L. V. Samchyshyna
Schmalhausen Institute of Zoology, National Academy of Sciences of Ukraine,
Kyiv, Ukraine, firstname.lastname@example.org
ВЫЕДАНИЕ DAPHNIA GALEATA
НИТЧАТЫХ И ОДНОКЛЕТОЧНЫХ ЗЕЛЕНЫХ ВОДОРОСЛЕЙ
Л. В. Самчишина
Институт зоологии им. И. И. Шмальгаузена НАНУ, Киев, Украина, email@example.com
Wellknown, that the grazing studies provide insight into foodweb relationships in lakes. They show an effectiveness of different types of filter-feeders in removing of cyanobacteria (blue-green algae) and other phytoplankton from water (Lampert, 1987). Most grazing studies focused on the clearance of phytoplankton by feeding laboratory-reared cultures to the grazers (Dionisio Pires, Van Donk, 2002). Grazing studies on filamentous cyanobacteria are usually performed with zooplankton, because zooplankton species have been the classical filter-feeders for use in lake restoration (Gulati, Van Donk, 2002).
Cladoceran genus Daphnia plays a key role in freshwater pelagic foodwebs. Daphnia galeata Sars, 1863 is one of the main cladoceran species represented in European eutrophic lakes (Vijverberg, Boersma, 1997). Several feeding studying have been done on this species (Gulati, Bronkhorst, Van Donk, 2001; Dionisio Pires, Ibelings, Brem et al., 2005). However, there is relatively little information on the degree of utilization of phytoplankton by this species.
Our experiments were designed to test the relative importance of lake-dwelling grazer Daphnia galeata on different shaped green algae: spherical shaped Scenedesmus obliquus and filamentous Chloromidium sp.
Daphnids D. galeata (stain Y9) were cultivated in a lab at temperature +17…+18°C and light (L : D 16 : 8 h, 6–8 µ mol m–2 s–1), fed by Scenedesmus obliquus (2 mg C/l). After the required amount of material had been obtained, 20 individuals of 8–22 days old were moved to each of treatment (in triplo) contained 0.5, 1.0 and 5.0 mg C/l of pure Scenedesmus and Chloromidium. In control vessels (each of treatment in triplo also) daphnids were absent.
Daphnids were not starved but acclimatized to the food 16–20 h before experiment. Then daphnids from each vessel gently were filtered, rinsed with filtered lake water and moved at experimental 50 ml erlenmeyers with food suspension. During experiment the content of erlenmeyers has been carefully manually shake by glass stick in order to avoid sedimentation of algae. For quantifying grazing, 6 ml of food suspension have been taken at time (t) 0, t 15, t 30 and t 60 and immediately processed at phytoplankton analyzer (Phyto-PAM) to account Chl a concentration. Then samples were fixed with glutarformaldegide. Individual dry weight (µg) was determined allometrically from length-weight relationship estimated for Daphnia galeata by Gulati, Bronkhorst and Van Donk (2001).
The clearance rate (CR, ml daphnid–1 h–1) was estimated by formula (Coughlan, 1969):
CR = V/(n*t)(ln(C0/Ct) – ln(C’0/C’t)),
there V = volume of food suspension (ml), n = number of daphnids in vessel (20), t = duration of experiment (in hour), C0 = algae concentration in vessels with daphnids at t0 (µg Chl a/l), Ct – algae concentration in vessels with daphnids at time t, C’0 – algae concentration in control at t0, C’t – algae concentration in control at time t.
All data are reported as mean ±SE. The experiment had been done at the May–August 2005 at the Netherlands Institute of Ecology (NIOO-KNAW).
D. galeata has shown the highest CR on unicellular green algae Scenedesmus obliquus in a treatment with algae concentration of 0.5 mg C/l. The CR was varied from 1.58 to 2.29 ml animal–1h–1. Scenedesmus considers as a good nutrient food for Daphnia and a value of concentration is above the incipient limiting level, which is of 0.2–0.5 mg C/l (Lampert, 1987). With increasing of food concentration till 1 and 5 mg C/l of Scenedesmus the CR of daphnids is decreased, but still positive (1 and 0.25 ml animal–1h–1 accordingly). As shown our experiments, D. galeata can eat filamentous green algae Chloromidium sp. but only at smallest concentration of the food suspension. The CR of D. galeata was up to 0.1 ml animal–1h–1 at concentration of 0.5 mg C/l of Chloromidium. Higher concentrations of filamentous green algae were completely not utilized by Daphnia.
The size of daphnids have been used in our experiment was varied from 1.53 to 2.07 mm. In comparing to literature data, bigger species of D. carinata (2.8 mm long) consumed all food items grazing on natural phytoplankton with a mean value of 5.15 ml animal–1h–1; smaller cladocerans, such as Moina (0.85 mm) and Ceriodaphnia sp. (0.60 mm) have mean rates of 1.07 and 0.97 ml animal–1h–1, respectively (Matveev&Matveeva, 1997).
In general, it is assumed that filaments clog at the feeding groove of the daphnids, making ingestion impossible (Hawkins, Lampert, 1989; Gliwicz, Lampert, 1990; Gliwicz, 1990). However, it has also been shown that daphnids can retard bloom formation of filamentous algae (Sarnelle, 1993). Gulati et al. (2001) showed that Daphnia galeata can grazed on blue-green filamentous Oscillatoria limnetica and it has a higher clearance rate on the shorter filaments. Laboratory studies (Burns, 1968 et al.) demonstrated that large particles of food reduce the filtering efficiency of zooplankton grazers.
Gliwicz and Siedlar (1980) found that cladocerans are able to reduce particle interference by narrowing the opening of the carapace and smaller cladocerans, with corresponding smaller openings, are less affected than large species. Unwanted smaller particles that enter the filtering chamber must be removed from the food groove by labral or post-abdominal rejections (Burns, 1968). Small filaments, however, may not always be rejected. They may also serve as a food source for cladocerans (DeBernardi et al. 1981) although feeding rates are usually lower than those on spherical-shaped cells (Porter, Orcutt, 1980).
Suuming up, filamentous green algae Chloromidium sp. may be grazed by Daphnia galeata at concentration of algae below then 1 mg C/l. Small cladocerans or immature individuals were less affected by filaments than larger species or bigger individuals. These laboratory experiments make a contribution to our knowledge of zooplankton-algae interaction. These studies are however, not completely clear about whether daphnids can or cannot feed on other species of filamentous algae.
I would like gratefully acknowledge to INTAS for support of my research activity. I would like warmly thanks to Dr. Bas Ibelings for inviting me at NIOO, to Dr. Ramesh Gulati for useful consultations and to Prof. Lampert for early introducing me in daphnids taxonomy.
Zoocenosis — 2007
Біорізноманіття та роль тварин в екосистемах: Матеріали ІV Міжнародної наукової конференції. – Дніпропетровськ: Вид-во ДНУ, 2007. – С. 102-103.