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1

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

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

Oceanologia

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2015

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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.

2

Influence of the local abiotic environment, weather and regional nutrient loading on macrobenthic invertebrate feeding groups in a shallow brackish water ecosystem

Veber T., Kotta J., Lauringson V., Kotta I.

Oceanologia

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2009

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No. 51 (4)

541-559

EN

This study evaluated the extent to which depth, sediment type, exposure to waves and coastal slope inclination modulate the relationships between regional nutrient loading, weather patterns and the species composition and dominance structure of macrobenthic invertebrate feeding groups in a brackish water ecosystem of the Baltic Sea. Irrespective of feeding function, the species composition and dominance structure of benthic invertebrate communities were determined by local abiotic variables such as exposure, depth and sediment type. Regional weather variables (average southerly winds, salinity, water temperature, ice conditions) either separately or interactively contributed to the variability of benthic invertebrates. Nutrient loading had significant effects on benthic invertebrates only in interactions with local abiotic or regional weather variables. Herbivores, deposit feeders and suspension feeders exhibited a stronger response to the studied environmental variables than carnivores. All this suggests that (1) the dynamic coastal habitats studied in this work are not very sensitive to shifts in nutrient loading and (2) local abiotic conditions and weather patterns largely define the observed biotic patterns. We believe that the benthic invertebrate time series will only be a better reflection of the nutrient loading signal if more years covering extreme events are included.

3

Density dependent growth of the red algae Furcellaria lumbricalis and Coccotylus truncatus in the West Estonian Archipelago Sea, northern Baltic Sea

Kotta J., Paalme T., Kersen P., Martin G., Herkül K., Möller T.

Oceanologia

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2008

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No. 50 (4)

577-585

EN

In an in situ experiment we evaluated the growth of the red algae Furcellaria lumbricalis and Coccotylus truncatus in the Archipelago Sea. The results showed that the growth rates of both species were similar but that growth decreased with increasing algal coverage. The effects were more pronounced for C. truncatus than for F. lumbricalis. Economic analyses aiming to establish sustainable harvesting limits for F. lumbricalis in the study area should take account of the density dependent growth of these red algae.

4

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

Pollumäe A., Kotta J.

Oceanologia

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2007

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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.

5

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

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

Oceanologia

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2006

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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.