Feeding behaviour of Centropages typicus in calm and turbulent conditions

Abstract

Feeding of the copepod Centropages typicus on the oligotrich ciliate Strombidium sulcaturn was studied in the laboratory under controlled, measured conditions of grid generated small scale turbulence. High levels of turbulence, F (kinetic energy dissipation rate) = 2.9 X 10-2 to 3 X 10-' cm2 s3, increased the clearance rate of C. typicus feeding on S. sulcatum by up to a factor of 4 in comparison to calm water values. At a level of turbulence of 4.4 cm2 s -~, we observed a drastic decrease in clearance rates to values equivalent to those in calm water. We suggest an explanation for the observed changes in predation rates with levels of turbulence. Video recorded observations of the behaviour of free swimming C. typicus conducted in calm conditions suggest that the copepod uses a cruising strategy to search and encounter S. sulcatum. In the presence of this cillate, C. typlcus increases the proportion of time spent swimming at a mean velocity of 3.5 mm S-': from 49.5'% in filtered seawater without ciliates to 79.5% in the presence of S. sulcatum (1 cell ml-l). Furthermore, a qualitative change of the swimming behaviour is triggered by the presence of the ciliate, resulting in an increased proportion of time spent slow swimming in a 'helical' mode. Our results suggest that high levels of small scale turbulence substantially increase predation rates of crunsing copepods.

Effects of small‐scale turbulence on copepods: The case of Oithona davisae

“…Although predicted encounter rates under turbulence increase monotonically and would anticipate larger feeding enhancements at higher turbulence intensities, our study has shown quite a different pattern for O. davisae: from positive enhancement at low turbulence intensities and the absence of net effect at intermediate intensities to the presence of pernicious net effects at the highest turbulence intensities. A similar pattern of turbulence-dependent feeding response has been observed previously in other ambush copepods (Saiz et al 1992;Saiz and Kiørboe 1995;Caparroy et al 1998) and in fish larvae (Landry et al 1995;Dower et al 1998). It seems to be the result of enhanced encounter and the action of, above certain threshold turbulence intensities ( Ͼ 10 Ϫ3 cm 2 s Ϫ3 for O. davisae), offsetting detrimental effects on feeding, such as lower perceptive performance or a lower capture success , which would impair the ability of the copepod to detect, attack, and ingest encountered prey.…”

“…Presently, direct empirical evidence has been demonstrated for only two similarly sized, related genera of copepods-Acartia (e.g., Saiz et al 1992;Saiz and Kiørboe 1995) and Centropages (Caparroy et al 1998)-which responded similarly to turbulence. On the contrary, Lagadeuc et al (1997) reported that the vertical distribution of several copepod species was affected differently by mixing, suggesting species-specific responses to turbulence.…”

“…This study was supported financially by the Spanish grants SERET (MAR98-0854) and ZOOTRANSFER (REN2001-1693) and by the Programa Ramón y Cajal through a contract to A.C. scales and influence the encounter rate of smaller sized predators, higher turbulence intensities can begin to interfere with their detection and capture mechanisms (MacKenzie et al 1994;Kiørboe and Saiz 1995), resulting in a trade-off between benefits and detriments. Thus, a few studies have observed negative effects on the feeding of both fish larvae (Landry et al 1995;MacKenzie and Kiørboe 2000) and copepods Caparroy et al 1998) at relatively high levels of turbulence ( Ͼ 10 Ϫ1 -10 0 cm 2 s Ϫ3 ), exhibiting a dome-shaped feeding response to turbulence intensity.…”

“…For simplicity, when effects were not statistically significant, they were plotted on the zero line. Centropages on S.s., Centropages typicus feeding on the ciliate Strombidium sulcatum (Caparroy et al 1998); Acartia on S.s., Acartia tonsa feeding on the ciliate Strombidium sulcatum ; Oithona on Oxy, Oithona davisae feeding on Oxyrrhis marina (this work); Acartia on T.w., Acartia tonsa feeding on the diatom Thalassiosira weissflogii ; Temora on T.w., Temora stylifera feeding on Thalassiosira weissflogii (unpubl. data).…”

“…In the last 15 yr, both laboratory experimentation (e.g., Saiz 1994;Landry et al 1995;Caparroy et al 1998) and modeling exercises (e.g., Kiørboe and Saiz 1995;Visser and MacKenzie 1998) have demonstrated that the increase in particle contact rates from turbulence affects such processes as aggregate formation and planktonic trophic interactions. Theoretically, the (root mean square) turbulence velocity adds to the particle relative motion, enhancing encounter as an inverse function of the velocity difference between particles (Rothschild and Osborn 1988;Kiørboe and Saiz 1995).…”