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Determine Appropriate Sampling Effort for Reliable Assessment
- Classify coral reefs
- Develop testable hypotheses
- Define data collection protocols
- Biological sampling
- Screen attributes to define metrics
- Determine appropriate sampling effort
- Define data protocols
- Validate decision processes
- Define biocriteria
- Implement monitoring programs
- Diagnose causes of degradation
- Evaluate management effectiveness
- Communicate results
Consider seasonal patterns and define an index period.
For biological systems in temperate regions, seasonal patterns may strongly influence when organisms can be collected. Seasonal patterns may be less of a concern for monitoring tropical coral reefs than are patterns associated with years or longer time periods. Global climate patterns can influence coral survivorship and may occur over cycles that last several years. In this case, it may be necessary to sample the same set of reference sites every year to define reasonable expectations for local reefs in the context of changing global conditions.
Consider the level of replication needed and optimal sampling unit size.
Some water bodies, such as lakes, can be easily recognized as discrete units. For a continuous resource, such as coral reefs or rivers, the individual sampling units are not as easy to define. Each sampling unit, or reef station, must be defined as a piece of the continuous reef. The size of the sampling unit matters: it must be large enough to reliably characterize reef condition in that location but it must be small enough that data collection can be completed within a reasonable amount of time. In general, for regional survey sampling, many sites with coarse information are preferred over a few sites with detailed information.
Figure. Radial belt transect used to sample coral reefs.
In the US Virgin Islands, coral metrics derives from different sized sampling units will be compared to determine the optimal area to measure at each reef station. The sampling protocol uses a belt transect to delineate a sampling unit. To define the belt, a center point is marked and 2 lines are attached to the center and used to define 2 concentric circles. The belt transect is the area inside the larger circle and outside the smaller circle.
To determine the optimal size for sampling units, each belt transect will be divided into 4 sections and the section noted for each coral colony measured. Results for each reef station will be compared from 1/4 transects and 1/2 transects. Duplicate samples from different crews on the same or nearby reef stations will provide data to compare 1/4 and full transects.
Figure. Divers delineate a radial transect by stretching a line from a central tripod. The line tender holds the line taut while the coral counter measures and records colony size and identity.
The different sized sampling units will be compared in 2 ways. First, metrics calculated from each size of sampling unit will be tested for correlation with a gradient of human disturbance. We expect larger sample areas to be both more highly correlated with disturbance and to be less variable because larger areas represent more information. The second test will compare the variance of coral metrics calculated from the different sized sampling units. If different sizes have similar correlation with disturbance and similar variability, the smallest sampling unit will be selected.