A comparison of three methods for estimating Macrozoobenthos diversity and abundance in a tropical seagrass meadow
The intertidal reef flat surrounding the Island Barrang Lompo in the Spermonde Archipelago / Indonesia is covered by an extensive seagrass meadow dominated by Enhalus acoroides and Thalassia hemprichii. In this study three methods for estimating the diversity and abundance of macrozoobenthic organisms were compared: 18 replicate sediment cores (16 cm diameter, to 30 cm depth) were taken and the content was sieved over a 1 mm screen. All organisms living (partly) on top of the sediment or leaving visible signs of their presence (e. g. burrow openings, sediment expulsion mounds) were counted within three replicate circles of 6 m diameter. Three replicate plastic foils (3 * 4 m) were installed on top of the sediment and their surface covered with a thin layer of sand. Subsequently, all organisms that either lived on the surface or were found emerging under the plastic foil in search of oxygen were collected after 24, 48 and 72 hours. The by far largest number of species (ca. 250) was found using the plastic foil method, followed by the corer (ca. 75) and the counting circles (ca. 30). Estimates for the abundance of small species that live on or near the surface were highest with the corer method. Larger and deep burrowing species were only caught with the plastic foil and their numbers were much higher than estimated from surface signs. It is concluded that the plastic foil method has a high potential to enhance studies of both diversity and abundance, especially regarding large and deep burrowing organisms which have no surface activity, are impossible or very difficult to catch using other methods, and therefore often underreported.