الفهرس 
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Abstract
Summaries
English Summary
Sexual reproduction of corals is one of the essential processes for the stability and integrity of coral populations. Hence, this study was conducted to assess the reproductive and spawning patterns of two reef-building scleractinian corals belonging to genus Acropora, namely Acropora cytherea and Acropora tenuis inhabiting Hurghada, northern Red Sea. Histological and in situ examinations were carried out on 16 tagged colonies from the two coral species (8 for each species) in two selected shallow reef sites located in the north and south of Hurghada.
Coral fragments were collected monthly from March 2018 to June 2018 and from October 2018 till May 2019 for dissection and histological analyses. Data of the dissecting microscope examination of a decalcified colony branches of both studied Acropora spp. revealed that gonads in both species are re-arranged in similar patterns, oocytes are found to be in long thick strings with variability in shape that may be rounded or oval, while spermaries were found in short to long thin strings. Oocytes were generally round in shape as in Acropora cytherea to oval as in Acropora tenuis respectively.
Histological observations confirmed the hermaphroditism activity for both species through developing their male and female sexual gametes in separate mesenteries in the same polyps.
Seasonal changes in the mean diameter of mature oocytes was averaged through the reproductive seasons respectively for both populations of A. tenuis and A. cytherea sampled over 12 months.
Only 4 colouration patterns were observed from the investigation of fracturing live branches in tagged colonies in both Acropora spp. matching with the histological examination in both species that advert for the existence of 4 gametogenesis developmental stages (I, II, III, IV) and each stage extended for around 2-3 months.
The present results indicated that A. cytherea and A. tenuis were hermaphroditic broadcast spawners with a single annual gametogenic cycle (7 months) that began in October 2018 and terminated in April 2019, and both oogenesis and spermatogenesis were occurring for 7 and 6 months, respectively.
oocytes stage I in the two Acropora species was firstly appeared in the middle of autumn season (October and November 2018), In this stage the oocytes characterized by creamy colour. The mean (±SD) diameters of oocytes stage I ranged between 272±2.68 and 310.60±5.15 µm while Stage II of oocytes, dominated in December 2018 and January 2019 and were found to be round to oval in shape with mean (±SD) diameter ranged from 322.40±3.24 to 358.70±3.77 µm. The oocytes in stage II appeared with coloration gradient from yellow to orange. Through stage III
the oocytes sizes have increased, the mean (±SD) diameter ranged from 373.20±3.77 to 391.90±4.65 µm. The peak of this stage formation was observed in March 2019. Finally in April 2019 oocytes development completed when the maturity stage IV was noted in 100% of the investigated colonies in both species and the mean (±SD) oocyte diameter varied between 415.60±2.30 and 419.70±2.62 µm. According to our observations on oocytes maturation the oocyte colour was changed from pale pink to pink.
Regarding to spermaries development of Acropora cytherea and Acropora tenuis, Stage I began as early as in November 2018. The mean (±SD) diameters of this stage ranged from 61.57±0.50 to 83.06±1.08 µm. Stage II of spermaries was commonly observed in December 2018, with moderate increase in numbers and size. Stage III of spermaries reached its ceiling in March 2019, with mean (±SD) diameters varied between 141.90±2.10 and to 163.30±2.90 µm. Stage IV of spermaries development was recorded in March 2019 and spiked to its highest level in April 2019 as 100% of colonies recorded this stage.
Both species exhibited conspicuous spawning synchrony amongst colonies of the same species, and the time of spawning was mostly correlated with lunar cycle and photoperiod (day length). They spawned around the full moon in April 2018 and 2019. A. Cytherea spawned two days before the full moon (30 Apr)
in April 2018 and one day before the full moon (19 Apr) in April 2019. A. tenuis spawned one day before the April full moon in 2018, while in 2019 it spawned in the full moon day (19 Apr) and one day after the full moon. This study provided information that will aid in future coral reef restoration and management. Further research on reproduction of additional coral species is required in order to provide a better perspective of reproductive patterns in Red Sea scleractinian corals.