Following decades of global extermination, the general population of the great cormorant (Phalacrocorax carbo L.) is on the rise. The lack of regular predators, highly skilled fish rapacity, rapid metabolism, significant rate of excretion and ability to form large nesting colonies on relatively small areas lead to numerous environmental consequences of cormorant presence. Here we comprehensively review the occurrence and distribution of this species and, in particular, its multi-faceted impact on terrestrial and aquatic ecosystems and the main routes through which these impacts are being manifested. The bird-induced chemical loading and its biological and ecological consequences, and the effects on microbial pollution and pathogen dispersion are discussed in particular. The need for further investigation to fully elucidate particular effects is stressed throughout the paper. It is concluded that the environmental effects of great cormorants are rather complex, can lead to serious ecosystem modifications and that the presence of these birds should be taken into consideration in ecological assessment and monitoring.

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The complexity of ecological impacts induced by great cormorants

In the resource-limited Arctic environment, vegetation developing near seabird colonies is exception- ally luxuriant. Nevertheless, there are very few detailed quantitative studies of any specific plant species responses to ornithogenic manuring. Therefore, we studied variability of polar scurvygrass Cochlearia groenlandica individual biomass and leaf width along a seabird influenced gradient determining environmental conditions for vegetation in south-west Spitsbergen. We found seabird colony effect being a paramount factor responsible for augmented growth of C. groenlandica. The species predominated close to the colony and reached the highest mean values of individual biomass (1.4 g) and leaf width (26.6 mm) 10 m below the colony. Its abundance and size declined towards the coast. Both C. groenlandica individual traits signifi- cantly decreased with distance from the colony, soil water and organic matter content and increased with guano deposition, soil d 15 N, conductivity, acidity and nitrate, phosphate and potassium ion content. Our study supports the hypothesis that seabirds have fundamental importance for vegetation growth in poor Arctic environment. Highly plastic species such as C. groenlandica may be a useful instrument in detecting habitat condition changes, for instance resulting from climate change.

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Variability of polar scurvygrass Cochlearia groenlandica individual traits along a seabird influenced gradient across Spitsbergen tundra

Black spots for aquatic and terrestrial ecosystems: impact of a perennial cormorant colony on the environment

Myxomycete distribution patterns were investigated in a colony of great cormorants (Phalacrocorax carbo sinensis) established in a pine forest in the Curonian Spit, western Lithuania. Ornithogenic impact on the forest resulted both in vegetation changes and altered types and characteristics of myxomycete substrata. The lowest myxomycete species richness was found in the most active part of the colony with the newest and most numerous nests. The myxomycete assemblages of the active part of the colony also showed the biggest differences from the reference zone (oligotrophic pine forest). The general abundance of myxomycetes in the territory of the colony was higher due to the presence of the species that are not characteristic of pine forests. The most abundant species in the territory were Badhamia apiculospora and Perichaena cf. corticalis. Along with other facultative coprophiles, such rare species as Comatricha mirabilis and Arcyria leiocarpa were found sporulating in the colony. The Bray-Curtis ordination revealed a tripole gradient of myxomycete distribution in the colony. It was hypothesized that the first continuum may reflect myxomycete assemblage transition from hypertrophic to oligotrophic habitat; the second continuum may reflect myxomycete assemblage distribution from habitats with limited diversity of available substrata, extreme levels of nutrients and high pH to habitats with high diversity of available substrata, moderate to high levels of nutrients and pH, and the third continuum may reflect myxomycete assemblage distribution from habitats with lower diversity of available substrata, low levels of nutrients and pH to habitats with high diversity of available substrata, moderate to high levels of nutrients and pH.

Myxomycetes in a forest affected by great cormorant colony: a case study in Western Lithuania

Lichen community changes were investigated on trees within a colony of great cormorants (Phalacrocorax carbo sinensis) established in a pine forest on the Curonian Spit, western Lithuania. The impact of birds on the forest has altered the number and characteristics of substrata available to lichens. The lowest number of lichen species and occurrences was registered on trees in the most active part of the colony with the highest nest density. Lichen community patterns were most strongly related to P and Ca content in substrata and pH values. Some acidophytic species showed negative correlations, both with long-term and short-term ornithogenic influence. However, three acidophytes (Chaenotheca ferruginea, Lepraria incana, Coenogonium pineti) demonstrated an affinity for the transitional zone and recently occupied trees, and furthermore, C. pineti apparently reacted positively to a short-term ornithogenic influence but negatively to a long-term one. These three lichens, along with algae, were the main, and often the only, components of epiphytic communities on trees at the edge of the colony and apparently indicated the crucial point of the acidophytic community under the increasing load of nutrients. All nitrophytic species showed an affinity for a long-term bird influence and reacted negatively to a short-term influence. Only free-living algae (predominating species Desmococcus olivaceus) showed a clear affinity for trees occupied by bird nests. Hypogymnia physodes was found to be an indicator for early environmental changes following eutrophication. The study also showed that high concentrations of P did not have a mitigating effect on the detrimental impact brought about by increases in N and pH levels, but was possibly equally detrimental to acidophytic lichens.

K. Żółkoś

Papers

The effect of Grey Heron [Ardea cinerea L.] colony on the surrounding vegetation and the biometrical features of three undergrowth species