The Role of the Mesobenthos in the Size Structure
of an Intertidal Ecosystem

A. A. Udalov and I. V. Burkovskii

Biological Faculty, Moscow State University, Moscow, Russia

Received November 12, 2001

Abstract—The inclusion of the mesobenthos, i.e., the organisms with sizes intermediate between those of the
adult meiobenthic and macrobenthic animals, into the size spectrum of the White Sea intertidal benthos allowed
us to verify the hypothesis of the existence of a size gap in the intertidal organisms and the actual independence
of the meio- and macrobenthos from the size units. The meio- and macrobenthos size ranges were shown to
overlap significantly, with a relationship between the degree of overlap and the type of macrobenthic species
development. This means that the organisms with direct development exist for a long time (months or years)
within the meiobenthic size category, whereas those with a planktonic larva pass it very quickly (for a few days).
Essential differences between the size spectra of marine and brackish-water communities were revealed. The
large portion of macrobenthic species with a planktonic larva among the marine intertidal organisms, the similar
sizes of the settling planktonic larvae, and the simultaneous and mass character of their settlement are respon-
sible for the appearance of the gap in the size spectrum of the marine benthic biomass and cause the partitioning
of the community into isolated meio- and macrobenthic size units. In the brackish-water communities, the
mesobenthos is represented by a permanent component (oligochaetes and midges). With a rise in the individual
body size, a uniform increase in the biomass takes place, without its discernible decrease in the meiobenthic
range. In the brackish-water biotopes, the mesobenthos is diverse and comprises from 30 to 40% of the benthos
biomass.

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