Atmospheric cyclones and seasonal cycles of biological productivity of the ocean
S.A. PIONTKOVSKI* AND K.A. AL-HASHMI
Sultan Qaboos University, PO Box 34, Al-Khod 123, Sultanate of Oman
Remotely sensed wind speed, translation speed, atmospheric pressure, atmospheric precipitation rate and chlorophyll-a concentration were used to verify the hypothesis that the response of the phytoplankton community to propagating atmospheric cyclones should be associated with the phase of the seasonal cycle of this community and the translation speed of a cyclone. For the 12 cyclones investigated from the Indian Ocean, Pacific Ocean and the Mediterranean Sea the maximal sustained wind speed varied twofold, whereas the translation speed of cyclones and the chlorophyll ratio (characterizing chlorophyll concentration before and after cyclone passage) varied by 10-fold. It was shown that cyclones affecting the phytoplankton community approaching its seasonal maximum either could not stimulate or stimulated a weak response of further increase of chlorophyll-a concentration (due to explicitly available nutrients). Controversially, cyclones affecting the community approaching its seasonal minimum could induce gradual increase of chlorophyll-a concentration. An exponential type of relationship between chlorophyll ratio and translation speed of cyclones was evaluated. In the range of translation speeds from 1 to 10 ms−1, the increase of chlorophyll- a concentration due to cyclone passage was most pronounced with regard to slow moving cyclones.
Keywords: Atmospheric cyclones; Chlorophyll-a; Arabian Sea
Spatial-Temporal Distribution of the Palinurid and Scyllarid Phyllosoma Larvae in Oman Coastal Waters
Sergey Khvorov1*, Sergey Piontkovski2, and Elena Popova3
1Marine Science Fisheries Centre, Ministry of Agriculture and Fisheries Wealth
P.O. Box 227, Sultanate of Oman
2College of Agricultural and Marine Sciences, Sultan Qaboos University
P.O. Box 34, Al-Khod 123, Sultanate of Oman
3Institute of Biology of the Southern Seas, 2, Nakhimov av.-Crimea
99011, Sevastopol, Ukraine
The Bongo Net samples collected between 2005 and 2008 in the Sea of Oman and in the north-western part of the Arabian Sea (near Massirah Island) were analyzed, for a pilot assessment of seasonal and spatial distribution of the phyllosoma larvae. In the samples collected, 84% of all phyllosoma larvae were from the family Palinuridae, while the others were contributed by family Scyllaridae. All larvae of Panulirus homarus were in the first development stage and had a mean body length of 1.30±0.89mm. The phyllosoma larvae of the less abundant family Scyllaridae were in the second, third, and fourth development stages, which had a mean length of 2.3mm, 3.3mm and 4.63mm, respectively. In terms of seasonal changes, the phyllosoma larvae tend to appear in Omani waters in February, reaching their maximum numbers in April. The abundance of phyllosoma P. homarus was as much as twofold higher in the Arabian Sea compared to the Sea of Oman.
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
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