Bermuda’s coral reefs are the northernmost in the world, and one of our richest natural resources; providing a storm surge barrier and a home to a diverse array of marine organisms. It’s important to be able to paint an accurate picture of coral reef diversity and population density of species. A population survey using a quadrat can be an effective way of conducting a survey of a large space in a short amount of time.
Coral Diversity Survey
A quadrat is just a two foot long square with perpendicular lines of twine passing through it to divide it in to four one foot square sections. the idea of a population survey is to place these quadrats at random in an ecosystem and observe the species inside. Quadrats, of course, can only be used to survey plants or sessile animals to maximize their accuracy. Often, quadrats, if dropped a significant number of times, can be more accurate than using a transect line since there is less guesswork involved.
I have used quadrats to conduct reef surveys underwater, and this was done with a larger group. Surveying only works if the quadrat is dropped a significant number of times and at random. There can sometimes be a tendency to drop a quadrat where you know there is a high species diversity in order to inflate your data, or where there is little species diversity in order to lessen the work you have to do!
To conduct your own survey you will need:
- A weighted quadrat or hula hoop. You may want to attach a string to your quadrat for easy retrieval.
- Species ID sheet.
- Clipboard, underwater paper, and pencil to record data.
- Swimsuit, snorkel and mask (no diving required!).
It’s sometimes easier to conduct a survey with a partner – one person acting as a scribe and one diving down to directly observe species. To prevent repeatedly diving down to great depths, it can be beneficial to switch the scribe and diver periodically, and to conduct your survey in shallow water. Once in the water, find the reef and drop the quadrat randomly upon it. After you drop it, swim down and have a look at what is inside.
What’s inside will fit in to one of the following categories:
- Hard (stony) corals. These are diverse in form and sustainable in different habitats. They are resistant to waves. Examples: Brain Coral, Mustard Hill Coral, Starlet Coral.
- Soft coral. These are less diverse in form and sway in the waves to capture particles; this allows them to live in both high and low wave energy conditions. Examples: Common Sea Fan, Sea Rods and Sea Feathers.
While corals and sponges are both animals and can be easily confused, they are different physiologically. Sponges do not have nervous, digestive or circulatory systems and survive by constantly pushing water through their bodies. Corals are made up of polyps which have a symbiotic relationship with zooxanthellae algae.
By estimating the percentage (out of 100) that each of the above categories occupies in our quadrat, an accurate picture of the reef can be painted. Reef Watch is an annual fundraising initiative by the Bermuda Zoological Society (BZS) which allows teams to enter and conduct reef surveys while also raising funds for all of BZS’s research/conservation projects. You can enter with your family/friends and submit your data while endorsing one of Bermuda’s most valuable resources; our reefs.
Fish Diversity Survey
This survey does not use a quadrat because fish move, and so are impossible to record using the quadrat method. A fish survey can be achieved easily, however in a less accurate way than the coral survey method. It involves snorkeling around a site for a a prescribed period of time and recording all identifiable species of fish. The abbundance scores of the species are also recorded.
For the survey you will need:
- A swimsuit, snorkel and mask.
- Clipboard, underwater paper, and pencil.
- Fish ID sheet.
Swimmers are encouraged to record as many species as possible and to actively search for fish in the entire water column. This method is less reliable than the quadrat method because of fish’s mobility and human error – it is easy to count the same fish twice, or to incorrectly ID a fish (especially if you are inexperienced).
The REEF volunteer fish survey project is an ongoing project relying on volunteer “citizen scientists” to submit fish population data from around the island. The data is stored in a universal database to be used by scientists on island and around the world. REEF’s database reports are able to be accessed by the public here.