Infauna greatly modify the sediments in which they live. One form of m
odification occurs via the organisms' secretions. In a number of famil
ies of Polychaeta and Hemichordata, the worms' secretions include halo
genated aromatic compounds such as bromophenols. To determine how the
presence of such compounds affects juvenile infauna, we directly added
synthetic bromophenols to natural sediments at field concentrations a
nd observed the responses of recently settled juveniles of 2 bivalve a
nd 1 polychaete species. In nature the bromophenols are secreted into
sediments by a capitellid polychaete. A significant percentage of the
bivalve juveniles (50 and 67%) did not burrow into the sediments exper
imentally contaminated with bromophenols, while all the bivalve juveni
les burrowed into the control sediments. The arenicolid polychaete juv
eniles burrowed into the experimentally contaminated sediments, but th
e rate of burrowing of these juveniles was significantly slower in the
contaminated sediments than in the control sediments. The addition of
bromophenols to sediments, therefore, had a significantly negative ef
fect on acceptance of the sediment by recently settled juveniles of al
l 3 species. These results are consistent with the concept of such sec
retions determining the composition of assemblages in areas with bioge
nic producers of haloaromatic compounds.