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Ecomorphological adaptation in three mudskippers (Teleostei: Gobioidei: Gobiidae) from the Persian Gulf
and the Gulf of Oman (Hydrobiologia)
Gianluca Polgar*, Mehdi Ghanbarifardi, Salvatore Milli, Ainhoa Agorreta, Mansour Aliabadian, Hamid Reza
Esmaeili, Tsung Fei Khang
*corresponding author: Universiti Brunei Darussalam, Faculty of Science, Environmental and Life Sciences
Programme, Jalan Tungku Link BE1410, Brunei Darussalam; [email protected]
Online Supplementary Information (Online Resources): supplementary text
Supplementary text S1: study sites, sedimentological and geomorphological overview
The Persian Gulf is a shallow, semi-enclosed marginal sea situated among the Arabian Peninsula in the west, the
Taurus Mountains in the north, and the Zagros Mountains in the east and northeast. It is connected with the Gulf of
Oman and the Indian Ocean through the Strait of Hormuz, and extends for about 1000 km in a NW-SE direction,
having a width varying from a minimum of 56 km near the Strait of Hormuz to a maximum of 338 km (Fig. 1). Its
coastal topography is mountainous along the east coast, and flat along the west coast. This is also reflected in its
bathymetry, with a shallow bank area < 20 m deep in the southwestern sector, and a 40-80 m deep trough in the
eastern sector, extending in a northwest direction along the east coast (Fig. 1). Beyond the Strait of Hormuz, the sea
bottom drops quickly to > 2000 m into the Gulf of Oman (Fig. 1). The Persian Gulf shows a great spatial variation in
salinity and temperature due to its arid climate (Clarke & Keij, 1973; Reynolds, 1993). The surface winds in the
Gulf are prevailingly westerly or north-westerly throughout the year. These winds generate wave and related
longshore currents propagating along the east coast where barrier islands and spits are developed. The surface winds
in the Gulf of Oman are influenced by the Indian monsoon system, which seasonally reverses between northwesterly in winter (October-May) and south-easterly in summer (June-September). Water circulation in the Gulf
basin is strongly influenced by its morphology and by high temperatures and evaporation rates. Generally, due to
high evaporation rate, surface waters are denser in the northern sectors of the Gulf where they sink to the bottom,
flowing out through the Strait of Hormuz and spilling intermittently into the deeper and less dense waters of the Gulf
of Oman. This outflow induces a surface inflow of less dense Indian Ocean waters through the Strait of Hormuz,
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which is deflected along the east coast, forming a northward-directed cyclonic circulation and producing an inverseestuarine type water exchange (Rochford, 1964; Wyrtki, 1973; Reynolds, 1993; Bower et al., 2000; Prasad et al.,
2001; Swift & Bower, 2003). The Persian Gulf has an oscillation period of 21.6-27 hours for tidal waves (Defant,
1961). This produces semi-diurnal and diurnal tidal waves that generate resonant interactions in the basin, leading to
a system of amphidromic points and maximum tidal excursions in the northern sector of the Gulf (up to 6 m during
spring tides: data of Jan 2014; National Cartographic Center, Hydrographic and Tidal Department, Teheran,
http://www.ncc.org.ir/; Online Resource Tab. S2). This peculiar water circulation and the arid climate determine
high salinity conditions (~ 40 ppt), which are associated with impoverished Indo-Pacific marine communities
(Purser, 1973).
Supplementary text S2: sediment analysis.
Sediment samples were oven-dried at 100°C for 24 hours to constant weight, and subsamples of 500 g were
analysed for grain size. Sieve analysis was performed with a set of 11 sieves (mesh size: 24.4, 19.1, 12.7, 9.53, 4.76,
2.38, 1.19, 0.594, 0.297, 0.150, and 0.074 mm). The percent difference between the total weight of the sieved
materials and the initial weight of each sample was 0.2-0.8%. Subsamples (50 g) of all the passing fractions at 0.074
mm (#200 sieve) were analysed with ASTM 152H soil hydrometers. Measurements were taken at fixed time
intervals (1, 2, 4, 8, 16, 30, 60, 120, 240, 480, and 1440 min) applying temperature, zero and meniscus corrections,
and assuming a conventional specific gravity of soil particles (Gs) = 2.7 (ASTM 2014a,b). Sediment grain-size
curves (passing fractions) were plotted, and coefficients of curvature (Cc) and of uniformity (Cu) were calculated for
sands (Holtz & Kovacs, 1981). Particle-size retained fractions were then classified following the USCS scale
(Unified Soil Classification System; Holtz & Kovacs, 1981; Online Resource Tab. S3), and samples classified
plotting them on the ternary grain-size diagram of Shepard (1954, modified by Schlee, 1973) built with SEDPLOT
(Poppe & Eliason, 2008).
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