summer, due to high temperatures and poor water dynamics.
In further monitoring it will be necessary to measure oxygen
early in the morning. If any critical situation is noticed
adequate measurements must be taken (to reduce feeding or
even to stop feeding during the morning and to feed fish
mostly during the afternoon).
Horizontal profile of oxygen saturation in the bay depends
mostly on the currents. The movement of water masses is
caused by tides and possible general direction of the currents
is clockwise. The influence of the cages is restricted on small
radius of only a few meters from the cages. Horizontal
influence of the cages is vertically confined only on the depth
of the cages (5 m).
According to production records and estimated load per ton
of the fish produced, it was assumed that the total load of
nutrients was 3.8 t/y of phosphorus and 29.3 t/y of nitrogen.
Good exchange of water between the bay and the main basin
throughout a year caused good dispersion of nutrients load.
The highest nutrients concentrations were recorded in warmer
part of a year what is directly related to increased food supply
from June to September (during optimal summer temperatures
– above 20°C). No clear relationship between nutrient supply
and concentration of phosphorus and nitrogen components in
the water was found. There were no significant differences in
the concentrations of phosphate in water column as well as
between the cages and control station. The same situation is
noticed for nitrate and nitrite.
The phytoplankton community was diverse and consisted
mostly of diatom and partly of dinoflagellates, what is typical
for Middle Adriatic coastal waters [8]. We found out that
phytoplankton chlorophyll increases were associated with
adequate nutrient loading increases, what was in accordance
with theories of the relationship between nutrient loading and
primary production in shallow and sheltered aquatic system.
Some authors [9], [10] were not able to confirm such clear
relationship nutrient levels-primary production while others
[11] thought that nutrient enrichment would stimulate
phytoplankton growth only when the particular nutrient was
limiting factor of phytoplankton growth. Due to relatively low
primary production and great variety of phytoplankton
community conclusion that monitored location was not threat
by fish farming operations can be made. Oxygen saturation,
nutrient loading, phytoplankton growth…, also proved that
surrounding waters of fish farm in of monitored location were
not much depressed by farming operations. Despite of high
nutrient loading during long farm history, the studied location
did not show any signs of eutrophication. Good condition of
the bay could result from the bottom morphology and high
flushing rate, which prevented accumulation of nutrients. But
many of potential problems could be avoided by increased
attention in the next years. Most probably such monitoring
programs should include chemical measurements of
enrichment as well as studies on temporal variability of
macrobenthos and fouling communities. If the problems
emerge negative impacts can be reduced by proper selection
of cage micro-location (off-shore or semi off-shore) and by