Weak coupling between heterotrophic nanoflagellates and bacteria in the Yellow Sea Cold Water Mass area

A study was carried out to investigate the grazing pressure of heterotrophic nanoflagellates （HNF） on bac-teria assemblages in the Yellow Sea Cold Water Mass （YSCWM） area in October, 2006. The results show that the HNF abundance ranges from 303 to 1388 mL-1, with a mean of 884 mL-1. The HNF biomass is equivalent to 10.6%-115.6% of that of the bacteria. The maximum abundance of the HNF generally occurred in the upper 30 m water layer, with a vertical distribution pattern of surface layer abundance greater than middle layer abundance, then bottom layer abundance. The hydrological data show that the YSCWM is located in the northeastern part of the study area, typically 40 m beneath the surface. A weak correlation is found be- tween the abundances of HNF and bacteria in both the YSCWM and its above water layer. One-way ANOVA analysis reveals that the abundance of HNF and bacteria differs between inside the YSCWM and in the above water mass. The ingestion rates of the HNF on bacteria was 8.02±3.43 h-1 in average. The grazing rate only represented 22.75%±6.91% of bacterial biomass or 6.55%±4.24% of bacterial production, implying that the HNF razinR was not the major factor contributing to the bacterial loss in the YSCWM areas.

Abundance pattern of heterotrophic nanoflagellates in the southern Taiwan Strait

The analysis of 103 samples collected quantitatively from the southern Taiwan Strait (22°4'-24°3'N, 117°'-119°9'E), China, in August 1997 indicates that the abundance of heterotrophic nanoflagellates (HNF) ranges from 391 to 1 846 × 103 cell/dm3, with an average of 949 × 103 cell/dm3, and 96.2% of cells are in size of 2-22 um in all HNF met in the samples. The HNF cells are 9.83-45.79 μg/dm3 after conversion from cell number to carbon content, with an average of 22.82 μg/dm3. The HNF abundance is relatively low in comparison with other areas. The nitrogen and phosphorus nutrients of the water are lower than previous investigations, which may be caused by the El Nino. The biomass of HNF is higher in southern waters, where cell concentration is 3-5 folds higher than that in other waters, and nearly 2-fold as high as the average of the investigated areas. The HNF is mainly habitat in 0-30 m water layer. Both horizontal and vertical HNF distribution must be influenced by hy-drographical dynamic process to a great extent. Continuous in situ observations of HNF indicate the 24 h diurnal rhythm, with two peaks, one in night at one station (Station 9701) and one during the period of 12:00 - 24:00 at another (Station 9704). The factors controlling the diurnal variation of HNF are unclear, although vertical migration of HNF is obviously.

Spatiotemporal distribution of protozooplankton and copepod nauplii in relation to the occurrence of giant jellyfish in the Yellow Sea

The occurrence of the giant jellyfish, Nemopilema nomurai, has been a frequent phenomenon in the Yellow Sea. However, the relationship between the giant jellyfish and protozoa, in particular ciliates, remains largely unknown. We investigated the distribution of nanoflagellates, ciliates, Noctiluca scintillans, and copepod nauplii along the transect 33~N in the Yellow Sea in June and August, 2012, during an occurrence of the giant jellyfish, and in October of that year when the jellyfish was absent. The organisms studied were mainly concentrated in the surface waters in summer, while in autumn they were evenly distributed in the water column. Nanoflagellate, ciliate, and copepod nauplii biomasses increased from early June to August along with jellyfish growth, the first two decreased in October, while N. scintillans biomass peaked in early June to 3 571 pg C/L and decreased in August and October. In summer, ciliate biomass greatly exceeded that of copepod nauplii （4.61-15.04 ~tg C/L vs. 0.34-0.89 pg C/L）. Ciliate production was even more important than biomass, ranging from 6.59 to 34.19 ~tg C/（L.d） in summer. Our data suggest a tight and positive association among the nano-, micro-, and meso-zooplankton in the study area. Statistical analysis revealed that the abundance and total production of ciliate as well as loricate ciliate biomass were positively correlated with giant jellyfish biomass, indicating a possible predator-prey relationship between ciliates and giant jellyfish. This is in contrast to a previous study, which reported a significant reduction in ciliate standing crops due to the mass occurrence ofN. nomurai in summer. Our study indicates that, with its high biomass and, in particular, high production ciliates might support the mass occurrence of giant jellyfish.

