Spatial distribution of phytoplankton in the eastern part of the North ...

achromaticum has previously been found by e. g. DODGE (1982) from British Isles and byTRIGUEROS et al. (2000) in the estuary of Urdaibai in northern Spain. It seems that this species isable to tolerate wide range of salinity in marine and brackish waters. The species found mainly atthe oceanic end of the transect were Protoceratium reticulatum, Protoperidinium cerasus andProtoperidinium pyriforme. Minuscula bipes, Pentapharsodinium dalei, Protoperidiniumpellucidum and Zygabikodinium lenticulatum were found at all stations of the transect, but theircontribution to the total quantity of algae was rather low.The species of the genus Dictyocha (mainly the species D. speculum) showed a different spatialdistribution along the transect. Contrary to diatoms and dinoflagellates, they were mainly found inthe middle part of the transect. Only the skeleton bearing stadium was found in all samples,although this genus is able to form other stages, which don’t require silicate and therefore don’tcompete with diatoms for it.Three distinct groups of stations were found based on differences in species composition – threestations at each end of the transect, and two stations in the middle. Different algal speciesdominated in each group. Spatial differences of phytoplankton composition along the transect wassignificant in RDA analysis, showing differences between coastal and oceanic species. REID et al.(1978), who investigated the spatial distribution of phytoplankton ofCalifornia, published similar results. They found that the planktoncomposition at stations 100 km apart in the along shore direction wasmore similar that at stations hundreds of meters apart in the offshoredirection.The dependence of depth, salinity, temperature and fluorescenceon the species composition was not proved. For illustration, the p-values from the results of RDA analyses are given in Tab. 6.environmentalvariablesp-valuescoast 0.001depth 0.18temperature 0.29salinity 0.41fluorescence 0.69Table 6. The results ofMonte-Carlo permutationtests of all environmentalvariables.The individual species showed four types of distribution along the transect, as shown in Fig. 18(coastal, oceanic, with a maximum of abundance in the middle part of the transect, or moreabundant at both ends of the transect.). Most of the species occurred in either the eastern or thewestern part of the transect, in coastal or open oceanic environment, respectively. With theexception of Skeletonema costatum, the ecological preferences of most other species correspondwith published data. A preference for coastal environment has previously been published for e. g.Coscinodiscus wailesii (EDWARDS & JOHNS 2002), Emiliania huxleyi (YANG et al. 2001), andThalassiosira angulata and T. nordenskioeldii (REIGSTAD et al. 2000). The genus Chaetoceros is,23