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

Abstract

This study investigates the diel vertical distribution and the diet of the most important chaetognath species found in the 0-50 m surface layer of a coastal area in the eastern Mediterranean during a 24-hour period in July 2004. Among the recorded chaetognaths, Sagitta enflata was the most abundant species (41.6%), followed by S. minima (32.5%) and S. serratodentata (20.8%). Those three species exhibited a "twilight migration" pattern, with only small differences among them. Vertical separation was found between S. enflata and S. minima. Both species preyed mainly on cladocerans, although copepods were the most abundant group in the zooplankton assemblage. The chaetognath species followed partially the diel vertical migration of their prey. S. enflata showed high feeding intensity at different times in both day and night, while S. minima fed more intensively at midday (12:00) and at dusk (20:00), and S. serratodentata in the morning (08:00). It seems that in order to coexist in an area of low productivity the chaetognath species follow the basic ecological rules of space, time and food-type separation, in order to reduce the inter-and intra-specific competition. The high preference of S. minima and especially of S. enflata for the cladocerans made them probably the most important predators of cladocerans during summer.

Behaviour-dependent predation risk in swimming zooplankters

“…Mobile prey that, through a distinctive signal, elicit the sensory hairs are attacked: the chaetognath makes a bout with a rapid flick of the tail, the prey is blocked with the grasping spines and swallowed (Feigenbaum 1991). Adult copepods and copepodites are the main food resource of adult chaetognaths (Øresland 1987), while younger developmental stages may prefer copepod nauplii (Feigenbaum 1991); on occasion, cladocerans can become the mainstay of chaetognaths (Kehayias and Ntakou 2008;Kehayias and Kourouvakalis 2010). Feigenbaum (1977) hypothesised that the movement pattern and the swimming speed of the prey might affect its predation risk.…”

Preliminary results on the feeding and gut content of Flaccisagitta enflata in coastal areas of İskenderun Bay (northeastern Mediterranean Sea)

“…Chaetognath species observed in the study area were evenly distributed in the Mediterranean Sea (Kehayias et al 1994(Kehayias et al , 1996Batistic et al, 2003;Duro and Saiz, 2000;Kehayias, 2003Kehayias, , 2004Kehayias et al, 2005;Kehayias and Ntakou, 2008;Kehayias and Kourouvakalis, 2010) and also in the İskenderun Bay (Terbıyık and Sarıhan, 2008;İşmen et al, 2003;Hazar, 2006;Terbıyık Kurt and Polat, 2013). (Terbıyık et al, 2007;Terbıyık and Sarıhan, 2008;Terbıyık Kurt and Polat, 2013).…”

“…(Terbıyık et al, 2007;Terbıyık and Sarıhan, 2008;Terbıyık Kurt and Polat, 2013). There are few studies on chaetognath feeding behaviour in the Mediterranean Sea and most of these studies reported data from the Aegean Sea (Kehayias et al, 2005;Kehayias and Kourouvakalis, 2010), Adriatic Sea (Batistic et al, 2003) and Western Mediterranean Sea (Duro and Saiz, 2000). The feeding ratios (FCR, NPC) determined in the present study are in agreement with the data reported from other regions of the Mediterranean Sea (Table 3).…”

“…Various studies on the distribution of chaetognath species have been conducted in world oceans (Itoh et al, 2006;Kosobokova and Hopcroft, 2010;Coston-Clements et al, 2009;Pierrot-Bults and Nair, 2010;Noblezada and Campos, 2008), especially in the Mediterranean Sea (Andreu, 1992;Kehayias et al 1994Kehayias et al , 1996Duro and Saiz, 2000;Kehayias 2003Kehayias , 2004Batistic et al, 2003;Terbıyık et al, 2007;Kehayias and Ntakou, 2008;Kehayias and Kourouvakalis, 2010). Besides studies on chaetognath distribution, the feeding and predation impact of chaetognaths on their prey has been the subject of several inadequate studies in the Mediterranean Sea (Kehayias et al, 1996;Duro and Saiz, 2000;Batistic et al, 2003;Kehayias, 2003;Kehayias et al, 2005;Kehayias and Kourouvakalis, 2010). These studies were conducted in the Western Mediterranean, Aegean and Adriatic Seas.…”

Chaetognatha of the Namibian Upwelling Region: Taxonomy, Distribution and Trophic Position

“…Other authors already discussed that plankton nets with 200 µm mesh size could have under-sampled the smaller Chaetognatha species such as S. minima [33]. It is well known that the mesh size in plankton nets is a trade-off between the gain in larger species and loss of the smaller ones [34]–[35]. Despite these difficulties, we can present extensive and important data about the vertical and horizontal distribution of the Chaetognatha species with an emphasis on the ontogenetic development as well as being able to determine the trophic position of selected Chaetognatha species in the Benguela Upwelling System (BUS).…”