A Turku resident made an unexpected discovery during morning dog walks this October. Heli Pettersson found two living shore crabs in her apartment complex yard, about one kilometer from the sea coast.
Pettersson was walking her Irish wolfhound puppy when she spotted the first crab on the lawn. "It was dark at six in the morning," she recalled. "I wondered what the puppy was afraid of. I turned on my phone flashlight and saw it waving its claws. I thought, my goodness, what an angry-looking animal."
The crab remained in the yard the next day but appeared sluggish. "I felt sorry for it. I thought we should put it out of its misery." Pettersson contacted her sister, who had marine aquarium experience, but the crab had already died and was placed in a freezer.
Days later, Pettersson's puppy found another identical crab in the same area. This crab also died and was collected in a dog waste bag, destined for the University of Turku's zoological museum.
Retired conservator Ari Karhilahti from the university museum identified the creatures as shore crabs, which appear on the global list of 100 worst invasive species. "They're persistent and good at reproducing," Karhilahti explained.
Only a few sightings of shore crabs exist in Finland. All three crab species found in the country were first discovered in the Turku region, with specimens kept at the university museum.
Karhilahti noted it's impossible to determine exactly how the crabs reached the apartment yard. They could have walked the kilometer from the sea, though he questions why only two appeared. Human transportation remains another possibility.
Native to Atlantic coasts of Europe and North Africa, shore crabs have spread worldwide through human activity. While Finland's Species Information Centre states they cannot reproduce in Baltic Sea conditions, Karhilahti doesn't rule out the possibility.
The crabs likely died from the cold, as they normally remain in water during such weather conditions. Pettersson now wonders if more will appear, noting "there's never two without a third" but hoping none come given her puppy's curiosity.
The repeated appearance of these invasive crustaceans so far from water suggests either remarkable crab determination or human involvement in their relocation.