Relationship between bacteria, phytoplankton and heterotrophic nanoflagellates along the trophic gradient

Abstract

Bacterial and heterotrophic ndnoflagellates (HNF) abundance, as well as bacterial production and chlorophyll a levels, were measured at live sites extending from the coastal zone toward the open Adriatic in the period from March to October "i995. The investigated areas were grouped into trophic categories according to concentrations of chlorophyll u. All the biotic-parrsmeters increased along the trophic gradient, ledding to eutrophy, but they did not increase at the same rate. The bacterial biomass : phytoplankton biomass {BB : chl u) ratio decreased from about 10 in the very oligntrophic area to 0.8 at the eutrophw site. In contrast, the bacterial abundance : HNF abundance ratio iB : HNF) increased from 1000 bacteria per 1 tlagellate in the oligotrophlc system to .1700 bacteria flagellate' in the eutrophic area. Decreasing BB : chl a and :ncreasing B : HNF ratios along the trophic gradient might rellect the dflterent structures of the microbial food web. Relationships between bacterial abur~danc:e and production, and chl a and t-{NF showed that bacterial abundance along the trophic grddient was regulated by the interplay between nutrient supply and grazing pressure. But in the oligotrophic system, bacterial abundance was more closely related to bacteriaL production and chl u than m the eutrophic system, suggesting stronger control of bacteridl abundance by substrate supply C)n the other hand, the coupling between bacteria and HNF, and uncoupling between bacterial dbundance and production in the eutrophic system, showed that the importance ot bactenovorv increased in richer systems.

Identification and Characterisation of Microbial Populations Using Flow Cytometry in the Adriatic Sea

“…Abundance of heterotrophic bacteria obtained by flow cytometry in the investigated coastal area and in the open Adriatic Sea area ranged from 10 5 to 10 6 cells mL -1 and results are similar to previous values obtained by epiflurescence microscopy reported for the eastern coast of Adriatic Sea (Krstulović et al, 1995;Krstulović et al, 1997). Seasonality in the bacterial community in the most investigated coastal areas ( Figure 5), with maxima in the spring-summer period and minima during winter was also determined, as in the previous reports on central Adriatic (Krstulović, 1992;Šolić et al, 2001).…”

Seasonal and spatial distribution of Bacterioplankton in a fluvial-lagunar system of a tropical region: density, biomass, cellular volume and morphologic variation

“…Carvalho et al (2003) and Coveney and Wetzel (1995) also did not find a relationship between the chlorophyll and the bacterioplankton, during the studies carried out in oligotrophic and mesotrophic environments. The dependence of bacterioplankton of dissolved organic carbon released by the phytoplankton (Kisand et al, 2001) and the effect of the bacterivory in the control of the populations (Krstulovic et al, 1997) was more typical in the eutrophized environments (Gonzalez et al, 2000). Moreover, the low levels of chlorophyll denoted the importance of bacterioplankton for the trophic structuring of this environment, where significant relation between the bacteria and the phytoplankton was not observed.…”

The role of ciliates within the microbial food web in the eutrophicated part of Kaštela Bay (Middle Adriatic Sea)

“…Significant correlations between these biotic parameters suggest strong relationships in the microbial food web (Table 2). Earlier studies on the relationship between bacteria, phytoplankton and HNF in the eutrophicated part of Kaštela Bay showed that as much as 64% of variation in bacterial abundance could be explained either by variability in abundance of HNF or by predatorprey dependence (Krstulović et al, 1997). However, our data showed a slightly weaker link between bacteria and HNF abundance (r=0.40, N=36, P<0.05) and suggested that organisms other than HNF could be important predators of bacteria and/or that other loss processes could be more important than predation.…”