Sedimentary characteristics of some island beaches and their effects on nesting numbers of marine turtles, Red Sea, Egypt.

Abstract

The impact of beach sands on nesting numbers (NN) of two species; the hawksbill Eretmochelys imbricate and the green turtle Chelonia mydas on three Egyptian Islands was syudied. The influence of grain size on nests number varied across the three island beaches. The study revealed that gravel fraction showed low values, sand fraction of sediments has heights values and lower abundance of the fine sediments at three studied beaches. Moreover, the average percentage of biogenic content (66.90%, 68.02%, and 60.17%) was recorded in small Giftun, big Giftun and Zabargad beaches respectively.Correlations (Pearson's correlation) among sediment texture, mean grain size (Mz), sorting, biogenic content and number of nests of three studied islands showed that the NN have a positive correlation with biogenic content and no correlation was found between NN and Mz in the studied beach sediments at the three Islands. The Hierarchal Cluster Analyses (HCA) dendrogram of sediment type, grain size characteristics, biogenic content and number of the nests (NN) in beach sediments along the three studied Islands are supported by Pearson's correlation coefficient.The condition of the offshore approaches seems to be important in choice of a nesting beach, for example, the tourism activities at Giftun Island make Hawksbill turtles vulnerable to these activities. In contrast, Green turtles at Zabaragd Island seem to prefer beaches of fine sediments or sub-tidal reefs.