Original Paper

Biodiversity and Conservation

, Volume 22, Issue 13, pp 3223-3232

First online:

Evaluating the efficacy of land snail survey techniques in Hawaii: implications for conservation throughout the Pacific

  • Torsten H. DurkanAffiliated withPacific Biosciences Research Center, University of Hawaii
  • , Norine W. YeungAffiliated withPacific Biosciences Research Center, University of HawaiiSmithsonian Institution, National Museum of Natural History
  • , Wallace M. MeyerIIIAffiliated withDepartment of Biology, Pomona College
  • , Kenneth A. HayesAffiliated withPacific Biosciences Research Center, University of HawaiiDepartment of Biology, Howard UniversitySmithsonian Institution, National Museum of Natural History Email author 
  • , Robert H. CowieAffiliated withPacific Biosciences Research Center, University of Hawaii

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Abstract

Terrestrial micromolluscs (snails with an adult maximum shell dimension <5 mm) constitute a considerable proportion of the land snail fauna of the Pacific. However, micromolluscs are often underestimated in biological surveys because of size bias. It has been argued that visual searches are preferable on Pacific islands because: (1) size biases are limited based on the understanding that most native Pacific island land snails are very small, and (2) amount of labor is less than other methods such as soil surveys and adequate for inventory purposes (though not for abundance assessments). To test whether visual surveys and soil surveys were accurately recording all taxa, land snail inventories were completed in three forest reserves (5 sampling sites in each) on the island of Oahu, Hawaii. Visual surveys involved 30-min visual search in a 10 m2 site; soil surveys involved sieving leaf litter and topsoil from four 0.3 m2 quadrats and extracting snails with the aid of a microscope. The data indicate a size and microhabitat bias associated with both techniques. Visual surveys consistently collected large arboreal and litter-dwelling species but missed a significant portion of micromolluscs, while soil surveys collected micromolluscs but missed larger snails. Because of such biases, employing both methods is critical for collecting all taxa at a survey location. As such, we recommend that future land snail surveys on Pacific Islands incorporate both survey techniques. Obtaining a complete inventory is critical if we are to understand species distributions and patterns of diversity and make well-informed conservation recommendations.

Keywords

Gastropoda Inventory Micromolluscs Mollusca Sampling methods