Document Details
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Document Type |
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Thesis |
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Document Title |
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SOME BIOLOGICAL ASPECTS AND POPULATION DYNAMICS OF THE CORALLIVOROUS GASTROPOD DRUPELLA CORNUS ON THE JEDDAH COAST. بعض النواحي البيولوجية وديناميكية جماعة أكلات المرجان |
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Subject |
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Faculty of Marine Sciences |
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Document Language |
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Arabic |
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Abstract |
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Drupella are found on coral reefs throughout the tropical and subtropical shallow waters of the Indo-Pacific region including the Red Sea. Drupella are muricid gastropod, obligate corallivorous and their population outbreak can cause significant coral mortality. In this study, surveys were conducted along Jeddah coast to detect the distribution and to identify Drupella species on Jeddah coast. According to morphological characteristics and radula morphology, there was only one species of Drupella was recorded along Jeddah coastal water which is Drupella cornus. These surveys along Jeddah coast also revealed that densities of Drupella were less than dangerous level of Drupella outbreaks (≥3individuals/m2), even high densities of Drupella were observed during study population dynamics of Drupella cornus because of large aggregations of recruits and juveniles of Druplla. Also, these surveys revealed that Bohaitat, Bayadah and Entrance of Obhur Creek are having the highest mean densities of Drupella compared to other studied sites on Jeddah coast.
Belt transect surveys were conducted at two sites in Jeddah coast (Bohairat and Bayadah) during April, August and December 2016 to study abundance, size frequency distribution and prey preference of Drupella cornus. A total of 956 snails were collected from 55 clusters where the majority of them (78%) were found on live coral. We found by using ANOVA of more than two varibles (site, sampling period and age classes) that there were no significant differences in snail densities among sites and among the sampling periods but there was significant differences (df=2, P=0.01) in the individuals number of age classes (recruits, juveniles and adults). Jevniles constitute 69% of total number of D. cornus collected in this study followed by recruits 21% and finally by adults 10%. Nearly all recruits and juveniles were restricted to branching live corals whereas adults associated with several substrates (e.g. live coral, coral fragment and rock) and coral colony growth forms (e.g. branching and massive corals). Size frequency distribution implied that new recruits constituted clear separated age cohort in the sample April 2016 at Bohairat. Prey preferences of Drupella cornus in field have studied with respect to prey availabilty. Resource selection ratios revealed that species of Acropora are preferred prey to D. cornus at the two study sites, whereas Pocillopora and Stylophora were attacked by Drupella cornus because of their high availability.
Six coral associated crabs were examined for predation on egg capsules of D. cornus under laboratory conditions for 48 hours. High predation by consumption of 90% (±14.14, n=2) of initial egg capsules have been observed by Cyclodius nitidus, compared to very low consumption of 5% (±7.1, n=2) of initial egg capsules by Trapezia digitalis. In the case of Trapezia bidentata, damaged capsules have been observed with mean 30% (±14.14, n=2) of initial egg capsules during 48 hours, but none of the damaged capsules was opened. There was no evidence of predation or signs of attacks observed on egg capsules of D. cornus caused by the other three examined crabs, Trapezia cymodoce, Cymo melanodactylus and Pseudoliomera speciosa.
Maturity stages of the gonads were investigated by histological observations of its gonads (testis and ovary). Five stages were distinguished and described as: early active, late active, ripe, partially spawned and spent phase. The external color of ovary was white or creamy while that of the testis was orange or yellow at ripe phase. Shell length of Drupella cornus at first maturity were13.3 mm in males, and 13.7 mm in females. Spawning behavior of D. cornus was observed in the situ and in rearing tanks. Spawning of D. cornus occurs over the year with peaks during April - July 2016 and October 2016 - January 2017. Drupella cornus has kidney- shape, with distinct concave and convex sides. Results also showed that there are significant positive relationships (P<0.0001) between shell length classes (based on age of the snail) and size of egg capsule and between shell length classes and number of fertilized eggs inside each capsule. While fertilized egg has spherical shape, with diameter ranging 120 -180 µm, and there was no significant variations in egg diameters of shell length classes. |
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Supervisor |
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Prof. Hassan Abdel Meguid Ramadan |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1440 AH
2019 AD |
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Added Date |
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Sunday, April 7, 2019 |
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Researchers
| جعفر عمر باعمر | BaOmar, Gaafar Omer | Researcher | Doctorate | |
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