The vertical distribution and abundance of Gammarus lacustris in the pelagic zone of the meromictic lakes Shira and Shunet (Khakassia, Russia)

Abstract

The vertical distribution and abundance of Gammarus lacustris in the pelagic zone of two fishless meromictic lakes, L. Shira and L. Shunet, in Southern Siberia (Russia), was studied with the underwater video recording system and using vertical hauls. In both lakes, during summer stratification, Gammarus was distributed non-homogenously, with a stable peak in the metalimnion. The average depth of Gammarus population in the pelagic zone was significantly correlated with the depth of the thermocline. Gammarus abundances obtained using vertical plankton hauls with net were quite comparable with those obtained from video records. The peak abundance of Gammarus in the pelagic zone of the lakes observed with underwater video amounted up to 400 individuals m -2 , while the peak animal densities in the metalimnion reached 50 ind. m -3 . The data are compared with previously published abundances of Gammarus in the littoral of Lake Shira. Both littoral and pelagic can be equally important habitats for amphipods in meromictic lakes. The absence of fish in the pelagic zone, high oxygen concentration, low water temperature, increased seston concentration, elevated water density in the metalimnion and the anoxic hypolimnion can be the most probable combination of factors that are responsible for the peak of Gammarus in the metalimnion of these lakes.

Vertical stratification of physical, chemical and biological components in two saline lakes Shira and Shunet (South Siberia, Russia)

“…Using data of Tolomeyev et al (2006) and Gladyshev et al (2000), we can assume that Gammarus feeds on all three major components of the lake seston, namely, detritus, green algae and Cyanobacteria , in proportion to their relative concentrations in the lake. The modelled vertical distribution of Gammarus has a biomass peak at the metalimnion, which agrees with field data of Zadereev et al (2010). Comparing the vertical distribution of seston carbon in the pelagic part of Lake Shira for 15 days, with and without Gammarus in pelagic waters, it appears that Gammarus is able to control the seston carbon (Fig.…”

“…14 mM Salinity up to 66 g L -1 loop and bacterial and ciliates communities in the chemocline on the macrobial food web and energy budget in the mixolimnion. Moreover, we still do not quite understand the effect of Gammarus population (Zadereev et al 2010) on the pelagic food web. The studies of trophic interactions are the subject for futures studies.…”

“…Again, the role of hydrophysical and biological factors in this distribution is not well understood. On the one hand, the average depth where the population occurs is consistently associated with the thermocline (Zadereev et al 2010). The thermocline of these 2 saline lakes is the depth zone where the amphipods are maximally buoyant.…”

“…mainly because monimolimnion is anoxic. To answer the question if presence of Gammarus in the pelagic part is consistent with its habitat requirements, especially depth preference, we monitored the vertical distribution of this amphipod in the centre of the lakes employing video surveillance system during summer stratification in 2005(Zadereev et al 2010). Gammarus appears to be distributed non-homogenously during summer stratification, with a stable peak in the metalimnion (Fig.…”

“…For this, we use a complex mathematical model that was developed for meromictic Lake Shira . The terminal species in the food web of our lakes are amphipods Gammarus lacustris, which tend to occupy pelagic parts of both lakes (Zadereev et al 2010). It is unusual behaviour for this predominantly benthic amphipod and we discuss which factors promote such a behaviour.…”