Résumé:
This preliminary study was carried out at the Sidi-mejdoub beach in the town of Mostaganem, and focuses on some ecological and morphometric parameters of the marine worm, genus Ophelia, (Opheliidada, polychatea), living at the intertidal sandy substrate part of the Sidi-mejdoub coast. In this concept we adopted the random method of quadrat of (25x25 cm) side, however 700 specimens of annelids were collected monthly from the month of February to June 2023, that is to say two seasons. The results show a low density of 20 ind/m². The granulometric nature of the site reveals a predominance of the average coarse fraction (> 250 μm). The organic matter value was 0.90 g. The y' regression formula including both sexes for the length (mm) - weight (g) relationship proved to be y = 7E -05x2.3981 indicating allometric growth, confirmed by Student's t test with P<0.05) and with the observed (t) value greater than (t -theor=1.96) for a 5% risk.
The monthly variation in annelid growth was significant; the single-factor ANOVA (month-wise) showed a highly significant difference with (Student t test, p< 0.05). Over the study period, the Ophelia population detected individuals ranging in size from [07.00 to 55.00 [mm. On the other hand, the size frequency distribution is characterized by a single mode, with a length between [23.00 -25.00 [mm. The structure shows more than 50% of individuals with a length ranging from [19.00-.31.00 [mm, with an absence of juveniles shorter than 07.00 mm. Adult individuals can reach a length of 55.00 mm.The reproductive aspect of Ophelia females shows a significant presence of free eggs in the coelomic fluid.
