First evidence of some dinoflagellates reducing male copepod fertilization capacity

Evidence is presented that hatching failure in Temora stylifera eggs can depend on poor sperm quality. Three dinoflagellate diets, Prorocentrum micans, Gymnodinium sanguinium, and Gonyaulax polyedra, significantly modified spermatophore production and reduced the fertilization capacity of male sperm after 6-12 d of continuous feeding. Two other diets, the dinoflagellate P. minimum and the prymnesiophycean Isochrysis galbana, had no effect on hatching success, which remained high (>89%) and stable with time. A reduction in fertilization capacity was neither due to maternal effects nor to male age since hatching success returned to normal upon the introduction of freshly caught wild males or males conditioned with a good diet such as P. minimum for the same length of time as couples fed with the poor diets, P. micans, G. sanguinium, and G. polyedra. Confocal microscope images of unhatched eggs colored with a nucleus-specific fluorescent dye confirmed that these eggs had not been fertilized. Experiments with Calanus helgolandicus females, which did not require reinsemination and which were fed the same diets that induced hatching failure in T. stylifera, showed no change in hatching success with time.