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Mesozooplankton of the Omani shelf: taxonomy, seasonality, and spatial distribution
Sergey A. Piontkovski, Asyla Al-Mawali,Ahlam Al-Kharusi, WardalMuna Al-Manthri, Sharon Smith & Elena Popova

Abstract
The total zooplankton biomass was determined for 216 samples collected during seasonal surveys onboard a research vessel. Some of these samples were processed to the level of species. In 2007–2008, the Omani shelf was populated by a highly productive epipelagic plankton community. The chlorophyll-a concentration was high throughout the seasonal cycle and likewise the zooplankton biomass, where seasonal values varied from 543 to 723 mg m-3. Spatial distribution of zooplankton biomass over shelf waters was highly heterogeneous, with maximal heterogeneity observed during the South-west Monsoon. The mean biomass and size structure of the zooplankton community did not exhibit statistically significant seasonal changes. On the species level, seasonal changes dealt with a massive appearance of the copepod Calanoides carinatus s.f. in shelf waters, to which organisms migrated from the deep, during the South-west Monsoon. The population represented mainly by c4 and c5 copepodite stages ascending to upper layers during its ontogenetic migration has occupied the entire Omani shelf area. However, this migration did not contribute markedly to seasonal variation of the total zooplankton biomass.
Keywords Zooplankton , Arabian Sea , Coastal upwelling , Ontogenetic migration

Dynamics of potentially harmful phytoplankton in a semi-enclosed bay in the Sea of Oman
Khalid A Al-Hashmi 1 *, Sharon L Smith 2, Michel Claereboudt 1, Sergey A Piontkovski 1, Adnan Al-Azri 1
1 College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O. Box: 34, Al-Khod
123, Sultanate of Oman.
2 Rosenstiel School of Marine & Atmospheric Science, University of Miami, 4600 Rickenbacker
Causeway, Miami, Florida 33149.

ABSTRACT
The dynamics of potentially harmful phytoplankton in relation to environmental parameters was investigated in the semi-enclosed Bay of Bandar Khayran (Sea of Oman) from April 2006 through April 2011. In total, 24 potentially harmful algal species were identified, including 11 species of dinoflagellates and eight species of diatoms. The dinoflagellates Prorocentrum minimum (Pavillard) Schiller, 1933, Scrippsiella trochoidea Balech ex Loeblich III, 1965, and Noctiluca scintillans (Macartney) Kofoid and Swezy, 1921 were most abundant during the Southwest Monsoon (SWM, July–September) and Northeast Monsoon (NEM, January–March) seasons, while other species occurred in low abundance and with no clear seasonal patterns. A dense bloom of Cochlodinium polykrikoides Margalef, 1961 that affected the distribution and abundance of other harmful algal species (HAB) was observed for the first time in the Sea of Oman during 2008–2009. Prorocentrum minimum increased in abundance during and after the decay of the Cochlodinium bloom while S. trochoidea was suppressed during this bloom, increasing thereafter once again. Noctiluca scintillans disappeared in the late SWM and NEM of 2008 and SWM of 2009, when blooms typically occur annually. Prorocentrum minimum and S. trochoidea persisted throughout the annual cycle of all years, enhancing their capability to bloom in the region under favorable conditions of high light intensities and relatively warm waters of low turbulence.

Seasonal variability of size-classes of phytoplankton biomass in a sub-tropical embayment, Muscat, Sea of Oman
Al-Hashmi K.; Claereboudt M.; Piontkovski S.; Al Azri A.; Amin S.M.N.

Abstract
The contribution of three different cell size classes of picoplankton: 0.74-2 μm, nanoplankton:2–20 μm and microplankton, >20 μm of the phytoplankton population and their relationship to environmental conditions were studied over two annual cycles at one station in Bandar Khyran Bay, Sea of Oman, from May 2006 to August 2008. Nanoplankton was the most important class contributing 54.4% to total Chl a (range 6-82%). Its seasonal highest concentrations was during the cold periods when temperature ranged from 28-29 °C in fall and near 24 C in winter when the supply of nutrients was sufficient to sustain their growth. Picoplankton had the second level of the contribution, comprising (23.5%, range 4-74 %) of the total Chl a. and their concentration was generally constant (0.04-.06 μg l–1) throughout the study period. The drop of picoplankton population coincided with an increase in the microplankton and nanoplankton populations indicating a high grazing pressure exerted on the picoplankton population. Microplankton size-class occupied the third level of the contribution comprising (22.2%, range 3-65 %). Their general concentration was below 0.1 μg l–1 and only dominant when temperatures were lowest and nitrate, nitrite, silicate and phosphate concentrations were the highest. The temporal variability observed was associated with changes in the nanaoplankton indicating that in some cases, it is the small fraction of phytoplankton that drives changes in abundances and productivity.
Keywords: Phytoplankton, Chlorophyll a, Size-class, Picoplankton, Nanoplankton, Upwelling, Sea of Oman

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