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

Abstract

Adult females of the marine copepod Acartia hudsonica Pinhey were fed the unicellular diatom Thalassiosira constricta (10.4 pm equivalent spherical diameter) at 4, 8, 12, and 16 "C, to determine whether there was a threshold food concentration below which feeding ceased or was sharply reduced. Field-collected copepods were acclimated for 24 h at 2000 cells ml-' T. constricta, and then transferred to a range of low food concentrations (15 to 876 cells ml-l). Gut pigments were determined fluonmetrically after a 5 h period of feeding, which was calculated to be sufficient for gut contents to equil~brate to the new food concentration. Experiments were carried out during the same phase of the diel cycle (05:OO to 10:OO h) and were terminated near midday, a time when feeding rate was relatively stable, in order to standardize the effects of the die1 feeding rhythm. Lower feeding thresholds of 280, 127, 282, and 214 cells ml-' respectively at 4, 8, 12, and 16 "C were indicated by segmented linear regression analysis of the relationship between gut pigments and phytoplankton concentration. These thresholds corresponded to carbon concentrations of 30.5, 11.6, 20.7, and 16.4 pg C 1-l, and were not significantly different at the 4 temperatures. Die1 changes in gut pigment content were measured at 8 and 12 "C, at a T. constricta concentration of 2000 cells ml-l. Highest gut contents occurred at night, and were ca 4-fold higher than the lowest measured gut contents. Total daily ingestion rates were respectively l l 460 and 14 430 cells d-l, or 1.34 and 2.40 ~g C and 0.24 and 0.42 pg N d-l, and 33.4 and 56 5 % body C and 23.3 and 38.5 % body N d-l. The instantaneous gut evacuation rates were also determined at the 4 temperatures, with mean values of 0.0239, 0.0494, 0.0518, and 0.0645 min-' respectively at 4, 8, 12, and 16 "C, yielding a Q," of 1.88.

Egg production of Acartia bifilosa in the small temperate estuary of Mundaka, Spain, in relation to environmental variables and population development

“…Assuming a C:chl of 50, the calculated amount of phytoplankton carbon ingested by carbon body weight (mean: 323%, range: 200 to 600%) was much higher than values reported for this species in the Gironde estuary (Irigoien & Caste1 1995), and for other Acartia species under laboratory and field conditions (EClerrboe et al 1985, Wlodarczyk et al 1992, but in the same range of maximum ~ngestion rates obtained for A. tonsa under standardized temperature and food conditions (Thompson et al 1994). The total carbon ingested as phytoplankton could not satisfy the estimated daily carbon demands if the lowest C:chl ratio found in the literature (C:chl = 20) is assumed.…”

Active transport of particulate organic carbon and nitrogen by vertically migrating zooplankton in the Sargasso Sea

“…A number of studies have shown that crustacean guts are often cleared within 45 min or less (e.g. Dagg & Wyman 1983, Morales et al 1991, Wlodarczyk et al 1992, Landry et al 1994, suggesting most of the gut content would be defecated before the crustaceans reach the bottom of the mixed layer. However, the crustaceans examined in these previous studies were epipelagic species or were not strong diel vertical migrants.…”

Short term feeding responses to starvation in three species of small calanoid copepods

“…Since A. tonsa has an enzyme production that responds quickly to changes in food concentration (Hassett & Blades-Eckelbarger 1995), there is no limiting factor other than gut volume for the intake. One hour of starvation is on the same time scale as gut clearance time at 20°C for A. hudsonica (12 to 15 min, Q," = 1.88; Wlodarczyk et al 1992) and Centropages ha.matus (32 mi.n, Q, , = 3.8; Kiorboe et al 1982) and accordingly occurred even after a short time without food. For Calanus helgolandicus that normally empties its entire enzyme pool daily (Nott et al 1985), the increase observed by Runge (1980) after 22 to 26 h starvation may be interpreted similarly.…”