Seasonal dynamics of microzooplankton communities in the Sea of Oman (Arabian Sea)
N. Aberle1 and S.A. Piontkovski2
1Norwegian University of Science and Technology, Department of Biology, Trondheim Biological Station, 7491 Trondhjem, Norway
2Sultan Qaboos University, College of Agricultural and Marine Sciences, Dept. of Marine Sciences and Fisheries, P.O. Box 34, 123 Al-Khoud, Sultanate of Oman
Seasonal dynamics of microzooplankton and changes in environmental condition were analysed during a one-year field sampling campaign in the Sea of Oman at two different stations. Monsoon winds in this region cause distinct seasonality patterns with high primary productivity during the west monsoon in summer (June to October) and north-east monsoon periods in winter (November to March). Microzooplankton in the Sea of Oman showed several biomass peaks throughout the year. In general, higher biomass occurred during the south-west monsoon when compared to the north-east monsoon period with maxima of 190 mg C l1at the inshore station Bandar Al-Khyran at 1m and 308 mg C l1 at 10m water depth. At the offshore-station, peaks of 372 mg C l1 (1m) and 256 mg C l1 (20m) occurred during the south-west monsoon. A strong coupling between phytoplankton and microzooplankton was observed during monsoon periods but some microzooplankton peaked during inter-monsoon periods when chlorophyll concentration was low (Bandar Al-Khyran: 372 mg C l1 at 1m and 196 mg C l1, 10m; Offshore-station: 419 mg C l1, 20 m). The initiation of phytoplankton blooms in the Sea of Oman was bottom-up controlled due to strong seasonal nutrient influx during south-west and north-east monsoon periods. Highest microzooplankton biomass occurred during monsoon periods with a dominance of Noctiluciphyceae and peaks of 7596 mg C l1 at Bandar Al-Khyran (1m) and 5942 mg C l1 (10m). Copepod nauplii, Amoebozoa and Larvacea contributed substantially to microzooplankton biomass throughout the year. Ciliophora contributed low proportion to the total microzooplankton biomass peaking both during monsoon and inter-monsoon periods. During the spring inter-monsoon, choreotrich ciliates (tintinnids) showed distinct peaks of 15.9 mg C l1 at Bandar Al-Khyran (1m) and 17.7 mg C l1 (10m) as well as 18.2 mg C l1 at Offshore-station (20m). The interplay between bottom-up controlled primary production and top-down control mechanisms regulates the phenology patterns of specific microzooplankton groups in the Sea of Oman thus pointing at complex trophodynamic interactions at the lowermost foodweb level in this low-latitude ecosystem.
protozoa, protozooplankton, nauplii, appendicularia, Noctiluca, tintinnid
Abundance and Diversity of Fish Larvae Assemblages in Omani Coastal Waters of Salalah Region (the Arabian Sea)
1Nadir M. Al-Abri, 2Sergey A. Piontkovski, 3Mahnaz Rabbaniha, 2Mohammed Al-Abri and 1Tatyana Chesalina
1Marine Science and Fisheries Center, Muscat, Sultanate of Oman.
2Sultan Qaboos University, P.O. Box 34, Al-Khod 123, Sultanate of Oman.
3Iranian Fisheries Science Research Institute, Agricultural Research, Education and Extension Organization, Tehran, Iran.
Due to the paucity of fish larvae research in the western Arabian Sea and the Sea of Oman, an extensive regular sampling program has been conducted in Omani coastal waters, from 2013 to 2015, over six regions (namely Khasab, Sohar, Muscat, Ashkarah, Doqum and Salalah), of which the Salalah region was analyzed in this paper. Monthly samples of fish larvae were collected from the sea surface and were accompanied by CTD casts, zooplankton sampling and modeling of regional circulation. A total of 734 fish larvae specimens including 38 families and 43 genera were collected and identified in terms of their morphology and morphometric characteristics. The bulk of ichthyoplankton catch were contributed by larvae from 5 families- Pomacentridae, Scombridae, Blenniidae, Mullidae and Clupeidae. The highest abundance of fish larvae (162 ind/100 m3) was observed during the South-west Monsoon. The most diverse family were Carangidae and Pomacentridae, represented with five species and followed by Blenniidae, Scombridae and Terapontidae represented with three species each. The annual mean of the Shannon diversity index was 0.95±0.6. Canonical Correspondence Analysis of the major fish larvae family abundance, sea surface temperature, chlorophyll-a and zooplankton biomass showed that temperature and zooplankton were the most influential variables.
Sergey A. Piontkovski1*, Muna H.Al-Tarshi2 , Sabrina M.Al-Ismaili3 , Sultana S.H.Al-Jardani3 and Yasmin H.A.Al-Alawi3
The western Arabian Sea is known for its intensive upwelling developed seasonally along the Omani coast as well as for numerous mesoscale eddies originating in and passing through waters with seasonally high or low primary productivity. The frequency of cyclonic and anticyclonic eddy occurrence for the 13 year period (from 2002 to 2015) retrieved with 4-km spatial resolution from MODIS-Aqua sea surface height anomalies, and data on wind speed, atmospheric anomalies, geostrophic currents and landings of large pelagic species (Yellowfin tuna, Kingfish and others) were analyzed, in order to elucidate the interannual variability and statistical linkages between parameters. The linear increase of eddy occurrence over years was observed during intermonsoon seasons, against the background of decreasing wind speed and the kinetic energy of the main geostrophic flow. Along with that, a positive correlation between the number of eddies and the variation of fish catches was elucidated. Presumably, the increasing number of cyclonic eddies could mediate the variance of fish catches, making them less predictable over years. The mechanism of this link could be based on the impact of cyclonic eddies on the oxycline depth. Concentrations of dissolved oxygen less than 1.5-2.5 ml L-1 reportedly act as the hypoxic threshold for the Yellowfin tuna. An enhanced number of cyclonic eddies could generate more heterogeneous spatial distribution of threshold concentrations- by lifting them to the upper layers and creating an unfavorable environment for populations of large pelagic species.
Mesoscale eddies, Arabian Sea, fish landings, remote sensing, dissolved oxygen concentration