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1

Factors describing the distribution of the zooplankton community in the Gulf of Finland in the context of interactions between native and introduced predatory cladocerans

100%

Pollumäe A. , Kotta J.

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tom No. 49 (2)

277-290

EN

Mesozooplankton communities were studied monthly at six sites in the Gulf of Finland during six ice-free seasons. The abundances of different zooplankton taxa were related to temperature, salinity, eutrophication level (total nitrogen and phosphorus), phytoplankton Chl a and density of predatory cladocerans, including the non-indigenous Cercopagis pengoi and the native Leptodora kindtii. The results indicated that variability in the zooplankton communities was correlated not only with predation by mesozooplankton but also with bottom-up effects. Predation by the non-indigenous C. pengoi may significantly affect the dynamics of Cladocera and Rotatoria in the Gulf of Finland during the summer season.

2

Effects of physical disturbance, isolation and key macrozoobenthic species on community development, recolonisation and sedimentation processes

80%

Herkül K. , Kotta J. , Kotta I. , Orav-Kotta H.

Oceanologia

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2006

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tom No. 48 (S)

267-282

EN

The relative effect of physical disturbance, isolation and key macrozoobenthic species on community development and sedimentation processes were studied in an in situ factorial field mesocosm experiment in the northern Baltic Sea. Differences in abundance and biomass structure of recolonising invertebrates were due to exposure and isolation. The initial invertebrate communities had a negligible effect on the final communities. However, the organic matter content of the sediment in isolated cages increased with the initial number of invertebrate species. The main conclusion of the study: physically driven fluxes override the effects of biological interactions in shallow water systems of the northern Baltic Sea.

3

The short-term effects of crude oil on the survival of different size-classes of cladoceran Daphnia magna (Straus, 1820)

80%

Lennuk L. , Kotta J. , Taits K. , Teeveer K.

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tom No. 57 (1)

71--77

EN

We studied the acute effects of crude oil on the size-class population structure of the cladoceran Daphnia magna. D. magna were tested in three size-classes: small (1.4 mm, SE = 0.013), medium (2.5 mm, SE = 0.026), and large (3.1 mm, SE = 0.022) with six concentrations of crude oil (10, 50, 100, 400, 600, and 1700 mg L-1). The most important results of our experiment were as follows: (1) Crude oil had no significantly effect on D. magna below concentration 100 mg L-1. (2) An increasing crude oil concentration above 100 mg L-1 sharply decreased the survival of D. magna, (3) and survival varied among size classes. Being in contact with the concentration of 400 mg L-1 and above, all cladoceran specimens died after 96 h.

4

Effects of physical disturbance, isolation and key macrozoobenthic species on community development, recolonisation and sedimentation processes

80%

Herkul K. , Kotta J. , Kotta I. , Orav-Kotta H.

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nr S

EN

The relative effect of physical disturbance, isolation and key macrozoobenthic species on community development and sedimentation processes were studied in an in situ factorial field mesocosm experiment in the northern Baltic Sea. Differences in abundance and biomass structure of recolonising invertebrates were due to exposure and isolation. The initial invertebrate communities had a negligible effect on the final communities. However, the organic matter content of the sediment in isolated cages increased with the initial number of invertebrate species. The main conclusion of the study: physically driven fluxes override the effects of biological interactions in shallow water systems of the northern Baltic Sea.