Embryonic Development

Abstract

Embryonic stages of marine animals have been used extensively in explorations of effects of contaminants and toxicity testing. This chapter provides a review and summary of the nature of observed adverse effects and toxic levels on embryonic development for important classes of chemical pollutants. Early life stages are generally more susceptible to environmental contaminants than later stages, so many studies focus on embryos or larvae. Embryos can be exposed to developmental toxicants during oogenesis in exposed females, during the brief period between shedding of gametes and fertilization, and after fertilization. Studies have shown that chemicals incorporated into the egg during oogenesis can produce malformations in the embryos that subsequently develop from these eggs. In most experimental studies, however, embryos are exposed to chemicals after fertilization. Exposures can be throughout embryonic development or during shorter time periods. Although many toxicity tests still use hatching success as the endpoint of interest, common responses include delayed development and formation of abnormalities. Chemicals can affect morphogenetic movements such as gastrulation, tissue interactions such as induction, growth, and degeneration or cell death, which is an inherent part of embryonic development. Some responses do not become apparent until larval or juvenile stages.