Mass occurrence of unattached Enteromorpha intestinalis on the Finnish Baltic Sea coast

The occurrence and summer biomass of an unattached Enteromorpha intestinalis mat was studied in Olkiluodonvesi on the Finnish Baltic Sea W coast between 1993 and 1997. Enteromorpha intestinalis thalli had lost their tubular shape, spread, and formed unattached monostromatic sheets. The mats were found in areas of soft sediment and sandy substrates where water depth was one to six metres. Optimum growth was at one to two metres. The mats were 5—15 cm thick with biomass maximum of 97 tn in an area of 3.7 km2in 1993. Even during severe winter conditions, monostromatic E. intestinalis appeared in healthy state. In early spring, just after the ice melt, small amounts of E. intestinalis were found floating on the surface. Massive floating were observed after sunny and calm weather periods with low water level. On both occasions, E. intestinalis was moving within the water column.