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Vidar Øresland, Abundance, breeding and temporal size distribution of the chaetognath Sagitta setosa in the Kattegat, Journal of Plankton Research, Volume 5, Issue 4, 1983, Pages 425–439, https://doi.org/10.1093/plankt/5.4.425
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Abstract
During a hydrographical survey in the northern Kattegat, 1975 to 1977, vertical plankton hauls were taken monthly at four stations between Göteborg and Frederikshavn. Hydrographical parameters were measured at 10 stations along the transect. Sagitta setosa J. Mailer was by far the most dominant chaetognath (99% of individuals). Sagitta elegans Verrill and Eukrohnia hamata Möbius occurred simultaneously with inflowing high saline water during autumn and winter. The transport of S. setosa by currents was an important factor influencing the abundances and the breeding period in the Kattegat. The abundance peak in 1977 was only one fifth of that found in 1975. The start and the duration of the breeding period (defined as presence of stage 1 individuals <3 mm) varied between the three years. Breeding occurred between the middle of July and December with a peak in August and September. Changes in size distribution were small during winter and spring, possibly due to low temperatures. S. setosa has probably a life span of one year in the Kattegat. Some earlier results regarding the number of breeding periods of S. setosa per year are questioned. It is proposed that the number of generations per year of S. setosa and the start and the duration of the breeding period(s) in western European waters should be regarded as an open question until further information is available.