Horizontal dynamics of zooplankton in subtropical Lake Blanca (Uruguay) hosting multiple zooplankton predators and aquatic plant refuges

Abstract

In the subtropics, the effects of macrophytes on trophic interactions are more complex than in temperate lakes. Fish, particularly the smallest species and individuals, aggregate in high numbers in the vegetation, and a strong predation pressure on zooplankton by shrimps and invertebrates, such as Chaoborus, can occur in these systems. We studied seasonal and diel changes in zooplankton and their potential predators (both fish and invertebrates) and physical and chemical characteristics among open water and vegetated habitats (emergent and submerged plants (SP)), in the subtropical Lake Blanca (34°54¢ S; 54°50¢ W), a shallow system with an extensive and complex littoral area and high abundance of vertebrate and invertebrate predators on zooplankton. We found differential horizontal distribution of some zooplankton species under the scenario of high abundance of small omnivorous-planktivorous fish and Chaoborus, especially in the seasons with intermediate catch per unit effort of fish. We found indications of a diel horizontal migration (DHM) opposite than described for temperate systems, as the two main cladocerans Bosmina longirostris and Diaphanosoma birgei were found in higher densities in the submerged plant beds during night, in spring and autumn respectively. Although we need experiments to prove DHM, Chaoborus seemed to be the main trigger of the apparent DHM, followed by small omnivorous fish. During summer no spatial differences were found likely because of high densities of fish in all habitats. In absence of piscivorous fish, the distribution of fish Jenynsia multidentata seemed to be conditioned by food availability and by predation risk of waterfowl. The refuge capacity of aquatic plants for zooplankton in subtropical systems seems weak and with consequent weak or no cascading effects on water transparency, as under very high fish and invertebrate densities (summer) the refuge for zooplankton was lost.

Pelagic and littoral cladocerans (Crustacea, Anomopoda and Ctenopoda) from reservoirs of the Northwest of São Paulo State, Brazil

“…Very few works, however, have been studied the DHM in shallow lakes at tropical and subtropical regions (e.g. Meerhoff et al 2006, Iglesias et al 2007). According to Iglesias et al (2007), in the tropics and subtropics, the effects of the macrophytes on trophic interactions are more complex than in temperate lakes.…”

“…Meerhoff et al 2006, Iglesias et al 2007). According to Iglesias et al (2007), in the tropics and subtropics, the effects of the macrophytes on trophic interactions are more complex than in temperate lakes. In shallow subtropical lakes, the aquatic plants offer refuge to zooplankton only when fishes and invertebrate predators are not abundant.…”

Effect of surrounding trees and dry rush presence on spring zooplankton community in an urban pond complex

“…Therefore, it is not only the abundance of different small water bodies in landscapes, but also the macrophyte mosaic within a single pond that will support as well as contribute to the increase of biological diversity. The presence of macrophyte species has a significant influence on the species richness and community structure (Balayla and Moss, 2003;Iglesias et al, 2007;Ejsmont-Karabin and Hutorowicz, 2011;Dalu et al, 2012). Additionally, the different plant habitats are fundamental for particular groups of zooplankton, creating various life conditions and anti-predator refuges of varying effectiveness (Stansfield et al, 1997;Balayla and Moss, 2003;Sˇpoljar et al, 2012).…”

“…Moreover, most research on small water bodies has concerned the summer season (To˜nno et al, 2003;Iglesias et al, 2007;Lucena-Moya and Duggan, 2011;McGavigan, 2012), when the majority of environmental factors, e.g., availability of a suitable food source or heterogeneity relating to the complexity of macrophyte cover, occur within optimum values. Hence, life conditions for inhabiting organisms are very advantageous at that time.…”

Reversed Diel Horizontal Migration of Fish: Turbidity Versus Plant Structural Complexity as Refuge

“…If predators are present among littoral vegetation and water quality outside the macrophyte stands is not favorable for visual @tion, prey animals may prefer the open water area instead of littoral vegetation zone even during daytime. Some studies have shown that in such situations zooplankton may show reversed DHM behavior, migrating from the vegetation zone to spend the daytime in the open water and returning to the littoral zone for the night (Numinen and Horppila 2002, Iglesias et al 2007). For fish, a common pattern of horizontal migration is movement away from the shordittoral zone at dusk or night to feed on abundant resources and returning to the shore at day (Bohl 1980, Gliwicz et al 2006 To clarify the habitat choice by small fish between a struct~ually complex refuge and a turbidity refuge, we conducted a study in the Kirkkojhi basin in southern Finland The lake is characterized by a very turbid open-water area that is surrounded by zones of floating-leaf and submersed vegetation where water turbidity is substantially reduced due to the reductive effect of macrophytes on sediment resuspension Nurminen 2003 and.…”