Macrophytes as refuge or risky area for zooplankton: a balance set by littoral predacious macroinvertebrates

Abstract

1. Zooplankton use macrophytes as day-time refuge areas when trying to escape from pelagic predators. But macrophytes can also host a diverse and abundant macroinvertebrate assemblage and zooplankton are also likely to face predacious macroinvertebrates once they enter the littoral zone. This study aimed to elucidate the role of macroinvertebrates in determining the refuge capacity of macrophytes. 2. We conducted a field enclosure experiment using plastic bags and complementary laboratory feeding trials to test how macroinvertebrates counteract the benefits to zooplankton of the macrophyte refuge. The field experiment consisted of three treatments with different macroinvertebrate assemblages: without predators (WP), low abundance and diversity (LAD) and high abundance and diversity of predators (HAD -which represents lake conditions). 3. Populations of Diaphanosoma brachyurum, Bosmina huaronensis and Moina micrura (Cladocera) and of both male and female Notodiaptomus incompositus (Copepoda, Calanoida) declined (by nearly 80%) in the presence of HAD in comparison to WP and LAD treatments. 4. Feeding trials revealed that Buenoa sp. (backswimmer), adults of Palaemonetes argentinus (grass shrimp) and Cyanallagma interruptum (damselfly) had a significant negative impact on cladocerans (D. brachyurum, B. huaronensis) and the calanoid copepod population (males, females and copepodites). These predators showed a strong predation effect ranging from 75% to 100% reductions of zooplankton populations. 5. The refuge effect offered by macrophytes to zooplankton depends on and is balanced by the predacious macroinvertebrate assemblage that plants host. The risk of confronting littoral predators is high and macroinvertebrate presence can turn the macrophytes into risky areas for zooplankton.

Diel horizontal distribution of microcrustaceans and predators throughout a year in a shallow neotropical lake

“…Bosmina and calanoid copepods were more sensitive to littoral invertebrate predators in contrast to cyclopoids, in experiments in a South American lake (González Sagrario et al, 2009). Nevertheless, Bosmina can undergo DHM in some lakes, as in a subtropical Uruguayan lake, where B. longirostris performed reverse DHM in spring, probably escaping from chaoborid predation .…”

“…In the littoral zone, migratory organisms can be constrained by onshore predators and lower food quality (Smiley and Tessier, 1998;Wojtal et al, 2007;González Sagrario et al, 2009), by quality of refuges concerning the composition of macrophytes , by unsuitable physical and chemical features, such as low dissolved oxygen within macrophyte stands (Miranda and Hodges, 2000). Actually, this habitat can even be avoided by some zooplanktonic organisms (Dorgelo and Heykoop, 1985;Meerhoff et al, 2006).…”

Fish but Not Macroinvertebrates Promote Trophic Cascading Effects in High Density Submersed Plant Experimental Lake Food Webs in Two Contrasting Climate Regions

“…<3 m in all cases) in Uruguay (30)(31)(32)(33)(34)(35) • S, Lakes Diario, Blanca and Nutrias) and in Denmark (55)(56)(57) • N, Lakes Kogleaks, Stigsholm and Bølling), covering a gradient in submerged macrophyte cover (range: 0-70% plant volume inhabited (PVI), sensu [44]), salinity, pH, turbidity, total nutrients and phytoplankton chlorophyll-a (Chl-a) ( Table 1). In each lake, we conducted a mesocosm experiment during summer (January-April in Uruguay and August-October in Denmark).…”

“…Experimental studies have elucidated the effect of planktivorous fish predation on zooplankton communities in subtropical and Mediterranean shallow lakes [24][25][26][27]. Other studies including field surveys have focused on the effects of fish predation on zooplankton structure [27,28] and behavioral shifts [25,[29][30][31] or the impact caused by predacious littoral macroinvertebrates [32]. A common feature is that predation on zooplankton in subtropical lakes is high [20,33] and that the zooplankton, therefore, is dominated by small cladocerans, nauplii and rotifers [29,[34][35][36][37][38][39], resulting in a lower grazing pressure on phytoplankton in subtropical lakes than in similar lakes located in colder climates [40].…”

“…The typically positive effect of submerged macrophytes on water clarity in temperate shallow lakes [44,45] is substantially reduced in warm lakes [46,47], not least because macrophytes do not act as proper refuges for large zooplankton [29,30]; instead, they host small fish [23,48,49], as well as potential predatory macroinvertebrates like the shrimp Palaemonetes argentinus [32], sometimes in extremely high densities [25].…”