Phytoplankton production and taxon-specific growth rates in the Costa Rica Dome

During summer 2010, we investigated phytoplankton production and growth rates at 19 stations in the eastern tropical Pacific, where winds and strong opposing currents generate the Costa Rica Dome (CRD), an open-ocean upwelling feature. Primary production (¹⁴C-incorporation) and group-specific growth and net growth rates (two-treatment seawater dilution method) were estimated from samples incubated in situ at eight depths. Our cruise coincided with a mild El Niño event, and only weak upwelling was observed in the CRD. Nevertheless, the highest phytoplankton abundances were found near the dome center. However, mixed-layer growth rates were lowest in the dome center (∼0.5-0.9 day^-1), but higher on the edge of the dome (∼0.9-1.0 day^-1) and in adjacent coastal waters (0.9-1.3 day^-1). We found good agreement between independent methods to estimate growth rates. Mixed-layer growth rates of Prochlorococcus and Synechococcus were largely balanced by mortality, whereas eukaryotic phytoplankton showed positive net growth (∼0.5-0.6 day^-1), that is, growth available to support larger (mesozooplankton) consumer biomass. These are the first group-specific phytoplankton rate estimates in this region, and they demonstrate that integrated primary production is high, exceeding 1 g C m^-2 day^-1 on average, even during a period of reduced upwelling.

Isolation and Characterization of Microcystis-Grazing Protozoa P1 from Lake Dianchi

The incidence of algae blooms is increasing in China and worldwide, causing serious environmental problem. A protozoan P1 was isolated from the water samples of Lake Dianchi, which had potent grazing effect on some kind of cyanobacteria. It should be belonged to Ciliophore, Oligohymenophorea, Philasterida based on morphological characters observed by the optical microscope. The main influencing factors of the protozoan grazing properties including: algae species, protozoan density, culture temperature, time and pH value were investigated in batch experiments. The results showed that the protozoan P1 had strong ability to graze the cells of Microcystis wesenbergii. The greater the initial protozoan density, the faster the degradation of chlorophyll-a. The removal rate of chlorophyll-a after 4 days was 78% at the optimum temperature 25°C, pH 7 when using a lower inoculation quantity of 2%. The protozoan P1 was easy to cultivate and reproduce rapidly. It could be applied in the ecological environment to control the Microcystis water bloom.

Hydrography and plankton temporal variabilities at different time scales in the southwest lagoon of New Caledonia: a review

The New Caledonia SW lagoon is wide (5-20 nautical miles) and semi-closed. It is influenced by both the open ocean and the high island within a meteorological context subject to seasonal, inter-annual and longer term variations. The short-term variability (>1 day) of meteorological, hydrographical and planktonic parameters is illustrated by a 5-month long time series and is linked to local or remote wind, and precipitation. Seasonal and inter-annual variabilities, inferred from a 10-year long station by spectral analysis, appear clearly for all parameters. Seasonality is the main scale of variability as the island lies near the tropic of Capricorn. Inter-annual variability of a 3-4year periodicity is poorly related to the Southern oscillation index (an equatorial climatic index), stressing the need for a separate tropical index. Long term trends appear on several parameters but their reliability depends on the length of the records. Considering only the longest records (1958-2005), surface temperature appears to have increased since the end of the 1960s in Noumea area. Finally, as a result of greater terrestrial influence, shallower depths, and longer water turnover times close to shore, the temporal variability amplitude decreases from the shore to the barrier reef.