Behera, B.

Mishra, P.

Mohanty, P.K.

Pradhan, U.K.

Sahoo, R.K

English

NOPR

Indian Journal of Geo Marine Sciences Vol. 48 (03), March 2019, pp. 280-282    Technical Note   Changes in sediment texture by turtle mass nesting at Rushikulya rookery U.K. Pradhan1*, P.K. Mohanty2, P. Mishra1, B. Behera2 , & R.K Sahoo2 1National Centre for Coastal Research, NIOT Campus, Chennai, India 2Department of Marine Sciences, Berhampur University, Odisha, India *[E-mail: uma22pradhan@gmail.com] Received 02 August 2017; revised 08 January 2018 The sandy beach is one of the most rigorous habitats for organisms on earth; however, the number of species represented is limited due to sediment deposition, transport and erosion by wind, wave, tide, current and fluvial supplies. The nature of sediment type, compactness and its changes play a vital role in beach habitat and its stability. Several studies have been carried out by numerous researchers to find out textural behaviour and its variability along the coast over last decades1,2,3.  The beach sediment changes that occur naturally and due to human interference are well studied whereas the change of textural behaviour due to the mass nesting (arribada) of Olive Ridley Sea Turtles are underestimated at the nesting site along Odisha coast. Olive Ridley sea turtles are gentle, ancient reptiles adapted to life in the ocean, identified as endangering species under threat. At certain times of the year, egg-bearing females must come ashore to lay eggs deep in the warm sand of tropical beaches. The nesting site is influenced by several environmental factors, such as moisture of the beach, sediment characteristics, compaction, temperature range, human activity4 and favourable conditions as beach slope, wind direction and sea level2, which is observed in February to April , mostly for the site interest. The nest cavity dug with the rear flippers and ~ 100 to 150 eggs are laying and covered with sand5. Present study exhibit the changes on sediment environment due to arribada of Olive Ridley sea turtles at Rushikulya rookery (Fig. 1). Olive Ridley turtles migrate every winter to the Odisha coast and nest en mass at three major rookeries, viz., Gahirmatha, Devi, and Rushikulya. Conspicuously, the major nesting sites fall either on islands or unstable beaches adjacent to river mouths. Rushikulya rookery along south Odisha coast (Fig. 2), discovered as a world-wide mass nesting site for Olive Ridley sea turtle (Lepidochelysolivacea), extended approximate 5km of the beach located immediately north of the Rushikulya river mouth from Purunabandha to Kantiagada village6. A total of 3.09 lakh turtles nested in approximately ~1 km2 (~5 km ×  ~0.2 km) area of Rushikulya nesting beach, between 11th and 18th March 2015, with huge enmass nesting  about 1.23 lakh held on 14th March 2015 night (Report, 2015, Odisha Forest Department). It gives a clear idea that the subsurface sediment are dug by no of turtles for nesting in a small area, may changes the sediment characteristics of nesting beach (Fig. 1). Sediment samples were collected along four transects starting from  Gokharkuda to the Kantiagada for three positions of beach viz. foreshore (FS), midshore (MS) and backshore (BS) with an interval distance of 1 km as shown in Figure 2. A total of 24 samples collected during two periods as 10 days before and five days immediate after mass nesting of olive ridley sea turtle for the year  2015. The samples were washed with fresh water and dried at 70 to 80 oC in a hot oven. Washed sediments are treated by 10 to 30% of acid wash (HCl) to remove the carbon components from sediments. A weight of 100 g of dried sample was sieved at ½ Φ (phi) interval using automatic sieve shaker (AS 200) and A.S.T.M. (American Society for Testing and Materials) 20 cm diameter sieves for 10 minutes. The 8no sieves are used starting from mesh size 63µm to 1mm by separating ½Φ scale.  