Abstract
The characteristics of coral reef sampling and monitoring are highly variable, with numbers of units and sampling effort varying from one study to another. Numerous works have been carried out to determine an appropriate effect size through statistical power; however, these were always from a univariate perspective. In this work, we used the pseudo multivariate dissimilarity-based standard error (MultSE) approach to assess the precision of sampling scleractinian coral assemblages in reefs of Venezuela between 2017 and 2018 when using different combinations of number of transects, quadrats and points. For this, the MultSE of 36 sites previously sampled was estimated, using four 30m-transects with 15 photo-quadrats each and 25 random points per quadrat. We obtained that the MultSE was highly variable between sites and is not correlated with the univariate standard error nor with the richness of species. Then, a subset of sites was re-annotated using 100 uniformly distributed points, which allowed the simulation of different numbers of transects per site, quadrats per transect and points per quadrat using resampling techniques. The magnitude of the MultSE stabilized by adding more transects, however, adding more quadrats or points does not improve the estimate. For this case study, the error was reduced by half when using 10 transects, 10 quadrats per transect and 25 points per quadrat. We recommend the use of MultSE in reef monitoring programs, in particular when conducting pilot surveys to optimize the estimation of the community structure.
Highlights
The intrinsic value of coral reefs and their relevance in terms of services provided to human societies makes them an object of constant observation, because some ecological processes operating in the reefs occur at large spatial and temporal scales, coral scientist face the challenge of obtaining data while keeping a compromise between high precision, reproducibility, and statistical power, with low cost and time (Aronson et al, 1994)
1) In order to increase the number of sampling sites, we used a variation of the Global Coral Reef Monitoring Network protocol (2016) and used four instead of five 30 m transects, 15 photo-quadrats per transect, placed one another meter, and 25 random points per quadrat
We evaluated the potential of the pseudo multivariate dissimilarity-based standard error as a tool to determine the appropriate number of transects to sample coral assemblages
Summary
The intrinsic value of coral reefs and their relevance in terms of services provided to human societies makes them an object of constant observation, because some ecological processes operating in the reefs occur at large spatial and temporal scales, coral scientist face the challenge of obtaining data while keeping a compromise between high precision, reproducibility, and statistical power, with low cost and time (Aronson et al, 1994). Coral reef typical sampling and monitoring have usually relied on plot methods, like belt transects; plotless methods, like line-intercept method; or a combination like the point-intercept method. The CARICOMP protocol relied on the chain method to identify the substrate underneath each chain link on ten 10m transects (CARICOMP, 2001); while AGRRA protocol gets estimates from six 10m transects for shallow reefs (Lang et al, 2010). The copyright holder for this preprint It is made available under coral cover (Nadon and Stirling, 2006; Leujak and Ormond, 2007)
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