158
M. Campolmi et aI.
noon. Temperature did not show any correlation
with tide.
Salinity values ranged from 37.8 (October) to
43.8 psu (July). Significant (P fluctuations were very low in May (0.5 psu). In
March, the salinity values averaged 38.4 psu and
the day-night variations were significant
(P appeared to be correlated negatively with tide in
March (p = -0.84; P -0.67).
In almost all the surveys, dissolved oxygen
showed a clear diel cycle with maximum saturation in the afternoon and a minimum in the early
morning. The variations in oxygen concentration
and saturation levels over the 24-h period were
significant (P<0.05) only in July (3.9-9.1 mg/I;
81.9-146.1%), In general, these parameters
appear to be affected by two different phenomena: the day-night cycle of photosynthesis and
respiration processes and the movement of water
masses with different oxygen contents through
the sea mouth (Ferrari et al.198Sa).
The pH values were fairly high in all the 24-h
sampling surveys. Significant (P The speed and direction of the current
recorded during the four surveys are shown in
Fig. 2. A clear periodicity of current direction was
!)'-10 MAY 1996
19-30 JULY 19!1ti
Sl.1
12-%3 OCTOBER 1996
Fig.2. Current speed (an's- l ) and direction (degrees), and zooplankton abundance (ind. m- 3 x 100) during the four 24-h cycle
surveys