Feeding and Growth Characteristics of a Diatom-Feeding Flagellate Isolated from the Bottom Sediment of Onagawa Bay, Northeastern Japan

In recent years, several marine heterotrophic nanoflagellates have been reported to feed on diatoms much larger than themselves. However, very little is known about the grazer-prey relationships between heterotrophic nanoflagellates and diatoms in aquatic ecosystems. A diatom-feeding flagellate was discovered in the bottom sediment of OnagawaBay. It fed and proliferated on diatoms, especially Skeletonema costatum sensu lato. This study determined growth and ingestion rates of the flagellate on Skeletonema costatum s.l. under laboratory conditons. Its grazing pressure on the sinking flux of S. costatum s.l. was calculated by combining field data. Specific growth rate of the flagellate increased with increasing prey concentration. The maximum specific growth rate was 0.79 d–1 and maximum ingestion rate of the flagellate was 0.66 ng·C·grazer–1·d–1. Calculated grazing pressure of the flagellate on S. costatum s.l. flux was up to 25.6%. The results imply that the flagellate has a considerable grazing impact on S. costatum s.l. flux at least in a restricted season of the year. Therefore, the present study suggests that this benthic flagellate plays an important role in pelagic-benthic coupling inOnagawaBay.

Influence of agriculture and aquaculture activities on the response of autotrophic picoplankton in Laguna Macapule, Gulf of California (Mexico)

Introduction:The lagoon is a component of coastal zones,whose populations of autotrophic picoplankton(APP)remain largely unstudied.These lagoons display high-nutrient productivity and additionally may also be subjected to anthropogenic activities.This study selected Laguna Macapule,located on the eastern shore in the mid-region of the Gulf of California,due to the fact that a drainage network servicing the surrounding agricultural region(>230,000 hectares under cultivation)directs irrigation runoff,shrimp farm effluents,and urban wastewater containing large quantities of nutrients to be discharged into this lagoon.We propose to identify the APP’s response to various types of environmental and anthropogenic influence in this highly impacted coastal lagoon.Methods:Two sites(separated by 2.7 km)were monitored from December 2007 to December 2008.One,located at the entrance to Laguna Macapule(oceanic influence)and the other a discharge canal(eutrophic conditions)inside the lagoon at El Tortugón.Results:APP was the numerically dominant phytoplankton fraction(15×106 to 620×106 cells L−1)with coccoidal cyanobacteria as the dominant fraction throughout the year.Peak levels were reached in spring-early autumn and they were the second largest contributor to biomass.Abundance of APP cells corresponds to the lagoon’s eutrophic status.Maximum numbers and a higher average of APP were recorded at the El Tortugón channel during the warm season(months with SST higher than 24°C).The general positive relationship of the APP’s annual cycle at both sites as well as a negative relationship with heterotrophic nanoflagellates(HNF)abundance,supports the idea that natural forcing,in particular sea surface temperature(SST)is the predominant influences on APP’s seasonal variability.Conclusions:Distinguishable significant differences in APP abundances and nutrients were recognizable between the two sites.The interplay of these variables contributed to lower densities of APP in winter and high densities in springearly autumn.N:P=~4 suggests that spring-early autumn abundance of the APP autotrophic component was sustained by urea from shrimp farm discharge water.Thus,a total nutrient-based approach is likely the most suitable tool for establishing nitrogen limitation of biological production in Laguna Macapule and similarly impacted ecosystems around the world.