Abstract
Background: the context and purpose of the studySemi-quantitative scales are often used for the rapid assessment of species composition and abundance during time-limited surveys. The semi-quantitative SACFOR abundance scale was developed to support the observation of marine habitats, communities and species and is widely used in the UK. As such, there is now a vast accumulation of SACFOR data. However, there several acknowledged limitations associated with its format that prevent re-analysis.Methods: how the study was performed and statistical tests usedA conversion process is proposed here that allows: (i) the merging of taxa within counts or cover data sub-sets; (ii) observations, based on either counts and cover, to be unified into one matrix; (iii) counts and cover data to have an equal weighting in the final matrix; and (iv) the removal of the influence of body size and growth form from the final values. To achieve this, it is only possible to preserve the ordinal structure of the data set.Results: the main findingsSimulations verified that the SACFOR conversion process (i) converted random cover and counts data whilst maintaining the majority of the ordinal structure and (ii) aligned abundance values regardless of whether it was recorded as a cover or count. A case study is presented, that uses real SACFOR observations, to demonstrate the conversion process and the application of statistical analyses routinely used in ecological assessments.Conclusions: brief summary and potential implicationsIt is hoped that the SACFOR conversion process proposed here facilitates: (i) the quantitative re-analysis of the burgeoning SACFOR data repository; and (ii) initiates a debate on alternative methods for the conversion of SACFOR data into analysable end products.
Highlights
The full quantification assessment of the seabed communities is often not possible or necessary
Simulation 1: the fidelity of the conversion process for SACFOR count classes converted to numerical values Simulation 1 generates a random counts dataset, encodes using the SACFOR scale, and applies the numerical conversion process to these codes
The SACFOR conversion process advocated here allows: (i) the merging of taxa within counts or cover data subsets; (ii) observations, based on either counts and cover, to be unified into one matrix; (iii) counts and cover data to have an equal weighting in the final matrix; and (iv) the removal of the influence of body size and growth form from the final values
Summary
The full quantification assessment of the seabed communities is often not possible or necessary. Periodic tidal exposure, high ship costs and the limited bottom time of diving operations, all constrain the time available for the collection of information This constraint is acute when undertaking descriptive or inventory surveys. When standard quantitative sampling that results in counts of individuals or measurements of cover is not practical, biologists have developed various semiquantitative scales, called abundance scales, for the rapid assessment of abundance and cover (e.g. the SemiQuantitative Macroinvertebrate Community Index (Stark, 1998) and EPOS ANTARKTIS Scale (Arnaud et al, 1990) These scales typically contain 5 to 7 broad categories and lack the precision of quantitative methods, they do allow the coarse assessment of abundance both accurately and quickly (Hawkins and Jones, 1992). The Domin scale of cover and abundance (Dahl and Hadac, 1941) remains at the heart of the UK’s National Vegetation Survey (Rodwell et al, 2006)
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