These are some of the research techniques we teach in our Cape RADD filed course and actively use in our research projects. Many of these techniques are standardised around the world so that measurements can easily be compared. Learning these skills will prepare you for a career in marine biology at places like NOAA where these techniques are actively used to monitor reef and fish systems.
Line Point Intercept
The line point intercept method is borrowed from terrestrial research where it is used as a fast and precise method for quantifying soil and vegetation cover. In the marine ecosystem it is used to identify and assess coral, algae, bacteria, sessile macroinvertebrate, fish and sand cover. Two 25 m transect lines are set in a single file with a 5 m inter-transect space, and measurements of species presence are taken by SCUBA divers at 20 cm intervals along these transects. Photographs are also taken at 2 m intervals for analysis with the software Coral Point Count with Excel extensions. The Roving Diver Technique can also be used along this transect with divers recording species richness in a 3-5 m swath on either side of the transect line
Schmid, W. D. (1965), Distribution of Aquatic Vegetation as Measured by Line Intercept with Scuba. Ecology, 46: 816-823. doi:10.2307/1934014
Schmitt, E. F., Sullivan, K. M. (1996), Analysis of a Volunteer Method for Collecting Fish Presence and Abundance Data in the Florida Keys. Bulletin of Marine Science, 59: 404-416.
This technique can also be used with the LPI method, or independently as a point intercept method where random points are sampled within an area of interest. When used with LPI a 0.18 m2 photoquadrat framer is placed at each interval along the transect line to take a downward facing photograph of the substrate. Additional metadata is collected to supplement each photograph, particularly where visibility may be difficult. Each photograph is then georeferenced in QGIS to estimate area and percent cover.
Preskitt, L. B., Vroom, P. S., Smith, C. M. (2004), A Rapid Ecological Assessment (REA) Quantitative Survey Method for Benthic Algae Using Photoquadrats with Scuba. Pacific Science, 58: 201-209. doi:10.1353/psc.2004.0021
This method is also used in conjuction with the LPI, often to estimated coral condition and demographics. Divers collect data along the LPI transects in five 2.5 m segments, with a 2.5 m gap between each segment. All coral colonies whose centre falls within 0.5 m on either side of the transect line are identified. Maximum diameter of the colony is recorded, as well as the maximum diameter perpendicular to the maximum diameter. Extent of mortality is estimated, along with any evidence of disease . In cases of disease, the percentage of the colony affected, lesion severity, and levels of coral predation are also recorded.
Walters, R. D. M., Samways, M. J. (2001), Sustainable dive ecotourism on a South African
coral reef. Biodiversity and Conservation, 10:2167-2179.
Stationary Point Count
In this Underwater Visual Census, divers record the number, size, and species of all fishes observed within imaginary cylinders 15 m in diameter at the 7.5 m and 11.5 m marks along a 30 m transect line. The first 5 minutes of the survey are spent creating a list of all the fish species that are observed within or passing through their cylinder. After the first 5 minutes, divers then proceed through their species list and count the number and estimate total length of each fish.
Bohnsack, J. A., Bannerot, S. P. (1986), A stationary visual census technique for quantitatively assessing community structure of coral reef fishes. NOAA/National Marine Fisheries Service, (NOAA Technical Report NMFS, 41)
Baited Remote Underwater Video Station
This is a system in which fishes are attracted into the field of view of one or more underwater cameras. In the case of multiple cameras, fish length and distance from the camera can be estimated using stereo techniques. Footage is subsequently analysed to record diversity, abundance and behaviour. This low impact technique allows for minimally invasive and cost effective monitoring of fish populations for long term study.
Mallet, D., Pelletier, D. (2014), Underwater video techniques for observing coastal marine biodiversity: A review of sixty years of publications (1952–2012). Fisheries Research, 154:44-62. doi:10.1016/j.fishres.2014.01.019
This is a technique commonly used in terrestrial ecology to estimate population size. In this technique a portion of the population is captured, marked and released back into the population. After a period of time another portion of the population is captured and the number of previously marked individuals in this sample is used to estimate the total population size. Additional parameters like survivability can also be estimated using extensions of this technique.
Seber, G. A. F. (1986), A Review of Estimating Animal Abundance. Biometrics, 42:267-292. doi:10.2307/2531049
Hook-and-line sampling provides a method where biases due to diver presence can be eliminated. Estimates of relative density can be made directly from catch records. This method also allows access to non-sessile species for studies that require capture, such as the mark-recapture techniques employed by tag-and-release studies.