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Methods Manual for Managers: 

      Field Techniques for Algal Research


These methods were developed for research with the Hawaii Coral Reef Initiative Program and are being compiled for a Methods Manual to be distributed by HCRI.  The manual was written by Linda Preskitt and edited by Celia M. Smith and I.A. Abbott of the University of Hawaii, Botany Department, Honolulu, Hawaii.


Algal Collection


     Handling and Pressing

Photoquadrat Framer

Sediment Trap

Light Measurement

Alizarin Stain

Nutrient Enrichment

Photoquadrat Survey Method


To quantitatively assess the benthic community.



Photoquadrat framer

Digital camera with underwater housing



Waterproof data sheets

Ziplock bags

Mesh dive bag

Transect line


Camera Instructions

Settings depend on the type of camera being used. This method was devised using an Olympus C3040Z digital camera in an Olympus underwater housing with 128 Mb Smartmedia and an Ikelite substrobe DS-50 with TTL slave sensor. Set the camera on automatic, forced flash to trigger the slave sensor, and SHQ (super high quality) resolution which yields approximately 55 pictures per media card. When taking pictures, press down part way on shutter for approximately 2 seconds to allow auto focus to engage, then completely depress shutter to take picture.


Datasheet Instructions 

The data sheet is very important for later photo analysis on the computer. Cryptic species in holes or depressions or darker species may be difficult to interpret on the photographs. Information noted on the data sheet will help decipher these hard-to-see areas. The data sheet includes codes for the most common algal species, substrate types, invertebrates and corals that may appear in quadrats. The data sheet also has a map rectangle for each quadrat in which a map of the quadrat will be sketched. During data sheet completion, the second diver "maps" the quadrat by drawing the areas of concern for algae, corals, substrate, etc. and marking with codes.



Determine number of quadrats per transect (minimum 10 per 25 m). Generate random points (statistical program or Microsoft Excel) for placement of framer along transects. Lay out two 25 meter transects parallel to the shore, at least 10 meters apart. If permanent transects are desired, mark the beginning and end of each transect and record location and heading.


Before proceeding with the quadrats on the transect, a sample photoquadrat is taken two meters off the transect in an area with similar topography and flora to that on the transect.




The second diver maps the location of the algae and organisms in the quadrat. This preliminary photoquadrat provides a photographic reference to facilitate analysis of digital quadrats later in the laboratory. Algal specimens are also collected from the sample quadrat for laboratory identification and voucher specimens.


The two divers move along the transect together with one diver operating the camera and the

other changing the framer number and marking the datasheet for the quadrat. For each quadrat the photoquadrat framer's short edge is placed next to the transect with the lower left hand corner of the framer positioned at the random point. The second diver corrects the frame number located on the side of the bottom framer and a photograph is taken. Before moving the photoquadrat, the second diver also fills out the data sheet by listing the macro-algae and organisms within the quadrat by code, to species if possible. The relative abundance of the 5 most abundant algae is noted by using a scale of 1 - 5 with 5 being the most abundant. This number is placed next to or under the corresponding algal code on the data sheet. The second diver also draws a quadrat map of dark areas or cryptic species that may be difficult to identify in the photograph and marks the areas with the appropriate algal codes. Once the data is recorded and the map completed, the photoquadrat framer is moved to the next random point and the previous procedure repeated until all quadrats on each transect are completed (Preskitt et al.).

Algae that cannot be identified in the field are collected for later identification. If permanent transects are installed, minimize algal collections within the quadrats or collect representative sample away from transect.


Photoquadrat Analysis

The digital photographs are downloaded to a computer and placed in a file with date, location and project. Each photograph is reviewed in Adobe Photoshop®. Rotate each photograph so framer material is even on all margins, then crop all the pictures evenly. It is recommended that the framer be minimized so there is less chance of random points falling on the framer in the photographic analysis program. If desired, color correct to lighten dark areas or adjust color to aid in identification.


There are a number of programs that can be used to analyze digital photographs. Area can be calculated with SigmaScan® or ImageJ (, and percent cover is calculated with randomly generated points with Sigma Scan® or Photogrid® (C. Bird, University of Hawaii, Botany Dept.). Photogrid® was designed specifically for ecological application and was used in the design of this method.



Preskitt, L.B., P.S. Vroom, and C.M. Smith. A Rapid Ecological Assessment (REA) Quantitative Survey Method for Benthic Algae using Photo Quadrats with Scuba. Submitted to Pacific Science.


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