DO DIATOMS ARREST EMBRYONIC-DEVELOPMENT IN COPEPODS

Evidence is presented on the harmful impact of a diatom (Thalassiosira rotula) on the reproductive biology of the copepod Calanus helgolandicus. When adult females were fed the diatom, both total egg production and hatching success were significantly lower than with the dinoflagellate Prorocentrum minimum. Embryonic development in the copepod was arrested when eggs were exposed to diatom but not dinoflagellate extracts from these same species of phytoplankton, Depending on the age of the eggs before exposure, cell division was blocked either prior to fusion of male and female pronuclei, or during mitosis. Embryos underwent strikingly abnormal development. The structural anomalies included a dark brown, opaque outer membrane, globular cytoplasm, blockage of pronuclei, or dispersed chromatin scattered in the egg matrix of non-hatched eggs either spawned by naturally occurring females, spawned by females fed with diatoms, or in embryos incubated in diatom extracts. The production by several species of diatoms of inhibitory compound(s) detrimental to the development and survival of their principal grazers may have major implications on secondary production and on the flow of energy in the marine food web.