FÄRJOR GER FART ÅT ALGER? / Ferry traffic speeds up phytoplankton
Ships, especially huge car-ferries, cause shore erosion and influence the littoral benthic communities along the archipelago routes between Sweden and Finland. Less is known about effects on pelagic communities (phytoplankton). Some effects of ships waves and currents were studied in the Mariehamn ferry harbour area, southern Åland (N. Baltic Sea) in the summer of 1996. Chaotic mixing occurred in the harbour area. In July the ferries caused a pumping effect on a marginal area, the Svibyviken inlet: warm, algae-rich water was drawn out of the shallow inlet and was replaced by colder upwelling water. Reversed biomass transport was docu-mented in August. Similar pumping effects must be important along the ferry routes through the archipelago. It is suggested that ferry-induced mixing and water and biomass transport contribute to the eutrophication of
the archipelago waters.