Two techniques of ostracod (Ostracoda, Crustacea) extraction from organic detritus-rich sediments

Abstract

The performance of two simple techniques of ostracod (Ostracoda, Crustacea) extraction from detritus-rich bottom sediment: sediment aeration and sedimentary environment deterioration, was tested on samples collected in a large lowland river (River Odra, western part of Poland). The aeration technique, applied to preserved samples, involved bubbling air into the sediment sample overlain with water. The animals would adhere to the bubble surface, whereby they would be brought to the water layer and cling to the water surface. The environment deterioration technique, applied to unpreserved sediment (assumed to contain live ostracods), involved placing a sediment-filled hour glass in a water-filled vessel overnight. At night, meiobenthic animals would leave the sediment and move to the aqueous phase from which they could be easily collected. Compared to hand sorting, both techniques substantially (by an average of about 87% in aeration and about 70% in deterioration) reduced extraction time. In terms of efficiency, performance of both techniques was species-dependent. The aeration technique was found to be selective towards smooth-carapace species, and performed satisfactorily (extraction efficiency of more than 80% in most cases) due to the preponderance of smooth-carapace species in the area of study. The deterioration technique, too, showed significant between-species differences in amenability to extraction; those species supposedly less tolerant to deteriorating conditions and possessing swimming setae would be preferentially extracted. The ostracod assemblage in this study was dominated by species capable of swimming and supposed to have low tolerance to deteriorating conditions, for which reason the technique, in most cases, performed with efficiency exceeding 60%.