Life Cycle, Abundance, Gonadic Stages and Size Frequency Distribution of the Chaetognath Sagitta elegans Verrill in the North-eastern Irish Sea

• Published in: Estuarine, coastal and shelf science Vol. 37; no. 1; pp. 15 - 25
• Main Author: Alvarez-Cadena, José Nicolás
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 1993; Elsevier
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Demecology; Fundamental and applied biological sciences. Psychology; gonadic stages; Irish Sea; life cycle; Marine; Protozoa. Invertebrata; Sagitta elegans; Atlantic Ocean; North Atlantic; Irish Sea; ANE, Irish Sea; gonadic stages; Irish Sea; life cycle; Sagitta elegans; Marine environment; Sexual maturation; Chaetognatha; Reproduction; Life history; Seasonal variation; Body size; Population structure; Invertebrata; Zooplankton; Ecological abundance
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1006/ecss.1993.1038

Plankton was collected to the east of the Isle of Man from February 1986 to November 1987. Sagitta elegans overwintered mainly as gonadic stage II, with a small number of stages I and III. Stage III became dominant in the population in March; animals in stage I were the main component of the population in April with the onset of spawning. Small animals in stage I of c . 2 mm length were recorded from April until the end of the summer. Animals of this species died after spawning and no mature specimens stage III were caught by mid-autumn. From the present data a 1 year life cycle is proposed for Sagitta elegans in the study area. However, in June-July of both study years a second important spawning took place which was more pronounced in 1987. More work is needed to investigate whether this second spawning peak was due to early maturation of animals born 3 to 4 months earlier. S. elegans was more abundant in summer and attained a maximum length of 23·6 mm. Minimum size was found to be 1·2 mm and animals hatched in March-April reached a mean size of 11 to 13 mm by November in both study years.