Distribution Of Planktonic Rotifers Research Articles

Study of the effects of photoperiod and salinity in the Alvarado strain of theBrachionus plicatilisspecies complex (Rotifera: Monogononta)

The survivorship and distribution of planktonic rotifers are influenced by salinity and photoperiod. In this study we performed life table experiments with the estuarine rotifer Brachionus sp., “Alvarado” strain (collected in Veracruz, Mexico). Three salinities: 7.5, 15 and 30‰, and two photoperiods: constant light and 16:8 h (light:dark) photoperiod at one temperature (25±2°C) were assessed. The microalgae Nannochloropsis oculata (1×106 cells.mL−1 ) was supplied as food. We recorded the hatching percentages at different temperatures, and we included morphometric data of adult rotifers, neonates and parthenogenetic eggs. Results showed that the highest estimated values of net reproductive potential (Ro), intrinsic growth rate (r ) and reproductive value (Vx) were obtained at 15‰ and 16:8 h (light:dark) photoperiod, followed by continuous light, respectively. The lowest reproductive rate was observed at 30‰ and 16:8 h (light:dark) photoperiod. Hatching reached 100% after 20 h at temperatures of 25 and 30°C. The morphometric analysis of the lorica suggests that this B . “Alvarado” strain belongs to the SM clade of the B. plicatilis species complex. This strain of Brachionus is: (a) euryhaline, (b) high growth rate, (c) small size. All these characteristics suggest that this strain can be potentially used as live food for larval fish and for the development of toxicity tests.

Distribution of planktonic rotifers in Spanish reservoirs: Changes after 15 years

Distribution of planktonic rotifers in Spanish reservoirs: Changes after 15 years

Seasonal changes in the abundance and distribution of planktonic rotifers in Grasmere (English Lake District)

SUMMARY. The planktonic rotifers of Grasmere, a small lake in the English Lake District, were studied from August 1969 to December 1972. Twenty‐four species were recorded but five were very rare. The remaining species were divided into three groups according to their seasonal occurrence: spring to autumn species (Keratella quadrata. K. cochlearis, Gastropus stylifer, Asplauduia priodonta. Kellicottia Umgispina, Conochilus hippocrepis)., spring to early summer species (Polyarthra dolichoptera, Synchaeta tremula, S. pectinata, S. stylata, S. oblonga, C. unicornis), summer to autumn species (Polyarthra vulgaris, P. major. Filinia terminalis, S. grandis, Ploesoma hudsoni, Trichocerca capucina, T. similis). The months in which each species was abundant are given. Keratella quadrata and Filinia terminalis were most abundant in the deepest stratum, Kellicottia longispina and Conochilus spp. were most abundant in the upper and middle strata. Trichocerca spp. showed no pronounced vertical distribution, and all the remaining species were most abundant in the upper stratum. Keratella cochlearis and Kellicottia longispina attained their highest densities over a wide range of temperature and oxygen concentration. Filinia terminalis, Conchihis spp., Asplanchna priodonta. K. quadrata, and Polyarthra spp., attained their highest densities within a narrow range of temperature and oxygen concentration. Optimum ranges are given for each species.Major changes occurred between 1971 and 1972 when Asplanchna priodonta. Kellicottia longispina, Conochilus unicornis and Filinia terminalis increased in abundance, whilst Keratella quadrata. Gastropus stylifer, C. hippocrepis, Polyarthra spp., Synchaeta spp. and Ploesoma hudsoni decreased in abundance. These changes are discussed in relation to the temperature and oxygen requirements of each species and also to the probable enrichment of the lake after the opening of a new sewage works in June 1971.