Experiment One
Data collection for algae and snail eggs was made at weeks 1, 2, 4, 6, 8
and 12 of the experiment. Periphyton measurements were recorded from 100
cm2 clay tiles suspended vertically 15 cm from the
bottom of each tank (approximately 20 cm below the water’s surface),
facing south along the northern wall of each tank. Five clay tiles were
added to each tank when they were initially filled with water in June
2011 and July 2015. Each visit, a tile was collected and the
phytoplankton removed using a scrub brush and wash bottle of de-ionized
water to fill a 50mL falcon tube. A separate 50 mL water sample from the
center of the tank was collected for phytoplankton abundance.
Phytoplankton and periphyton chlorophyll (measured as
F0), were measured from samples stored in darkness for
1h, using a handheld fluorometer (Z985 Cuvette AquaPen, Qubit Systems
Inc., Kingston, Ontario, Canada).
Snail egg masses and hatchling density were estimated using two 15 x 30
cm pieces of Plexiglass placed in each tank; one suspended vertically 10
cm from the bottom of each tank and one resting horizontally along the
tank bottom. Visual searches for dead crayfish in tanks with crayfish
predators occurred at 24 and 48 hrs after insecticide addition, and upon
each snail egg sampling session. At the end of the experiment (week 12),
we quantified the number and mass (g) of live snails of each species and
live crayfish in predator tanks. All snails and macroinvertebrates were
collected and subsequently preserved in 70% ethanol. We determined
snail infection under a dissecting microscope by cracking each snail’s
shell and inspecting the hepatopancreas and gonad.