The logarithmic Udden–Wentworth grade scale was used for sediment classification7,8. The grain size of sediment was measured by Φ (phi) scale with the expression of logarithmic as Φ = - log2 D, where D is the grain diameter in millimetre. The statistical parameters viz. mean, sorting, skewness and kurtosis were calculated by Folk and Ward method9 using GRADISTAT Program10. PRADAN et al.: CHANGES IN SEDIMENT TEXTURE BY TURTLE MASS NESTING   281The sediment at all locations is unimodal in nature throughout the observations during both periods. Figure 3 depicts textural parameters and its changes during the two periods. A Significant difference in the mean size of sediment was found between before and after the mass nesting at the nesting beach. The mean size of sediment observed ranged from fine sand (2.8Φ) to very fine sand (3.4Φ) during and before the mass nesting (Figure 3a). After mass nesting, the entire nesting beach sediment changed to medium with a range of 1.1 to 1.8Φ. The sediment sorting (Figure 3b) was found well sorted (0.47Φ) to moderately sorted (0.96Φ) before the nesting due to continuous interactions of wind, wave, current and river flow. But the sediment observed moderately sorted (0.70 to 0.85Φ) after nesting, except at foreshore of transect-4 that was found moderately well sorted (0.62Φ). The sorting coefficients values increased after mass nesting, whereas the mean size decreased. The beach sediment varied from symmetrical (0.1) to coarse skewed (-0.2) before the mass nesting, and most of the sediment found as coarse skeweed. After the nesting, the skewness of sediment observed as symmetrical (0.09 to -0.1). Mostly, during both periods, the sediment was negatively skewed, except that at transect-4 (Figure 3c). Krutosis of beach sediment before nesting varied from platykurtic (0.88) to mesokurtic (1.10) while, mostly mesokurtic (0.91 to 1.10) at all locations after nesting (Figure 3d).  As a result, the mean size is decreasing whereas sorting, skewness and krutosis are increasing after the mass nesting. The study concluded that mass nestingof Olive Ridley Sea Turtles at Rushikulya have a significant impact on textural behaviour at nesting beach. The present study is helpful information useful in coastal habitat management further.  Acknowledgement Authors would like to thank the Department of Marine Sciences Berhampur University, Odisha and National Centre for Coastal Research, Chennai for all the supports and facilities.  References 1 Chauhan, O.S. Sediment dynamics at Puri and Konarak beaches, along northeast coast of India. Indian Journal of Marine Science, 1992, 21, pp. 201-206. 2 Barik, S., Mohanty, P.K, Kar, P., Behera, B. &  Patra, S. Environmental cues for mass nesting of sea turtles. Ocean & Coastal Management, 2014, 95, pp. 233-240 3 Pradhan, U.K, Mishra, P., Mohanty.,  P.K. & Behera, B. Formation, growth and variability of sand spit at Rushikulya River mouth, South Odisha coast, India. Procidia Engineering,2015, 116 pp. 963-970.  4 Mortimer, J.A. Factors influencing beach selection by Nesting Sea Turtles. In: Bjorndal, K. (Ed.), The Biology and Conservation of Sea Turtle. Smithsonian Institution Press, Washington, 1982, DC, pp. 45-53.  Figure. 3 — Sediment textural parameters a) Mean, b)Sorting, c) Skewness and Krutosis (d)  Figure. 1 — Turtle mass nesting at Rushikulya  rookery    Figure. 2 — Study map with sampling stationsINDIAN J. MAR. SCI., VOL. 48, NO. 03, MARCH 2019   2825 Pandav, B., Choudhury, B.C.& Shanker K., The Olive Ridley sea turtle (Lepidochelysolivacea) in Orissa: An urgent call for an intensive and integrated conservation programme. Current Science, vol. 75, no. 12, 1998, pp. 1323-1327. 6 Pandav, B., Choudhury, B.C. & Kar, C.S. Discovery of a new sea turtle rookery in Orissa, India. Marine  Turtle News Letter, 1994, 67, pp. 15-16 7 Udden, J.A. Mechanical composition of clastic sediments. Bull. Geol. Soc. Am, 1914, 25:655-744.  8 Wentworth, C.K. A scale of grade and class terms for clastic sediments. Journal of Geology,1922, 30, pp.377-392. 9 Folk, R.L.& Ward, W.C. Brazos River bar: a study in the significance of grain size parameters. Journal of Sedimentary Petrology, 1957, 27, pp. 3-26. 10 Blott, S. J. & Pye K. GRADISTAT: A grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth Surface Processes and Landforms, 2001, Vol. 26, No 11, pp. 1237-1248.              

Changes in sediment texture by turtle mass nesting at Rushikulya rookery

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Changes in sediment texture by turtle mass nesting at Rushikulya rookery

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