Typhloplanid flatworms (Mesostoma and related genera): Mechanisms of predation and evidence that they structure aquatic invertebrate communities

Abstract

Mesostoma species and other typhloplanid flatworms are predators found in a wide variety of habitats . Laboratory observations of some Mesostoma spp found in shallow aquatic habitats (referred to as `littoral species') have revealed a wide variety of prey killing mechanisms : 1) mucus trapping, 2) sit-and-wait predation, 3) releasing a toxin into the water, and 4) active searching. We review the existing literature on these mechanisms . We also describe for the first time the predatory behavior of a pelagic Mesostoma sp . found in Brazilian lakes .The existing literature is also reviewed to assess the potential impact of Mesostoma species and related genera on the aquatic invertebrate community . Mesostoma has a high potential for population increase and has been found in high densities in some shallow aquatic habitats . Single prey experiments show that a number of Mesostoma species feed heavily on mosquito larvae, some chironomid larvae and some daphnids but considerably less on most copepods and ostracods . Prey preference experiments reflect the same trends . Hence, these predation studies suggest that the flatworms, at high densities, should reduce populations of certain prey speces and, consequently, alter community structure . Field studies support this prediction . Mesostoma species, at high densities, appear to be important predators of mosquito larvae in shallow aquatic habitats even under conditions where high densities of planktivorous fishes had little impact. They also appear to alter zooplankton community structure . However, much of the field evidence is correlational and not experimental . No studies have assessed the impact of pelagic typhloplanids on zooplankton community structure .It is concluded that many more manipulative field experiments are needed to assess the impact of typhloplanids on aquatic invertebrate communities .

Demography and feeding behavior of Stenostomum leucops (Dugés, 1828)

“…They could be a link in channelizing energy between the pelagic and benthic zones but there are few studies on the interaction of organisms from both zones (Threlkeld, 1994). Published data suggest that an increase in density of flatworms leads to decreased zooplankton such as Daphnia and Bosmina (Caramujo and Boavida, 2000), and Moina (Blaustein and Dumont, 1990). In this study we observed highest densities of S. leucops on E. dilatata and A. glabra, both species share a similar habitat of littoral regions of water bodies as the worm (Kolasa and Tyler, 2010).…”

“…Freshwater turbellarians can be found in headwater streams to large rivers and in wetlands to large lakes where they are part of the bottom, surface and interstitial benthos (Schwartz and Hebert, 1982;Blaustein and Dumont, 1990). They can also be found in very small streams and brooks or on different types of substrates (e.g., moss, vascular plants, wood snags, detritus, gravel, or sand) in the littoral areas of rivers (Noreña et al, 2005).…”

“…Turbellarians use various mechanisms to capture their prey, including: active search, sit and wait, toxins release or secretion of mucus traps (Blaustein and Dumont, 1990). For example, it has been shown that Mesostoma lingua is able to prey on Daphnia magna releasing a toxic mucus trap that paralyzes the prey, and then, engulfs it with the ventral area of its body and sucks the prey (Dumont and Carels, 1987).…”

Zooplankton of Fishless Ponds of Northern Patagonia: Insights into Predation Effects of Mesostoma ehrenbergii

“…The fact that copepods were readily consumed by Mesostoma differs from previous studies on lakes of the Northern Hemisphere, where cladocerans were more consumed than copepods (MALY et al, 1980;SCHWARTZ and HEBERT, 1982;ROCHA et al, 1990;BLAUSTEIN and DUMONT, 1990). HEBERT (1982, 1986) suggested a large impact of Mesostoma on intermediate-sized cladocerans (~1.2 mm) in the arctic, and hence a shift from a cladoceran-dominated to a copepod-dominated community structure.…”

“…On the other hand, Mesostoma had low consumption rates on the copepod B. michaelseni, which is about the same size as C. dubia. We did not use smaller cladocerans, such as chydorids, in our experiments because previous studies indicated that these small prey (< 0.5 mm) are ignored by Mesostoma (SCHWARTZ and HEBERT, 1982;BLAUSTEIN and DUMONT, 1990).…”