Abstract:
This study provides baseline information on the physico-chemical parameters and the
zooplankton community at the Polhena reef, from November 2010 to February 2011, the
inter monsoons to dry season. Water samples were collected from seven stations at 15 days
intervals to measure the physico-chemical parameters and for zooplankton identification and
quantification. Average salinity, 28.8ppt-35.4ppt, TDS 29.56 g/L-39.23 g/L, DO 7.35
mg/L-10.36 mg/L, BOD 0.32 mg/L -1.95 mg/L, TH 5012 mg/L-5816 mg/L. Lowest values
of all these parameters were occurred in the inter monsoon period and the highest average
readings were recorded in the dry season. Average water temperature was 27.7 °C-29 °C,
TSS 56.37 mg/L-70.19 mg/L, in which the highest average readings were recorded in the
inter monsoon period and the lowest was recorded in the dry season. pH was approximately
a constant.
Increased average Phosphate concentration was recorded in the dry season as 0.8 mg/L.
Nitrite concentrations fluctuated without any distinct pattern, recording the highest average
concentration as 0.063 mg/L in mid December. No significant changes in average DO
levels, water temperature, BOD levels, salinities, TDS, TSS and TH levels, pH, and N02*
and P043' concentrations at different stations. Nevertheless the temporal changes of average
DO levels, water temperatures, BOD levels, salinities, TDS, TSS and TH levels, P043'
concentrations at the site were significant. In the dry season, higher average DO and BOD
levels, increased salinity, TDS and TH levels, decreased water temperature and TSS level
were detected. The average total zooplankton abundance increased in the dry season. The
highest was recorded as 45,638.14 ind / m3 on Feb.01 and the lowest was recorded as
6,507.71 ind / m3 on Dec.01. The zooplankton community was identified into 17 groups,
dominated by Copepods, Crustacean nauplii and Foraminiferans respectively. Their relative
abundances were calculated as % by number of individuals. Copepods made up ~ 96% at
station 3 in February, the highest relative abundance (%) of any group at any station. Nauplii
stages appeared with peaked abundance of -40% at station 7 in the end of December.
Foraminiferans occupied -50% of the total zooplankton community at station 1 in February.
Relative abundance of Veliger larvae peaked to -22%. Abundance of Trochophore was
recorded as -14% at station 5 in late November. There were Barnacle nauplii, Zoeal stages
of Decapods, Isopods and Polychaetes which were limited to fewer stations. Hydrozoan
larvae, Radiolarians, Ostracods, Appendicularians, Cirripedians Chaetognaths, Tintinnids
were far less abundant.
