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Variability of dinoflagellates and diatoms in the surface waters of Muscat, Sea of Oman: comparison between enclosed and open ecosystem

Khalid A Al-Hashmi(1)*, Joaquim Goes(2), Michael Claereboudt (1), Sergey A. Piontkovski (1), Adnan Al-Azri (1), Sharon L Smith (3)
1-Khalid A Al-Hashmi* (Corresponding author); College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman. This email address is being protected from spambots. You need JavaScript enabled to view it.
2-Joaquim Goes; Lamont Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA This email address is being protected from spambots. You need JavaScript enabled to view it.
1-Michael Claereboudt; College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman. This email address is being protected from spambots. You need JavaScript enabled to view it.
1-Sergey A. Piontkovski; College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman. This email address is being protected from spambots. You need JavaScript enabled to view it.
1-Adnan Al-Azri; College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman.  This email address is being protected from spambots. You need JavaScript enabled to view it.
3-Sharon L Smith;The Rosenstiel School, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149 USA. This email address is being protected from spambots. You need JavaScript enabled to view it.

ABSTRACT
We investigated the distribution patterns of phytoplankton species over a one year period (from April 2010 to February 2011) at an open ocean location off the coast of Muscat, Sea of Oman (OFF) and the other at Bandar Khayran (BK), a semi enclosed bay located downstream of the southeastward Sea of Oman coastal current. Although these two locations come under the influence of the semi-annually reversing monsoons, and experience nutrient influxes associated with the southwest (SWM, June-Sept.) and the northeast monsoons (NEM, Nov.-Feb.), they are hydrographically distinct. At both stations, a total of 133 phytoplankton taxa were identified and quantified over the sampling period. The two stations showed higher phytoplankton abundance, higher diversity and higher chlorophyll concentrations during the SWM and NEM seasons, a reflection of phytoplankton populations responding to injection of nutrients during these two seasons. Phytoplankton communities at both at BK and OFF were dominated by dinoflagellates and showed no significant differences in dinoflagellate community composition. In addition, no clear trend of dinoflagellate or diatom species succession was observed during the study period. Among the dinoflagellate population, Prorocentrum minimum, Gymnodinium sp., Scrippsiella trochoidea, Gymnodinium simplex and the mixotroph Noctiluca scintillans. On the other hand, Lauderia punctata, Bacteriastrum elongatum and Paralia moniliformis, Chaetoceros spp. Guinardia striata and Thalassiosira spp. were the most dominant diatoms.
Key words: Dinoflagellate, diatoms, monsoon, upwelling, Sea of Oman, Arabian Sea, coastal environments

The Omani shelf hypoxia and the warming Arabian Sea

S.A. PIONTKOVSKI* AND H.S. AL-OUFI
†Department of Marine Science and Fisheries, CAMS, Sultan Qaboos University, P.O. 34, Al-Khod
123, Sultanate of Oman;
Ministry of Agriculture and Fisheries Wealth, P.O. 467, Muscat 113,
Sultanate of Oman

Abstract
Interdecadal changes in oxygen depletion, with a special reference to artisanal landings of large pelagic fishes, were analysed. Data from 53 expeditions incorporating 29,043 vertical profiles of temperature and 2114 of dissolved oxygen implied an increase in temperature of 1.2 °C over the past 50 years in the upper 30 m layer of sea water during the south-west (summer) monsoon. The thermal stratification of the water column increased and the oxycline shoaled from 153 m in the 1960s to 80 m in the 2000s. Concentration of dissolved oxygen <3.5 mL L−1 is known to induce symptoms of stress for many tropical pelagic fishes, compressing them within upper layers and exposing them to fishery. The habitat compression by the Oman shelf hypoxia has two components: a seasonal oxycline shoaling and an interdecadal trend.
Keywords: Hypoxia; Oxycline; Fish landings; Arabian Sea

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