Crayfish Predation on Snails in Different Environments

By: Diontae Matthews, Kathryn Schwartz, Chris Symons

Background Information.

Certain species of snails react to chemical cues given off by active crayfish. (Alexander, et al. 1991)

An experiment was conducted earlier this month in which the results showed that the average snail size is bigger in ponds with fish and detritus. (ZOL 440)

Introduction

Previous experimentation found that, in ponds with fish, snails were actually significantly larger than the ponds without fish.

It was speculated this was due to the presence of fish-created detritus, which could provide cover to snails and allow them to feed while protecting them from predators.

Question Do detritus v. sand habitats play a role in snail survival from crayfish predation?

HypothesisHabitat (detritus v. sand) will influence survival rate by changing the behavior

of Gyraulus snails

Why do we care?Snails eat algae and can help keep ponds

clearSnails play an important role in the food web

of ponds they are found inThis could help display the optimal foraging

theory in the crayfish

MethodsCollect predator (Northern Clearwater Crayfish, Orconectes propinquus) and prey

(Gyraulus snails)Setup tanks and include bubblers to simulate a high oxygenated habitat (fast

flowing streams)Create two different habitats-

DetritusSand (No detritus)

Data collection and analysis

Results

T-test ran with the data from the two habitats collected over time.p=.0014df=28

Results Continued

Discussion“Crawling above the water line… is an adaptive response to predation”

(Alexander et al. 1991)

Size of snails eaten.“Predators feeding selectively on certain prey sizes can

affect the size distribution of prey populations” (Nystrom and Perez, 1998)

Snails gravitated to detritus, but crawled up walls if detritus was absent.“Snails… migrated up vertical surfaces in response to

chemical alarm signals from feeding crayfish” (Lewis, 2001)

Discussion Pt. 2Potential Errors:

Certain crayfish eat detritusStudy conducted found that 100% of crayfish stomachs surveyed

contained detritus or grain sediment. (Alcorlo, et al. 2004)Duration of trial period was shorter than ideal.

Given more time, we may have been able to see a more distinct difference in snails eaten

Snail size measurementsThis is an important measure because it may show prey

preference

Snail behavior in response to different predators- swimming vs. grounded

Crayfish preference for smaller v. larger snails

Snail behavior in detritus/no detritus with a predator that doesn’t eat detritus

Whether or not snails develop less hard shells, when they have the protection of detritus (snail shell size is adaptable - Auld/Relyea, 2010), etc.

Future Implications

Questions?SOURCES:

Alcorlo, Paloma, Marina Otero, and Walter Geiger. "Feeding Preferences and Food Selection of the Red Swamp Crayfish, Procambarus Clarkii, in Habitats Differing in Food Item Diversity." Crustaceana 77.4 (2004): 435-53.

Alexander, J. E., and A. P. Covich. "Predator Avoidance by the Freshwater SnailPhysella Virgata in Response to the Crayfish Procambarus Simulans." Oecologia 87.3 (1991): 435-42. Web. 31 July 2015.

Lewis, David Bruce. "Trade-Offs Between Growth And Survival: Responses Of Freshwater Snails To Predacious Crayfish." Ecology (2001): 758-65. Print.

Nyström, Per, and Jose Pérez. "Crayfish Predation on the Common Pond Snail (Lymnaea Stagnalis): The Effect of Habitat Complexity and Snail Size on Foraging Efficiency." Hydrobiologia 368.1-3 (1998): 201-08. Kluwer Academic Publishers. Web. 31 July 2015.