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Coastal Algae off GoteborgIn Relation to Gradients in Salinity and PollutionBy PER ERIK LINDGRENDescriptive introductionNear the town of KungaJv, the Gota River splits intotwo arms running on each side of the island ofHisingen. The northern arm, the Nordre River,passes about 15 km, mostly of farming land with amoderate population, before it discharges into theNordre Firth. The southern arm, retaining thename of Gota River, runs across about 15 km ofindustrial countryside and about 10 km of city andseaport, until it gradually widens, forming the AlvsborgFirth.The city of Goteborg (Gothenburg), the secondin Sweden, with a population of 400,000 and considerablefactories and shipping trade (includingimportation and refinery of mineral oils), stilldischarges nearly all of its household and industrialwaste water into the Gota River and estuarywithout precedent purification, although a largepurification plant is under construction.Both estuaries have the shape of open funnelsand contain many small islands. Outside of boththere is an archipelago of large and small islandsreaching about 15 km off the coast. The twoestuaries and the corresponding parts of the seawardarchipelago form two parallel gradients insalinity, from less than 0.1 %o in the rivers to about22 %o at sea. The latter value is, in its turn, a stepin the salinity gradient along the Kattegat-Skagerrakcoast, but all values are extremely variable, bothoff-shore and still more inshore. The water quantitiesin the N ordre River are three times larger thanin the Gota River. As a consequence the water inthe N ordre Firth is more brackish than in themouth of the Gota River .The islands are low, rocky and poorly wooded,although an increase in the growth of birch, aspen,rowan (Sorbus aucuparia) and oak (includingQuercus petraea) is now observed since grazing ismostly discontinued (except for sheep grazing onsome islands still largely bare). There are largefishing villages on several of the islands.The rocky shores are generally low but fairlysteep, and the waters within the fringe of skerriesare shallow, with a maximum depth of 23 m only.There are extensive clay banks covered by 2 or 3 mof water and even less, including one stretchingacross the Nordre Firth. The tides are insignificant.The waters off the mouth of the Gota riverThe vegetation and flora of the water varies as aparallel to the salinity and, if present, the pollutiongradients. From a study of littoral and sublittoralcommunities a division into vegetational districtswas carried out. For the southern area the followingfour districts were discerned (see map, Fig. 1).THE OFF-SHORE DISTRICT.-This district includesthe waters of the outer fringe of the archipelago}most of the wide Askim Firth to the south, andsome of the sounds between certain off-shore islands(the Styrso group). It may be defined as thearea where the littoral vegetation shows no particulardifference from that nearest to the north (e.g.off the large island of Tjorn) or to the south (offthe Onsala peninsula). It was characterized as theFucus spiralis-Calothrix district in LINDGREN(1962). Many algae are confined to this district(e.g. Codium fragile, Polysiphonia Brodiaei, Coral-.Acta Phytogeogr. Suec. 50