Effect of Preservation on the Weight of Marine Benthic Invertebrates

Abstract

It would be convenient if preserved animals could be used to determine fresh-weight biomass. However, marine annelids, nematodes, bivalves, amphipods, and isopods all lost weight when preserved and stored in 70% isopropanol. In 10% formalin only bivalves lost weight significantly; the other groups showed evidence of small increases or decreases. Many animals preserved in alcohol decreased sharply in weight within a few minutes, probably due to dehydration. In formalin most increased at first, then slowly decreased. The response to preservatives is complex, involving short-term changes of water content and long-term changes of tissue composition. Precision, though not accuracy, of preserved wet weights can only be achieved after specimens have been in preservatives for a month or more, especially in the case of isopropanol. For these reasons, wet and dry weight biomass figures should be determined from fresh, unpreserved animals.Key words: fixation, preservation (organisms), biomass determination, benthos