Trophic Cascades in Salt Marsh Ecosystems

Question 1

salt marshes

Answer 1

found in protected coastal waters of protected temperate zones

• one of the most productive ecosystems

Question 2

importance of marshes

Answer 2

• pollution filters
• protect shorelines from erosion
• important for fisheries production

Question 3

abundance of plants in an ecosystem

Answer 3

can be controlled from bottom up or top down

Question 4

bottom up

Answer 4

abundance is limited by the resources available to the plants

i.e. water availability, sunlight, and nutrients in the soil

• salt marshes were originally thought to be bottom up

Question 5

top down

Answer 5

controlled by the animals that eat the plants
- controlled by herbivores and their predators

Question 6

salt marshes and bottom up

Answer 6

• salt marshes were originally thought to be bottom up until a researcher walked through the salt marshes and discovered an abundance of snails

Question 7

snails

Answer 7

• marsh periwinkle snail
• medium sized snail (up to an inch long)
• go up and down grasses w/ tides

Question 8

hypothesis

Answer 8

if the salt marshes were controlled by the snails eating it (from the top down)

to test: measuring plant growth
- set up comparison plots in the marsh
(bottom-up) added nutrients (fertilizers) to some plots and not others
- add fertilizer into pantyhose and centrifuge that
- use exclusion cages
= 6 months
- 100% increase in plant growth (confirmation of bottom up theory)

(top-down) added snails to some plots and not others
- fertilized plants were yummy and effectively wiped out marsh in those plots

Question 9

exclusion cages

Answer 9

1m squared roofless corrals
- made of hardware cloth and tomato stakes which are corner anchors that keep them out

Question 10

conclusion from experiment

Answer 10

• abundance of grass and marshes, full of periwinkle, is controlled top-down
• if given the chance, the snails will eat all the grass
  next question: what keeps the snails in check?

Question 11

what keeps the snails in check?

Answer 11

blue crabs
- eat snails and mussels

experiment:
- tether (glue snails to pieces of fishing line) snails that’s tied to a PVC pipe
- placed snails in healthy areas of the marshes (w/ lots of grass)
= 90% of the snails were killed by blue crabs

• placed areas with little grass
• no sign of predation,
• all but 1 snail survived

experiment suggested; where the marsh is healthier, there are more less snails bc they’re being eaten by the crabs
- but this just shows correlation

REAL EXPERIMENT:
- put out cages to exclude some blue crabs
- baby snails entered w/ planktonic larvae
- over 2 year period, the snail numbers increased inside cages where we did not allow crab access
- here, all the grass was dead

Question 12

whatever surpresses snails

Answer 12

has a positive impact on the plants

Question 13

trophic cascades

Answer 13

• crabs protect the grass by controlling the number of snails, who if left unchecked, would eat all the grass

Question 14

who did the experiments here

Answer 14

Dr. Brian Silliman
- Duke Marine Lab