Pelagic ciliates (Protozoa, Ciliophora) of different brackish and freshwater lakes — a community analysis at the species level

The pelagic ciliate communities from 58 north German lakes differing in their origin (natural lakes and artificial ponds), morphology (from shallow ponds with a maximum depth of below 0.5 m to relatively deep lakes with a maximum depth of more than 10 m, surface areas from below 10 ha to more than 100 ha), trophic state (from mesotrophic to hypertrophic) and salinity (freshwater lakes and brackish water lakes) are described and compared at species level. Each lake was comprehensively sampled quarterly in the years 1996 and 1997, respectively. Applying a quantitative protargol stain, about 140 ciliate species could be identified and quantified in all investigated lakes. 35 species, mainly members of the Prostomatida and Oligotrichida, were found commonly in all types of lakes at all seasons and dominated the pelagic ciliate communities. 3 species were common in freshwaters, but never occurred in brackish lakes. In the brackish waters a mixture of common freshwater species and marine species was found with 13 species exclusively occurring in brackish waters. Lowest ciliate cell numbers were observed for deep freshwater lakes, highest cell numbers were determined for brackish waters. Highest species richness was found in artificial peat ponds with an average of 24 pelagic ciliate species in spring samples. The range of occurrence for the identified species was wide for most common species. However, the influence of some environmental factors could be enlightened.     

Oceanographical patterns during a summer upwelling–downwelling event in the Northern Galician Rias: Comparison with the whole Ria system (NW of Iberian Peninsula)

Summer upwelling and downwelling processes were characterized in the Northern Galician Rias during July and August 2008 by means of sampling carried out onboard R/V Mytilus (CSIC) and R/V Lura (IEO). Thermohaline variables, dissolved oxygen, nutrients, chlorophyll, phytoplankton, ciliates and zooplankton abundances were measured at sections located in the Rias of Viveiro, Barqueiro and Ortigueira and their adjacent shelves. Ekman transport was calculated from QuikSCAT satellite, upwelling intensity estimated with upwelling index from the average daily geostrophic winds, and SST maps obtained from NASA GHRSST satellite. Ekman transport and SST behaviour showed two different patterns: (i) offshore and upwelling favourable conditions on 13–22nd of July; (ii) onshore and downwelling favourable conditions from 23rd July to 19th August. During upwelling, TS diagram showed an intrusion of Eastern North Atlantic Central Water affecting the continental shelf but not the rias. Nutrient salt concentrations increased with depth, reaching their maximum values near the mouth of Ortigueira Ria. During downwelling, coastal water increased its temperature (18.5–19.8 °C) and was retained inside rias; nutrients were nearly depleted, except for the innermost ria (estuarine zone) due to fluvial nutrient inputs. In this inner area, the maximum of chlorophyll-a (Barqueiro Ria) was observed. Low phytoplankton abundances were measured in both cases, even though a short increase in the plankton biomass was observed inside rias during upwelling, while under downwelling a small red tide of Lingulodinium polyedrum was detected. During the upwelling period Northern Rias tend to be mesotrophic systems as revealed by nutrient concentrations, chlorophyll levels and plankton abundances. On the contrary, in similar situations, the Western Rias behaves as eutrophics.     

Respiration,growth and grazing rates of three ciliate species in hypoxic conditions

Marine hypoxic episodes are affecting both marine and freshwater bodies all over the world. Yet, limited data exists with regard to the effects of decreasing oxygen on protist metabolism. Three ciliate species were therefore isolated from Hong Kong coastal waters. Controlled hypoxic conditions were simulated in the lab environment, during which time growth, respiration and grazing rates were measured. Euplotes sp. and a Oxytrichidae-like ciliate showed decreased growth and respiration below 2.5 mg O₂ L⁻¹, however Uronema marinum kept steady growth and respiration until below 1.5 mg O₂ L⁻¹. Euplotes sp. and the Oxytrichidae-like ciliate had the highest ingestion rate, which dropped significantly below 3.0 mg O₂ L⁻¹. U.marinum grazing rates were affected at and below 1.5 mg O₂ L⁻¹, correlating with their drop in growth and respiration at this lower concentration. This study illustrates the slowing metabolism of key grazing protists, as well as species-specific tolerance in response to hypoxia.