Optimizing Costs to Collect Local Infauna through Grabs: Effect of Sampling Size and Replication

Lidia N Álvarez,Fernando Tuya,Rodrigo Riera,Sara García-Sanz,Néstor E Bosch

doi:10.3390/d12110410

Abstract

Most ecological studies require a cost-effective collection of multi-species samples. A literature review unravelled that (1) large-sized grabs to collect infauna have been used at greater depths, despite no consistent relationship between grab size and replication across studies; and (2) the total number of taxa and individuals is largely determined by the replication. Then, infauna from a sedimentary (sandy) seabed at Gran Canaria Island was collected through van Veen grabs of three sizes: 0.018, 0.042 and 0.087 m2 to optimize, on a simple cost-benefit basis, sample size and replication. Specifically, (1) the degree of representativeness in the composition of assemblages, and (2) accuracy of three univariate metrics (species richness, total infaunal abundances and the Shannon-Wiener index), was compared according to replication. Then, by considering mean times (a surrogate of costs) to process a sample by each grab, (3) their cost-efficiency was estimated. Representativeness increased with grab size. Irrespective of the grab size, accuracy of univariate metrics considerably increased when n > 10 replicates. Costs associated with the 0.087 m2 grab were consistently lower than costs by the other grabs. In conclusion, because of high representativeness and low cost, a 6.87 L grab appears to be the optimal sample size to assess infauna at our local site.

Highlights

Most ecological studies, in community ecology, require collection of multi-species samples through varying sampling techniques, e.g., quadrats, cores, grabs, transects, traps, etc
We firstly investigated the influence of the depth of collection and sampling effort on the size of the grab used across studies
The replication used across studies was insufficient to reach a plateau for the total number of taxa (Figure 1C), while a plateau beyond ~150 samples was observed for the total infaunal abundance (Figure 1E)

Summary

Introduction

In community ecology, require collection of multi-species samples through varying sampling techniques, e.g., quadrats, cores, grabs, transects, traps, etc. At the start of any ecological study, researchers often select the size and replication of their sampling units based on previous studies and, less often, using results from initial pilot studies [1,2,3]. The choice of these sampling properties is, a complicated task with direct implications in subsequent costs, in terms of time and money. The size of a sampling unit is primarily determined by the target organism’ size and distribution pattern, i.e., random, uniform or clumped [5].

Methods

Results

Conclusion