الفهرس Only 14 pages are availabe for public view
 |  | from | 177 |  |  |
| | | from | 177 | | |
Abstract
The present study deals with the brachyuran crabs of the Suez Canal as a very important group and highly effective in the marine ecosystem of the canal. The present study yielded the following results:
1- A total of ten species of brachyuran crabs were recognized and identified during the present survey. They included ten genera belonging to seven families. The families Leucosidae, Portunidae and Majidae were represented each by two species while the other four families, Goneplacidae, Grapsidae, Pilumnidae, and Xanthidae each include just one species.
2 – Epibiota of the brachyuran crabs collected from Suez Canal during the present study comprised 71 taxa, 43 taxa were epiflora while the other 28 were epifauna. The epiflora of the brachyuran crabs were represented by four groups: diatoms, dinoflagellates, blue green algae and green algae. Diatoms were represented by 30 taxa, followed by blue green algae (7 taxa), dinoflagellates (4 taxa) and green algae (2 Taxa). Epifauna of the brachyuran crabs collected from Suez Canal during the present study comprises 28 species belonging to 8 different animal groupings of polychaetes (7 species), cnidarian hydrozoa (5 species), bryozoans (4 species) tunicates (4 species) sponges (3 species), suctorian Protozoa (2 species), barnacles (2 species), and molluscs (one species). A total of 16 epibionts were identified to the species level, where the remaining 11 taxa were identified only to the genus level.
3 – Brachyuran crabs of the Suez Canal can be considered as a Red Sea immigrant fauna to the Suez Canal. The latter can be considered as a link in the process of transportation between the two seas; in some cases it acts as a barrier against migration process. Moreover Suez Canal can be considered as a habitat itself.
4 – During the present study paralytic shellfish poison was not detected from the Suez Canal 14 Brachyuran crabs.
5 - The fishery of brachyuran crabs in the Suez Canal is mainly concentrated in the area of the eastern and western coasts of Bitter Lakes. They are represented by a single edible species, the swimming crab Portunus pelagicus that occurs with a considerable abundance in the catch. On the other hand, there are about twelve other species of brachyuran crabs that were being fished as by catch and had a negative impact on fishery effort and fishery nets.
6 - In M. subgranulata, there was a predominance of males in all months, except in October where the ratio was 1:1. However, in S. aspera, the sex ratio was more or less constant throughout the season, except in February and March where females exceeds males. There were no seasonal variations for the two species.
7 - M. subgranulata has a prolonged breeding season that commences in April and terminates in October. S. aspera followed the same pattern but the breeding season started from May and extended until December.
8 – In M. subgranulata, 50% of the females at about 32 mm carapace width were mature and the smallest mature female had a carapace width of 24 mm.In S. aspera, female ranged from 26 to 60 mm carapace width. The estimated size for 50% sexually mature female was 36 mm carapace width and the smallest mature female was at size of 28 mm carapace width.
9 - In M. subgranulata, the lowest gonad index was discernible in September and February for males and in March for females while the highest value was observed in March for males and in July and June for females. For males S. aspera the lowest average value was in October but values showed an increase during the summer months May– July In females, the highest peak of gonadosomatic index was in August and the lowest was noticed during February - April
10 - For M. subgranulata, the total number of eggs ranged from 10332 to 58760 with an average of 27459 eggs per female crab. The smallest ovigerous female was at 24.8 mm carapace width, 5.82 g total weight. On the other hand, the largest ovigerous female had a width of 37.3 mm, 25.37 g total weight.
In S. aspera, the total number of eggs ranged from 2351 to 13600 with an average of 5149 eggs per female crab. The smallest ovigerous female was at 28.7 mm carapace width, 14.3g total weight while the largest female was at 51.3 mm carapace width, 81.34 g total weight.
11 - In M. subgranulata, no individuals in post moult stages were observed during the period of study. In males of S. aspera moult activity was observed in almost all size classes. They do not undergo a terminal anecdysis, but continue moulting even though at longer intermoult intervals (Figure 5.10). In females, the case is not the same; they have a terminal ecdysis where it was at 42 mm carapace width in S. aspera.
12 - In M. subgarnulata, the size range of the population varied between 32 and 52 mm carapace length for males and between 30-52 mm CL for females. On the other hand, males S. aspera showed a wider range (25 to 75 mm CL), while those of females had a smaller one (30 –70 mm CL).
13 - Recruitment to the population of M. subgarnulata started in July 2002 and September 2002. In S. aspera the recruitment of population was observed in December 2002.
14 - Isometric growth was observed for males and females of both species where the value b was more or less equal to 1.
15 - Positive allometric growth was observed in males and females of M. subgranulata between carapace width (on one side) and chela length and claw length (on the other side). Negative allometric growth was found between carapace width (on one side) and claw width, claw breadth and abdomen width (on the other side) of both sexes. Penis length also showed a negative allometric growth in males. The same pattern could be observed in S. aspera.
16 - Males of both species showed a marked positive allometric growth after maturity, but this was not the same case in females.