediments and eutrophication: Mytilaster lineatus, Cerastoderma sp., Abra ovata (Philippi), Hydrobia acuta (Gastropoda), and Amphibalanus improvisus (Cirripedia). The spatial and temporal variations in the structure of dominant species and numerical abundance of meroplankton in the Sea of Azov are likely to be associated with water temperature fluctuations, pelagic predators, and eutrophication. Under anthropogenic stress and predation pressure, most larvae of benthic invertebrates are apparently unable to complete metamorphosis and contribute to recruitment to parental populations. Thus, the numerical density of meroplankton in the Sea of Azov can significantly vary, even over one month. DOI: 10.1134/S1063074008050015 Keywords: Meroplankton, taxonomic composition, abundance, dynamics, eutrophication, Sea of Azov.
The inland shallow Sea of Azov was in the past the world’s most productive body of water. At present, the ecosystem of the sea is experiencing an acute ecological crisis leading to the degradation of biocenoses, increasingly more frequent “blooms” of blue-green algae, the hydrogen sulfide pollution of bottom sediments, the hypereutrophication of waters, mortalities of aquatic organisms due to suffocation, and a mass development of the invading predatory ctenophore Mnemiopsis leidyi [3, 20, 24, 31]. With the catastrophically decreasing bioproductivity of the Sea of Azov, the main resource for the recruitment to its benthic populations is the larvae of benthic animals. In 2003, the author of this paper investigated the taxonomic composition and distribution of meroplankton in the Sea of Azov [19]. In June 2003–2005, monitoring was performed to elucidate the interannual variations in the structure and spatial-temporal dynamics of numerical density of meroplankton, which have a significant influence on the abundance of commercial species. This paper examines the numerical density and taxonomic structure of the meroplankton community of the Sea of Azov on the basis of the results of the 2003– 2005 surveys. MATERIAL AND METHODS Material was collected from June 11 to 29 in 2003– 2005 in the Sea of Azov during expeditions of the Murmansk Marine Biological Institute (Kola Science Cen-
ter, Russian Academy of Sciences) (Fig. 1). Zooplankon was sampled with a Juday net (mouth opening 25 cm, mesh size 120 µm) from the 5–13 m depth range. At some shallow-water stations, samples were concentrated by filtering 100 liters of water through an Apstein net. Samples were fixed with 2–4% neutral formalin and processed routinely in the laboratory. The numerical density of meroplankton was calculated by taking into account the net catchability coefficient [30]. The biomass of meroplankton was calculated according to the tables of Petipa [17]. Identification of species was based on keys provided in [2, 5–7, 10–12, 18, 28, 33, 34]. RESULTS The benthic invertebrate larvae of twenty-six species and superspecific taxa were identified in the Sea of Azov in June 2005–2007: Polychaeta, 7; Cirripedia, 1; Decapoda, 5; Gastropoda, 5; and Bivalvia, 8 (see table). The highest abundance of meroplankton was observed in 2003 and 2005: 15000–20000 indiv./m3 on average, which is nearly 2–2.5 times greater than the value in 2004 (Fig. 2). The values obtained closely match the interannual differences in the water temperature in the investigated years. In June 2003 and 2005, average surface water temperature was up to 21.3–21.7°C; in June 2004, it was somewhat lower, 19.2°C (Fig. 3). In 2003 and 2005, veliger and veliconch larvae of bivalves mostly contributed to the total abundance of
263
264
SELIFONOVA
47°
TB NA EA
CA WA
46°
SA KS 2004
2003
2005
BLACK SEA 35°
37°
39°
Fig. 1. A schematic map of location of sampling stations in the Sea of Azov in June 2003–2005. Study areas here and in Figs. 3 and 5: NA—northern, WA—western, CA—central, SA—southern, EA—eastern, TB—Taganrog Bay, KS—Kerch’ Strait.
2003
2004
0 4 10–14 21–26 42–52 84 122
