Due to its location, Harakka is home to both urban and archipelago species. On your hikes in the spring, you might hear eider ducks burbling to their chicks as a nearby fieldfare tries to drive a crow away from its nest. The gulls have taken over much of the southern and central parts of the island. However, even more so than gulls, an invasive species, the barnacle goose, has spread to the island.
In addition to the barnacle goose and the common gull, the nesting birds of Harakka include the lesser black-backed gull, the Eurasian oystercatcher, the common eider, the Canadian goose and the common starling. In addition, the mute swan has nested for several years in Vanha-Räntty.
In Harakka, you can find several species of birds that visit the island occasionally on their way by. Such species include, for example, the white-tailed eagle, the common greenshank, the great grey shrike, the Eurasian hobby, the Eurasian sparrowhawk, the brant, the grey heron, the Eurasian eagle-owl, the long-eared owl and many passerines. Various aquatic birds rest in the peaceful waters between Särkkä and Harakka. Hawks, on the other hand, are sometimes seen sitting on the roofs of buildings or flying over the island.
A total of 415 butterfly species have been observed on Harakka. Approximately half of the species are native to the island. The island's permanent butterfly population consists mainly of fairly common species, such as green-veined whites, small tortoiseshells and peacock butterflies.
Typical habitats for the green-veined white are meadows and fields. Across the country, the abundant small tortoiseshell thrives in flowery, semi-open and open spaces. The peacock butterfly can only overwinter in the south of the country. It thrives in a wide variety of semi-open environments, such as beaches, gardens and parks.
Fluctuations in the butterfly population
In recent years, human activity has, apparently, not had a significant impact on the Harakka butterfly population, but the possible overgrowth of the meadows to the north of the embankment, for example, could significantly reduce the diversity of the island's butterfly species.
The most influential factors in the annual fluctuations of butterfly sightings on the island have been droughts, cold early summers and the occasional arrival of large numbers of migrating butterflies. In the summer, the species found in Kaivopuisto park also often arrive at Harakka. In addition, migrating butterflies come from different parts of the southern coast of Finland and from Estonia.
The diversity of different sites and their long-term human impact have made Harakka a gem of vegetation with a long and comprehensive flora observation series. In the 20th century, 360 wild plants were known to have grown on the island, some of them only so-called visitors.
The current number of vascular plant species is 312. Relative to area, the figure is the highest in the Helsinki archipelago. Of the species, 169 are likely to be native. In other words, a little less than half have come from direct or indirect human intervention. A large number of species arrived in Harakka in the supply transports of Russian troops, some of which have become well established.
Harakan kasvillisuuttaa seurataan kartoituksilla. Viimeisin laaja kasvillisuuskartoitus on tehty tutkielmana vuonna 2013. Harakan kasvillisuuskartoitus toistetaan vuonna 2023.
Lichen thrives on rock surfaces
Lichens are fungi that live in symbiosis with photosynthetic cyanobacteria or algae. Symbiosis allows some lichens to exist in very extreme conditions, where other vegetation does not thrive. The diversity of the Harakka lichen species is maintained especially by the island's wide open rock surfaces, abandoned concrete structures and mature deciduous trees and shrubs. 91 species of lichen have been found on the island of Harakka.
Monet jäkälälajit ovat hyvin herkkiä ympäristön muutoksille, kuten ilmansaasteille tai pienilmaston kuivumiselle.
Jäkälälajien esiintymiseen vaikuttavat monet ekologiset tekijät, kuten valo, lämpö, kosteus, suolapitoisuus, typpipitoisuus, happamuus, ilmansaasteet ja kallioilla myös esim. rautapitoisuus. Lumipeitteellä ja rantoihin kohdistuvalla jään kulutuksella sekä tallauksella on myös merkitystä.
Traces of volcanic activity
The island of Harakka is characterised by a prevalence of rock in its surface area. The mosaic-like patterns on the sheepback rock formations at the shore show signs of volcanic activity, mountain formations, rock stratification, and movements of ice masses during the last glaciation period. The rock of the island is largely composed of types of rocks originally born from lava.
The bedrock of Harakka is mainly dark gneiss (gneissic amphibolite, mica gneiss, veined gneiss and amphibolite, mainly in the eastern area). In the southern part of the island, there is mica gneiss containing pyrrhotite in the bedrock.
Harakassa viimeisen jäätiköitymiskauden jäljet näkyvät mm. suuntautuneina silokallioina. Jäätikön virtausta kohti olevien silokallioiden vastasivut ovat kuluneet loiviksi ja sileiksi. Niiden pintaan jää on hionut jäätikön viimeisen virtaussuunnan mukaisia uurteita ja siihen nähden poikittaisia, jäätikön menosuuntaan aukeavia sirppimurroksia.
Pehmeimmät kivilajit silokallioiden pinnasta ovat kuluneet kokonaan pois. Kivilajien erilainen kuluminen näkyy myös saaren eteläosan rantakallioissa, joihin jäätikön sulamisvesien pyörittämät vedet ovat kuluttaneet hiidenkirnuja.