Diel migration and feeding patterns of the chaetognath, <I>Sagitta friderici,</I> off the west coast of South Africa

Abstract

The vertical distribution patterns of adult and juvenile Sagitta friderici were investigated over a 48 h period, using samples collected at different depth strata with an RMT 1 x 6 net.Juvenile chaetognaths were generally found at depths of less than 50 m throughout the day and night, and exhibited limited diel migration patterns. Adults, on the other hand, migrated more extensively and were generally found below 50 m during the day and scattered throughout the water column or near the surface at night. Using the mean depths at each sampling time, the migration patterns of adult chaetognaths closely followed that of the large calanoid copepods. Juvenile chaetognaths, on the other hand, showed no significant correlation with any group of copepods. The greatest proportion of chaetognaths with food in their guts were not found at the depths of maximum cope pod abundance, suggesting that the chaetognaths had not been feeding at the depths where they were caught. There was little evidence of a diel feeding rhythm, with no significant difference between the number of prey per chaetognath during the day or night. The majority of food items ingested were cope pods (85.7%), while cannibalism on smaller chaetognaths occurred in 2.4% of the samples. The size of copepods consumed by adult chaetognaths was estimated from the width of the copepod mandibular blade, and was found to range from 0.16-1.96 mm prosome length. Although there was a large range of prey sizes which any given predator could consume, there was a clear trend of increasing prey size with increasing predator size. The energetic equivalent of ingesting a single cope pod represented 47.4% of the body carbon of the juveniles, but only 16.7% for the adults. Consumption of two or more copepods increased this to 30.3% body carbon of the adults, but cannibalism on smaller chaetognaths represented an average of 46.8% of adult body carbon. Assuming equal handling costs, this implies that cannibalism is energetically much more advantageous for the adults than consuming copepods. Digestion times of cope pod prey items were estimated from an exponential equation relating digestion time to temperature using values from the literature for six different chaetognath species. This yielded an ingestion rate of 0.5 copepods chaetognath-I d-', which resulted in 1.0-5.3% ofthe cope pod standing stocks or 2.4-14.0% of the copepod production being consumed per day by the Sagitta friderici population.

Distribution, abundance and biomass of Chaetognaths off São Sebastião region, Brazil in February 1994

“…Literature indicates, less than 30% of chaetognaths are found with 1-3-preys in their guts (Sullivan, 1980;Stuart & Verheye, 1991;Vega-Pérez & Liang, 1992, Liang & Vega-Pérez, 1995. In this study, in average, less than 10% was found with food in their gut.…”

Diel vertical migration and feeding of chaetognaths in coastal waters of the eastern Mediterranean

“…Satiation as the major factor contributing to the midnight sinking of chaetognaths has been reported for several species (Pearre 1973(Pearre , 1974Stuart & Verheye 1991;Gibbons 1994). Our results on the vertical distribution, the feeding intensity and the presence of unidentified food, point that satiation was probably among the reasons why chaetognaths left the surface to disperse and distribute deeper at midnight: after the intake of large quantities of food at 20:00, the specimens of S. enflata sank to deeper layers to digest their food (24:00) and this was confirmed by the increase in the proportion of the unidentified food remains in the gut contents.…”

“…The diel vertical migration (DVM) of zooplankton is a common phenomenon in all aquatic ecosystems, and chaetognaths have also adopted this behavior at least partly for feeding purposes (Pearre 1973;Stuart & Verheye 1991;Gibbons 1992Gibbons , 1994Øresland 2000). Despite the great importance of this phenomenon, there are only two references about the diel migration of chaetognath species such as Sagitta enflata (Grassi, 1881), S. minima (Grassi, 1881), S. setosa Müller, 1847 and S. friderici Ritter-Záhony, 1911 in the Mediterranean (Pearre 1974;Andreu 1992), while there are no attempts to relate this behavior to feeding.…”

Vertical distribution and trophic structure of the macrozooplankton in a shallow temperate estuary (Ria de Aveiro, Portugal)

“…Vertical distribution patterns of zooplankton are complex phenomena involving several categories of behaviours that change from species to species, and even from individual to individual, and depend on factors such as endogenous rhythms, age, sex and spawning (Wooldrige and Erasmus, 1980;Hammer, 1981;Orsi, 1986;Saint-Jean and Pagano, 1990;Stuart and Verheye, 1991;Hays, 2003). Vertical migrations of zooplankton are nearly ubiquitous in both freshwater and marine systems and thus are well documented in the literature (Enright, 1970;Schwassmann, 1971;Decoursey, 1983;Lampert, 1989;Neilson and Perry, 1990;Hays, 2003).…”

“…Many evolutionary hypotheses have been developed to explain the mechanisms behind zooplankton vertical migrations. Predator evasion (Zaret and Suffern, 1976;Gliwicz, 1986;Harding et al, 1986;Simard et al, 1986;Dodson, 1988;Bollens and Frost, 1989a,b;Giske et al, 1990;Neill, 1990;Stuart and Verheye, 1991;Yamaguchi et al, 2004) and longitudinal transport control (Brookins and Epifanio, 1985;Epifanio, 1988;Hill, 1991aHill, ,b,c, 1995 are currently the most favoured hypotheses. Enright (1977) also suggested that vertical migration provides metabolic advantages.…”