Intertidal Quadrat Studies: Overview

Why is the intertidal zone important?

The intertidal area is an important indicator of the overall health of the marine environment.

It is home to many intertidal species, and it acts as a nursery for numerous subtidal (deeper water) species.

Because it’s easily accessible -- you can get there every time the tide goes out -- the intertidal zone gives us a great opportunity to learn about marine life.

But it is also the area most vulnerable to human impacts such as trampling, over-harvesting, pollution from plastic, debris, oil spills and shoreline development. So it's important to practice careful stewardship when you're visiting the intertidal zone.

What are intertidal quadrat studies?

Quadrat studies are biological assessments that use a grid system as a method of collecting data.

Georgia Strait Alliance's intertidal quadrat studies gather data on the abundance and diversity of species on the beach, at specific tide heights. We repeat the studies each year, at the same locations, in order to gather data on changes in the marine life. This information is important in assessing the overall biodiversity of local beaches.

In our intertidal quadrat studies, we use square frames (quadrats) that are 50cm x 50cm and are strung with string to form a grid with 36 intersections.

These quadrats are put down on the beach along a transect line (a line that runs perpendicular to the shoreline) at 1.0m, 1.5m, 2.0m, 2.5m, 3.0m, and 3.5m above the zero tide line.

Intertidal life within each quadrat frame is identified and recorded, using one method to identify what is on top, and another for what lives underneath the rocks.

What is required to do quadrat studies?

1. A bedrock and/or cobble beach, with rocks that are no smaller than the size of a fist and not so large that they are difficult to turn over.

2. A low tide that goes below 1.0m (the best times for low daytime tides in our region are spring and summer).

3. Volunteers must learn to lay out the transect line and position the quadrat frames along it. The line can be set up with measurements taken in relation to stable landmarks, so that we can reposition it in the same place for later studies.

4. Volunteers must learn how to identify common species on the beach and how to look at and record what is there.

5. Detailed instructions for doing an intertidal quadrat study.

What is Georgia Strait Alliance’s history with quadrat studies?

Our inspiration came from in 1991 at the State of the Strait conference, which we hosted in Nanaimo. Shannon Bard, a biology student at the time (now a professor at Dalhousie University), presented a paper titled, “The Effects of Pulp and Paper Mill Effluent on the Marine Environment and its Life”, which summarized the results of an intertidal population study that she had conducted using quadrat studies.

 

We began using quadrat studies in 1992. Since then, we have introduced hundreds to quadrat studies. We have worked with schools in the Nanaimo area and have produced two educational resources: The Straitkeeper’s Handbook, a book of activities for teachers, and Beach Critters, a short video showing a group of young people carrying out a quadrat study.

 

In 1994, we began working with the Burrard Inlet Environmental Action Program to train adult volunteers in a more rigorous methodology, in order to gather usable data. In 1998 the program was taken over by the Vancouver Aquarium.

 

Starting in 1997, we coordinated a series of quadrat studies in the mid-Vancouver Island area. Today, active teams of these volunteers, called “Straitkeepers”, carry out quadrat studies each summer in the Victoria area and on Pender and Cortes Islands.

 

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