Difference between revisions of "Sampling"
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[[image:sampling.JPG|thumb|right|Fig. 1. Field sampling studies provide crucial information to determine the status and dynamics of marine population and communities. Photo © J.Atalah]] | [[image:sampling.JPG|thumb|right|Fig. 1. Field sampling studies provide crucial information to determine the status and dynamics of marine population and communities. Photo © J.Atalah]] | ||
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Revision as of 18:29, 10 March 2009
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Field sampling programs provide the information needed to determine the status and dynamics of populations and communities and thus are the basis for many kind of research. The physical and biological complexity and dynamism of most marine ecosystems results in high spatial and temporal variability in almost any measured parameter. Sampling methods and procedures need to be carefully analysed and selected so as to take into account this high variability of most marine systems.
The steps in designing a field sampling program include:
- Identifiying the study goals including the questions to be anwered by the study or the hypothesis to be tested.
- Developing and effective and statistically powerful study design.
These steps are followed by selecting study sites, the biological units to be sampled, the sampling design, lay out, and units to be employed, and the type of data to be obtained.
Contents
Site selection
Site selection is an important decision in any sampling program and it should be based to the study objectives. Because most sampling program involves comparisons among sites, they should be physically similar in order to meaningfuly compared and to avoid any confound conclusion. Some geophysicfal variable that have to be cosnidered when choosing for sampling sites include: wave exposure, depth, sustratum type and slope, topographical heterogeneity, salinity and the degree of human or natural perturbation. Site selection protocols should involve identifying a set of sites that are similiar in terms of abiotic characteristics, and then randomly choosing a subset for study from thsi site pool. Additionally, sampling should be focused in on habitas of high value or to high sensitivity to suspected stressors and, if it is useful to consider trends over a large region, on habitats that are broadly present.
Biological units
Sampling Design
Types of sampling studies
Field sampling studies can be clasified into four categories: [1]
1. Baseline studies
Data are collected to define the present state of a biological population or community. They are also called "one-off" studies, because by definition, they are not replicated in time. Results can be used to produce a record of a baseline condition prior to a given perturbation. Another goal of one-off study is to stablish a baseline for the system against which any future impact can be tested. The lack of temporal replication in baseline studies does not allow to quantify natural variability in biological parameters and, thus, to distinguish future changes from a particular stressor from those related to natural variations.
2. Impact studies
Impact studeis are designed to determine the changes brought about a particular disturbance or stressor by comparing the status of natural or unimpacted biological parameters with their status under unimpacted conditions. Green’s [2] work on impact sampling design was pioneer in the development of impact assessment studies and statistical methods. Since then various authors has discuss the advantages and disadvantages of different impact study designs. [3] [4] [5] [6] [7]. Several sampling designs has been used in performing field studies to test impacts. One of the most robust and commonly used is the asymmetrical BACI design (before-after control impact design), where data are colleted on multiple ocassions from both before and after an impact, usually from one impact and several controls sites.[8] [9] [10] Another commonly used sampling design is the gradient design where sites are distributed ar various distances from a central impact sites, creating a gradient and of control and impact conditions.
3. Monitoring studies
These are designed to detect any changes from the present state. By definition, monitoring studies involve reapeted sampling in time. Monitoring programs in marine environments have focused on chemical, physical, and biological parameters, for example detecting microbial contamination of beaches, determining the concentration of potential harmful material on fish, estimating the population abundance of an endagered species inside a marine reserve. Some key aspects of an effective monitoring program are [11]:
- It must be carried out over a long periods and designed to account the natural variability of the system.
- It must be designed using the best available ecological concepts, study design, and principles.
- The data must be collected in a consisted and well-documented manner to achive required continuity and reliability.
- The program should be designed to detect changes and impacts based on sound statistical analyses.
4. Pattern and process (ecological) studies
These studies involve describing distribution and abundance patterns of organisms, with the intention of identifying the processes resposible for them. For this, prupose descritive ('mensurative') and experiemntal approaches should be used. [12]
For details of the different tools available to for sampling a range of different marine environments see: Sampling tools
References
- ↑ Kingsford M, Battershill C (1998) Studying temperate environments. Canterbury University Press, Christchurch, New Zealand, 335 pp.
- ↑ Green, R. H., 1979 Sampling design and statistical methods for environmental biologists. Wiley, New York.
- ↑ Underwood, A. J., 1991. Beyond Baci - Experimental-Designs for Detecting Human Environmental Impacts on Temporal Variations in Natural-Populations. Australian Journal of Marine and Freshwater Research 42: 569-587.
- ↑ Underwood, A. J., 1992. Beyond BACI: The detection of environmental impacts on populations in the real, but variable world. Journal of Experimental Marine Biology and Ecology 161: 145-178.
- ↑ Underwood, A. J., 1994. On Beyond BACI: Sampling Designs that Might Reliably Detect Environmental Disturbances. Ecological Applications 4: 3-15.
- ↑ Osenberg, C. W. & R. J. Schmitt, 1996. Detecting ecological impacts caused by human activities. In Schmitt, R. J. & C. W. Osenberg (eds.), Detecting ecological impacts: Concepts and applications in coastal habitats. Academic Press, San Diego: 3-16.
- ↑ Ellis, J. I. & D. C. Schneider, 1997. Evaluation of a gradient sampling design for environmental impact assessment. Environmental Monitoring and Assessment 48: 157-172.Ellis, J. I. & D. C. Schneider, 1997. Evaluation of a gradient sampling design for environmental impact assessment. Environmental Monitoring and Assessment 48: 157-172.
- ↑ Underwood, A. J., 1991. Beyond Baci - Experimental-Designs for Detecting Human Environmental Impacts on Temporal Variations in Natural-Populations. Australian Journal of Marine and Freshwater Research 42: 569-587.
- ↑ Underwood, A. J., 1992. Beyond BACI: The detection of environmental impacts on populations in the real, but variable world. Journal of Experimental Marine Biology and Ecology 161: 145-178.
- ↑ Underwood, A. J., 1994. On Beyond BACI: Sampling Designs that Might Reliably Detect Environmental Disturbances. Ecological Applications 4: 3-15.
- ↑ Murray SN, Ambrose RF, Dethier MN (2006) Monitoring rocky shores, Vol. University Of California Press, Berkeley and Los Angeles, California
- ↑ Andrew NL, Mapstone BD (1987) Sampling and the description of spatial patterns in marine ecology. Oceanography and Marine Biology: An Annual Review 25: 39-90
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