Rotifer dynamics in three shallow lakes from the Salado river watershed (Argentina): the potential modulating role of incident solar radiation

Abstract

In turbid Pampean lakes, incident solar radiation is a major driver of plankton seasonal dynamics. Higher light availability in summer translates into higher primary production, and therefore more food for zooplankton grazers. However, experimental evidence suggests that food produced under the high irradiance conditions prevailing in summer are less suitable to sustain rotifer population growth than that produced under the lower irradiance conditions typical of winter. Here, we analysed time series datasets corresponding to three shallow lakes from the Salado river watershed. This analysis provided evidence for similar seasonal patterns of rotifer relative abundance over a large geographic area. In addition, we performed life table experiments to test the hypothesis that natural seston produced in winter could sustain higher population growth rates than seston produced in summer. We suggest that the natural seasonal changes in temperature and food generate successive time windows, which may be capitalized by the different grazer species, resulting in predictable phenology of grazer populations.

Species‐specific phenological trends in shallow Pampean lakes’ (Argentina) zooplankton driven by contemporary climate change in the Southern Hemisphere

“…However, other observed trends in air temperature (increases in July, August, and December and a decrease in June) did not translate into significant trends in Lake Chascomús water temperature. Lake water temperature typically correlates with regional-scale air temperatures (Adrian et al, 2009), but among-year differences in thermal inertia Despite the lack of distinct seasonal landmarks in Lake Chascomús (e.g., ice melting, water column stratification), several zooplankton species display striking recurrent seasonal patterns or phenologies (Diovisalvi, Rennella, et al, 2015;Diovisalvi, Salcedo Echeverry, et al, 2015 and Figure 3). In this paper, however, we focused exclusively on species that showed significant phenological changes in the long run.…”

“…Brachionus havanaensis is a warm stenotherm rotifer (Ruttner-Kolisko, 1976) that develops dense populations in shallow Pampean lakes. In Lake Chascomús, it becomes the dominant species during late summer and autumn, but it is absent from the water column during the coldest months of the year (Diovisalvi, Rennella, et al, 2015). The delay in the end date of its seasonal distribution (i.e., the 90% quantile of the Weibull function) implies the widening of its temporal niche (Hampton, 2005) toward the end of the autumn.…”

“…Despite the lack of distinct seasonal landmarks in Lake Chascomús (e.g., ice melting, water column stratification), several zooplankton species display striking recurrent seasonal patterns or phenologies (Diovisalvi, Rennella, et al, ; Diovisalvi, Salcedo Echeverry, et al, and Figure ). In this paper, however, we focused exclusively on species that showed significant phenological changes in the long run.…”

“…Moreover, two independent pieces of information provide further support to our interpretation that the shift in B. havanaensis phenology was a direct response to increases in May water temperature. The first piece of evidence comes from the study by Diovisalvi and coworkers (Diovisalvi, Rennella, et al, ), who performed life‐table experiments at two different temperatures (9 and 20°C). They reported that the egg production of B. havanaensis was high at 20°C, but halted at 9°C.…”

“…Thus, the physical environment can be expected to provide fewer (and from a researcher's perspective, less predictable) cues to trigger phenological responses of plankton. On the positive side, the noticeable seasonal succession of Pampean lakes zooplankton (Diovisalvi, Rennella, & Zagarese, 2015) entails a progressive replacement of species, which are likely adapted to different ranges of temperature and other environmental conditions. Under such circumstances, studies with whole year coverage maximize the chances of detecting phenology trends, and for analogous reasons the use of metrics that capture the whole seasonal distribution of activity for the focal organisms should be preferred (Miller-Rushing, Inouye, & Primack, 2008).…”