Microphytobenthic community composition of two sub-Arctic intertidal flats in Huna Bay (Northern Iceland)

Marine microphytobenthic community composition in relation to habitat characteristics of sub-tidal flats in temperate and Arctic regions is well described. For sub-Arctic areas, especially for northern Icelandic intertidal flats, information is sparse or absent. To investigate sub-Arctic microphytobenthic community composition, surface sediments were collected during neap tide at six stations, along two transects in the Hunafloi in and near Skagastrond from March to October 2013. Variations in environmental factors were considered as well as microphytobenthic density (abundance and chlorophyll a). Overall, 137 species and sub-specific taxa were identified in surface sediment samples (106 bacillariophytes and 31 other taxa). Of these, 53% are considered as marine or brackish water species in the literature. Forty-three per cent of the marine taxa originated from the planktonic realm, suggesting considerable bentho-pelagic coupling in the investigated area. The primary producers in both transects in the Skagastrond area were mainly Bacillariophyceae (up to 85% of the total communities, with overall mean value of 35.6 and 42.8 x 10(2) cells cm(-2) in transects I and II, respectively). All communities were characterized by a dominance of epipelic Navicula species with temporal successions of secondary species, including several pelagic species (e.g. Actinocyclus). The non-diatom taxa at all stations in transects I and II included pelagic species such as Stichococcus bacillaris (Prasiolales, Chlorophyta), and cryptophytes, dinophytes, haptophytes and other ochrophytes. Characteristic environmental features such as short growth periods, high glass and basalt fractions in the sediment composition and seasonal fluctuations in terrestrial runoff, as well as strong hydrodynamic forces, influenced the community patterns observed in the present study and further comparative studies with other areas in northern Iceland are required.