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The Relationship between Algal Blooms, Fish Kill Incidents, and Oxygen Depletions along the Omani Coast

S.A. Piontkovski1), H.M.H. Al-Gheilani2), B. Jupp3), Y.V.B. Sarma1), and A.R. Al-Azri1)
1) Sultan Qaboos University, CAMS,PO Box 34, Al-Khod 123, Sultanate of Oman
2) Marine Science and Fisheries Center, Ministry of Agriculture and Fisheries, P.O. Box 467, Muscat 113, Sultanate of Oman
3) GEO-Resources Consultancy, P.O. Box 175, Mina Al Fahal, Muscat 116 Sultanate of Oman

* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

A persistence of hypoxia is a common feature for the Sea of Oman, and the western Arabian Sea. By using historical data complemented by ongoing measurements, the relationship between the frequency of harmful algal blooms, fish kill incidents, and oxygen depletions, was investigated. In the Sea of Oman, the seasonal pattern exhibited a tendency of fish kill incidents to
increase, from January to November. In the western Arabian Sea, the pattern was different- maximal occurrence of fish kill incidences was observed in December and January. In 1988-2011, the number of harmful algal blooms accompanied by fish kills was 4 times higher for the Sea of Oman (N= 91) compared to the Arabian Sea coast (N= 22), whereas the total number of fish kill incidents was about the same (22 versus 25). This means that the Arabian Sea coast faced more frequent harmful blooms than the Sea of Oman. The Sea of Oman coastal time series of the dissolved oxygen concentration implied a
steady decline throughout the year, from January to December. The fish kill incidents in this region were mainly driven by oxygen depletions, whereas in the Arabian Sea these incidents were mediated by the harmful algal blooms along with the oxygen depletions. In analyzing the Omani coast as a whole, the Ridge Multiple Regression Analysis implied the dissolved oxygen concentration and monthly occurrence of algal blooms as the two variables explaining 75% of the seasonal variations in fish kill incidents.
Keywords: Hypoxia; Fish kills; Arabian Sea; Harmful algal blooms

Interannual Changes in the Sea of Oman Ecosystem

Sergey A. Piontkovski*,1, Hamed M.H. Al-Gheilani2, Barry P. Jupp3, Adnan R. Al-Azri1 and Khalid A. Al-Hashmi1
1Department of Marine Science and Fisheries, Sultan Qaboos University, P.O. Box 34, Al-Khod 123, Sultanate of Oman
2Marine Science and Fisheries Center, Ministry of Agriculture and Fisheries, P.O. Box 467, Muscat 113, Sultanate of Oman
3GEO-Resources Consultants, P.O. Box 175, Mina Al Fahal, Muscat 116, Sultanate of Oman

Historical data were used to estimate interannual tendencies for the Sea of Oman over the past 50 years. Declining trends were shown for the atmospheric surface level pressure in the region affected by the Siberian High atmospheric anomaly, the zonal component of wind speed, concentration of nitrates, biomass of diatoms and sardine landings. Changes in Zooplankton biomass showed no clear trend. These trends were associated with and accompanied by rising atmospheric temperature, sea surface temperature, annual variability of the kinetic energy of mesoscale eddies, frequency of fish kills (along with the death of other animals- dolphins, turtles, and sea birds) and harmful algal bloom incidents. In terms of interannual coupling between physical and biological processes, the evaluated trends imply that the weakening of the Siberian High atmospheric anomaly results in the decline of the zonal wind speed and a regional increase of air temperature. This in turn increases the temperature in the mixed layer which strengthens thermo-haline stratification of the water column. Increasing stratification prevents the penetration of nutrients into the mixed layer and does not favor the interannual increase of biological productivity, although annual variation of biological productivity has increased, from 1997 to 2008.
Keywords: Gulf of Oman, long term changes oceanography, chlorophyll a, climate change.

Interannual changes of the Arabian Sea productivity

Department of Marine Science and Fisheries, Sultan Qaboos University, Al-Khod, Sultanate of Oman

Inter-annual changes in temperature and chlorophyll a across the Arabian Sea (subdivided into 61 2-degree regions) were analysed. For each 2-degree region, from appropriate databases, remotely sensed chlorophyll a, sea surface temperature, and wind speed time series were retrieved. Spatial and temporal trend analysis showed physical - biological oscillations with dominant periods of 12 and 6 months (reflecting the seasonality of monsoonal winds) with a globally warming trend, but no overall increase in chlorophyll during the period 1997 - 2009. Variation coefficients of the inter-annual time series of chlorophyll a implied high variability in western regions of the sea in comparison to eastern regions. The basin-wide maps of chlorophyll distribution did not show the enlargement of the productive area over time and overall, not only did the Arabian Sea not get more productive, but several regions in its eastern basin showed a decline in chlorophyll a concentration.

Key words: Arabian Sea, chlorophyll a, global changes, marine ecosystems

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