Prey switching behaviour in the planktonic copepod Acartia tonsa

Abstract

The copepod Acartia tonsa has 2 different prey encounter strateg~es. It can generate a feeding current to encounter and capture immobile prey (suspension feeding) or it can sink slowly and perceive motile prey by means of mechanoreceptors on the antennae (ambush feeding). We hypothesized that A. tonsa adopts the feeding mode that generates the highest energy intake rate; i.e. that prey selection changes according to the relative concentrations of alternative prey (prey switching) and that the copepods spend disproportionately more time In the feeding mode that provides the greatest reward. Based on earlier observations, we also hypothes~zed that turbulence changes food selection towards motile prey. We tested these hypotheses by examining feeding rates and behaviour in adult females of A. tonsa feeding in mixtures of 2 prey organisms, a diatom (Thalassiosira welssflogjj) and a ciliate (Strombidium sulcatum). Our data demonstrate prey switching in A. tonsa, both in terms of behaviour and in terms of feeding rates on the alternat~ve prey. The time allocated to ambush and suspension feeding changed with the composition of the food, and clearance of diatoms was, accordingly, negatively related to the availability of ciliates. In contrast, clearing of ciliates was almost constant and independent of the availability of the alternative prey (diatoms), probably because this particular ciliate species (in contrast to most other microzooplankters) is unable to escape a feedlng current and, thus, can also be captured by suspension feeding copepods. Finally, we demonstrate that turbulence favours the selection of cillates as prey. We suggest that prey switching by copepods may provide survival windows for microzooplankters during blooms of net phytoplankton because predation pressure from the copepods is then less. This may explain why microzooplankton populations often peak concurrently with net phytoplankton blooms and apparently independently of their own food.

Prey switching by Acartia clausi:experimental evidence and implications of intraguild predation assessed by a model

“…Acartia spp. tend to reduce their clearance rates for algae below some threshold food abundance (Deason 1980, Kerboe et al 1985, Paffenhofer & Stearns 1988, Durbin & Durbin 1992, Kierboe et al 1996. For diatoms, the clearance rate decreases when the abundance is below -100 to 500 cells ml-l, or -4 to 40 pg C 1-l. For smaller flagellates the level where clearance rate starts to decrease seems to be higher (Kerboe et al 1985: maximum clearance rate at 150 1-19 C 1-' for Rhodomonas baltica; Gismervik unpubl.…”

“…The authors argued that this discrepancy could be related to the fact that this particular ciliate species was not able to escape the feeding current of A. tonsa. Thus the copepod might have been able to clear cilia t e~ also in the suspension feeding mode (Kierboe et al 1996).…”

Seasonal Variability of Mesozooplankton Feeding Rates on Phytoplankton in Subtropical Coastal and Estuarine Waters

“…their feeding modes from filtering feeding to ambush feeding have a carnivory degree of 0.75. For example, Acartia species ingest more microzooplankton than phytoplankton in most cases to conquer food limitation or to fulfill nutritional requirement according to many studies (e.g., Kiørboe et al, 1996;Rollwagen Bollens and Penry, 2003;Yang et al, 2010), thus we defined this group as omnivorous species with a high carnivory degree (0.75). Because we only focus on the ingestion on phytoplankton and microzooplankton, species that simultaneously apply other feeding behaviors were also assigned to category of omnivores or carnivores, depending on what trophic levels they generally influence.…”

“…It has been reported by many field studies that when omnivorous species dominate in assemblage, mesozooplankton or copepods (a major group of mesozooplankton) often prefer feeding on microzooplankton to phytoplankton due to larger sizes and higher nutritional quality of microzooplankton (e.g., Stoecker and Capuzzo, 1990;Gifford, 1991;Fessenden and Cowles, 1994;Atkinson et al, 1996;Nejstgaard et al, 2001;Zeldis et al, 2002;Calbet and Saiz, 2005;Liu et al, 2005b;Gifford et al, 2007). Predation on microzooplankton is also an important feeding strategy of omnivorous species that are able to switch their feeding behaviors to conquer food limitation or to survive during nuisance phytoplankton blooms in coastal waters (Kiørboe et al, 1996;Nejstgaard et al, 1997;Gifford et al, 2007). On the other hand, microzooplankton are generally the main source of phytoplankton loss at most marine systems (Calbet and Landry, 2004).…”

Coprophagy and coprorhexy in the copepods Acartia tonsa and Temora longicornis: clearance rates and feeding behaviour

“…We examined the influence of fecal pellet size, feeding mode, and the presence of an alternative food source on the clearance rates. A. tonsa was chosen for behavioural analysis because it, like some other copepods, may switch between ambush feeding, where the copepod is inactive while perceiving moving (or sinking) prey particles, and suspension feeding, where prey particles arriving in the feeding current are captured (Jonsson & Tiselius 1990, Kiørboe et al 1996.…”