The sampling of benthic macroinvertebrates using two; different methods: Waiting Trays and an Ekman Collector

ALVES¹, R.G. & STRIXINO¹, G.

¹Departamento de Hidrobiologia - Universidade Federal de São Carlos, km235, CEP 13565-905, São Paulo, Brasil.

ABSTRACT: The aim of this study was to compare the structure and composition of the benthic macroinvertebrate community in the sediment of the Diogo Lake, in samples obtained using two different methodologies. Metal trays with a total surface area of 0.1m² were deposited directly onto the sediment of the lake. Also simultaneous samplings (total: 4, one per month) were done with an Ekman grab, having an area of 0.025m². The sediment in the interior of the trays was characterized by an absence of the > 1mm fraction and also by average values of organic material and nitrogen higher to those found in sediments collected by the Ekman grab. The numeric density values of Polypedilum and Cricotopus obtained using the two collection methods presented significant differences. The elevated abundance of Cricotopus in the waiting trays contributed to the fact that the diversity index value of Chironomidae was inferior and significantly different from the value obtained from the sediment. Campsurus, which was the macro-invertebrate of greatest numerical density in the collected sediment using the Ekman grab, was not significantly high in the trays. Among the Oligochaeta, B. sowerbyi was the most abundant species in the sediment, while L. hoffmeisteri was the most abundant in the trays. The structure and the composition of the macro-benthic community obtained using the two collection methods presented a low percentage of similarity (PSC equal to 27.25%), suggesting that the distinct collection methods are capable of generating different information about the structure of the local fauna.

Key-words: Artificial substrate, Ekman, Chironomidae, Polymitarcyidae, Oligochaeta.