EGG-SHELL CHARACTERISTICS OF GANNETS SULA-BASSANA, SHAGS PHALACROCORAX-ARISTOTELIS AND GREAT BLACK-BACKED GULLS LARUS-MARINUS EXPOSED TO DDE AND OTHER ENVIRONMENTAL-POLLUTANTS

Structure, strength and chemical composition of egg shells of gannets Sula bassana, shags Phalacrocorax aristotelis and great black-backed gulls Larus marinus have been studied in relation to egg residues of DDE. For each species, eggs that were highly contaminated with DDE tended to have thin shells. For the gannet, shell thinning was mainly due to loss of the vaterite cover. For the shag, cover loss was again considerable, but the true shell was also significantly reduced in thickness. Gull shells do not have a cover, and for the great black-backed gull most of the shell thinning was due to a reduced palisade layer. The different types of structural defect observed in the shells of these and other species could result from a single biochemical lesion such as enzyme inhibition in shell gland tissue. As the thickness of the shell decreased, so shell strength for the gannet and shag did not decrease as markedly as for the gull and other species. Partial loss of cover had little effect on strength compared with loss of true shell. Had the cover been entirely missing, however, strength would have been seriously affected. © 1979.