| dc.description.abstract | From 1974 to 1978 R/V "G.M. Dannevig" was used for 7-8
cruises yearly in the Langesund area. Parameters sampled at 7
stations were: temperature, salinity and oxygen in standard
depths, phytoplankton studies in the upper 12 m (primary productivlty,
chlorophyll a and counting in microscope). Zooplankton
and ichthyoplankton were sampled by Bongo net in the upper
50 m. Echo sounder was run continuously and occasionally recordings
were sampled by pelagic trawl.
The hydrographic results are given in a separate report (Dahl, 1982).
The fluctuations in the phytoplankton stock were greatly influenced by the river Skienselva discharge, especially in the
inner parts of the fjord system. At the innermost station there
was no regular spring bloom but rather a summer maximum. Going
outwards gradually the spring bloom of diatoms became more pronounced
and the summer bloom of naked monads of less importance.
In 1977 an extensive renewal of deep water led to high
values of phytoplankton production. Also for zooplankton the
highest values were observed this year.
Variations in both volume and composition of zooplankton
species followed the same pattern at all stations outside
Frierfjord.
In Frierfjord the supply of zooplankton from outer areas
meant a lot, most clearly seen in 1977 after the renewal of
deep water. However, also the fresh water outflow from Skienselva
influenced the area.
Echo soundings showed the yearly presence of sprat in Frierfjord
from February to June. Eggs were found in the same period
with the highest values from April to June. Outside Frierfjord
only small quantities were found in June. Mackerel eggs and
larvae were found at the outer stations in June. | en |
