Assessment of three techniques for measuring the biodiversity of molluscs on rocky intertidal shorelines in eastern Thailand

Abstract

Three methods for comparing biodiversity of molluscs are compared on rocky intertidalshorelines near Kungkrabaen Bay, Thailand: timed visual searches, qualitative quadrats, and quantitativequadrats. Visual searches recorded the largest number of living species, 32.3 ± 2.5 (SE), significantly higherthan in either the qualitative (26.5 ± 0.3) or quantitative (24.8 ± 1.0) quadrats. Including dead shells increasedthe mean number of species recorded per site in the visual searches to 60.8 ± 7.1. The numbers of speciesrecorded by individual surveyors at the four sites varied considerably, with more experienced surveyorsfinding more species. It is concluded that a one-hour search is most cost effective. The type of informationthat is required should determine the method chosen. To determine total species diversity in an area, avisual search of living animals and dead shells should be made by an experienced surveyor. Qualitativeor quantitative quadrats are most appropriate where the surveyors are volunteers with little experience incollecting molluscs. Quantitative studies can be used for other purposes such as analyzing trophic structureand species abundance.