Monthly variation of gonadic stages of Sagitta euneritica (Chaetognatha) in The Bahía Magdalena lagoon complex, Baja California Sur, Mexico

Abstract

The abundance and the proportion of gonadal stages of the chaetognath Sagitta euneritica in the lagoon complex Bahia Magdalena (CLBM), Baja California Sur, Mexico, was determined. The sampling was made during March, June, July, August, September, and November 1982. Sagitta euneritica was the species numerically dominant and most widely distributed species, with 81% of the total abundance of the chaetognaths, and was found mainly in the juvenile stages 0 (34%), I and II (21% and 40%). The stages III and IV were found in low percentages, implying that mature organisms are likely found in the immediate coastal zone. The size-structure analysis showed small organisms from June to August, increasing in September and November; consequently that the CLBM can be the area acting as a breeding area for this species. The analysis of variance between the percentages of the stages by area and by month showed that in March the organisms of stage I were significantly different (p = 0.05). Individuals of S. euneritica were found in a wide temperature range from 15.5 to 29.5 °C. The maximum number of chaetognaths in the Magdalena Bay area was related to the cold water temperature and the maximum in the area of Almejas Bay was associated with a gradual increase of the water temperature in summer-autumn. The distribution of S. euneritica in the CLBM tends to be heterogeneous, also with a high size-structure of organisms predominantly immature, as a survival strategy of the species.