Phytoplankton communities in rock pools on the Åland Islands, SW Finland – environmental variables, functional groups and strategies

Studies of rock pools tend to focus on the surrounding emergent habitat. Moreover, research on phytoplankton in small, nutrient-rich water bodies is limited. Summer phytoplankton species, functional groups and life strategies, as well as physicochemical variables potentially influencing the phytoplankton, were surveyed in 34 brackish rock pools. Except from total nitrogen and total phosphorus, the pools were chemically quite similar. Phytoplankton abundance and biovolume consisted mainly of charophytes (Zygnematales), unidentified small flagellates, cyanobacteria, chlorophytes and dinoflagellates. Many of the phytoplankton functional groups were representative of shallow, nutrient-rich and lightabundant environments. The majority of the common and abundant species were classified as C-strategists (invasive opportunists). Total nitrogen, total phosphorus and phytoplankton biomass varied greatly between the rock pools, and were positively related. The rock pool depth and macrovegetation presence–absence played a central role in shaping the phytoplankton species distribution. Frequently occurring species, present in the majority of the rock pools, seldom dominated the phytoplankton. Species dominating the phytoplankton rock pool assemblages were not common components of the phytoplankton flora. Studies of rock pools tend to focus on the surrounding emergent habitat. Moreover, research on phytoplankton in small, nutrient-rich water bodies is limited. Summer phytoplankton species, functional groups and life strategies, as well as physicochemical variables potentially influencing the phytoplankton, were surveyed in 34 brackish rock pools. Except from total nitrogen and total phosphorus, the pools were chemically quite similar. Phytoplankton abundance and biovolume consisted mainly of charophytes (Zygnematales), unidentified small flagellates, cyanobacteria, chlorophytes and dinoflagellates. Many of the phytoplankton functional groups were representative of shallow, nutrient-rich and lightabundant environments. The majority of the common and abundant species were classified as C-strategists (invasive opportunists). Total nitrogen, total phosphorus and phytoplankton biomass varied greatly between the rock pools, and were positively related. The rock pool depth and macrovegetation presence–absence played a central role in shaping the phytoplankton species distribution. Frequently occurring species, present in the majority of the rock pools, seldom dominated the phytoplankton. Species dominating the phytoplankton rock pool assemblages were not common components of the phytoplankton flora.