A lesson plan for exploring the marine invertebrate diversity at Garrison Bay
Introduction
The microhabitats of Garrison Bay provide an excellent system in which to explore the roles of biotic and abiotic variables, such as substrate type and desiccation, in structuring the distributions of species in the intertidal. Interesting comparisons can be made between the composition and abundance of marine invertebrates found in association with different microhabitats (e.g., rocks, wood, shells, and mud) at the site.
Soft sediment is the primary substrate in terms of aerial extent at Garrison Bay. Much of the diversity that you will be exploring is found in, on, or around the mud. Precautions should be taken to minimize your impact on the soft sediment habitats found at the bay. As you will discover, moving across the tidal flat can be challenging and results in a swath of churned up mud. Try to restrict the movement of your group and all activities to small subsets of the intertidal zone, leaving much of it in the state in which you found it.
Click here for a copy of the
handout provided during the 2004 MIZ class field lesson, which includes
major themes and questions, temperature graphs, and a species checklist.
Lesson Goals
Supplies Needed
Surficial Transect Exercise
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Dead Shell Microhabitat Exercise
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Preparation
Surficial Transect Exercise Lay out transect across different microhabitats using two ropes, stakes, and flagging tape. The two ropes should be spaced approximately one meter apart and run from the upper intertidal diatomaceous layer to the lower intertidal mud, and intersect exposed rocky patches along the way. |
Dead Shell Microhabitat Exercise Buckets of water should be placed along the edge of the dock along with sieves to facilitate sieving of samples in the case where low tide precludes sieving directly in the bay. |
Activities
Timeline
I. |
Introduction (10 minutes) |
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II. |
Sketch from the log, looking towards the northeast, a portion of the intertidal noting microhabitats or changes in surficial characteristics (5 minutes) |
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III. |
Sediment depth demo (10 minutes) |
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IV. |
Split into two groups
(approximately 5 students each) with each group doing one
of the two activities (45 minutes)
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V. | Groups rotate - Group A to shell microhabitat activity and Group B to Transect (45 minutes) | ||||||||||||||||||
VI. |
Discussion &
synthesis
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VII. | Opportunity to make mud angels and compete for a bag of candy (5 minutes) |
Sediment depth demonstration
Using a shovel, excavate a hole in the mud to show the students the layering of sediments with depth (diatomaceous upper layer, anoxic mud, and clay layer).
Discuss the influence of each of these layers on the distribution
of organisms in the sediment, as well as the physical factors creating
these depth gradients. How might the inclusion of coarse shell material
in the sediment affect the infaunal environment?
Discuss the role of the diatomaceous layer in contributing to high oxygen
content at the sediment-water interface, its role in inhibiting sediment
mixing and water infiltration into the sediments below the diatomaceous
layer, and its contribution to the preservation of traces and organisms
in the fossil record.
Also, point out different types of surficial features
on the mud for students to look for throughout the exercises (e.g. sizes
and types of burrows, tracks).
Provide a few examples of organisms and their associated burrow and/or
trail (e.g. Paranemertes and its mucous trail, Abarenicola and the coiled
sediment excrement near its burrow).
Transect Exercise
Starting in the upper intertidal, groups should traverse the transect, making note on their faunal list of different taxa they observe. Groups should indicate what microhabitat each species was found in.
Encourage groups to excavate a few small holes using either a shovel or trowel to look at infaunal diversity.
Encourage groups to explore some of the burrows they observe - can they determine what animals are responsible for those burrows?
Dead Shell Microhabitat Exercise
Have students pick up approximately 5 dead shells located on the sediment surface which contain sediment. Using the sieves, students should screen wash the sediments within the shells and keep a list of the diversity and abundance they observe.
Students should then use the shells to scoop up surficial sediment, sieve it, and compare their results with what was observed in the dead shell microhabitats.
Are there any differences you observe between the animals found living in association with dead shells and those living directly in the surficial sediment?