When we collected the isopods and snails to use as our herbivores in this study, I wasn't actually sure if they would eat the eelgrass. Diatoms (a type of phytoplankton) grow on eelgrass and both the isopods and the snails eat the diatoms off the eelgrass.If the micrograzers were just eating the diatoms, the phenolic acid levels would not change. Last week, after the herbivores had been collected, I put the snails and isopods in separate containers holding only eelgrass that had been cleaned of all the diatoms. This way they would be forced to eat the eelgrass. However, I wasn't sure if they would eat the eelgrass or wait until they found their preferential food.
After the weekend had passed, I checked the containers to see if they had eaten any eelgrass. In the isopod container, the isopods had bitten the edges.
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| Isopod and damaged eelgrass |
In the snail container, the snails had mowed the center of the eelgrass, turning it into lace.
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| Snails and damaged eelgrass |
These results were surprising to me because I did not think the snails would actually eat the eelgrass and that the isopods would cause more damage. Judging by these pictures and the other eelgrass strands, the snails were actually more effective in causing mechanical damage to the eelgrass than the isopods.
While these results were good, the snails and isopods have not been causing the same kinds of damage in the actual experiment. They were put in to the trial tanks on Wednesday. On Friday, the eelgrass was inspected for damage. While I could see a couple of snails and isopods on the plants, I couldn't observe any damage. I did not take the plants out of the tank and do a thorough examination so there could have been unseen damage. However, the trial tanks do have diatoms in them, so it is possible that the snails have gone back to eating diatoms. The tanks will be checked over the weekend and next week to see if damage has occurred.
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