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Joosten and van den Hoek: World-wide relationships between red seaweed floras 195 Abstract Distribution data on a world-wide scale of 613 red algal genera occurring in 22 climatically defined coastal regions were analysed with correspondence analysis (with detrending, with and without downweighting of rare genera). In the ordinations a climatic trend and a latitudinal trend could be readily distinguished. Distinct groups of regions could be identified by means of genera-by-region plots of the ordination with downweighting of rare genera. Two directed graphs illustrating nearest neighbour relationships and close neighbour relationships between the regions, respectively, were based on an asymmetrical coefficient of association. In the directed graphs overlapping relations between the regions are apparent. These results and possible explanations can be summarized äs follows: A warm temperate to tropical group of regions (including all four tropical regions, three warm temperate regions in the Northern Hemisphere, and one warm temperate region in the Southern Hemisphere) possibly represents a formerly continuous Tethyan flora. Long ränge dispersal and Gondwanaland connections are possible modes of origin of a disjunct group of temperate regions in the Southern Hemisphere, including southern Australia, New Zealand and southern Africa. The warm temperate SE Pacific region is related to the warm temperate NE Pacific and SW Pacific regions. Its depauperate nature is possibly due to the 1 Nino' phenomenon. The Antarctic region and the cold temperate regions of the Pacific and Atlantic coasts of South America and the subantarctic islands form a distinct cluster in all the analyses. The separateness of the temperate Pacific and Atlantic floras in the Northern Hemisphere contrasts with the relatedness of the Southern Hemisphere temperate floras. This separateness is ascribed to their long Separation by the Bering Land Bridge (up into Pliocene, 2.10 6 y).

A study has been carried out on the development of an ecological assessment method for shallow lakes in The Netherlands. Analyses of eutrophication characteristics of 93 lakes with, in total, 127 sampling localities gave insight into some of the steering variables, such as total-P, total-N, chlorophyll-a and transparency. On the basis of phytoplankton species composition, three main groups of lakes could be distinguished. The first group, characterized by persistent filamentous Cyanobacteria, had the highest summer means of chlorophyll-a and totaI-P. The second group was characterized by non-persistent filamentous Cyanobacteria, occurring in low abundancies, and at lower chlorophyll-a and totaI-P concentrations. The third group of lakes was characterized by the absence or very low abundance of the filamentous Cyanobacteria. As a result of these analyses, criteria for the abatement of eutrophication in shallow lakes could be refined.

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