. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ON NEREIS DIVERSICOLOR 339 PART II. OBSERVATIONS IN THE ISEFJORD, DENMARK General description of the area In a geographical sense the Isefjord (Fig. 2), in the northern part of the island of Zealand to the west of Copenhagen, is intermediate between British waters and the Baltic, while its mean surface salinity of 20°/00 is midway between salinities at Tvarminne and Plymouth. The hydrography of the Isefjord has been sum- marized by Nielsen (1951). His account shows that this body of water is char- acterized by a stability of
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ON NEREIS DIVERSICOLOR 339 PART II. OBSERVATIONS IN THE ISEFJORD, DENMARK General description of the area In a geographical sense the Isefjord (Fig. 2), in the northern part of the island of Zealand to the west of Copenhagen, is intermediate between British waters and the Baltic, while its mean surface salinity of 20°/00 is midway between salinities at Tvarminne and Plymouth. The hydrography of the Isefjord has been sum- marized by Nielsen (1951). His account shows that this body of water is char- acterized by a stability of salinity greater than that of the south Finnish coast. The Isefjord has an area of 280 square kilometers and is so shallow (mostly less ISEFJORD- 2A«-V LABORATORIET 2B» 2C «»_p- 3A 3B- . _Z—^ N"1- °[. FIGURE 3. Vellerup Vig, showing sampling stations. Details in Table II. Arrows marked F and L show limits of Fuctts and Littorina on the shore. than 10 meters) that despite the presence of a sill at its mouth, salinity stratifica- tion rarely occurs. According to Nielsen's observations, mean surface salinity in the Inner Broad (southern part of the fjord) is °/00. with extremes noted of and °/00. while at depths of 4-6 meters the corresponding values are (). The Isefjord is thus polyhaline in the sense of Valikan- gas (1933). In comparison with conditions near Tvarminne it is notable that the lowest salinity of °/00 was obtained in March, immediately beneath the ice, and that the difference in salinity between surface and 5 meters at that time was only °/oo- The Isefjord freezes easily and may have an ice cover for three months in cold winters, although there is evidently not such a marked seasonal lowering of salinity beneath the ice as is experienced in Finnish waters. The reason for this is doubtless the slight fresh water drainage into the Isefjord, which has a very small watershed (800 sq. km.) and receives only sm
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
