Coupling Between Heterotrophic Nanoflagellates and Bacteria in Fresh Waters: Does Latitude Make a Difference?

Abstract

Recent studies reported comparatively lower heterotrophic bacteria (HB) abundances in tropical regions, indicating that factors involved in bacterial losses could be more relevant in the tropics. Heterotrophic nanoflagellates (HNF) are considered the main predators of HB in aquatic ecosystems, and one should expect higher abundances in the tropics because of differences in the food web configuration (absence of large daphnids). However, there are no comprehensive studies comparing HB and HNF abundances in a latitudinal gradient. We hypothesized that HB abundance would be lower in the tropics because HNF abundance would be higher, resulting in a tighter HNF–HB coupling. To test this hypothesis, we compiled a large dataset of HB and HNF abundances from tropical and temperate freshwater environments. We found that both HB and HNF abundances were lower in the tropical region, and that HNF-HB coupling does not differ between temperate and tropical regions. The lower HNF abundance and lack of coupling may be explained by a strong top-down control on HNF and/or their herbivory preference. Besides, no relationship was found between bacterial specific growth rate and either chlorophyll-a and HB abundance, indicating that bacterial losses may have an important role in tropical freshwaters. Thus, we found that HNF is likely not the main controllers of HB abundance, and that grazing by ciliates and cladocerans, together with the physiological effects of higher temperatures, may explain the high bacterial loss rates in the tropics.

Temperature sensitivities of microbial plankton net growth rates are seasonally coherent and linked to nutrient availability

“…This synchronous variation in the temperature responses of the three microbial groups has other potential implications. In a sort of time‐for‐space substitution, the latitudinal gradients in the temperature regulation of heterotrophic prokaryotes recently found (Morán et al, ) could perhaps be extended to other planktonic groups, from phytoplankton (Ward, ) through heterotrophic nanoflagellates (Segovia et al, ) to higher trophic levels. The complex interactions between resources, predators and prey within marine microbial food webs are far from having been completely captured in our experimental design.…”

Temporal dynamics of rotifers' feeding guilds shaped by chlorophyll‐a, nitrate, and environmental heterogeneity in subtropical floodplain lakes

“…In floodplains, rotifers are among the most abundant zooplankton groups (José de Paggi & Paggi, 2007;Lansac-Tôha et al, 2009). They show a high species richness in the active (Bonecker et al, 2005) and passive community (Battauz et al, 2014) and are an important component of aquatic food webs (Miracle et al, 2007;Segovia et al, 2016). They are also sensitive to temporal dynamics, responding to climate change (Meyer et al, 2017), pollution (Sládeček, 1983), changes in trophic state (Oh et al, 2017), and predation (Auer et al, 2004).…”

The commonality of core biological groups across freshwater food webs

“…In this sense, a control of cladocerans and copepods led by fish could positively influence protists as a result of lower predation pressure (Jeppesen et al 1998; Attayde and Hansson 2001). Thus, an increase in the abundance of these protists could affect bacterial abundance negatively (Segovia et al 2016). However, despite zooplankton affect their prey, especially ciliates, those effects rarely translates into remarkable shifts in the basis of the microbial food web (Zollner et al 2003).…”