THE ROLE OF DETRITUS IN THE NUTRITION OF TWO MARINE DEPOSIT FEEDERS, THE PROSOBRANCH <i>HYDROBIA ULVAE</i> AND THE BIVALVE <i>MACOMA BALTHICA</i>

TLDR

Population density of Hydrobia ulvae and Macoma balthica is higher in fine‑grained deposits than in coarse ones, likely because finer sediments provide greater surface area for microbial growth rather than simply more organic debris. Laboratory experiments indicate that these deposit feeders consume microorganisms, whose greater abundance in fine sediments drives the rapid population increase, and the term “detritus” is recommended to be replaced with “organic debris.”.

Abstract

Observation on the shore show that the density of the population of the prosobranch Hydrobia ulvae and of the bivalve Macoma balthica at Whitstable varies considerably With the grade of deposit, dense populations being found in fine deposits and sparse populations in coarse deposits. From laboratory experiments it seems probable that these animals feed by abstracting proteins, which can be assessed as nitrogen, from the bodies of microorganisms in the deposits and that the micro‐organisms are more abundant in fine deposits than in coarse ones. As a result of these conclusions it is suggested that the rapid increase in population density of Hydrobia ulvae and Macoma balthica , and by inference of other deposit‐feeders, towards regions of fine‐grained deposits is attributable to the increase in density of the micro‐organism population. this, in turn, is related to the surface area of the deposits rather than to the abundance of organic debris. Finally, the nature of detritus is discussed and it is recommended that this term is replaced by “organic debris”.