Map 24 Issued from : S. Zamora Terol in Tesis Doc. Univ. Politèc. Catalunya, 2013 [p.71, Fig. 3].
Oithona davisae feeding rates as a function of food concentration (C).
(A) Clearance rate (F, ml. female-1 d. -1).
(B) Ingestion rate (I, cells female-1 d-1).
(C) Weight-specific ingestion rate, as percentage of body carbon ingested per day (daily ration, DR, %) are shown.
Exponential decay and Ivlev's equations fits are also shown.
Symbols marked with an asterisk correspond to extreme values not used in the equation fitting.
<< Experiments on adult females coming from continuous culture in laboratory (Institut de Ciències fel Mar (Barcelona, Spain) in October 2000), routinely fed the heterotrophic dinoflagellate Oxyrrhis marina (ESD = 16 µm), which were at the same time fed the cryptophyte Rhodomonas salina (ESD = 8 µm).; all incubations and experiments conduced in a temperature room at 18 ± 1¨C.
Clearance and ingestion rates were determined for each food level according to Frost's equations (Frost, 1972).
Clearance rates were fitted to an exponential decay function:
F = Fmax e-l C.
Where Fmax is the maximum clearance, C is the concentration of food and I is the decay rate.
Ingestion rates were fitted to a type II functional response model using the Ivlev (1961) equation:
I = Imax (1 - ea C).
Where Imax is the maximum ingestion rate, C is the food concentration and a is the rate at which ingestion approaches the maximum rate.
The critical or saturating food concentration (Ks, i.e. the threshold concentration below which feeding is food limited, was calculated as the food concentration at which ingestion equals 95% of the maximum ingestion rate (Almeda & al., 2010).
For the females corresponding to the feeding experiments, the percentage of ovigerous females was determined, and their mean clutch size was quantified buy dissecting all eg sacs present. The average population egg production rates (EPR, eggs female-1 day-1), computed for the ensemble of ovigerous and non-ovigerous females was calculated using egg-ratio method according to the equation modified from Uye & Sano (1995).:
EPR = CS x OF/TF xI T.
Where CS is clutch size (eggs female-1, OF is the number of ovigerous females present in the sample, TF is the total number of females, and IT is the interclutch time (days).
The authors hvve used the interclutch time determined by Uye & Sano (1995) instead of the hatching time (as found in the litterature, Sabatini & Kiørboe, 1994; Castellani & al., 2005), because the interclutch time for O. davisae is longer than the embryonic time at the corresponding experimental temperature (respectively, 2.5 and 1.8 days, Uye & Sano, 1995).
Weight-specific rates were estimated from size measurements and carbon content-size relationship from the litterature. In the case of Oxyrrhis marina biovolume estimates from the Multisizer Counter were converted into carbonj using the conversion factor 0.123 pg C µm-3. (Pelegri & al., 1999). The carbon weight of both eggs and females were estimated by taking digital pictures. For each experimental condition at least 200 eggs and 20 females were measured. (C µg).
The egg diameter (ED µm) was estimated as equivalent circular diameter and then the egg carbon content (µgC) was calculated using the Uye & Sano's equation for O. davisae:
C = 5.32 x 10-8 x ED3.04.
For adult females estimation of individual biovolume (µm3 at each food level by using the minor and major axis of the cephalothorax to build an ellipsoid. Then using only the major axis, homologous to the prosome length (PL µm), thecarbon content was estimated for all conditions using the Uye's equation:
C = 1.26 x 10-4 x PL1.31. Finally, average carbon content: biovolume factor, 6.74 µgC µm-3, used to estimate the female biomass from the biovolume measurements.
Clearance rates found show values (average ± SE) ranged from 7.3 ± 0.39 to 0.63 ± 0.06 ml swelt clear /female/day at the lowest and highest food concentration, respectively.
Ingestion rates increased asymptotically when increasing food concentration, showing saturation food concentrations (Ks of 249 cells mL-1, and maximum ingestion rates of 737 cells /female/day.
In terms of weight-specific rates, daily ration (DR) varied from 30% of body carbon ingested by day at the lowest concentration tested, to maximum values of 80% body C/day. The saturation food concentration of Oxyrrhis marina in terms of carbon was 56 µg C L-1. >>