Biodiversity of a River Ecosystem

Grade: 7th Grade
Three 1-hour sessions and a 2-hour field trip to the San Lorenzo River or local tributary. Optional 1.5 hour River Health Day
Location: Classroom and San Lorenzo River/local tributary

Materials, transportation and teaching provided free by the Coastal Watershed Council
Supported by generous funding from the County of Santa Cruz Green Schools Program, City of Santa Cruz, the Joseph and Vera Long Foundation.

Supports Next Generation Science Standards:
MS-LS2-3: Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem.
MS-LS2-1. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.
MS-LS2-4. Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
MS-LS2-5. Evaluate competing design solutions for maintaining biodiversity and ecosystem services.

Lesson Series Overview:
Before the 1956 construction of the San Lorenzo River levee there was a large population of Steelhead Trout. The construction of the levee removed critical riparian habitat and consequently the population of Steelhead trout declined. A key factor in the population decline is the reduction of benthic Macroinvertebrates present in the river, a main source of food for Steelhead Trout. Benthic macroinvertebrates depend on the habitat diversity of vegetation in the stream and along the banks of the river for food and shelter. Benthic Macroinvertebrates are small organisms without a backbone that are easy to see without a microscope and spend all or part of the life in or on the bottom of a stream. They are critical to a river ecosystem serving as a foundational piece of the aquatic food chain, support nutrient cycling and decompose leaf litter into smaller pieces.  Students will investigate the relationship between the availability of riparian vegetative resources and benthic macroinvertebrate population size and explore how human development can improve habitat for benthic macroinvertebrates and in turn, habitat for Steelhead Trout.

Students will:
Session #1 (Classroom): Investigate the unique life cycle and habitat requirements of benthic macroinvertebrates and develop a model of how benthic macroinvertebrates interact with the aquatic ecosystem.

Session #2 (FIELD TRIP): During a field trip to the lower San Lorenzo River or local tributary, make observations and collect data on vegetative resources (coarse woody debris, leaf litter, canopy cover) and collect samples of benthic macroinvertebrates in transects.

Session #3 (Classroom): Construct graphic displays of vegetative resource availability and number of benthic macroinvertebrates found in transects during field trip. Analyze and interpret data to provide evidence for how availability of vegetative resources effects the population of benthic macroinvertebrates in the stream.

Session #4 (Classroom): Apply knowledge gained to construct an argument for how human development (logging, levee construction, bank stabilization and log removal) would effect the population size of benthic macroinvertebrates and identify a restoration or mitigation effort that would help ensure habitat diversity and maintenance of benthic macroinvertebrate diversity.

Optional Session #5 (Field Trip): Students participate in a River Health Day along the banks of the lower San Lorenzo River to remove invasive plants or plant native trees and shrubs. River Health Days typically last 1.5 hours and occur year round. All materials provided. Email Mollie Behn, Education Coordinator, at if interested.

Schedule “Biodiversity of a River Ecosystem”
If you are interested in scheduling the “Biodiversity of a River Ecosystem” lesson series and the optional River Health Day, please use the below registration form. Please contact Mollie Behn, Education Coordinator, with any questions at

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