International Journal of Oceans and Oceanography ISSN 0973-2667 Volume 8, Number 2 (2014), pp. 137-152 © Research India Publications http://www.ripublication.com
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
[email protected] 2-Joaquim Goes; Lamont Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
[email protected] 1-Michael Claereboudt; College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman.
[email protected] 1-Sergey A. Piontkovski; College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman.
[email protected] 1-Adnan Al-AzriCollege of Agricultural and Marine Sciences, Sultan Qaboos University, P.O.Box: 34, Al-Khod 123, Sultanate of Oman.
[email protected] 3-Sharon L Smith;The Rosenstiel School, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149 USA.
[email protected]
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
Paper Code: 27767 IJOO
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Khalid A Al-Hashmi et al 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
Introduction The distribution of marine organisms, including phytoplankton, in coastal areas is greatly influenced by physical, biological and chemical processes that operate over a range of spatial and temporal scales [1, 2]. In general, coastal environments can be categorized into two main ecosystems based on their physical and hydrographic attributes [3, 4]; open water and semi-enclosed ecosystems. Semi-enclosed ecosystems include lagoons, estuaries and embayment and are characterized by restricted depths, higher inputs of nutrients and fresh water and higher turbidity due to tidal flushing and bottom sediment resuspension. Offshore open-water ecosystems are much deeper and hence less impacted by sediment resuspension and are generally not light restricted. In shallow semi-enclosed coastal embayments such as these, phytoplankton biomass, and species composition are largely controlled by light, temperature and nutrient availability [5, 6], which are not only highly variable but can have a huge impact on phytoplankton biomass production [7]. At certain times of the year especially during the inter-monsoon periods, stratification can exert a major control on light and nutrient availability [8,9] with potentially large consequences for cycle of phytoplankton abundance and biomass variability [10]. Phytoplankton species composition for Bhandar-Khayran (BK) and the offshore region of the Sea of Oman (OFF) over an interannual cycle have never been reported and neither compared before. In this study we investigate in the spatial and temporal variability of phytoplankton in these two environments, focusing on diatoms and dinoflagellates. Our investigation was driven by two working hypotheses: 1) the differences in physical properties and their annual cycle between the semi-enclosed and open ecosystem could result in large variations in phytoplankton dynamics between the two locations, and 2) the composition of native phytoplankton communities is different between the two locations, largely as a result of differences in environmental conditions.
Methods This study was carried out in coastal waters of Muscat near the embayment of Bandar Khayran, the largest semi-enclosed bay on the southern coast of the sea of Oman with an approximate surface area of 4 km2 and an average depth of 10 m. Two stations were sampled; one inside the Bay (BK, 23°31′454″ N, 58°43′614″ E); the other
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offshore (OFF, 23°35′342″ N, 58°38′123″ E) located in the open water represented conditions occurring outside of the direct influence of the embayment (bottom depth = 100 m) (Fig.1). The investigation was carried out from April 2010 until February 2011. Sampling was carried out twice a month, during which, seawater temperature, conductivity and depth were measured with an Idronaut-Ocean Seven 316 CTD probe fitted with an additional sensor for Chlorophyll a (Fluorescence). Surface values for temperature (SST) and in-situ fluorescence were averaged over the depth of the mixed layer (maximum gradient in temperature) for comparison with seawater chlorophyll a concentrations measured in water samples obtained from discrete depths. Seawater samples were also collected for nitrate, nitrate, phosphate, ammonia and silicate in acid-washed 50ml polyethylene bottles, frozen and analyzed later using a 5-channels SKALAR® Flow Access auto-analyzer according to methods in Strickland and Parsons, [11] as modified by the manufacturer of the analyzer [12]. Water samples (500 ml) for phytoplankton species identification and cell count determination were collected and preserved with 1% Lugol’s iodine solution. In the laboratory samples were allowed to settle in 20-mm diameter tubes. In order to concentrate the phytoplankton samples a reverse filtration cone fitted with a 1 µm pore size, Nucleopore filter® size was used to prevent loss of phytoplankton during the concentration process [13]. Whenever possible microscopy based taxonomic analysis of the concentrated material was undertaken to species level. The identification and taxonomic studies are based on the following references: [14, 15, 16]. Phytoplankton community structure recorded at the two stations was analyzed with nonparametric multivariate methods using Primer v.5® [16]. Prior to analysis the data were Root 4 transformed to reduce the effect of a very abundant species to the pattern. Bray-Curtis similarity index, which reflects changes in relative abundance as well as species composition, was used to obtain multi-dimensional scaling (MDS) ordinations. Community relationships were examined with two-dimensional plots. The similarity/permutation test ANOSIM [17] was used to establish statistical differences between stations, based on the Bray-Curtis similarities measure. Simper test (in Primer 5) was used to find similarities in phytoplankton community between stations. Simpson’s biodiversity index (in Primer 5) was used as a measure of biodiversity of phytoplankton. BIOENV procedure (in Primer 5) and principle component analysis (PCA) were used to correlate phytoplankton community structure with environmental variables (Temperature, salinity, oxygen nitrate, nitrite, silicate and phosphate). Paired t-tests were used to test significance in variables (dinoflagellate and diatoms) between linked data sets. Seasons were determined according to the strong seasonal signal created by the monsoons. Spring Intermonsoon (SIM) (April-June); South-West summer Monsoon (SWM) (July-September); Fall Inter-monsoon (FIM) (October-December); North-East winter Monsoon (NEM) (January-March).
Results Sea surface temperature (SST) varied from ~23 to 31oC and showed a bi-modal
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distribution with a primary summer SST peak in June and a secondary peak in October (Fig.2). The first 2-3oC drop in SST was recorded during the SWM months of July-August followed by the second steady drop from a high of ~31oC in the first week of Nov. (FIM) to ~23oC by mid Feb (NEM). At both OFF and BK, the salinity showed a slight decline during the late SWM upwelling period (July-August) (Fig.2). These conservative physical variables exhibited similar trends at both the locations in 2010-2011. Dissolved oxygen (DO) were highest (>7 ml l-1) during the peak SWM and during the NEM seasons dipping to values 0.05) (Fig.2). Patterns of nutrient changes at the two stations revealed two peaks in inorganic nitrate and phosphate concentrations during the SWM and NEM. Concentrations of these two nutrients did not differ appreciably between the two stations throughout the year, except during the SWM and NEM) when the concentrations were lower at OFF than at BK. (Fig.3). Patterns of ammonia and silicate fluctuations were not systematic and appeared to be independent of changes in physical processes and/or hydrographic conditions associated with the SWM or the NEM unlike changes observed for nitrate and for phosphate. Furthermore the concentrations of both ammonia and silicate differed appreciably between the two stations (paired t-test, n=22, p
