Copepod grazing behavior in simulated natural light and its relation to nocturnal feeding

Abstract

To investigate the role of light in controlling copepod grazlng behavlor, feeding responses of adult female Acartia tonsa Dana were determined under light conditions similar to those in natural, subsurface waters. Measured feeding responses were then related to feeding behavior under similar light conditions in nature. Copepods were adapted to a range of light intensities before being offered food (Thalassiosira weissflogii, 0.5 mm3 1 -l ) . Thirty min later gut contents were measured by gut fluorescence of chlorophyll a and pheopigment a. The grazing index was inversely related to the light intensity at which the copepods were adapted. The most dramatic change in grazing occurred at light levels close to those found in the copepod's natural habitat during twilight. An endogenous nocturnal feeding rhythm was found in a separate experiment. A 96 h field study in the Newport River estuary, North Carolina, USA, revealed a nocturnal feeding pattern in A. tonsa and a negative correlation between feeding and light intensity during daylight hours. No significant correlations were found between copepod feeding and in situ concentrations of chlorophyll a, pheopigment a and combined pigments. These results challenge Gauld's (1953) hypothesis that nocturnal grazing results from nocturnal vertical migration into a food-rich layer; they offer a reasonable explanation of how light may time grazing. Results indicate that migration and feeding may be independent behaviors separately controlled by light cues.

Effect of temperature on lower feeding thresholds, gut evacuation rate, and diel feeding behavior in the copepod Acartia hudsonica

“…In this study the ca 4-fold amplitude of the feeding rhythm in Acartia hudsonica was comparable with the 3 to 4-fold amplitude observed in A. tonsa (Stearns 1986, Stearns et al 1987, Kleppel et al 1988, Durbin et al 1990). The total daily food consumption at 8 and 12 "C (33.4 and 56.5 % body C respectively) was similar to values obtained at those temperatures (37.2 and 67.9 % body C) in a n earlier study with A. hudsonica females also fed Thalassiosira constricta, where ingestion was determined from the change in the abundance of cells over 24 h (Durbin & Durbin 1992).…”

“…(Kleppel et al 1985, Stearns 1986, Stearns et al 1987, Durbin et al 1990), supporting Petipa's (1958) hypothesis of a die1 variation in filtering rate. Die1 variation in feeding rate appears to be controlled independently of diel vertical migration to and from the chlorophyll-rich surface layer (Stearns & Forward 1984a, b, Head et al 1985, Stearns 1986, Dagg et al 1989.…”

“…(Kleppel et al 1985, Stearns 1986, Stearns et al 1987, Durbin et al 1990), supporting Petipa's (1958) hypothesis of a die1 variation in filtering rate. Die1 variation in feeding rate appears to be controlled independently of diel vertical migration to and from the chlorophyll-rich surface layer (Stearns & Forward 1984a, b, Head et al 1985, Stearns 1986, Dagg et al 1989. Field studies have suggested that die1 feeding rhythms are reduced under low food availability (Boyd et al 1980, Dagg 1985, Dagg & Walser 1987, Daro 1988), but in the laboratory Durbin et al (1990) found that the diel feeding rhythm in A. tonsa persisted under both high and low food conditions.…”

“…Mackas & Bohrer Sorting and acclimation. For the threshold experi-1976, Nicolajsen et al 1983, Kleppel et al 1985 ments 800 to 2000 adult female Acartia hudsonica , Stearns 1986, Durbin et al 1990), but have were isolated by pipetting into a clean, 20 1 polynot previously been investigated in A, hudsonica. Gut ethylene container with Thalassiosira constricta at a evacuation rates were determined at 4,8, 12, and 16 "C concentration of 2000 cells rnl-' filtered seawater.…”

Diel changes in the egg production rate of Acartia tonsa (Copepoda, Calanoida) and related environmental factors in two estuaries

“…reviews by Cushing 1951 andBainbridge 1961) and daily feeding (Stearns 1986 and references therein), diel egg laying by copepod zooplankters is a shortinterval, cyclic behavior that is sparsely documented. Although few copepod species have been tested specifically for such behavior, it is becoming clear that dramatic changes in egg production can occur on a time scale of hours (Harding et al 1951, Marshall & Orr 1952, Mullin 1968, Spindler 1971, Valentin 1972, Gophen 1978, Saint-Jean & Pagano 1983, Marcus 1985, Runge 1985.…”